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I built up George Giblet's version of the later Harmonic Percolator. (http://www.geocities.com/george_giblet/effects/percolator_later_rev1_1.png)

So far so good. It sounds great through my test bench amp, but the proof is in the pudding (or probably my AC30). I put in a socket for the Ge tranny and went through a few different trannies until something sounded special. All that I tried sounded pretty good and had a good range of cleanish to overdrive. Some were random unmarked ones I inherited somewhere. Some were ECG 158s that I bought years ago. So far the winner is some one-off purchase of an unknown transistor that I got from Electronic Goldmine a year or two ago. This one had way more gain and when the input control was maxed, it went into a fantastic sounding fuzz that would compress and swell up in a very cool and splatty way. It still had a nice range of clean with the input control dialed down (or my guitar's volume control).

Anyone else have any reports about this version?

Roger

i played with that circuit while back. i liked it but ended up making some changes. i don't have my folder with me though. i do remember it was a bit thin for me. i'll check my notes when i get a chance. rylan

Since I haven't tried it through a "real" amp, I can't tell if it's thin or not, so I'll look out for that.

Do you recall if you tried transistor substitutions, or was it more or less tailoring capacitors and resistors until you liked it better?

What interests me in this circuit is the non-Albini video clip which shows how the harmonic character of it lets more complex chords cut through. I'm not looking for something completely clean and clear (I still haven't found a use for my Roland GR-300's hex-fuzz!) but I would like to have one pedal that has a unique tone among the pedals I already have (which, of course is already too many). :)

Roger

I just passed by a compulsive Percolator seeker phase...

I tested several component values and trannies.

But I must admit, until now the best sound I achieved with Harmonic Percolator circuits was the Doug hammond's "The Brick" basic scheme, but using a diferent clipping/diode section.

Thereís something very special about that simple circuit. It's diferent, it gets good results with a good clean amp set, but with a good tube crunched amp it really delivers!!!

Just for the record, this circuits isn't my version, it's a trace of the actual circuit.  There's a few versions of the actual circuit and that appeared to be the one people like.   Because of  transistor differences you might need to play around with the values.  Look in the archives for some tips/ideas.

Has anyone measured the DC voltages at the
Emitters node VDC?
Q1 collector VDC?
Q2 collector VDC?

This will help understand what is going on with a nice sounding version of this circuit

Interesting circuit both transistors are forced to run at the same collector currents being in series and having no other DC current paths because of C2, C3 and C6.

It is a 2 stage circuit
  First stage gain, Q1s gain with the feedback network of the 220K C to B / 100K input pot and source impedance (guitar)

  2nd stage gain, Q2s gain and the 750K feedback C to B /  R4 value

The size of the C4 cap(I think of it as an AC ground) will have an effect on how much the emitter node moves with signal

Also the voltage at the emitter node has an effect on the max gain from each stage by how it divides the 9VDC supply.

It is a two stage amp Q1 then Q2 at a lower than 9VDC for each stage

Looks like it would be sensitive to the transistors used and R1,R2,R3 and R4

Some of that behaviour was addressed in the original thread,

http://www.diystompboxes.com/smfforum/index.php?topic=55987.0

The circuit as is had the maximum gain and I seemed to recall the Vce voltages of the transistors were quite low.  The key could be how near saturation the transistors operate, the problem is large changes in the external components make small changes to VCE in that region.  Variations in the GE versions are likely to be related to leakage.

Yo

  Yeah I built one using that schem and a layout I did in Eagle. Used all the recommend values and types of components. Socketed the transistors and tried a bunch in both positions. All that seems to come out of mine is a pretty mediocre fuzzy overdrive. Maybe I'll rip out the circuit and build "The brick" in there.

--Brad

George

      I did not notice the 50ua total current draw before.  Good post 2nd page from your link.

  If I wanted to build a close version of this circuit I would make two circuit fragments to select transistors and C to B resistors for each stage.

Using voltages worked out by George in one of the posts.

Q1
A 10K and 50nf in series with the base, 20K collector resistor and fixed resistor and a pot wired C to B
AND a Power Supply set to 3.48VDC (from George's post).
  The 10K is a crude guitar sim with this type of biasing you are also affecting the feedback ratio and it also works with the open loop gain of the transistor.   So drop in a transistor turn the pot and look for 1V from ground to the collector if the feedback resistor is much greater or less than 220K try a different transistor. The input resistor and cap is for testing using a low output resistance signal generator.  2.48VDC  E to C


Q2
  A 20K (collector resistor value of Q1) in series with a 100nF to the base, a 91K collector resistor, a fixed resistor and pot for the 750K collector to base feedback resistor.
  A Power Supply set to 5.52VDC.
  Adjust the feedback resistor for 0.97VDC(4.45 -3.48).  The input resistor and cap is for testing using a low output resistance signal generator.  Q2s bias point is closer to saturation and set for more gain(.97VDC C to E)

Pick your transistors and feedback resistor and drop them in a board.  You don't want the feedback/bias resistors to be much different than the stock values if you want to build it close to the original because they affect the stages gain.

If you understand more about transistor you could pick other collector current and hfe transistors

Again has anyone measured a real good sounding HP operating points?

Did a DC test of the fragments and then with them connected together.

I find this circuit interesting because of the interactions.  Took two random, common, Si transistors 2n2222a (hfe 210) and 2n2907 (hfe 190).  Changed the Ic and collector resistors for more drive in this case around .1ma (100ua).  Selected the C to B resistors for the voltage at the collectors and therefore the Ic I wanted

Q2 fragment 47K collector, 470K C to B, 5.5VDC supply  Collector at .957

Q1 fragment 10K collector, 1.2 meg C to B, 3.53VDC supply, + to emitter, Collector at 1.057VDC ref to ground

Connected emitters and used a supply of 9VDC using Georges schematic as a starting point
Q1 collector .986VDC
emitters 3.42VDC
Q2 collector 4.37VDC
+ 9.02VDC

NOTE gain of Q1 and Q2 stage will be different: However the division of voltage is close to what George calculated and posted.

I think I will try Si diodes for more output when I box it up to hear what it does.

Are there no replys because people maybe don't understand what I have posted?  If so ask.

  To me this circuit should have both gain sections tested before building because of the series connection between the gain stages.
Ic collector current sound be close for both fragments and the gain in each stage is affected by both the transistor gain and the feedback resistors (C to B resistor and the source resistance feeding the base,  This also reduces the transistor distortion being feedback).
Note the signal inversion and in then at Q1 collector then at Q2 collector.

I went back through the old thread that George linked above. I didn't understand his "bypassed emitter" comments completely until I realized that each transistor is the emitter circuit for the other transistor. Almost like an "active load" in a cascode or mu-amp circuit- except it's in the emitter not the collector circuit.

I never measured Vc in either stage when I built the Brick. I just biased it by ear. DC-wise it is similar to George's schem except for the 100k in place of the 20k Rc in the first stage. AC-wise it is tuned differently. Also, the diode "offset resistor" in George's circuit is 4.7k instead of 10k in mine. I would like to breadboard George's circuit, check voltages and then compare with the Brick sound.

I've built three of these now to this schematic, and they have all sounded so good that people wanted to buy them. I make sure to get the Hfe's in the range discussed on the other thread, and they work great. I tune all 4 resistors, then basically end up back with the values George has given. This is using some East German Ge PNP Hfe 40-50, and a 2N2222A 180-200 for the Si.

I've built up three versions recently, and I've come up with a variant that I like a lot. I've changed a few things that might make it worth posting my schematic when I get a chance.

I built up 90% of the Brick version, but I was left with a question about the 1uf caps: whether they are polarized or not. I'd probably have to use 2 .47uf caps if they're not polarized. I don't think I've ever had such a large cap in my parts bin that wasn't electrolytic or tantalum.

Roger

Just use film caps for the 1uf's and it's a done deal. They are not polarized.

FWIW I had a little time this morning and built up George's schem on the breadboard. I used a 2n404a hfe 30 for Q1 and a 2n3565 hfe 220 for Q2. My voltages came out a little different than Gus came up with- I had 2.7v on the Q2 collector for example. Still sounded fine though. With R4=22k it is pretty wild - loud, lots of pinch harmonic emphasis, slightly "mis-biased" sounding even when gain and/or guitar is turned down. With R4 = 100k it is not as loud, sounds more "together" (not mis-biased) , but in either case just as fuzzy with the gain cranked. I had to run to the dentist before I had a chance to compare to the Brick, which is tuned differently (1u's instead of .1u's, etc).

I have another 2n404a as well as other assorted Ge's and Si's. I'd like to experiment with different transistors and see how they affect voltage levels and sound. I think what sounds "good" may be subjective, and maybe the Albini vid could be used to compare. I suspect the "wilder" it sounds the more it will sound like the vid.

i made quite a few and like them best with both transistors in the 80-100 range.

I've been looking at various incarnations of this circuit and I'm curious as to why George Giblet's schem only has two diodes. In the photos posted on Harmony Central (http://acapella.harmony-central.com/forums/showthread.php?s=744743d30c3b9df98947560e53137ade&threadid=1008997), there are three diodes on the PCB. Is it just a different version of the Percolator?

QuoteI went back through the old thread that George linked above. I didn't understand his "bypassed emitter" comments completely until I realized that each transistor is the emitter circuit for the other transistor.

I do not remember if I mentioned in the above link a mod I did to mine: a 100k pot between emiters --> kind of octave up fx. When pot is not at min, Ge emiter is fully bypassed, but Si emiter is not. (Mine has two Ge, 2sa102 and 2sd352, sounds a lot better)
Also, a fixed resistor between emiters of the order of the collector resistors, and no bypass cap turn the circuit into a nice clean even harmonics booster  ;)

mac

Quote from: danielwarner on June 19, 2008, 11:07:35 PM
I've been looking at various incarnations of this circuit and I'm curious as to why George Giblet's schem only has two diodes. In the photos posted on Harmony Central (http://acapella.harmony-central.com/forums/showthread.php?s=744743d30c3b9df98947560e53137ade&threadid=1008997), there are three diodes on the PCB. Is it just a different version of the Percolator?

That's D5 in Alf's version 2 schematic. Looks like input overvoltage protection. Those photos also show the 1k-2u2 from Q1-C to ground.

I compared George's circuit on the breadboard to my Brick. I much prefer the voicing of George's circuit. With the .047u, .1u, .1u caps it sounds fuller- the Brick is just too thin with the .01u input cap. However, the Brick is *much* louder, due to the 1n46 clipping diodes I used.

So far I'm drawing much more than the 50uA current in the spec sheet. I'm going to experiment with lower hfe npn si transistors and see if i can get the current down to see how that will affect the sound.

Mr Hammond broke my heart... Well, then I will retake the research. I agree with his comment about the Brick's being a bit thin sound, as the Mr Albibi's Percolator has an almost octave down kind of effect attached to it's sound. As I just bought some 2N404A (they looks like new ones) I will try them with the George's circuit. At least in the brick version, the Si I've tested sounded better than Ge as the NPN tranny. I must retry it with the George's circuit.

To be continued...

It is good to read people have tuned this circuit to other things but it might be cool to build it as stock as possible to understand what the design is about if you don't have access to a real one that is in good shape and working correctly

I think to understand what the original "is about" one has to measure a real one.
OR build one
Using the math done by George G. The 50ua(.05ma) current draw is important, knowing this and knowing the stock collector resistor values gives two DC points,  Ohms law R X I =E(voltage)  George took the more knowable transistor specs the Si NPN and did the math.

http://www.diystompboxes.com/smfforum/index.php?topic=55987.20

Break the two gain stages out
Use a adjustable power supply to try and bias the stages/ select a transistor separate because of the interaction when placed in series

Think of the first PNP stage as one that runs at 3.48VDC and you want the collector at 1VDC above ground with the 20K(20000 ohms X .05ma = 1VDC) and using a bias resistor of about 220K.  This stages gain will be a mix of the openloop gain of the transistor circuit  and the feedback (C to B) resistor divided by the source R before it

Think of the 2nd NPN stage as one that runs at 5.52VDC and you want the collector at .97VDC above ground (4.55VDC drop across the 91K) and using a bias resistor of about 750K.  This stages gain will be a mix of the openloop gain of the transistor circuit  and the feedback (C to B) resistor divided by the source R before it (750K/20K(collector R of 1st stage))

Then connect them together in the circuit.  I don't see the stages being emitter circuits for the other side I see a 47uf cap holding the emitters at a  more fixed DC value (AC ground) and dividing up the power supply voltage to the stages  That point might wiggle a bit and maybe that is part of the type of feedback in the video not knowing what the 47uf electro cap specs are after all the years in the circuit.  SO maybe try different caps values.

I played with this a lot more this morning.

Here's what I found:

1. Si NPN with hfe ~200 sounds good. My 2n3565 was 220 and I found a radio shack grab bag xsistor hfe 182 that I like the sound of better. I doubt that is due to hfe alone, since they are so close. Just pick something that sounds good with hfe in that general range. I tried hfe 97 xsistor and it didn't sound good to me.

2. Ge PNP with hfe ~40. This sounded better IMO than the same 2n404a type with hfe ~60. Again, I'm guessing any Ge PNP with low hfe should work. I tried one with hfe ~250 and it sounded good but lost a lot of the "harmonic magic".

3. Pay Attention to Gus's post about voltages. The only way I could get these voltages was with Q1 Rc = 100k. At 20k the Q2 Vc was 2.7v. The key IMO opinion is what Gus alluded to- keep Vce on Q2 to around 1v or so. That's where it gets really sensitive and you get the harmonic blooms and etc. Set Q1 Rc to set Q2 Vc to taste.

4. The diode shunt on the input (in HC photos and Alf's version 2) compresses the signal and smooths things out a little. Yes it actually is audible and sounds a little better IMO with it in.

5. The 2.2u/1k network on Q1-C helps smooth out high freq splat as well. This and the input diode will give it a more "refined" sound.

6. 10k in series with clipping diode gives a little more volume and better octave harmonics.

7. Like I mentioned before George's circuit voicing with the .047u/.1u/.1u coupling caps was spot on and sounds very good.

Here's a summary of what I've got on the breadboard: http://www.aronnelson.com/gallery/main.php/v/DougH/Perc/myPerc.GIF.html?g2_imageViewsIndex=1 (http://www.aronnelson.com/gallery/main.php/v/DougH/Perc/myPerc.GIF.html?g2_imageViewsIndex=1)

I'm going to perf this up and replace my Brick circuit board with it.

This is a fun circuit. Try picking lightly and letting the notes bloom. Or just finger with your left hand without picking. It pretty much plays itself.

Hopefully other people may try some of the debated circuit fragments on the breadboard and report back how they affect the sound.

Circuit looks interesting Doug.  I wonder, a med power Si for Q1?

For some reason I find this circuit  interesting

Q2 is set up opposite of what a RM is.  The RM is often biased more to cutoff and Q2 in the HP is closer to saturation This is the higher gain part of the bias range.

I have not heard or seen a real HP except in the video and pictures on the web.

looking at the HC pictures of the HP, what is the black cylinder in the middle of the board? it's got a bit of that red goop on it. and if it's already been mentions and i missed it, sorry. rylan

never the mind... rylan

One minor typo in my post above:

QuoteI found a radio shack grab bag xsistor hfe 182

Q2 hfe was actually 200. Not that it makes a significant difference...

Thanks for all your efforts.

Regard the biasing.  The calculation I did in the old thread were based on the 50uA supply current and working from there.   I've never been able to get a situation where I did actually get 50uA with the values in the circuit  - it's always more.

Using the values in my schematic (ie 750k's, 91k's etc)  the bias voltages I got (from some old simulations) were, going "down the chain"

                           Q1 & R4 Value
            Si+20k  Ge+20k Si+91k Ge+91k
Q2.C     3.1        2.8      5.3       5.1
Q2.B     2.6        2.2      4.9       4.7
Q2.E     2.0        1.6      4.4       4.1
Q1.B     1.37      1.41     3.74     3.92
Q1.C     1.29      1.36     3.69     3.89
** Q1.E  = Q2.E in all cases

So, (designators are for my schematic)
- When R4 = 91k the current is closer to 50uA.  Does that make the value correct? perhaps not!
  It could be the 50uA spec was for R4=91k; there were variations of the circuit over time.
  The 20k could be correct and the current was never updated in the spec!
-  The Q2.Vce voltage tends to stay around 1V by nature
   This is a consequence of the transistor gain and the value of R1.
   Smaller R1 values will drop Q2.Vce
- The Q1.Vce voltage is controlled by R2.
   Note Q1 operates with a very low VCe because R2 is quite low.


To: danielwarner
> In the photos posted on Harmony Central, there are three diodes on the PCB. Is it just a different version of the Percolator?

Yes there are other versions.  The Barge concepts schematic matched this circuit.  There was uncertainty to whether Q1 was a PNP or an NPN in the barge circuit.  Some of that was discussed in the old thread.

I built a circuit not tested yet

Q1 a 2n2907 PNP 190   moto metal can
Q2 a 2n2222a NPN 210 moto metal can

Q1
Using a supply set to 3.53 VDC (control is kind of coarse making it hard to set the voltage to a the .01)
Using a 10K collector resistor I wanted .1ma Ic
A 1.2 meg C to B  gave 1.057VDC at the collector of the 2n2907 for Q1

Q2
Using a supply set to 5.5VDC
A 47K collector resistor
A 2n2222a
A 470K C to B gave .957VDC C to E

Connecting the two fragments together
9.02VDC
4.37VDC Q2 collector
3.42VDC emitters
.986VDC Q1 collector
0VDC      ground


   Look close at the first stage.  It is basically the same as a FF input.  The FF bias and feedback comes from the C to B that is offset by the Vbe drop Q2 emitter tracks the Q1 collector offset by Vbe

Look at the HP there is a C to B feedback bias resistor.

Think about how the FF interacts with the pickup(s) tone control volume switching of a guitar
The HP is a lot the same: however it has a PASSIVE volume pot that adds series and shunt resistance to the input summing node of Q1 circuit.

Also what happens if you place FF after a device with a low output resistance?

George, my voltage readings came out similar to yours (for the Brick too). I think this is fairly "typical" if we are only tweaking the Q1 collector. To reach the 50ua goal as in the HP spec sheet I think you have to isolate ea stage as Gus suggested and bias them individually. It will probably take large tweaks to the feedback resistors unless you have the same transistors with the same characteristics that Giese used. I played with the feedback R's yesterday for a few minutes, but could not get the voltages and target Ic. I'm going to try it some more and may try Gus's approach (although I don't have an adj bench supply - so I'd have to jury rig something up). I'd like to get to the target 50uA if at all possible, just to see if there's any difference in sound.

I gave this a try today using Gus's method, I just hooked up an LM317 to get the voltages for the 2 circuit fragments and used a BC179 (hfe 250) for Q1 and a 2N3904 (hfe 190) for Q2.
I used a  680k for Q2s feedback resistor giving 0.94 volts on the collector but I had to use a 4M7 for Q1s feedback resistor get the correct voltage on the collector.

Joining the 2 halves together I get about the same voltages as Gus.

Q2 collector 4.54
Emitters 3.61
Q1 collector 0.95

I built the rest of the circuit following George's schematic at the top of this thread.

I've only had a quick play with it but compared to the Gearwise review of the BP-1 (http://uk.youtube.com/watch?v=vyv3267xGPM&feature=related) it seems to be in the right ballpark on the wilder sounds at least.
Compared to the cleaner sounds mine sounds too "misbiased" and splatty, I think I'll have to play with the collector resistors a bit more and try some of Doug's suggestions to see if I can improve things.

slacker

  Thanks for the feedback on you build.  I posted that bias method because I am wondering what the real design was about.  I think we will need to find a Q1 transistor(s) that will bias with resistor around the stock 220K.  4.7meg for Q1 will have the transistor operating close to its open loop gain in that fragment so "splatty" make sense.  The Q1 part looks like it be more of a problem to get "right"

   If you change the collector resistor of Q1 you will affect the gain of Q2 the 680K/20K part of the gain.  It seems to build it stock you will need to select transistors and feedback/bias resistors to get to adjust the operation points and gains of each stage

Maybe people here will find other voltage divisions and biasing/gain setups that they like better.  I think the simple break it in two parts to bias it will help with what ever people find they like if they want to reproduce the circuit

I posted an idea for a two npn circuit in another thread.
http://www.diystompboxes.com/smfforum/index.php?topic=55115.0

I did some thinking for a two NPN, Q1 collector resistor to the emitter of Q2 and Q1 emitter grounded

Q1 maybe try a Si med power device like a TIP29 or devices around hfe100
power supply set to 3.3VDC adjust the feedback resistor for the  collector at 2.5VDC ref to ground(1VDC drop across the 20K)

Q2 power supply at 5.5VDC and the collector at .95VDC(91K x .05ma = 4.55VDC drop across the 91K) adjust the feedback/bias resistor.

For the output I would try the warp type control(AMZ) the diodes to the outer legs of a pot and the wiper to ground a 10K should allow a little more output and you can adjust to taste

I think I'll have to go and read all the threads about this, because the answer's probably in there, but I presume the hfe of Q1 is important for setting the collector voltage using your method? Unfortunately I haven't got any other PNP transistors so I can't experiment with it any more at the minute.

I've got some low gain NPNs though so I can try your 2 NPN idea out.

two npn idea

http://www.aronnelson.com/gallery/main.php/v/gus/npnhpfragment.GIF.html

Howdy folks. Ive been following this thread for a couple of days now and whipped this thing up on the bread board today. I used a 2n2175s for Q1,its out of and old transistor radio that was made in australia. It has "AWV" printed on it,I guess thats the maker.HFE is about 40.Q2 I just used a 2n3904 HFE 210.The resistors I use after some experimenting are 100k and 680k as in dougs schematic.And on Q1 20k and 220k as in geoges schematic.Also I dont have pots connected to the circuit I just grounded a 100k on the input and also went to 100k on the output as it seemed to increase the octave effect. Now while im talking about the octave effect I notice through some fiddling that by lowering or raising the cap between the bases of the transistors i could change the range of the octave. But Im only getting the octave effect over about one octave on the guitar neck no matter what cap I use there.. I hope you understand what im saying as i dont explain myself well in writing. Anyway by fiddling with the cap i could change which octave was making the octave effect.LOL im confused now.Also twiddling that cap changes the voltages on the transistors. Are you guys getting the octave thing happening? Theres not been much mention of it. Anyway try caps from say .047uf up to .27uf or more or less if you like.

Heres my voltages with a 0.47 cap

Q1    E 1.51  B 1.42 C 1.36
Q2    E 1.51  B 2.09 C2.33

Im not sure if my little rant will help you guys as im out of my league but its too late now LOL
Have a nice day JOHNO

PS I left out the 1k and 2.2uf to ground as it took away too much grind for my liking also used 10k on the diode to ground as doug suggested,but i do have the diode on the input as in alfonsos schematic

>the cap between the bases.< Opps thats a typo. between Q1s collector and Q2s base is what i meant.

I had another crack at your idea Gus taking a different approach, I'm not sure how valid it is from the point of view of trying to understand the original but it seems to work.
For the PNP fragment I used the stock 220k feedback resistor and then "piggybacked" 2 BC179s, bases connected together and a resistor joining the emitters. I adjusted the value of the resistor to bias the collector to about 1 volt then hooked it up to my original NPN fragment and the voltages looked good.

Sounds pretty good now, at maximum gain it has a nice compression on the attack and it cleans up quite nicely with the volume control. Compared to just building the circuit stock using the same transistors which biases up with Q2's collector at somewhere around 3 volts it's a lot tamer, and to be honest I prefer the wilder version. Interesting though. 

Re. JOHNO's post:

That's good info and pretty consistent with the kinds of voltages I have been seeing.

Without having a real perc with xsistors Mr. Giese picked (and not somebody's clone), it's difficult to know where on the respective characteristic curves the operating points for these two transistors are supposed to sit (or how significant that really is). It's also difficult to know what the real "sound" is although you can get a good idea from the Albini vid. You can sort and pick through transistors until you find a pair that work with the known component values and with the spec'd Ic of 50uA.

Barring that, what I do know from experimenting with this a lot is you can get a decent fuzz sound with a lot of harmonics and an "almost octave" wildness (similar to the Axis fuzz) when it is cranked by using a variety of transistor types and making the necessary adjustments in Q1's collector resistor. Aside from the normal considerations of biasing and voicing with coupling cap size, you can get pretty darn close to the sound in the vid.

To be honest, I'm not really hearing anything real "special" in the vid or the circuits I've experimented with, other than it being a nice and fat, harmonically-rich fuzz with gain to burn. IMO there are a lot of ways of getting to that sound. From the standpoint of solving a mystery however- I completely understand the interest in it. I wanted to move on to other stuff and don't want to spend the time sorting through my transistors for the "right" one for this. But if you guys come across something definitive I would seriously love to hear about it.  I'm real happy with the circuit I have on the breadboard (I posted the schem earlier) and prefer it over the Brick. So that's what I'm going to build.

One thing I'd like to add is that all these Perc threads have been an absolute gold mine of info on this circuit. It would be nice to see this linked up in the Wiki somewhere.  All the variations, filtering options, biasing info is a great resource for anyone who wants to experiment with it.

And finally- here's a fun tweak I discovered by accident: Try connecting the output pot to the junction of the 1n34a and 10k (4.7k in George's schem) instead of the junction of the diodes. Increase or remove the resistor for more volume. This adds crossover distortion which sounds a little gritty but it will sustain almost infinitely at very low volumes.

>"To be honest im not hearing anything special in the vids or the circuits".  True it may not be any thing special but albini is defenantly getting an octave down thing happening to my ear when he is playing around the 5th fret. Im getting that too. I guess its just a happy accident as I havnt auditioned any other transistors in this circuit. Im only playing it through my champ and it has to be one of the best fuzz pedals i have built. I havent built a decent fuzz face yet and ive built a lot of them. Anyway thanks to you guys yet again for all your work and putting it out there for all to see cheers, JOHNO

Quote from: JOHNO on June 23, 2008, 09:06:59 AM
True it may not be any thing special but albini is defenantly getting an octave down thing happening to my ear when he is playing around the 5th fret. Im getting that too.

Which video is this? I've only found the "Pussy Fuzz" one and that doesn't sound that crazy to me.

The thread called "Harmonic Percolator vs barge concepts bp1" theres a post the by analog man? i think. Its about the 3rd of 4th post in that thread.

Cheers :)

Good feedback thanks for building the two NPN idea.

Lets think about this and the octave part both stages are inverting amps and can have different gains so they will try to wiggle the 47uf cap node and the waveforms,  When I have time I will look at this with a scope.  Maybe try smaller/bigger cap values allow more or less wiggle.

Im not sure if you were adressing my post gus but mine is the pnp npn version. the transistor is 2n217s. I wrote incorrectly im my other post. Its from a radio aparenltly built in 1964.

Quotealbini is defenantly getting an octave down thing happening to my ear when he is playing around the 5th fret.

I got more of that deep grunty sound on my wound strings by re-voicing it according to George's schematic.

Here's the vid with Albini demo-ing the Percolator: http://www.gearwire.com/bp1-albini-comparison.html (http://www.gearwire.com/bp1-albini-comparison.html)

i really appreciate the Gus aproach, as understanding the project principles could let us even investing on an evolution side of the thing.

Well, I don't know about someone else, but I found fascinating the sound achieved by mr Albini on that video. At first, what amazed me was the fact he has a so poor technique and the resulting sound remained interesting. With my new "components setting" percolator circuit I realised the indisciplined Albini's playing is part of the magic. My new combination of elements, in my own opinion, caught some of the magic I was looking for since I've heard it. Even when I play consistently, THE SOUND is there, but if I let the notes ringing, as a deliberately resonant playing, you can really find the magic.

The component values was close to Geroge's schematic with few changes: the output cap is 1uF, not 0.1uF. 100K for both colectors resistors, not 91k.  This configuration really gave me the closer sound to the Albini's version I've got . I don't even know if the Albini's Percolator is an example of how an original one is intended to sound.  But tha sound seduced me. It is far from the splat sound i got from the other versions with high hfe trannies, when the Harmonics, or guitar Volume pots are at Max. The sound is now piercing, compressed, but not that squeezed to death sound i've got.. I tested some 2N404A and 2N3565 trannies (and also several other types). but the best I found was an 2N404A hfe=30 and an 2N3565 hfe=140 combination. I will do the measures tonight, so I hope to post them tomorrow.

I've even tried the input-to-ground diode and the 1k resistor + 2u2 F cap in series from Q1 to ground. The diode is not so interesting in my last configuration. More about it later...
DougH said the RC combo refined the sound. I can't agree more. But it just happen to me when I used other "wrong" high hfe trannies. The diode also helped to reduce the splatyness in the sound. but when i got the magic sound with the "right" trannies, both elements was not needed, they even took the sound to other planet, in my opinion.

I'd love to see how your voltages came out, Alex.

I tried an NPN with ~90hfe but it did not sound good. But I had another wiring problem (see my "xover distortion" tweak earlier) so I may try it again, or at least see if I have an NPN that is lower than 200.

I hear what you are saying about "deliberately resonant playing". If you pick softly and let the notes "breathe", you start to see what the fun is about.

Well, I did the measure on the working beast. But I really don't know if you would like the results...

I've remeasured the trannies too. I've found two Si NPN's I liked most:
The infamous 2N3565 (not easy to find here in Brasil) was hfe=230 and a 2N2222 with a hfe=205.
The Ge PNP remained the 2N404A showing a hfe=40.

I changed both collector resistors from 100K to 91K. Feedback resistor for Si NPN = 680K and the Ge PNP = 220K. Input cap = 0.047uF polyester, the input-to-ground cap = 100 pF ceramic disc, bases cap = 0.1 uF tropical fish and output cap = 1uF polyester NP. The emissor to ground remained Tântalum 47uF. I, at this moment, gave up the 1K + 2u2F parallel to the Ge PNP collector resistor. And, as my config was very close to some of the known version pics, decided to keep the input diode-to-ground out of the circuit. Harmonic's Pot = 100K and Output Level Pot = 50K.

With both NPN's the measures was the same (power supply: 8.98v.):

Si NPN Collector = 4.70 v

Ge PNP Collector = 3.65 v.

Emissors = 4.03 v.

I did the output diode "clipping" stage with two 1N60 and a resistor of 10K. It works OK, but I will really put the switchable option to use a Si/Ge diode combo for more level and less compressed output in the finalized pedal.

Post comments:

I would like to get more "octave effect" and a bit less splat, retaining the wonderfull sustain when used with both guitar's Volume and pedal Harmonic's pot all opened up. And I like the HP most with my Parker P-30 (almost a Strato) with Golden lace Sensors. Hotter pickups are less interesting with HP in my opinion.

I hope to post some sound samples soon if anybody is interested.

Wow, that's really fantastic!! I could not get those voltages to come out like that with any of my transistors, even with similar hfe and resistor values. (Did you get the emitter and Ge PNP collector voltages reversed in your post?)

For more octave I would suggest lowering the Ge PNP collector resistor value. That seems to work with mine.

I played with mine for a few hours (too long) last night. Personally I'm kind of tired of the "octave up" sound. It sounds like an axis fuzz which is fine but I've already got one of those.

I went back to the 2n3565 NPN (hfe 200) because it sounds smoother than the other NPN's I tried. I am using a Ge PNP 2n404a 67 hfe but I have another Ge I'm thinking of using instead, one Joe G gave me a long time ago. I think it's a 2n614 or something like that? (Can't remember the p/n.) Anyway it has 160hfe and sounds smoother with less "octave up" than the 2n404a. I'm thinking of pulling the 2n404a out of my Brick, IIRC it was hfe 100. For some reason, higher hfe Ge's give me more of the sound I want. (Less splat and misbiased octave sound.) Incidentally I tried a couple AC128's and an AC188 and could not get them to work well. I couldn't get them to develop enough gain.

I am testing with a Squire Bullet Strat into my homebrew "vox" amp. One thing that is cool is G at the 5th fret D string produces this really wild harmonic/octave bloom that just takes off, even at real low volume. The circuit is very sensitive there. I agree that it sounds better with single coils.

FWIW I'm leaving out the 1k/2.2u filter now. I must have accidentally wired it up wrong the other day. I took it off and added it back and now it is just chopping out too much gain, which is what I expected to begin with.

Glad to hear you are making progress. Would love to hear a soundclip!

Has anybody used BD 135/136 in the circuit? Or some other Si/Si combo that worked?

I'm going to try 2n3904/2n3906 tonight.

The measurement was made using an asian "not-that-cool" digital multimeter direct on the built circuit working as it is.

Each value was measured from the referred point in relation to the ground. not divided in point-to-point parts (like Q1 collector-to-emissor voltage). But just a bit of basic arithmetic and you get all those values. Did I make it clear?

I've tested other Ge PNP's : AC128, AC188, 2SB54 and 2SB75. Nothing even touched the 2N404A, at least in my sampling universe.

I've tested other Si NPN's too: 2N3904, BC238, BC548, 2N5088 and I even tried a MOSFET 2N7000 (remembering Tim E.), which worked but with low gain and a mediocre overdriven sound. With Ge NPN's the thing didn't work at all, just crackling sounds at max.

I tested a pot in place of the fixed PNP collector's resistor to find a better value, but late at night it seemed going to the undesirable side, so I will try it out once again.

Soon I will provide a very unpretentious soundclip, maybe tomorrow.

I really like that "hoarse" (I don't know if it's the right word, as it's so similar to porn stuff...) and the octaved down effect. And I really would like to preserve those qualities and, if possible, even to refine and get more of them.

It's cool what we are geting here. I'm very happy with it.

Recently, in another internet stompbox forum, with a very good help from Mr Graemey, an old mysterious fuzz, the Baldwin Burns Buzzaround was reborn to original specs. Now I have two clones here, one PNP and one NPN.

I couldn't imagine this 2 months ago. And what a sound!

did some simple math

As a guess for Q1 using George G schematic

20K collector
Ic .05ma
Emitter at 3.5VDC

for a 2.5VDc drop C to E and 1VDC across the 20K
2.5VDC - .6VDC (Vbe) = 1.9VDC C to B

1.9VDC / 220K = about .009ma

.05ma / .009ma = about 5.5 Hfe?

So one would need a very low Hfe device
OR
greatly increase the C to B bias feedback resistor (1.9VDC/1meg =.0019ma,  .05ma/ .0019ma = Hfe about 26)
Or pick a higher total circuit IC and lower collector resistor value (maybe .1ma and 10K or ....)

This circuit is interactive and sensitive to the parts used

Hummmmmm...

P.S. -> Please, where you read "Emissor" in my posts, substitute it for "Emitter".

Alex, please ignore my comments about your voltages. I incorrectly read what you posted. I understand now.

Gus, thanks for the tips. I should have done the math myself. I got into a vicious parts swapping cycle last night, thinking I didn't have much time. Next thing I knew it was late and I got about 5 hours sleep...

So, with a ~40 hfe 2n404a, which I have, it looks like I'll need roughly a 1.5M feedback resistor to get the target 50uA current. I will give this a try- maybe if the voltages and currents make sense it will provide a reference for how it is "supposed to" sound. Then I can tweak from that point to make it sound like I want.

Alex, one thing I forgot to mention is I tried a Mullard Ge NPN I had and it sounded fine. I didn't notice much difference between that and Si NPN but if you want the novelty of "all Ge" it will work with the right transistor.

EDIT: Going back through George's math in the other thread I think one of the key points is that with Vce so low, there's a wide range of bias settings that will work. This reinforces my observation that I'm not getting drastic changes in tone with bias and/or feedback resistor changes.

I'm just posting to mention that I did try Gus's two npn idea. (2n2222a) It works just fine. I also spent a bit too much time jammin and messed up my bed-time.  For most of that time it was working (with low volume) even though I had forgotten to connect Q2's collector.
When I started taking voltage measurements I noticed the problem.

I used 1M pots at the feedback adjustment nodes. Lowering Q2's just seems to drop the volume. Changing the value at Q1 can add some voulme, but the distortion does not seem to change much.

The tone is similar to the Differential Distortion in the sense that as the signal/note fades, the distortion seems to remain fairly constant.
Also, as the note fades there is not any nasty crackling that I've noticed in a few fuzzes that I've breadboarded.
There seems to be a good amount of cross modulation. I identify this by bending one note while holding another and listening for the "divebomb" sound.

I did not notice any octave sounds. Maybe I should change the 100u cap and listen for differences.
today I'll try different components and get some voltages.

If I should post future comments in a new thread, just let me know

Interesting thread. It makes me wonder why they went and changed Q1 from a silicon to a germanium transistor. Maybe for lower gain or they thought it sounded better? I think the biggest problem with that is the leakage of the germanium. With the circuit only drawing 50uA it's all too easy to get at least that much leakage which will throw everything out. Maybe they had to select for very low leakage? It might be worth thinking about a low gain pnp silicon for Q1 to get around that the only disadvantage I can see is if it doesn't sound as good.

Well, I think I finally came to the conclusion of this for me. Last night I experimented with Q2 100hfe NPN and Q1 2n404a 40hfe. I used a 2.2M feedback resistor on Q1 and got the target voltages to come out pretty close to Gus and George's predictions. Unfortunately it sounded pretty horrible- thin, misbiased, fizzy sounding. Maybe that's the way it was intended to sound but I kind of doubt it. So after changing  back to stock feedback resistor and playing with the 2n404a's at 40-67hfe and a 2n614 I had with 160hfe, I came to the conclusion that with low hfe this had a wheezy "helium octave" sound (on the upper part of the neck) that I didn't like and just couldn't tune out. The 2n614 sounded much better in that respect but didn't have enough gain.

So I changed course and decided to just re-voice my Brick instead with the coupling cap values in George's schematic. I also swapped out the 1n46's for 1n34a's and used a 10k series resistor with one of the diode legs. There it was- nice full fuzztone with a fairly unique low freq growl that you hear in the Albini vid. No fizz, no wheeze, up above the 12th fret it maintains the thick, fat fuzz. Nice gain range and at lower settings it gave the strat a nice overdrive sound. It was late and I had to keep the volume down so I wasn't able to check the sustain/feedback/bloom stuff, but it did real well at low volume and sounds pretty sensitive.

Then I remembered that when I built the Brick I tried three different 2n404a's with hfe of 40, 67, and 100. I had chosen the 100 because it sounded the best. My conclusion is that first off, you need a 2n404a with an hfe of 100 or so. With hfe much lower than that, it does not sound good IMO. With the "right" transistor in there, you don't need the input diode or 2.2u/1k filtering or etc. At this point I suspect some of those circuit variations may have been band-aids to account for variations in transistors that were available. Secondly, I don't think collector voltage bias setting is that significant. With Vce of 1v, you have a lot of range within 9v to work with and move around without affecting the overall sound very much. It's like the first stage of a BMP with the grounded emitter in that respect. I don't know which version of the HP the "spec sheet" was intended for, but I don't believe the 50uA spec unless it had a 91k Rc on Q1 as well as Q2. With my circuit I was able to get the good sound with a 22k Rc on Q1 and Ic much higher than 50uA. So IMO the 50uA spec is essentially a red herring. Another thing I found out is it has plenty of output with the 1n34a's. The key is to use the 10k series resistor. That also affects the tuning and overall tone of it (you will see what I mean if you experiment with that resistor). One of Alf's original schems showed a 1k there IIRC, which will really limit the output signal swing.

This is not any kind of definitive "mystery solved" thing for the HP in general. But it does conclude this exercise for me and I'm really happy with what I ended up with.

Here's the schematic for my "updated" Brick: http://www.aronnelson.com/gallery/main.php/v/DougH/Brick/brick.gif.html?g2_imageViewsIndex=1 (http://www.aronnelson.com/gallery/main.php/v/DougH/Brick/brick.gif.html?g2_imageViewsIndex=1)

I'll try to come up with a sound clip later in the week.

I think I'd like to try to get hold of some more 2n404a's and sort them for higher hfe and build another one up on the breadboard. It would be interesting to see if I could get any sort of consistency and it might reinforce/disprove my premise that Q1 needs to have higher hfe.

QuoteWith my circuit I was able to get the good sound with a 22k Rc on Q1 and Ic much higher than 50uA. So IMO the 50uA spec is essentially a red herring.

Actually, I take that back... I just did a quick calculation with the Q2 Vc I measured last night (2.1v) and it looks like Ic was around 69uA, not that far off... Hmmm...

Still, as far as good sound is concerned, I don't think bias voltage setting is that significant for this.

Doug, I always found suspicious that current drain issue. At least with much accuracy...

WEll, I didn't have a lot of time to record the clips last night, so they was played in a hurry, but I think they will give a bit of the circuits sound.
Please, folks, forgive the lack of inpiration and cold-hands-playing!

There are both soundclips:

http://www.4shared.com/file/52700761/b7922c15/Perc2N2222.html
http://www.4shared.com/file/52700843/60f66886/Perco2N3565.html

and this is a hand drawn schematic:

(http://i285.photobucket.com/albums/ll73/alexfrias2008/SardonicPercloreto.jpg)

Those clips was recorded using a Parker P-30, with Golden Lace Sensor pickups, bridge pickup only.
The controls on the project was all crancked up, only the guitar volume control was tweaked while playing.
A Marshall Plexi emulation, as ZOOM insists that we believe in it, and just a bit of digital room reverb was used and all the recording was done through headphones, as no crancked amp or loud acoustic feedback was allowed late at night. Next time I will try it earlier...

Still not there, but the results are very interesting in my opinion. With more spare time I will try different values on Q1 collector to ground resistor, supposedlylower ones, as Doug said.

Interesting clips ... anybody from europe here? Where to get 2N404?

@Alex frias : you used metalcan 2N2222 or TO92?

Or can somebody who knows the circuit test BD135/136 ... are they any good for H.P. or a waste of time?

Alex, your clips sound great. :icon_wink: I love your playing and you have a really nice sense of touch.

In your clips I'm hearing a little of the "wheeziness" I was trying to dial out of mine. But that may be the way it's supposed to sound, who knows. In any case this is a subjective personal taste issue at this point. (After all the axis fuzz is supposed to sound like that when it is full bore.) I hear the bass growl in yours too, which is what I am getting as well.

I'll do a clip later this week and we can compare notes.

I just ordered 10 2n404a's and some more 2n3565's. I'm going to try to duplicate on the breadboard what I have in the Brick. Hopefully I'll find out if my hfe observations are correct and how easy it is to do a consistent build.

"@Alex frias : you used metalcan 2N2222 or TO92?"

Plastic TO-92, ordinary ones.

Soundclips: I just listen to the mp3 files I posted, I didn't listen to them after "wav->mp3" conversion, I used River Past, even an annoying aliasing noise can be heard, hummmm... some sound artifacts were created, but you still get part of the picture.

I don't want to look for excuses, but it's not the exact sound of the thing.

I think what you, Doug, are referring as "wheeziness" is part of the percolator's sound character when full cranked, but I think it can be less than mine exhibits right now. What I would like to achieve, if possible, is less "wheezzo", more sub-harmonic (octave down kind of) richness. At the same time retaining the lovely mutating sustain, the weird kind of polyfonic intermodulation and dynamics it has.

One thing some people are pointing at as a significant diferencial in Albinis vid is the singular instrument he is using. If its single coils has less power than is usual I believe it is good candidate to be blamed of "horrible" diferences between his HP-1 and the Barge claimed-clone. I still didn't listen to the Chuck Collins clone.

One thing I'm sure about this circuit: it is one of the most transistor sensitive I have notice. I think it surpasses Fuzz Face on that matter.

I like this thread it is fun and also cool how people are trying different things and posting about them.  The HP is still a mystery because none of us have a real working unit to try and measure voltages from.

Maybe more variations like the brick circuit will result from this and other threads about the HP.

I need to finish building the 2n2222a and 2n2907 one I started

I want to try a two 2n2222a (Hfe about 200) version at .1ma using the two npn circuit I posted
Higher Hfe at Q2
47K collector resistor and 470K C to B Q2 part

10K collector resistor and 1.2 meg C to B Q1 part

.047uf, .1uf and .1uf caps

QuoteWhat I would like to achieve, if possible, is less "wheezzo", more sub-harmonic (octave down kind of) richness

Alex, if you have a 2n404a with higher hfe, give that a try. I suspect that may be what improved the sound of my Brick.

Gus, I don't think collector voltages are that significant in this circuit. I think the current through the feedback resistor and base is more significant. Using large feedback resistors to reach a target voltage is not the correct approach IMO. That starves the base of current and really changes the operating point in a way that screws up the sound. I was thinking it needed around 4.5v on Q2-C but even at 2.1v it's only a 20-25uA difference in Ic- not much. Not enough to worry about IMO anyway. Plus, your voltage calculations are partially based on George's assumption that the NPN Q2 is 100 hfe. Don't know if that's true or not but in the end I don't think that or the voltages are that significant, because Vce (which is significant) is so low.

But by just listening, I'm hearing major improvement in sound so far with a higher hfe Ge PNP for Q1. I noticed it with both the 2n404a's and a 2n614. For some reason I could not get an AC128 or AC188 to work- just didn't produce enough gain. But with stock resistor values, 2n404a's work fine, regardless of Vc. It's just a matter of picking one with sufficient hfe IMO- kind of the antithesis of the lower hfe you want for something like a fuzz face.

Incidentally I tried a 2n5087/5089 pair and it worked fine. It was a little wheezy sounding too and not as smooth, but it did work. I think Ge PNP and the 3565 are the way to go for smoothness.

Doug

Looking at your Brick Schematic.

You have 2.1VDC at Q2 collector so you should have about 1.5VDC at Q1 collector  (9VDC -2.1VDC = 6.9VDC,  6.9VDC / 100K = .069ma,  .069ma X 22K is about 1.5VDC)

So collector to collector you have about .6VDC?

Well, I did more tests with my Sardonic Percloretor.

1 - A new combination of trannies.

The only 2N404A with significative higher hfe also shows a very high leakage... but sounds good anyway, but with a very reduced gain. So I tried it with a BC108 (hfe= 450). It worked but sounded worse than the 2N404A/hfe=40 + Si/hfe~200, what I liked most and considered as my reference combo.

This time a lot of AC128, AC188 and 2SB54 worked, but none with a sound better or even close to the reference combo. Aside from hfe's I didn't make any other measurement. Doug, I can't agree more: 2N404A is the right path for smoothness, perhaps 2N3565 too.

2 - I tested again several tranny combinations, this time also variating Q1 collector to ground resistance (100K to lower values) and it just gets worse in wheezzo department. Doug, I didn't notice any improvement in octave down effect... And in my opinion, the reference combo with a fixed resistor of 90K worked best, sound wise. Maybe I will try higher resistance values, but that was not the direction indicated by the pics on the net.

I am very happy with the sound as it is at this time, with the schematic I post using the reference combo. But I think it's not THE SOUND of the thing...

Anybody is or has a close friend to Mr Albini? I really would love to see his Percolator guts...

Gus- yes those voltages sound right. I will double check tonight.

Alex- I found that going too high with hfe seems to reduce gain too, at least with Ge PNP's (2n5087 worked okay gainwise). For me it seemed to be a balancing act with the 2n404a, needed high enough for good sound but too high it loses gain.

At my lunch time I did listen to the ToneFrenzy soundclip. Well, at first I think they didn't cranked up the thing. And comparing with the noises I got from mine version, I prefer mine. I even can't hear our lovely octave down side effect.

A funny thought occurred me: anybody tested this thing with batteries? I'll try it out just for fun!

Doug, I consider your observation very close to the idea that's growing up in my mind in direction to the key of the treasure.

Sometimes I reread our posts and find myself laughable. What an obsession!!!

QuoteAt my lunch time I did listen to the ToneFrenzy soundclip. Well, at first I think they didn't cranked up the thing.

Yeah, it's a lousy demo really. They fell in love with the low gain sounds so that's all the really demo'ed.

http://www.bargeconcepts.com/bp/bphistory.html

http://www.bargeconcepts.com/bp/hpschem.html

The above links and the video

Has to be NPN NPN? first link 4th paragraph

The 2nd link why have a EF "feeding" a gain stage that is sensitive to the source resistance "feeding" it?  as drawn it will force the top transistor to operate at it's max gain.  The first stage being an EF will remove the interaction with the guitar.  The one we are working from is a part of the feedback setting of the gain stage(like a FF type circuit)

I hope we can make a sticky or something to keep all the posts and threads about this circuit together.

I like the "has to be NPN" with no explanation why. Most of the BC stuff appears to be clones of things designed by others, except for routng and feedback looper stuff. I never understood why they stuck a buffer on the front either.

I made a video of the Brick today and I'll post a link when it's up on youtube.

Here's a youtube clip of the Brick: http://youtube.com/watch?v=1lc85IimYrQ (http://youtube.com/watch?v=1lc85IimYrQ)

The video is grainy because I compressed it down to 10% to shorten the upload time (it's 4 minutes +). It's also out of focus.  (:icon_redface: Getting used to a brand new camera. should have used macro...) Anyway, the main point was the audio which was through the camera mic and untouched (except by the youtube manglers probably). There's a lot of natural reverb in the clip because the camera was on the bench pointed away from the speaker. So it's mainly picking up the bounce. (Sounds kind of cool IMO.)

I played around with it more last night, and as Alex mentioned, I think it sounds much better with weaker pickups. With the PAFs on the Hamer it just sounded dull. But with either the single coils on the strat or the retrotron humbuckers on the hollow body epi this pedal sounds really good. It sounds like it comes "alive" with weaker pups whereas hot pups just swamp it. (Retrotrons are similar to the old DeArmonds, a weaker and more trebly humbucker.)

Well i guess thats one brick that wont get thrown through a window, it sounds sweet doug. Also watched you amp vid ,nice amp mate. You could have worn a hat though. Oh well you know what they say the more hair you loose the more head you get :o ;D

EDIT; Sorry doug thats dry aussie humour,think ive had too many beers,cheers

One idea that might be worth trying is to use a silicon PNP for Q1 then add a linearizing network, comprising of a diode in series with a resistor, across the Base and Emitter of Q1.

The same trick has been used for Q2 on the fuzz face.

Interesting ... do you have a schematic (just for the idea you posted)? I'm not sure if I understood correcly.  (just curious: how does it look like in a fuzzface?)

I received my 2n404a's yesterday and measured a couple of them. At least one is hfe 110. So I'm going to test my theory that it requires a 2n404a with hfe ~100 in order to sound "good". If I'm correct I'll do a quickie comparison video subbing a few different hfe values on the breadboard. It's so easy to do videos with this camera it's ridiculous...

Another thing I thought of with the "weak pickup sounds good" issue is it may just be a matter of tuning the input coupling cap to the pickup. I'll try a .022u with my PAFs and see how that sounds. A switch or Gagan-Easy-Face style input tone control could be used to compensate for different pickup types.

Okay, after playing with my 2n404a's this weekend I like the 2n404a hfe to be in the 80-130 range. It's a personal preference thing but below 80 it sounds "misbiased" and above 130 it starts losing "gain" (distortion and harmonics). Also, pickup types come into play. With PAFs, hfe > 130 worked better because there was a hotter signal from the guitar. With weaker pickups, lower hfe may be preferable. Of course you can find a balance that sounds good in both circumstances. However, with PAFs a .022u input cap sounded more defined, whereas the stock .047u tended to "mush out". I didn't notice much difference with/without the 100p, maybe it helps with RF.

After trying different hfe xsistors I measured voltages and didn't notice appreciable differences. I think this is a "current thing". I may build another one and put a switch or "thickness" control on it to compensate for different pickup types. But this concludes my experimentation with it. My advice if you want to build a perc type circuit, would be to get some 2n404a's and experiment, find the hfe you like. I got a 10 pack of them for around $20 on Ebay, delivered in less than a week. The hfe's ranged from 80 - 330.

Check out the video of the Brick, if you get a chance. This is my "reference" sound for this thing:

http://www.youtube.com/watch?v=1lc85IimYrQ (http://www.youtube.com/watch?v=1lc85IimYrQ)

Here's another derivative I had not seen before: http://www.rockandrollworkshop.com/index_files/harmonicannihilator.htm (http://www.rockandrollworkshop.com/index_files/harmonicannihilator.htm)

Hi, Doug, I saw this stuff in another net place, but when I heard the sample I gave up to believe it is capable to get a Percolator decent expresso out of it.

I think it was a kind of mix of a Percolator with some sound degrading circuit... I don't remember now...

Still no Mr Albini's friend appeared?

heres a vid of my perc it doesnt sound any thing like dougs and it sounds really misbiased through this amp,i'll have to fiddle with it some more. The circuit is still on the breadboard and all controls cranked right up. The amp is a homebrew thing I modded from an old 100w valve PA and is crystal clean without the effect plugged into it. Recorded into a rode mic straight into imovie. http://www.youtube.com/watch?v=NxBn1PDoGbI (http://www.youtube.com/watch?v=NxBn1PDoGbI) Please dont comment on my guitar playing.

Comments on doug's video clip and build.

Sounds nice and refined, sustains well and has few artifacts or nasties.
The camera is compressing the poop out of the dynamic range though!
Hear the back ground noise come up between loud sections?
Also notice how the level doesn't change when the volume is turned up.
Part of this is the amp compressing/distorting more and the camera's
limiter sucking that up

Another thing to keep in mind is that the amp sounds great by itself and has
a slight break up with the Brick in bypass. So some of that sustain and dirt is
coming from the amp for sure. Not a bad thing at all. Just pointing it out.

The build sounds very nice for sure.

Geez Doug, why don't you use a shittier amp!  :icon_razz:

john

I would like to make John's words as mine, about Doug's vid.

I also noticed a very compressed overall sound, an artifact very common when using the audio from camera's mic.

Well, the guitar/amp sound is very cool indeed, so we hope for the best when the Brick is activated. And it happens!

The thing, when cranked up, shows much less wheeziness than my version. A high point. Even that I like the wheezzo in my sound, I think we all here are trying to catch the specific HP-1 magic. So I think Doug is closer than me in this aspect. I didn't notice the sub octave effect, but the acoustic feedback was dumbs up. Infinite sustain!!!

I bought the last 10 2N404A I've found as NOS in an old electronics store, downtown Rio de Janeiro. So I will test the Doug's theory about the Q1's hfe. I found some BSX 20 Si NPN with very low hfe, so they will be the second try, as Q2. Soon I will receive more 2N404A and 2N3565 by mail and new tests will be done. Now you all know I'm into that obsessive compulasive search. 

Doug, did you keep the Q1's collector resistor as 22K?

One mor thing: I thought the wheeziness was an artifact linked to the more gained the circuit was working and it could be controlable by the Harmonic's or guitar pots. But I think it's possible to have a more cranked fuzz sound with less zingness by using a good balanced trannies.

Thanks, John. The camera audio is far from perfect, but given that it's really fairly accurate to what I hear in my ears at head level. The biggest issue is the dynamic range due to limiting etc and I can live with that. The room reverb was a little exaggerated but it's easier to pick it up with the camera than it is to set up two mics. In fact, I'll probably be sticking with the camera from now on since it's so darn easy to use. It's much easier than firing up the computer and messing with the mic and mixer and etc.

I don't agree that there's much "amp sound" in this clip at all. I can try it with a couple other amps to see, but the amp is dialed up very clean with single coil pups, and doesn't sound compressed or dirty IMO when the box is bypassed.

Thanks for the comments. :icon_wink:

QuoteDoug, did you keep the Q1's collector resistor as 22K?

Yes.

Two ways to control "wheez" IMO- raise Q1 Rc from 22k to 100k (91k), or use higher hfe xsistor for Q1.

Thanks for your comments on the clip. :icon_wink:

Doug
Maybe what I should have said is that the amp seems to be easily boosted into overdrive.
(It sounds great by the way) The same way boosters drive the amp into overdrive.
Played through a fender type amp I'm sure the Brick sounds very different and the
added level would show up as a level boost not compression/overdrive. (Naturally)

Is there a limiter or sensitivity selection for the on camera mic?
The quality of the room and amp are ok. Just the slow deep compression gets distracting.

Sorry for getting off topic.

john

I see what you mean by the 'breathing' of the camera mic, John. I don't think there are any settings to control that but I will check. I might record it again with the computer and sync it to some video and see how that turns out.

Well, we are talking top level video/audio productions here!!!

Jokes off, I'm here just to endorse Doug's theory about the best Q1's hfe. I've tested several 2N404A's and one "unknown" Ge PNP.
The 2N404A's with hfe around 100 sounded best. It deals with the gain and the quality of distortion and fuzziness (and fizziness in certain cases). 

At the end of the tests the subtleties were scaping from my ears. But I used 2N404A hfe=105 as Q1 and BSX 20 hfe=108 as Q2. The sound and playability was very good, but, even with a deteriorated perception, I think 2N3565 sounds smoother... When I obtain more conclusive answers I will do new soundclips to compare and try to help a little.

The 2n3565 sounded smoother than other xsistors I tried for Q2 too. It's subtle but I can hear it.

damn, i missed, like, three pages of this read.

will somebody put a summary after this epic discussion?

Go ahead and have at it.

Just to assure Doug's comments about Q1 2N404A hfe~100 I put a utub vid.
Using the same hand drawn scheme I posted titled "Sardonic Percloretor", now renamed "Expresso Tone Machine", with a 2N404A hfe=110 as Q1.
In the first part I used a BSX20 (metal can, for super-mojo!!!) with a hfe=105 for the Q2, then at the second part a 2N3565 with a hfe=203 was used.
The setup used to record thie audio was exact the same as the one used in my old soundclips, just for an easyer comparison.

http://www.youtube.com/watch?v=PWlNgtUCM4M

The only thing I didn't obtain from this circuit (in the soundclips) was that wonderfull acoustic feedback, for an obvious reason: I did all the recording through headphones.
But I tested it using a small Marshall combo and... Yes!!! It feedbacked as it was alive in a very musical way!

For me, this new seting of trannies sounds way better than the others I've been trying, so I really agree with Doug H. when he claims the magic is something about the "current thing", as I saw no significant differences in voltage measures. This new combo certainly is closer to what "I suppose" a good HP-1 sounds.

Sounds nice, Alex! Thanks for making the video. :icon_wink:

After all experimentation my conclusion at this time is the Doug's New Brick design gaves me the most interesting sound and performance close to how I "imagine" the original HP-1 is supposed to behave. And I must to thank Doug Hammond very much because it worthes any effort to get the right components and setings. The smoothest combination was achieved using the New Brick design with a 2N404A hfe=150 and a 2N3565 hfe=205. Several combinations achieved good results too, but always using devices around those hfe's. It's the real zen drive, because balance is the key word here!

Two observations:

1 - It's another beast when played with some volume from a good amplifier, it doesn't need to be that loud. It really comes to life and shows what differs it from the other distortion boxes. Even with medium to high Harmonics (Fuzz on the Brick) control position you can get very good sustain and the fantastically musical feedback.

2 - Using the Hamonics Pot or the Guitars Volume Pot you can control not only the distortion intensity, you can also TUNE the pedal behaviour! It's a beast actually!

Two mod's I've tested with good results: as said before, the Gagan's Easyface input tone control works great with the HP as a pickup matcher or to change some timbre character; using more diodes in series with the cliping one's can give a more "normal" drive sound and a considerable level boost.

Well, as you all can perceive, I'm very impressed!

Doug, thanx again and congratulations for your effort and sharing, your kindness and your very good performances on the demos.
Thanks to all people helping and sharing here too!

I would like to thank Doug as well.  I've been following this thread and finally built one up.  I happened to have a few 2N404's (not 2N404As) and Fairchild 2N3565's.  I found one of the 404s with a gain of 98 and an 3565 with a gain of 250.  It sounds amazing...everything I've ever wanted out of a fuzz circuit (other then the crazy skyripper stuff), the guitar tone and definition is retained, but with grit and low end grunt.

I tried a lot of different transistor combinations and different gains of the 'magic' combination of 404/3565 and found that they resulted in reduced gain or a very thin sounding circuit.

Thanks again!

Quote from: John Lyons on July 02, 2008, 05:14:59 PM
Maybe what I should have said is that the amp seems to be easily boosted into overdrive.
(It sounds great by the way) The same way boosters drive the amp into overdrive.
Played through a fender type amp I'm sure the Brick sounds very different and the
added level would show up as a level boost not compression/overdrive. (Naturally)

Hey John, I tried it with both my Octal Fatness dialed up clean and my clean SS amp (which has excessive headroom btw) and it sounded pretty much the same. Of course the amps all sound slightly different and I couldn't drive the SS amp as hard with the Brick volume control- but overall it sounded very similar.

Just wanted to follow up on that and report since I had tried it.

Ry and Alex,

Thanks for the comments. But you should really thank George, Gus and the many others that contributed to this and the older HP threads. George got the voicing "right" AFAIC and he and Gus both got us all thinking about the DC operating point and what it takes to make it sound "good".

The Brick is not a "design"- it's just the way I happened to build the Harmonic Percolator from all the various schematics that have been posted. I called it the "Brick" because of the way the finish on the box turned out and I wanted to avoid any issues using the name "Harmonic Percolator" which is now trademarked. Only difference is I removed what I considered "band-aids"- input diode and filtering, etc and changed the output pot to 100k. I even dumped my 1n46 diodes and went back to  the 'standard' 1n34a's that everyone else is using.

I don't want people to think the Brick is my design, because it's not. It's just another slight variation on the HP. I feel my only contribution to this has been finding a good target HFE for the 2n404a.

I'm glad you guys like the clip and were able to get your circuits sounding good. :icon_wink: This has been a cool thread.

"Hey John, I tried it with both my Octal Fatness dialed up clean and my clean SS amp (which has excessive headroom btw) and it sounded pretty much the same. Of course the amps all sound slightly different and I couldn't drive the SS amp as hard with the Brick volume control- but overall it sounded very similar.

Just wanted to follow up on that and report since I had tried it."


Ok, cool , thanks for the follow up. Thats good that it's not as sensitive to amp inputs.
Now I guess I ought to give this one a go now :icon_wink:
Thanks for the field testing here!

john

I would like to express my gratitude to everyone who gave the clues we have to work on!

But... it seems I can't stop yet! Yesterday I was playing with the "Brickolator" and very happy with it. Very cool sounds and lots of sustained mutant timbres, don't forget the very impressive and musical acoustic feedback.  Well ... I was still feeling it was lacking that stronger sub-harmonic-octave-down effect, so beautifull exaggerated on Albinis vid.

Then I gave a break and decided to reorganise the information stuff I have regarding the Harmonic Percolator in my computer HD.

I saw a there set of 3 pics that I completely forgot: they show a configuration very close to our George's PNP-NPN version.

I quickly made a PCB and tried the values I saw on the pics. What intrigued me was that Q2 10K collector-to-ground resistor, i didn't use values above 91K with success until DougH tell me that it has to do more with the trannies hfe matching. I built the circuit exactly as the following image (sorry for reusing the schem, if it hurts anybody, just tell me!):

(http://i324.photobucket.com/albums/k349/alexfriasmerco/PercolatorVersion2.gif)

If you get the same trannies with close hfe's you will get it! It has THE sound and it adds a very discernible sub-octave effect to. As I did few tests with different hfe trannies,  the best I achieve was with that combo shown at the picture. The sub octave is not completely stable, it appears at the note attack, then oscilates while it sustains, in some regions of the scale it's more evident than in others. it's not so evident as in a proper octaver, but much more elegant. I will try to find out a more accurate combination...

Hi Alex - what other trannies have you checked?
(of Ge's, I currently only have 2N219 PNP ...and AC141, AC 187, AF239, and a 2SA235 which may be faulty)
Any of these you tested? 2N404 seems hard-to-find in EU. Maybe I havent' looked at the right places. (I suppose that circuit would work "flipped", with a npn ge as well)

I saw you tested a 2n2222 for the Si NPN. Could be that 2N2219 also works?

Quote from: bool on July 14, 2008, 04:20:12 PM
Hi Alex - what other trannies have you checked?
(of Ge's, I currently only have 2N219 PNP ...and AC141, AC 187, AF239, and a 2SA235 which may be faulty)
Any of these you tested? 2N404 seems hard-to-find in EU. Maybe I havent' looked at the right places. (I suppose that circuit would work "flipped", with a npn ge as well)

Several AC188, AC128, 2SB75, 2SB54 and the 2N404A (also 5 unknown devices, but obviously they can't be used as reference). In this last attempt everything with medium to high hfe, many trannies sounded good, but, don't ask me why, THE SOUND I was looking for only was achieved with 2N404A. Some high hfe trannies exhibit a bit of the octave-down-at-attack effect.

Quote from: bool on July 14, 2008, 04:20:12 PM
I saw you tested a 2n2222 for the Si NPN. Could be that 2N2219 also works?

Don't know, but possibly...  i liked very much the combo: 2N404A hfe~250 + BSX20 hfe~100 (best octave-down effect), but the smoothest was the same Ge with 2N3565 hfe~120.

I soon will try to do a new "spectacular" video. :icon_rolleyes:

The pics I saw that took me to the 10K Q1's collector resistor value was in another forum, they was posted as Chuck Collins HP-1 clone guts. So I think I may thank to Mr Collins again...

Another stuff I reread was the Barge (Mis?)Concepts texts and schem. I was so tempted to give their NPN/PNP idea a try that I built a 3rd version of the circuit.
Well, I don't know what the hell they did to the PNP/NPN circuit to get it not working, but their (mis?)conception is by far very confused.

I've built the circuit according the Barge schems and the same referred pics.

At one part of the text about their BP-1 device Barge people says: "In the original HP-1, the identity of both transistors is concealed by a combination of a metal cylinder and some potting compound attaching the cylinder to the body of the transistor. What's missing on these two potted and completely unidentified parts is any way of distinguishing between them. In any kind of electronics manufacturing, it's vitally important to be able to tell what part you're dealing with, and to conceal two different devices in an identical way makes it impossible to easily tell which is which. However, it makes sense to not mark them if you don't have to - if they're both the same and there's no need to distinguish between them. As a piece of confirming evidence, the importance of this one cannot be overemphasized, even though it completely escaped us before the electronic truth materialized." This assumption it's not the most clever I've heard. What I understood is that the "Interfax" was never a big industry, so the production line would not be hard pressed to get a very high standard efficiency. And if you are using only 2 different kind of trannies (PNP and NPN), just put them in separate baskets after measuring and dressing to make them unrecognisable, prior to sold them on the PCB. Or even better, separate them also in hfe groups.

What really crosses my mind is the possibility of running out of 2N404A's and finding out an easier-to-find (and perhaps cheaper Si) alternative to substitute them. I finished the soldering process late at nite, so no audio tests are already made. As DougH said, some stuff added, as the input diode to ground and the 1K + 2.2uF in Q1's collector to ground, could be a form of "band-aids" or another tricky effort to accomodate different trannies and hfe values in the same project. But those are just possibilities...

I would love to get comments about it...

QuoteAnd if you are using only 2 different kind of trannies (PNP and NPN), just put them in separate baskets after measuring and dressing to make them unrecognisable, prior to sold them on the PCB.

Or just put their "disguises" on after they are soldered to the board.

Why not?

I hope to do tests with this new (NEW?) configuration, using NPN/NPN and PNP/NPN transistor-combinations to sse what we can get out of it.

Hard will be to find a Si PNP with different hfe values in my "stock", I think I only have 2N3406...

Anybody knows a complimentary PNP for the 2N3565?

Have not looked for a PNP but the few NPN 2n3568s I tested have a Hfe of about 120

I think this could be a possible candidate:

(http://i195.photobucket.com/albums/z210/alex_frias/2N3638.jpg)

Now that's pr0n ... no, no ... it's a MILF :)

just checked 10, 2n3638s  lowest Hfe was 150 most were >250

I admit my lack of attention to a very important thing: the collector-base resistor, in my third try, the version with the input-diode and the 1K+2.2uF in series from Q1 leg to ground, some more than exoctic glass resistors and unknown wax covered cap and trannies. The cap seems to be poted accidentaly, what could suggest the "disguises" was dressed after soldering... (CSI anybody?) Well, I don't know why I was thinking the collector-base resistor was at the same place the other versions showed, but as I replicate the pictured copper side of the pcb at the photos I perceived the differetial point.  It is actually a much more relevant clue than recognizability of transistors, I think. The resistor goes from base, I presume, to other leg. Now it even makes sense to me thinking about using two NPN's.

Barge pics:
http://bargeconcepts.com/bp/bppcb.jpg (http://bargeconcepts.com/bp/bppcb.jpg)

Yesterday I had a very busy day, so a little time was left to the tests I was suposed to do. The 2N3565 remained as the Q2 during the tests. Those quick tests showed the Si PNP's didn't work at all for Q1. The Ge PNP's worked but not as I would mean "properly". The Si NPN's produced some good overdriven sounds, but nothing that special. The values I've used for collector-base for both transistors was 750K, guessing the axial glass resistors were the same value... Some pictures in the Barge site shows the guts of their machine. I will pay more attention to figure out what they used in place of those resistors. Maybe use two trimpots (doh) to aproximate a best-value.

Well, I spend some time on the weekend trying to do my best with the supposed NPN/NPN version. I've changed the base-collectors resistors to what I understand from Barge  inside picture are 470K's. Just a so-so overdrive...

I then got back to the last PNP/NPN version I built.

My conclusion about this version is that it was the closest aproximation of the real thing sounds.

The component values used:

The caps are 100pF, .047uF, .1uF, .1uF e 47uF
Q2 collectror resistor 91K.
Q2 base-collector resistor 750K.
Q1 collector resistor 10K
Q1 base=collector resistor 220K
Diodes: 1N60
Diode resistor 4K7
Harmonics pot 100K A
Balance/Level pot 50K A
Q1 Ge PNP 2N404A hfe~380 (and a very leaking device)
Q2 Si NPN BSX20 hfe~75

To my taste, the more absurd the hfe and leakage for the Q1, better it is. But it lowers a lot of the overall gain. To keep the gain at a good level, the use of a Q2 with very low gain helps doing so. This balance between the transistors hfe are the key for THE sound, in my opinion it is getting cool above hfe 200 for the Q1.

I think I ended my tests as I'm very satisfied with the final sound. I tested the Doug's last shown schem with the same Q1 hi hfe / Q2 Lo hfe balance and achieved very close results.

Here a small video loosely playing with the prototype:
http://www.youtube.com/watch?v=VOAlUb7CCmg

Alex, that is the smoothest one you've demo'ed yet. Sounds beautiful! And the guitar cleanup is really great too. I hope that's the one that made it in your final build. :icon_wink:

I found that octave sound too with higher hfe transistors for Q1. I didn't mention it because I wasn't sure that's what you were talking about. It's inconsistent and only happens with certain notes and fret positions. (I didn't particularly like it because it wasn't consistent so I tried to tune that out of mine.)

In any case, you've really nailed the sound AFAIC. Patience & persistence pays off with this circuit. Hopefully others can reference this thread for some tips on tuning, hfe, etc so they can diy some decent sounding builds.

I think this is my final try about this one. I now have three PCB's populated with different versions. Both PNP/NPN's are very similar sounding when using close hfe transistor values. The twin NPN didn't work that great so, if I need it will be transformed in another great sounding PNP/NPN, or if somebody appears with some novelty about that version. I think Barge aproach is nothing like I would aprove in my own kind of research. At the technical side of view this circuit is side by side with the Fuzz Face: how far you can go with only 2 trannies and some resistors and caps. OK, the HP-1 uses TWO diodes and FF none, so it can be blamed by use of much more technology... ;D

One thing that's not in the video but I find is a very cool point of the unit is the acoustic feedback capability of it. It's monstruous and at the same time musicaly beautifull.
The octave effect I didn't managed it completely (on Albini's vid it's more on the lower register, in mine it appears in lower-middle notes) , but I do like the inconsistence regarding fret position and guitar volume/harmonics control pot seting. Distortion, in my opinion is a resulting balance between consistency and inconsistency. It's like dirty ying/yan. I even like some cheeseness, but judiciously used in a musical context. I still hear music as some sort of magical noise structures, something tha communicates with us in a more subtle emotional state, but much more effectively than words can do. So the sky is the sonical limit.

Now I have a very different sounding and ready to be explored new pedal. I hope my added 2 cents may be of any help to others looking for the same kind of stuff.

It sounds good Alex!
Thak you for posting your tests and results.

john

A note on the octave down effect of this pedal. The second stage of the percolater/brick is very similar to this electra distortion build. Which is noted for it's octave down behaviour.

http://www.home-wrecker.com/electra.html

And a general note. A difference I see with both circuits(and the Trotsky drive) is that there is no "coupling resistor" in between the output capacitor and the clipping diodes compared to most Dist+ type circuits. I assume the diodes give a variable load to the transistor depending on how much the diodes are conducting signal to ground. Do you guys think that has something to do with how these circuits are so spongy and why they can bloom?

Well, recently I read a topic here about the Jordan Bosstone and the supplied sound clip showed some octave down effect too (and several other noisy/sound artifacts...).

I think of building a J.Bosstone and try two or three things on it.

Regarding the Percolator: what I liked about it is that it is plenty of  "idiossyncrasies". The singing sustain and musical acoustic feedback are great bonuses. The sound artifacts, as its inconsistent octave down effect (only cranked up or close to it) and how it cleans up with the Harmonics or Guitar Volume control gives a seducing character to it.

My only complaint about the HP-1 is the noise ground, but... you know...

In spite of the present topic consists of six (!) pages now, there are no any attempts to explain why the subject creates so good sound  ???
So, let's try.
1. HP provides dynamic texture distortion due to the shift of the operating points of the PNP and NPN trannies caused by the "asymmetric" charge\discharge of the 47uF cap generally through the NPN transistor and clipping diodes. As we know Ge trannies are very sensitive to the operating point changes, so they produce much more "dynamic" tone change.
2. HP is not just "non-linear" amplifier, it's a kind of a resonant circuit with a positive feedback. Playing with all of its three caps one can convert it to low-frequency oscillator that can generate 80 to 200 Hz frequency pulses or to one-shot oscillator triggered by input signal. So it can divide the input frequency by two or even by three. That's why we can see the octave-dividing effect playing on several neck zones. This ability highly depends on coupling and electrolytic caps as well as on trannies' hfe.
3. Combination of the two above mentioned features creates very complicated effect on the circuit functioning, including DC and AC positive feedback loops and even kind of "automatic gain control" caused by the operating points shift, e.t.c. That's why the device is SO sensitive to it's parts characteristics.
As a matter of fact it's almost impossible to produce two HPs with the same sound. Also, they are sensitive to the ambient temperature changes.
So, I hope my "two cents" may trigger some more attempts to modify this wonderful device. For example, to change Ge trannies and diodes with Si ones (including Shottky),  use aluminium 47uF cap plus 1uF film instead of tantalum, e.t.c., e.t.c.     

I think you have done it and helped a lot! Thanks.

I was going for the empyrical side of it and what I saw is very well complemented by your explanation. One thing is clear: it's virtually impossible to do two units sounding exactly the same! I've tried it out but any small difference matters, eventhough it may be subtle...

Could you make any comment about the NPN/NPN version? I really had no success with this version...

Hi alex frias,
i think npn\npn HP version is not as interesting as "classic" pnp\npn one is. Classic HP has much more dynamics in sound texture because operating point shift is applied to both trannies' emitters (pls note that emitter is a "control" terminal of a tranny). In the npn\npn arrangement operating point shift affects only one emitter, hence we can assuume that op. point shift produces less affect on the distortion texture.
By the by it seems to be interesting to change Ge PNP transistor with the modern low-noise Si one and additional resistor in series with its emitter terminal to reduce its "excessive" gain. This measure can lower the overall noise and improve high-frequency roll-off of the input stage\pickup inductance. So we can expect the better (brighter) tone with humbucker pickups (again - lower hum). In this case the input pot ("Harmonics") resistance is not to be 100 kOhms, but maybe 250 or even 500 kOhms. Moreover, it may be omitted at all, because the volume pot can do it's "duty" with no additional noise caused by "Harmonics" pot.
But please note: all the written above is only theoretical assumptions. I didn't check them in reality to my regrets. Moreover, I'm not sure the proposed mods will sound as good as the "Brick" or Ge-Si versions do. It's almost impossible to compete with Doug H, as we know :-( 

OK, and Mr Hammond is among other things a real gentleman and it seems you are too!

I will try out some of your suggestions. I did some experiments with Si PNP, but at that time I didn't have any clue about the component values and their relation to the resulting sound. But at first I will keep the path I was folloing - PNP Hi hfe and NPN very low hfe.

A funny question: How can I simulate a leaking Ge device with Si trannies? I liked very much the leaking Ge PNP I used.

Regarding hi freq roll off, well, i't can be a good or a bad thing depending on the project...

Hi alex:
I'm sure it's actually impossible to simulate leaky Ge transistor with any components. Leakage is an internal property of the tranny. Moreover, it's combined with hfe and other mysterious Ge mojo :-)... Even if you'll find any theoretical solution, the sound won't be the same.
By the by, I have quite interesting Si project with BC550 (Hi-gain Si npn) and BC556 (Hi-gain Si pnp). As my spice simulator shows, the project have some distortion texture dynamics and frequency properties close to the classic HP.
At the same time I'm sure its sound will never be the same as that of the classic HP. Mojo is mojo :-(
If you have some time to try it, I'm ready to send you its chematic and some explanations. To my regrets I have no possibility to breadboard it in the nearest future. But it seems it worth some try as a differently sounding gadget.

DDD, Oh boy, you don't know what you have done... I'm an addict for this kind of project, so I will apreciate very much your offer and I ask you gently to send it to my personal mail:
alexfrias@viainterior.com

Last night I played guitar a lot and tried a number of things.

First, I did a personal version of Jordan Bosstone. It uses a NPN/PNP 2 trannies arrangement but in a different conception, anyway it makes good sounds and have some similarities with HP.

Regarding our beloved HP, I've tried some of your ideas. To my personal taste, or lack of it, I didn't find one Si/Si combination with interesting and complex tones like those I  found with Ge/Si. It's important to note that I used the last version I presented here in this topic, with the same component values. As DDD wrote, maybe some values will need to be changed or even some new components added in order to get more interesting tones.

Then I changed the transistor combination point of view, trying Q1 Si PNP/ Q2 Ge NPN. An interesting result was achieved, but this time leakage is not very wellcome. Leaking devices (as Q2) tended to sound misbiased. I've tried a lot of thannies (both Si and Ge) with low to high hfe's. As the fatigue arrived, my hearing tests turned blurred and inconclusive at this time, at least regarding the hfe's combination.  ASAP I do more tests, if relevant information arise from it, I will post again.

I hope Dough are doing well and accompanying this funny topic.

alex frias,
pls check for the e-mailed schematic.

Thanks, ASAP I hope to return with news!

Waiting impatiently for your news. ;-)

OK, time to see about reviving this very fascinating thread. Has anybody but Alex and Doug bitten the bullet and built one of these puppies? The demos are most amazing, just the whole component sensitivity thing is a bit daunting. Inquiring minds want to know...

Ben, Actually I have built it and I'm in the process of tuning it to have a little more bass. :icon_cool: I used the original xistors with gains around hFE=200.
I'm probably the only goomer to use the slide pots. That added a level of unnecessary fabrication complexity. I had an itch to build it like the crazy man from Milwaukee did. I recommend it if you like Fuzz of many flavors. The folks that are happy with their typically voiced distorshums need not concern themselves with FX like the HP.

I have a WMD Geiger Counter coming in the mail this week and the HP was a perfect "stepping tone" to that.


Have yerself some fun! 

Thanks, Daevid. I have to get me some Ge's, but maybe I will put it together with 2N3906 in a socket for the time being. It is right after Andy's Simple Fuzz on my list. Does your sound anything like the demos? How is it with HB as opposed to SC?
Thanks

Huuummmm, I'm happy seeing that this thread is still alive!

I rehouse my Expresso Tone Machine and decided not to keep the "Harmonics" knob as I use the Volume Guitar Control to get several textures from it. It's one pedal that I used in every gig.

Recently I usedid before a Scrambler I just built (following a Mr Hammer advice) and "Wow!!!" is the minimum I may say... You really have a "octave-up-coming-in" control at your guitar volume knob! Amazing and useful.

I tried some projects from Dimitri, a really nice and clever guy, in order to achieve a more "easy-to-find" parts HP circuitry. Sadly I had no success without the critical parts I've used. The project has some good sounds but nothing close to the character lof my ETM.

One issue I am convinced is that if you are planning to avoid the Ge PNP tranny, some modifications will be needed to keep the sound.

Can someone post the pinout for the "button" kine 2N3565? I don't see those in the data sheets.

I'm building one with 1uf lytics in the 100n ceramic positions and paralleling a 1n poly cap with
the 20K to gnd. I'm so feeble that I can't remember where I saw the thread showing the current layout
in Therimaniac's HP builds. This is apparently what works with a 2N4040A/2N3565 design.
Thank you in advance,

Noel.

Hey I'm new here, this is actually my first post. Anyway I have what seems to be a real life HP1 here in front of me, belongs to a friend. I can post gut shots and details of what is written on each component if ye want? I'm uploading scans of the guts to my flickr account right now. I presume this is a later version as the none of the components have been disguised.

Here's my parts list so far or at least the writing on each component:

Clipping diodes:   1 N 695 and 1or4Js 595 both read from the black line.

Red cap: 390 +/- 5% ODE? 9CCWV

C3/C6 Orange caps: 104

Green: 2D473K Tracon

Yellow: 47u 10

Backside: 102

PNP Germanium: 0533 2N404A (c interlocked with c logo)

NPN Silicon: 2N3565

Resistors starting at bottom of pic:

Hidden under green:    red-red-yellow      gold
                 Red-black-orange       gold
         White-brown-orange           gold
         Purple-green-yellow           gold
         Yellow-purple-red           gold

Cool!  What is the address of your flicker account?  Component and trace sides of the board would be great.

The clone I built from this thread has become my favorite fuzz pedal by far.  So much grunt and high end all at the same dirty time...

(http://farm3.static.flickr.com/2481/3552410542_69ef7c25e3.jpg)

(http://farm4.static.flickr.com/3405/3552415512_d76658749c.jpg)

(http://farm4.static.flickr.com/3664/3552421162_eda1eef500.jpg)

I need to buy a multimeter in the next few days so once I do I can take any measurements people want too. I plan to build one for myself anyway.

Oh my flickr address if you want bigger pics.

http://www.flickr.com/photos/moose23/

The Laconic Carbonator rears it's spastic head:
I just lashed one together with the new component data. I tried to keep the original mojeaux content
up there where ever possible. I'll finish fabbing the box for it and wire everything up so I can report
on the sound. The reason I'm posting these perfboard portraits because I'm only slightly too boastful
of my homage to the ones built by the crazy hombre from Milwaukee. Thanks to all the original folks
who worked so diligently to produce the actual effect. As has been stated, WTF were the folks at Barge
Concepts trying to build? LOL...

It's really remarkable, at least from my perspective, how accurate the "Brick" was all along. Another
freaky dealy was Alex Frias' experiments with crazy gain [hFE] xistor juxtapositions. The more offthewall
the numbers got, the circuits seemed to get more inline with the desired result.

Thanks to everyone that makes this hobby so rewarding,

Noel Grassy.
(http://i145.photobucket.com/albums/r222/noelgrassy/Free%20Stomp%20Boxes%20Archives/LaconicCarbonator3.jpg)
(http://i145.photobucket.com/albums/r222/noelgrassy/Free%20Stomp%20Boxes%20Archives/LaconicCarbonator1.jpg)

I have a Chuck Collins clone and mine has 1uf polarised electrolytic coupling caps.

The pin voltages are

PNP 2N404A

E 1.61 v
B 1.46 v
C 1.46 v

NPN 2n3565

E 1.62 v
B 1.93 v
C 2.49 v

I drew up a schem for mine:

(http://img3.imageshack.us/img3/8939/collinsschem.jpg)

Pic
(http://img41.imageshack.us/img41/4207/chuckcollinsperc0002.jpg)

Mine also has the 102 ceramic cap on the trace side.

a harmonic percolator clone made with the schematic in this thread has been used on the new Simple Minds album.

Looks like a nice yet simple build...it's on my list. :icon_wink:

Quote from: birt on June 07, 2009, 01:12:49 PM
a harmonic percolator clone made with the schematic in this thread has been used on the new Simple Minds album.

Interesting.

"It's alive, it's alive!!!"

Well I'm happy to see this recent movement about this thread. I'm absolutely obcesed by this little monster. And, yes, I will try those last tips just to say something about it.

Noel, what can you tell us about the glass encapsulated resistors you used?

And if the known band is using a kind of HP in its new record, good for them. So we must hope they use it for the light side of the force!

I've got a pair of 1n695's and am ready to try it on the breadboard again when I get some time. I suspect the diodes will be key.

Quote from: alex frias on June 12, 2009, 01:44:19 PM
"It's alive, it's alive!!!"

Well I'm happy to see this recent movement about this thread. I'm absolutely obcesed by this little monster. And, yes, I will try those last tips just to say something about it.

Noel, what can you tell us about the glass encapsulated resistors you used?

And if the known band is using a kind of HP in its new record, good for them. So we must hope they use it for the light side of the force!

i know what you mean i have built 4 of them. well one harmonic percolator and 3 harmonic jerkulators. my favorite being the jerkulator i made with old salvaged parts. anyway i don't really have anything to add other than my fascination.

Nice to see you, Mr Hammond, a honour, really.

Well, it's a so mojoable circuit... I can't bet anything for sure!

I'm really satisfiesd with my results about it, but you all know, it's unstopable. If there is another option, tip, clue, anything, we must try it out.

Heres my one on the verge of being wired up.
(http://i4.photobucket.com/albums/y115/quickkiwi/effects/IMGP1066.jpg)
Metal can 2N2222A and a 2SB171 with a gain of about 60 and leakage of 40 - 50uA.
(http://i4.photobucket.com/albums/y115/quickkiwi/effects/IMGP1062.jpg)
Not too much space in there but it'll be enough.

I found NOS 1N695 diodes and have posted for sale. No shortage of these, or of the 2N3565. For the germanium device, note that if you don't insist on a type number, you can have a bag of 5 devices with measured gains in the 50s and 60s for as little as $1.50 a pop. My SKU 0114B and 0114C. I have a fair stash of NOS 2N404 and 404A, and I will offer these audited at some point when I can make time to build a jig.

SD

So, Sean, how it sounds?

May you publish any kindo of sound samples?

Soon I will do a new video using my gig partner HP (Expresso Tone Machine for the old friends) with a new version with some small changes...
Let's see, and this time all done with real amps and mics.

Alex, I haven't tried on the end of a guitar yet, I've only used it on the end of a signal chain after one of my experimental instruments, clari(not),cmos nyquist then the jerkulator, but I managed to pickup that it had some very nice even harmonic distortion added as an after note... or octave I suppose, that came in a second or so as the note decayed off. I'm going to get a guitar out today and try some stuff but I haven't got my recording stuff together at all.

Finally finished the build, built it in a tomato can.  It is not a real HP for the top I used a 2n2222a, 47K collector resistor and a 470 K base to collector for the bottom 2n2907 part  I used a 10K collector resistor and a 1.2meg base to collector resistor.  I used a .047uf input cap and .1uf between stages and a .1uf output to 1n4148s 47uf cap at the emitters.  Used 100K audio pots at the in and out

Voltages 1.017VDC PNP collector, 3.31VDC emitters, 4.27 NPN collector.

It compresses and the sound will swell up if the input volume is max an the guitar volume is maxed if the volume is reduced it does not do this.  It feeds back in a controlled way.

Q1 a 2n2907 PNP 190   moto metal can
Q2 a 2n2222a NPN 210 moto metal can.

Even not being a real HP with the Ge PNP and having stock voltages it is a fun circuit

Sounds good, Gus. It is a lot of fun to play with.

I finally breadborded JJ's schematic and I must say, this is the best version of this I have heard yet. There is something very right about the way it sounds. IMO the two key elements are the 1u coupling caps (vs. the .1u I was using) and the 1n695 diodes. Yes, these diodes do make a difference. 1n34a's will work and sound okay but the 1n695's sound fatter and fuller. They are the same fwd voltage too so I think the difference is in the diode curves.

This is no longer a quirky funny sounding fuzz box but a real "tone machine" for lack of a better word. No whininess or upper octave- it's very smooth and oozes harmonics in a way that makes the guitar want to play itself. I'm not sure if it really needs the 390p or 1nf caps, if not I'm going to mod my "Brick" with the coupling caps and diode sections.

Been following this quietly. I like the upper octave.

It's still there, just more subtle.

Thinking about the diodes used with the HP.

From the posted voltages and resistor values.  +9VDC supply and 2.49VDC at the NPN collector and 91K. about 6.5 volts across the 91K for an Ic of about .07ma(70ua).   The available current is not that much for the diodes and the output volume control is a part of the load on the circuit.

So if I was to test diodes for this circuit I would check the voltage drop at a few different currents.  .07ma, .04ma, .10ma etc.  Another thing to check might be the diode capacitance  differences.   Also I would look for the spec for the junction capacitance of the diodes.

FWIW I measured the fwd voltages of both the 1n695's and the 1n34a's at .223 V.

I just looked up the diode test currents of the fluke 77

About .4mA (400uA)
At .6VDC it .3mA
At 1.2VDC it is about .2mA
At 2.0VDC it is about .1mA

So it look like at .225VDC the test current is >.3mA maybe to high to show the difference in the diodes at lower current.  Maybe a 9VDC supply and a 120K or so resistor(100k 150K add some together etc.)  9VDC -.225VDC = 8.775VDC
8.775VDC / .07mA = about 125Kohm.  Measure the diode drop with current like the Ic.  Maybe that will show the difference.

http://assets.fluke.com/manuals/7x2xiii_cieng0200.pdf

Sounds like a plan. I wondered if the more or less exact same voltage readings had something to do with my cheapo DVM. I'll give this a try when I get a chance.

BTW I modded the Brick last night and it sounds great. Subbed the .1u caps with 1u's and subbed out the 1n34a/10k diode network with the 4.7k/1n695's. Essentially it's the same sound as the HP circuit on the breadboard, slight variation but not enough to be significant IMO. I left out the 390p and .001u as they don't affect the sound, that I can tell. They may be there for RF and/or oscillation due to layout or etc.

OK, NOW I'm in a pickle...

First, I get an itch to build a Percolator, so I come here (naturally...).
I find this thread and see GG's schematic and I totally facepalm because I've built two percolators (one for me, one for a friend) using Alfonso Hermida's schematics (the one with "unknown transistor values") which I had to tweak to accommadate silicon transistors (I had no idea Q1 was a germanium).
They sounded... ok, not great. Almost, but not quite, entirely unlike a Percolator.

So I breadboarded one using all the advice I found here but for transistors I had to settle with what I had: a 2SB173 and a BC239.
How'd it sound? Very good.
Nice 'fat' tone to the fuzz, not overly buzzy nor bassy. Lots of sustain without a whole lot of noise to go with it, even though I'm playing an '84 Fender Bullet right in front of my CRT monitor. Whether I play chords or single notes, I can hear a very subtle-yet-audible decay into upper harmonics like it's begging to be fed back in front of a Mesa Boogie twin (which I sorely wish I owned *sigh*), even though I'm wearing headphones right now as I test it (family's asleep, you know).

I have now discovered a whole new world of Awesome. Thanks guys, you've made my day.

I was going to be happy and just box this one up and post a pic, but then the experiments began...  :icon_twisted:
I swapped around the various resistor values, but everything worked best using GG's original values.
Tried some other transistors for the BC239, but none sounded as good.
Then I very foggily remembered somebody on some forum or blog somewhere wondering if you could simulate Ge transistor leakage on a Si transistor by strapping a Ge diode from collector to base, ala Bazz Fuss (probably wrong, but somebody actually said it...).
So I tried it for Q1; a BC309 and an unmarked army-green glass Ge diode.
Guess what?

Yet another world of Awesome!

It actually sounds pretty good!
When I first tried it, it seemed to have just a tad more gain (which I don't mind at all, but putting a 47-100k on the collector instead of the 20k tames it down a bit) and there's a subtle difference in the overall tone, but closer than you'd expect.
There was no loss of fatness, and was not overly harsh like many silicons tend to be.
I noticed the harmonic bloom was a little more obvious, but that could be because of the increased gain.
It also sounded "quicker"; very responsive to pick attack, which I found very nice.
After playing for a while, I noticed I was using silicon diodes instead of germaniums for the clipping at the tail.
Swapped in the germaniums, didn't like it (too... fizzy), so I swapped the silicons back in.

So there's my pickle. Which one do I put in the box?
It would be exciting to have a reasonable facsimile of the original for bragging rights if nothing else, but I really like the sound of the mods I did.
I'd upload some sound clips if I wasn't stuck with free dial-up...  :icon_mad:
Would anybody like to try them and let me know what you think of the sound?




P.S. Using a metal pick adds extra mojo  :icon_cool:

QuoteSo there's my pickle. Which one do I put in the box?

That's easy- both.

Build two different versions and enjoy both of them.

*facepalm*
But I only wanted one. Oh well...

Heeeeyyy... How about if I tie both configurations to a 3pdt toggle switch?  :icon_cool: :icon_cool: :icon_cool:

My original schematic was on geocities, if you didn't already know geocities is closing near the end of oct 2009,  I've moved the schematic to photobucket,

http://i476.photobucket.com/albums/rr130/ggeffects/percolator_later_rev1_1.png

Hope no-one minds me bringing this thread up again.
I've been mucking about with it on the breadboard and am interested in Gus' suggestion to bias the two gain stages separately.
How do you go about this?
Do you treat each section as a  separate, closed circuit or just disconnect them by, say removing the 22uf cap or something?

Been thinking about this circuit again.

Now take a close look at the hfe vs Ic numbers in this PDF

http://www.datasheetcatalog.org/datasheet/philips/2N2222.pdf

Use ohms law and figure out the collector current Or read the thread

Some other notes from a sencore transistor checker hfe 200 cheap DMM($1.99 HF cen tech special like some might have) hfe 166, other transistor sencore hfe 190, HF 159

The hfe you measure with an inexpensive tester might not be the hfe of the transistor in circuit.

Selecting biasing resistor circuits.  This is instead of an adjustable power supply to select the resistors for the transistors used.

http://www.diystompboxes.com/smfforum/index.php?topic=85828.0

A 2 NPN HP like circuit idea.

http://www.aronnelson.com/gallery/main.php/v/gus/2npnHPlike.PNG.html

Current is .116ma.

Temp was 78F.

Not tested yet DC readings are from R1,R2,R3,R4,Q1,Q2 part that is built.  hfe readings measured with a cen tech DMM I bought from HF.

thanks for sharing!

Have you tested it with clipping diodes at the output?

just for the record,

si-npn, ge-pnp values:

rc, re: 90k
r1: 680k npn
r2: 220k pnp
npn hfe: 250
pnp hfe: 55; leakage: 70ua
ve: 4.1v, ie: 44ua

mac

Mac to be clear I am aware of the values you posted, they seem to be what people seem to like when trying to clone the circuit.

I posted something a little different to show the HP idea of series powered lower voltage supply gain stage, might be fun to experiment with higher current, different transistors etc.

FWIW I included hfe readings on the 2 NPN schematic from a $1.99 on sale centech brand meter from Harbor Freight.  The same transistors on a transistor tester measured Q2 200 and Q1 190.  The hfe vs Ic is curved and at .05ma I would think the hfe is lower.  I included the cen tech readings because people at this forum might have more DMMs like that than transistor checkers.

Gus,

I´m waiting a flight and in the meantime I did some math and solved the DC bias which is valid for all silicon versions, HP & Barge Concept, no matter if they have two npn, or a npn-pnp pair.

Please open your book on page 91 and see Harmida or Barge concept schematics :P

Let
ra: resistor to Vcc
rb: resistor to Gnd
r1: resistor from Q1 collector to base
r2: resistor from Q2 collector to base
d1,2: Vbe1,2
a1,2: (b1,2+1)

Note that both emiter currents are equal so,
ie1=ie2=i
(b1+1)*ib1=(b2+1)*ib2  [1]

and that
vcc=i*(ra+rb)+ib1*r1+ib2*r2+d1+d2  [2]

[1] --> [2]

ie2=(vcc-d1-d2)/(ra+rb+r1/a1+r2/a2)  [3]

if ra=rb=91k, r1=735k, r2=220k, b1=250, b2=50 then ie2=ie1=0.04ua, which are the values we found in the real world.

You can ask, how do I do to get half vcc at the junction of both transistors?
In this case you want

vcc/2=d1+ib1*r1+a1*ib1*ra
vcc/2=d2+ib2*r2+a2*ib2*rb

using eq[1] and assuming that d1=d2 then

r1/a1 + ra = r2/a2 + rb

If ra=rb then r2=a2*r1/a2

For b1=250, b2=70 and r1=735k then r2=206k.

In the case of the Barge concept where ra=91k and rb=22k then for the same values r2=5M!!!
I do not think that biasing at vcc72 is important in this case.

I did calculations including leakage and estimated values are close to the ones I posted above, but in this case germanium base current is negative in most of the cases.  It looks like the 220k resistor is draining leakage from the base, if not a leakage of 0.1ma across the 91k would be greater than the battery voltage. I remember to have tested germs with leakage well above 0.1ma and they worked fine.
Ideas?

Riiiing. Class dismissed!  :P

mac

hi everyone

i just built a harmonic percolator (first attempt...) based on this schematic http://www.fredric.co.uk/misc/HarmonicPercolator.sch.png with a tru bypass switching, and i get no sound when engaged (the sound gets through when bypassed).
this is point-to-point wiring cause i'm still not able to make my own PCBs.

i used a 2n404 and a 2n3565 from small bear, metal film resistors...
i double-checked for shorts and didn't find any, double-checked for transistors pinout, power supply polarity (i use a regular boss/ibanez like center negative supply, negative pole star grounded to the input jack) and am now clueless about what to do but rip everything out and redo it all over.

here are my eagle cad files :
- schematic https://dl.dropboxusercontent.com/u/1301693/harmonic%20percolator.sch
- and circuit board https://dl.dropboxusercontent.com/u/1301693/harmonic%20percolator.brd (i couldn't add bridges to the board file so i left two tracks open, put 2 bridges on the actual board)

if anyone has some advice, i'd be glad to here it!

regards

frances

oh shoot, nevermind!! i found my mistake...  :icon_redface:

Has anyone built the two npn 2N2222 HP like I posted? in this thread http://www.diystompboxes.com/smfforum/index.php?topic=68649.160 (http://www.diystompboxes.com/smfforum/index.php?topic=68649.160)

(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=43462&g2_serialNumber=2)

^ no, but I'm about to :)    i love anti-mojo circuits!

Gus- I was just wondering if you might have a book of your circuit designs? I'd buy it.

Gus,
What about replacing that 10k with a pot, and connecting the 100u cap to the wiper?
Or using a bigger pot as a variable resistor?
I did that with an all germ npn-pnp HP, I got a kind of 8-up effect.

I'll give it a try.

mac