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I 've cobbled up Marty's Tornado here and it sounds great! There is only one small problem.
There is what sounds like a leaky cap (sounds like a muffled waterfall). Is this a tell tale sign of a leaky cap?

Two people have build this with no problems or noise so something must be going on here.
I've checked the coupling caps between stages and they all seems fine and don't pass DC voltage.

(http://i41.photobucket.com/albums/e270/gaussmarkov/Forum%20Posts/schem-small.png)

Here are my voltages with a 9.6 volt supply:
Q1
D 4.5v
S 1.2v
G 0v

Q2
D4.5v
S 1.5V
G 0v

Q3
D 4.2v
S .2v
G 0v

Q4
D 9.6v
S 4.7v
G 4.6v

Q5
D 4.5v
S .5v
G 0v




Q6
D 4.5v
S .5v
G 0v

I don't fully understand the Mu amp section (Q3 and Q4)with respect to voltages but other than that the voltages look OK to me.

I've audio probed it and it seems to be after Q2
Any thoughts on what to check?
Thanks

John

 Yep, I've had that happen twice. Bad electro. Someone described it as a 'rumbling grindcore' sound. It comes and goes, can drive ya nuts.

There are only two electrolytic caps in this build 2.2uf and the 100uf power supply decoupling cap.
I used poly caps for the 1ufs and .68s. It would have to be a bad decoupling cap wouldn't it?
So the waterfall/rushing water sound is characteistic of a leaky cap correct?

John

John, all the voltages line up with mine quite close, though I have a battery
@ 8.6v so I'm proportionaly lower.
I also have a few circuit changes, this does not seem to change the voltage
readings much though.
Tripple check your Mu-amp section wire up and a re-touch of solder joints
won't hurt.
Constant or intermittant "hash" noise ?
Did you try the 1n cap across trim 3's outer lugs ? ( recommended )
Is your C16 a 1uf poly or an electro ?

MM.

I recently had a leaky cap on another project and the sound you are describing is exactly what I had.  Start changing caps....

John, could be a cap problem but I've spotted a small change from my build
and both my original schem and the clean copy :
From the Mu amp section, I exit with the 47n - C11 from the top end of R13, the 1k
rather than the lower end of it, so from Q4's source !
Not sure how significant this is as these nodes are connected with that 1k anyway .
Could be an impedance change, exiting source rather that the lower fet's drain ?

MM

what a diff`rence a node makes... :icon_rolleyes:

Quote from: puretube on March 01, 2007, 07:11:27 PM
what a diff`rence a node makes... :icon_rolleyes:

Care to expand Ton ?
Or just a friendly "extraction of urine" ....  :icon_wink:

I'm just curious that I may be finally learning something ....

I used all film caps except C13 at the source bypass cap, and the C20 100uf across the power supply.
Assuming I have a leaky cap I should be able to read DC voltage after the cap right?
None of the coupling caps. .02, .02. , .047 .033 and 1uf .
The Noise is a lowish contant white noise lind of like if you are tuned into a TV channel no reception with the volume turned high with and your hands over your ears. It has a slight fluctuation of crackle, barley though.

I'll check that R13 thing out as well.

My build is stock except I added that .004 cap across the trim pot at Q5. I thought it cut out too much sparkle so I scaled it back to 500pf.
I'm going to figure out this noise issue and then I'll try some of the modifications

Thanks folks.

John

the TCJ can explain it better in depth, (coz the following is not the complete & whole story, but food for consideration):

just imagine Q4 sitting alone there with its R13 between +9V and "ground" (@ the node of C10 & R13);

imagine a signal coming into the grid gate (i.e.: not shunted to "ground" by C10);

You will find no signal at the ground-node, but almost full signal at the node of source Q4 & R13;

compare with a cathode- or emitter- or source-follower, with R13 as the local feedback resistor...

(these nodes are just 1k apart, but they do make a heck of a difference  :icon_smile:)

John, this could be a particular "fet" causing this, I've had it with a few of
the Jfet circuits, it either requires a bit of "by ear" biasing at the trimpot
or when the Q is identified a swop out for a quiet one.
If you think that it's after Q2, wont be the Mu, so on the 5/6 Q's try adjusting
the trimpot down to "cutoff" and back to where the noise starts/go's
That may well be it .
Could just mean that 1 "Q" has to sit at 5-5.5v rather than 4.5v
It's worked for me a couple of times.
MM.

Well... I replaced all the caps except the pf caps to ground at the gates and the source bypass caps. I wouldn't think these would contribute to the "noise"
I tried biasing the fets with more voltage at the drain but until I got up to supply voltage the rushing noise was still there.
I replaced all the fets to no avail.

Here's a clip with clean, some chords and then the noise at regular volume and then brought up with the recording software to 4 times the level...then some single note stuff with reverb added.

www.mrdwab.com/john/Tornado.mp3

The gain was maxed for the clip and the tone was a about half up.

Unless someone thinks the PF caps and source bypass caps would contribute to the noise I guess this is where it stays.

Marty. When you replaced the cap and resistor with .1 and 82K in the tone control...what would you say is the difference this makes?
Another thing. Since you have modified it with a Second gain control after Q4, you would be attenuating the back ground noise unless you were full up. Pulling anthing after Q with mine and the signal and noise is cut.

John

John, I'm puzzled and sorry to hear that you have this problem  :icon_eek:
Before my little "tweaks" I didn't have a noise issue and I dont think that I've
reduced the overall gain, just added a pot to vary the gain after the Muamp.
It's a 2m2 pot wired in the "normal" way.
It's still quite "full on" when dimed and is totally noise free !
Can you identify exactly where it appears in the circuit ?

MM.

Marty

Mydementia built the same layout as I did and his was apparently fine so the layout is probably fine.
Hopefully I can figure it out as there are still a few components left unturned.

Any thoughts on the tone control changes and the difference it made?
Also why the 2m2 pot instead of a 1M and then 470K/470K divider? already have my enclosure finished so no room for the second gain pot. Although I may put in a trimmer and see how that goes...
Seems that the 2M+ resistance to ground is cancelled by the 470K to ground right after, at half it would be 1M in series and 1 me to ground then 470K in series right after. So 1million 470K in series before Q5!!!!!!  Given that large resistances are a big noise issue it's amazing the circuit isn't really noisy... I used a 820K carbon film resistor but that shouldn't cause that much noise. All the other resistors are metal film...


John

Quote from: puretube on March 02, 2007, 01:47:23 AM
the TCJ can explain it better in depth, (coz the following is not the complete & whole story, but food for consideration):

here you go:
http://www.tubecad.com/articles_2002/SRPP_Deconstructed/index.html

Quote from: Basicaudio on March 02, 2007, 07:34:12 PM

Any thoughts on the tone control changes and the difference it made?
Also why the 2m2 pot instead of a 1M and then 470K/470K divider? already have my enclosure finished so no room for the second gain pot. Although I may put in a trimmer and see how that goes...
John

The slight TC tweak is subtle and IMO the original works fine.
The 2m2 was a pot that I had around and I wanted to be able to drop the gain a lot
after the Muamp, for some more clean tones, this works quite well and doesn't induce
any noise at all.
Interaction of both gain pots is quite cool.
Keep lookin John, the answer is in that build somewhere !!

MM.

yep- most likely a leaky cap.  I saved my studio engineer the price of a new Sansamp.  Something was sounding strange and every time you plugged it in you heard whoooooooooshh...

I got fed up and etched a new board this afternoon, spent a few hours polulating the baord and wiring it up,  flipped on the amp and guess what.... Same thing!!!!!!!!!!!!!!

I think there must be an error in the schematic, layout or ? I spent a lot of time checking the correct values with a meterwhen I put the parts in this time.
Film caps except for the pfs to ground (which are ceramic) shielded wiring to the switch and in/out. Metal film resistors...

It does sound like a leaky cap but after making two units with new caps each time it's very unlikely to be a leaky cap.
The noise isn't very loud but it's surely there and I trust Marty would know if his was the same and also noisey.

It's after midnight here so I'm not going to look over the layout against the schematic now... Argh!

John

OK, so it must be a layout issue, schem's a worker and my vero build is a worker also.
There's a "LOT" more room on my build and power/ground/gain/tone leads are about as far
away from each other as possible !!
Seem like I've created a bit of a gain monster which is sensitive to layout.


MM.

 Marty, I checked your hand drawn schematic against Gaussmarkov's redraw and layout.
I only found on thing different. The 120pf across gate and source was drawn gate to ground on Gauss's shem and layout (C2).
That will not make much difference, maybe a little more treble roll off with the 120p gate to ground.

I'll have to take a look at the layout and see about any sketchy areas where critical components might be crossed. Then make a new layout...
FUN FUN FUN!

The only PCB layouts that I've built are things like tonepad etc, where they
are proven "workers" built by many dozens of people, not knocking the layout for
the sake of it, but with such high gains available, there's bound to be some changes
and revisions required.
Doing your own, or perfing/veroing your own will be very worthwhile.
I'd try to space things out a little on this one if I were you.
Mine is just too huge and I need to get a smaller one done, I'm scared that I'll
also run into similar problems !!

MM.

Quote from: MartyMart on March 04, 2007, 01:58:20 PM
The only PCB layouts that I've built are things like tonepad etc, where they
are proven "workers" built by many dozens of people, not knocking the layout for
the sake of it, but with such high gains available, there's bound to be some changes
and revisions required.
Doing your own, or perfing/veroing your own will be very worthwhile.
I'd try to space things out a little on this one if I were you.
Mine is just too huge and I need to get a smaller one done, I'm scared that I'll
also run into similar problems !!

MM.

john (basicaudio) thoughtfully pm'd me about this thread.  i have corrected the C2 connection to the source of Q1 and revised the original layout.  i would also be happy to space things out a bit.  are there some particular suggestions as well?

gm

i have also added some comments to gaussmarkov.net and the project file to alert people that my layout may be noisy.  i do not want anyone to mistake a problem with my layout as a problem with Marty's tornado circuit.

again, suggestions for improvement are welcome.

all the best, gm

I'm crap looking at PCB layouts !! however after a few minutes of going "square eyed"
it seems to be fine, dont see any obvious errors in there John.
Spacing seems better, lets cross some fingers !!

MM.

i'll reproduce john's layout in eagle and that will verify it.

i feel like a broken record on this point, but it may be relevant so i will repeat it:  maybe the "noiseless biasing" approach described by R.G. is helpful here?  this would involve reducing the magnitude of the 1M resistors in the voltage divider for the mu amp to 10K and adding an extra resistor (470K or 510K) coming out of the divider.  edit: one also adds a cap to the divider junction to shunt thermal noise.  admittedly R.G.'s example is a pair of 10M resistors where the thermal noise problem is probably greater.  but if the noise persists, maybe it's worth a try.

cheers, gm

Gauss, you may be right, after all the ROG "Thor's" muamp is set up like that,
1m from the 10k's and an additional 100uf to ground.
Whilst I "dont" have a noise problem, I'll try this tomorrow to see if I can get an
even quieter build !

MM.

i just checked john's layout with eagle, after adding the 1nF cap to the trimmer on Q5 and changing the output of the mu amp to be the source of Q4.  i laid it out on a .1" grid so it can be perfed as well as etched.  the width is 35 squares, so the board will measure something over 3.5" built this way.  i did squeeze things together a little to get this dimension.  i just thought it would give an idea of the size of this layout.  thanks, john, for putting this together.  i hope it brings the noise down.  i am interested to know.

there are two items that may need fixing.  first, the 47nF cap (C11 on my schem) does not connect to a 200K resistor that goes to ground in the schematic. it is between a 1K resistor and a 200K resistor that connects to another 200K resistor going to ground.  second, R19 & R20 (both 470K) have C14 (33nF) connected to their junction whereas I think it should be C15 (150pF) that is connected there.  the third difference with the schematic does not matter:  the order of R6 and C6 has been reversed.

i called this v 1.1 beta, following Marty's initial label.  :icon_wink:

here is a version that passes eagle's design rule check, so that it is consistent with the schematic:

(http://i41.photobucket.com/albums/e270/gaussmarkov/Forum%20Posts/BasicCheck.png)

here is the schematic that matches this layout:

(http://i41.photobucket.com/albums/e270/gaussmarkov/Forum%20Posts/BasicCheckSchem.png)

all the best, gm

Ahh! Good catches there Gaussmarkov! I missed those goofs...

Here is what I have now.

(http://www.mrdwab.com/john/Tornado-test-2.jpg)

I added an extra cap space for the Noiseless biasing setup 1M/1M, 100uf and 1M to Q4's gate .
If need be we can change the values from 1M to 100K, 10K etc. Not sure the cap is necessary but it doesn't hurt and can be taken out if need be.

Marty, Using a lower value for the biasing will give more current won't it? I Know that with, say a distortion + the high value Vref will starve the circuit a good bit. Not sure if this is the case here.

Gaussmarkov, Thanks for working on this with me! Your layout is "tighter" than mine. I snugged it up a bit some we'll see how it goes.

John

Quote from: Basicaudio on March 05, 2007, 10:37:28 PM
Ahh! Good catches there Gaussmarkov! I missed those goofs...

Marty, Using a lower value for the biasing will give more current won't it? I Know that with, say a distortion + the high value Vref will starve the circuit a good bit. Not sure if this is the case here.

Gaussmarkov, Thanks for working on this with me! Your layout is "tighter" than mine. I snugged it up a bit some we'll see how it goes.

nice john! 

i think the idea with the noiseless biasing is that you can keep the current the same.  the lower values in the voltage divider increase the current but you compensate with a high biasing resistor coming out of the divider into the gate of the transistor.  plus that resistor lets you put in the cap to sink thermal noise to ground.  unlike the distortion +, i think you want low divider resistor values, like 10K, not 1M.

gm

Sorry...I should have explained a little better. There was a thread about the Differences isn the Dist+ and DOD od250 schematics and the "better" sounding unit (OD 250)  has 10K/10 and 1M as the Vref. (no cap in the Vref through...) Mark Hammer brough up the value differences and suggsted lowring them as not to starve the circuit. I think the OD250 uses 22k/22k 470K.
I was thinking that 10K would be better or at least have more current with 10K and thn into a 1M and cap...

I'll have a look over the PCB one more time when I'm fresh and then try out the new layout (and hopefully the last one!!!!!!)
Three times is the charm with any luck...

John

yes, i wondered if you weren't thinking of that thread because i saw it also and thought it was pretty interesting.  there doesn't seem to be anything with such high resistors for both the voltage divider and the biasing resistors.

i hope this "linear" layout strategy does the trick.  i'd like to know where proximity matters and where it does not.  we still have lots of components right next to each other.   :icon_wink:  i just traced the signal path through my original layout and yours and i see the qualitative differences.  is that where you focused your efforts?

cheers, gm :icon_biggrin:

GREAT work on the PCB's chaps :D
OK, John on very close inspection at LOUD volume, I do have a touch of your "high mid hiss"
However, it seems to be a least 5 X quieter than your example and only with gain/tone maxed out.
This is absolutely fine and I have that with a BSIAB and several other high gainers too.
You must just have a "compounded" version of that for it to be so noticable.
I'll try the noiseless bias system and report back in the next 1/2 hr  OK ?

MM.

OK, it's very hard to tell after 7 minutes of rewiring but it seemed to make little or
no difference to use 10k pair/1M to gate and a 100uf from the pair to ground, just
made a mess of my board !!
There is and will be some hiss when these things are at "max gain" but to put it into
perspective, the hiss is around 1/3 the volume of a single coil "hum"  when  switch
on the gtr !!!

There's one other thing that could be done here, set-remove and measure the 50k
pots and use fixed resistors to the drains !
Fiddly for sure, but I think that would stablize the noise a bit more.

MM.

here's a schem of what we are currently working with.

(http://i41.photobucket.com/albums/e270/gaussmarkov/Forum%20Posts/v1-1betaschem.png)

Marty

The Noise I've been getting isn't the usual hiss. If I crank the tone and or gain I get a little hiss, which is fine.
The noise I get is a mutted sound as standing next to a huge waterfall and covering your ears. It has some mid and low mid content thyat sets it aparts from the usuall hiss fro high gain stuff. Next to the Dr boogie and BSIAB2 the noise is significant even with the gain and tone turned all the way off. It may be a side effect of having the Feedback section run across the board and near the previous gain stages...?
How is your feedback line run on your vero build? (the 6.8n/3.3M from the MuAmp to the first stage output) did you run it on the baord or float it over with a wire jumper?

Well I'll go ahead and build this new layout and cross my fingers. If you can hear me yell Marty from your place there...you'll know there is still a problem.

Thanks gauss for the new revised schematic! Nice to have something for reference.
Seems it's just you me and marty here....

John

Guys - just thought I'd chime in here...
I built my Tornado to GM's first layout (sounds like I have a cap in the wrong place after reading here a bit) but it works great.  I didn't make ANY subs and didn't take undue care in routing my wires (have a look at the picture below) and mine seems to work like Marty's...typical hiss at high gain/high treb but quiet otherwise.  I just made a couple more of GM's Beta1.0 boards but am going to wait until this issue gets sorted before I commit the parts...  Has anyone else built this circuit?  Now's the time to share!!

(http://aronnelson.com/gallery/albums/album136/Tornado_Layout.sized.jpg)(http://aronnelson.com/gallery/albums/album136/Tornado_Box_i.sized.jpg)(http://aronnelson.com/gallery/albums/album136/Tornado_Box_F.sized.jpg)

Quote from: Basicaudio on March 06, 2007, 11:28:06 AM
Thanks gauss for the new revised schematic! Nice to have something for reference.
Seems it's just you me and marty here....

John

that's enough for me!  :icon_wink:

i've been going over your layout and the rog thor layout trying to infer good practice for these high gain circuits.  i see that the signal path (ignoring feedback loops for the moment) does not meander much.  but there are always a few places where it parallels itself for a couple of components.  like an RC pair in series placed side-by-side.  so it's confusing.  does anyone have any rules of thumb on what things to avoid?

Quote from: mydementia on March 06, 2007, 11:57:14 AM
Guys - just thought I'd chime in here...
I built my Tornado to GM's first layout (sounds like I have a cap in the wrong place after reading here a bit) but it works great.  I didn't make ANY subs and didn't take undue care in routing my wires (have a look at the picture below) and mine seems to work like Marty's...typical hiss at high gain/high treb but quiet otherwise.  I just made a couple more of GM's Beta1.0 boards but am going to wait until this issue gets sorted before I commit the parts...

this is nice to hear.  but also confusing.  :icon_confused: :icon_biggrin: thanks for chiming in!  nice perf also.  that warms the %^&*les of my heart, because i layout for perf and then convert to pcb.

cheers, gm

I know next to nothing about the "do's n dont's" of PCB layouts ...BUT on 95%
of the perf/vero that I use, I keep ground/power/VB and signal as far from each
other as possible.
On vero, this means power top, ground bottom VB where required and signal
throughout the middle !!
Seems to work for me and usually that means at least 1cm between any of the above
for runs other than a tiny 9v link to pin 8 of an IC - for example.
Perhaps the ground plane on the PCB need to be larger ??

MM.

Quote from: MartyMart on March 06, 2007, 06:18:56 PM
I know next to nothing about the "do's n dont's" of PCB layouts ...BUT on 95%
of the perf/vero that I use, I keep ground/power/VB and signal as far from each
other as possible.
On vero, this means power top, ground bottom VB where required and signal
throughout the middle !!
Seems to work for me and usually that means at least 1cm between any of the above
for runs other than a tiny 9v link to pin 8 of an IC - for example.
Perhaps the ground plane on the PCB need to be larger ??

marty, thanks for helping with my question.  thinking along the same lines, in my last revision i put in some ground fill/pour (as i understand it, a "ground plane" is specific to multilayer (often 4 layer) boards in which there is a layer that is nothing but copper and that copper is grounded. hence a grounded "plane.")

i have been interested in this particular issue, keeping ground and +9v apart, and maybe you are interested in what i have read.  separation does not seem to be a universal principle.  i have also found online recommendations to keep these traces close together!  :icon_confused: :icon_wink:  for example, see page 12 of this document:   PCBDesignTutorialRevA.pdf (http://www.alternatezone.com/electronics/files/PCBDesignTutorialRevA.pdf)

in my tornado layout, i followed that recommendation.  i wonder if the reasoning is similar to the advantage of having a ground plane:   the changing current in a trace is accompanied by an equal and opposite image current in the ground plane so that there is less induced voltage on neighboring traces than without the ground plane.  by the way, the reference above also says to avoid unconnected copper fills; ground them or remove them.

and marty, i was wondering whether you could sketch your build for us so that we have another example of what works.  john asked about the connections for the feedback connection.  i would love to know roughly how you laid out the whole circuit.

cheers, gm

keep the outputs away from the inputz!

groundplane everything you don`t need, to save your etchant and the environment,
but don`t come too close...

Quote from: snap on March 06, 2007, 07:59:06 PM
keep the outputs away from the inputz!

groundplane everything you don`t need, to save your etchant and the environment,
but don`t come too close...

hey snap, thanks!  that reference i mentioned above also says to use ground fill liberally, but just for electrical reasons.  the environmental ones are good too.  :icon_biggrin:   i see that a lot of folks like to use extra wide traces for +9v, too.  my current guess is that if you are up in the 40mil neighborhood then you have met the "extra wide" criterion.

hmm.  i now realize that this could be a thread hi jack.  we should keep this focused on the tornado.  my bad.  i will start a new thread.

Well shit! I spent the day ignoring my "work" and built the new layout I posted above...and guess what! It's the got the same noise problem!!!!!!!!!
Not sure where to go from here.

Marty, if you could post or Email me a rough sketch of your layout or a pic that would be great.

John

dang, i'm sorry to hear that john. 

thinking about what i have read in other threads, i wonder if we could create a simple test for the presence of parasitic capacitive coupling in one of john's layouts using a copper clad board.  ground planes are used to fight unintended capacitive coupling, allowing the coupling to occur with the ground plane and, so, less with neighboring traces.  if john grounded a fresh board and placed it against the solder side of one of his builds, insulated by something very thin (but not a magnetic shield) could we get the ground plane effect?  if the noise reduced, wouldn't that confirm that some traces were capacitively coupled?

maybe there is some version of this idea that works even better?  if it works, i wonder if a more refined version couldn't be used to find the location of capactive coupling in a bad layout?

i'm afraid this sounds kind of crazy, gm  :icon_rolleyes:

John, that "sucks" !!
Sorry man, I feel responsible for your "mental torture" now  :icon_frown:
I dont have the hours free for a total draw up, so I'll take a couple of snaps
and mark it up quick in photoshop in the next few hours.
You'll get a picture of how BIG this circuit is  !!!

MM.

Board photo and details :
http://aronnelson.com/gallery/Martys-layouts-and-photos/Tornado_vero?full=1

It's HUGE isn't it !
You can see just how far apart the stages are and the pots too, there's quite a distance between the
Jfets  and quite a lot of copper too !!
I need to rebuild a smaller one and see where that gets me  :icon_eek:

John, Here's an mp3 of my build :
Gain/Tone full up recorded through Behringer DI/cab sim as usual
Silence then chords then pup switching and more silence
The bit of earth hum and pup switching is louder than the hiss by far.
This was recorded VERY loud so watch those speakers !!
I also have an end of circuit 2n2 cap "lifted" so have more high end going on !!

MM
http://aronnelson.com/gallery/albums/Martys-layouts-and-photos/Tornado_noise.mp3

How does this compare with your signal/noise ratio ?

hey,

i just got a nice note, through gaussmarkov.net, from a fellow named phil in nambour, australia who apparently does not use this forum. 

his opening comment about my layout is "The circuit layout looks very cluttered and with high impeadence/ high gain floating so close you are just lucky to even get it to work."  i was tempted to leave that out, but i am including it for assurance to john that he is not being singled out by the gods for mind twisting.  :icon_wink:

he also comments "I am completly lost as to the need of a feedback loop like that one, I would suspect that to be problematic.
It does pull the mid down a bit.  [-4 Db @ 1kHz] you are probably better without it.  The combined loading effect of the tone with no amplification at the end also puts the potential output at a great disadvantage."

he made a number of suggestions that sound helpful to me:

1) the trace on my layout from R16 to R17 under R19 alone is a big issue.  i have realized that this is one of my worst offenses in having a nonlinear signal path layout.  john's version fixed this.

2) don't have c10 and c11 side by side.  both john and i have this in our layouts.  it's relatively easy to change in mine, with no traces running under either capacitor, so john could experiment with that immediately.  he also says that this junction needs to be surrounded by ground.  also, one can see whether these components are a problem by checking whether they are microphonic!  gently tap on them and see.  (first time i have heard that one a stompbox circuit.)  marty, where are your c10 and c11 relative to each other?

3) correct the output of the mu-amp (john already noticed this but i have not updated gaussmarkov.net yet--i'd better get on it)

4) scale down the mu-amp voltage divider to 10k/10k with a 4M7 bias resistor (which we've discussed, but not with such a high bias resistor).  john, what did you use in your second build?  marty, did you try this?

5) lowering the value of R13 will decrease gain and help reduce oscillation problems

i think phil clearly knows a thing or two, given that he has spotted independently a number of the issues we have identified ourselves.  so i am passing on the rest.  and now i am going to go back and thank him!  :icon_biggrin:  and if i have time, make another layout.

cheers, gm

Alright! Looks like we have somefeedback (literally and figuratively)  to work with. I need to check out Gauss's post in detail but I have this clip for comic relief. Marty, seems my built has way more gain than yours. This is with the voltage at 6 volts across the board. I can get singing feedback with out plucking notes...

www.mrdwab.com/john/tornadonoise.mp3 

This is the newest board with the parts spaced out.

Gain full up, humbucker bridge, after I stop playing I turn down the gain all the way and that's the noise I get.The static varies. The underlying rushing noise is consistant with all the 3 builds.

EDIT: Almost forgot that I disconnected the Feedback when the clip was recorded. I couldn't hear much difference and wanted to see it it affected the noise at hand...

I need to go over the posts above with the original layouts. I just wanted to post this so you know i'm not crazy and to let you hear what's going on.
Thanks for the pics marty!. I need to study those now as well. Your clip is much more tame than mine. If I didn't know better I'd say it's not the same circuit!

Marty. No hard feelings obviously. Just strange that we have such different behaving builds. It does sound great. Just need to tame this beast.

John

Wow John - now I hear the waterfall you described earler. 
Maybe you could post some pix of your builds too... like I said in my post in this thread - my Tornado seems to work like Marty's... minor 'high gain circuit hiss' with gain maxed.  Any particular reason you biased all your FETs to 6V?  I biased mine to 4.5V per Marty's recommendation (original hand drawn schem in gallery). 
Are you reusing any parts in your builds?  Maybe you have a rogue JFET honking up the works?  I just went through a huge troubleshooting exercise with Brian over at ROG on my multiple misbehaving Thor builds - come to find out, the on-off-on switch I used (instead of single SPSTs for tone selection) was causing the problem (different switch in each build... but same wire proximity).
What an interesting problem...

GM - thanks for passing on the information on 'good' layouts... this thread will make all of us better at it!
Mike

Great info chaps, the feedback path came up in my original, posting someone mentioned
"problems" and "why?"
Well all I can say is without it, it just sounded like any "high gainer" and with it in place
it souded and responded - in a much more "amp&speaker" way , "speaker spank" is the
term that I used.
I tried the 2x10k silent bias with 1m to the fet - it's still there, but made little change for
me, no more and no less noise !
You seem to have a LOT more gain than me, perhaps my 2m2 pot and one or two tweaks
has made a HUGE difference, that I have not spotted.
Look at the build though - it's VERY close to the original schem !
I need to remake one as per the original schem, are you using the recommended Jfets in
all positions John ??
Thanks for all the input guys, frustrating but appreciated, I just wish that I knew more
"electronicly" about what's going on here !

I used all new parts on all three builds so far. I've socketed all the FETs and have changed all of them at least twice.
I biased them all over the place. Mainlt at 4.5v and for the clip I was having a bit of oscillation so I biased them at 6v to get some more headroom/clean gain.

Here are two of the boards I've built. The larger one is over 4 inches across!

(http://www.mrdwab.com/john/Tornadopic.jpg)

Marty
My builds are as the original schematic except for:
Taking the output from the source of Q4.
.001uf across Q5 trimmer
Tried 10K/10K 1M and 100uf cap at the Muamp but didn't notice a difference.
All the FETs are as called for in the original schematic. Q1-6 MPF102, 2N5457, 201, 201, 201, 201
I did try a 1M at the place you use a 2M2 (with the stock 200K/200K) and it acted like a volume/tone control cut almost all the tone as well as volume
I could barely notice the connection or disconection of the feedback loop. Slightly less mids possibly...

John



John

have you done swapped the trimpots for fixed resistors,
to check whether the noise origines from them?

Gauss posted comments from the Australian guy, who stated that with this
much gain and a "crowded" board we were lucky that it worked at all !
In a way I agree, this is like building a "Train wreck" amp and NOT looking
after the lead dress.
Slight differences aside, my build is WAY more spread out, it's 12.5cm X 4 cm  !!
That puts gain pot and I/O connections more than 16cm away from each other.
Ton has just mentioned the trimpots, which I offered as a suggestion a page or two
ago, well worth trying a "new" type, or measuring and using fixed values.
I'm going to remove the 2m2 "xtra" gain control to get original values back in that
area to see what happens.
I'll get back tomorrow on that one.

MM.

OK, I very quickly went back to the original, no 2m2 pot and the 200k pair
after the Muamp section back in as per the original.
Quite a bit more gain, much like yours now John but NO extra hiss/hash going on  :icon_eek:

With TC not maxed, it's quite quiet, earth hum is a slight problem which a box will solve.
Sorry ..... it looks like a layout / circuit size issue for sure.
I did'nt even use screened I/O cable yet either !

MM.

Quote from: MartyMart on March 07, 2007, 12:56:13 PM
Great info chaps, the feedback path came up in my original, posting someone mentioned
"problems" and "why?"
Well all I can say is without it, it just sounded like any "high gainer" and with it in place
it souded and responded - in a much more "amp&speaker" way , "speaker spank" is the
term that I used.

marty, i hope you did not get the impression that i criticizing the circuit.  i recalled that you had already addressed this but felt that i should not edit what phil had to say.  so i was just passing it along.

Quote from: MartyMart on March 07, 2007, 02:00:50 PM
Gauss posted comments from the Australian guy, who stated that with this much gain and a "crowded" board we were lucky that it  worked at all !  In a way I agree, this is like building a "Train wreck" amp and NOT looking after the lead dress.

again, passing on the comments regardless of how much i like or dislike them.  :icon_wink:  my original layout  has taken quite a beating.  the way i see it, this has been a great project from the learning perspective.

all the best, gm

Gauss, no problems at all, I'm VERY grateful that there's even interest in this :D
I'm just a bit frustrated for John and want to resolve this asap !

MM

Yeas, Marty... I'm frustrated about the noise but I just want to say that the circuit is huge sounding and I applaud your getting it designed built. Thanks! No way am I blaming you...

We're almost there and some new light hasw been shed on it which will help. It's a learning proces and if we can tame this then were learning something...
I'll try out using a fixed resistor for the trimmers. Not sure that will do anything but at this point who knows. I do get some DC scratch when turning them but that's expected I would think. No?

John

John: the signal`s ground from your Q1 has to "travel" all the way around the board, to reach the groundpoint of your Q2...
(here the signal strength is weakest);

on it`s way from Q1 to Q2, it passes through all the meshes of the higher order FETs` groundpoints, where larger signals are operating
and larger currents are flowing to and fro, with the battery and big cap somewhere in the middle...

this is not exactly a "star-ground", but rather a "string-ground";

now usually this is a danger for hum- or motorboating problems,
and it may not be the (a) reason for the hiss,
but worth a try testing to break up the ground trace somewhere right of the safety diode
and wiring a jumper from gnd Q1 to gnd Q2.

If I interprete Marty`s pics well, he got the power supply connections (battery and big cap) right at the input, with shortest possible wires...

QuoteI do get some DC scratch when turning them but that's expected I would think. No?

that`s "crackle OK"  (term created by Zachary Vex  :icon_wink:), and can be regarded as "normal"...
(I asked about fixed resistors, coz I had read Marty mentioning it, but a look at the build pix showed the trimpots,
so I just wanted to repeat that issue, to make sure it has been tried.

(I have the carbon-pot t-shirt, even with DC-decoupled circuits... depends largely on manufacturer...)

Good call marty and reiteratione Puretube!
I replaced the Trimmers with FIxed metal films and the Noise is significantly reduced and the static/crackle is gone.
This makes sence because trimmers generally are 20% or maybe 10% tolerance carbon with less than decent specs.
There is a good bit of hiss still but were getting there.

I had the ground issue on my mind as well. I'll have to look at it and try your suggestions. Thanks!

Here's a new clip, a bit with the gain up then no playing,  and then turning the gain all the way down to hear the hiss.

www.mrdwab.com/john/Tornado_fixed_trimmers.mp3

Still a good bit of hiss with the gain down but as long as we are getting postitive results eventually we'll get there.
Don't know why the metal riffs...I guess the high gain brings out the dark side....!

John

GREAT ! - getting better :D
Yes Ton, my 9v enters the board and is imediately reverse protected and filtered ( 100uf/100n ) direct
to ground, with a short jumper.
All other grounds then run the whole length, input->Q1->Q2-> etc to output ground.
This is one continuous "path" with no odd routing of ground nodes.
Worth a shot !
MM.

i've been working on a tight layout with guard traces, ground fill, linear signal path, +9v close to ground, signal ground distinct from power ground.  here is what i have so far, a 23 x 23 version (2.3" x 2.3").  there's a little more fussing for actual component placement, but i think i am getting close.

green is ground, red is +9v, blue is the basic signal path.  i have kept the feedback loop well guarded by ground traces or ground fill.  because i made it with eagle it is 100% consistent with the latest schematic.

i am unsure about how where to place the ground pad and where to break the ground trace that frames the layout.  the current arrangement is not right, because it leaves the principle supply filtering at the end of the chain--so i'm sure that gap at the bottom should be filled.  where do you think the break should go?

cheers, gm

(http://i41.photobucket.com/albums/e270/gaussmarkov/Forum%20Posts/tornbeta4.png)

Gauss, that's looking VERY nice indeed - kick me if I'm wrong here but this is what
I've spotted.
Your 9v connection from battery/PSU runs left and right of it's entry, so while it's filtered
one side , on the other it hit's a trimpot directly - very close to the actual physical connection.
My 9v "entry" is at one end of a strip, is filtered and then goes on to the first trim pot.
Does that make any difference at all ?? .... or am i going mad  !!
Perhaps electronicly it's fine that way .....

Peace,
marty.

I'm with Marty here...
I'd run the +9V and Ground on the left side of the diode and cut the ground trace at C22 and the +9V trace approx where the GND label is (with a pair of pads to the left of the diode).  Then I'd run a trace/jumper from the filtered side to the of the +9V rail to get filtered power to all inputs. 
I'm used to doing layouts linearly, left to right... you guys and your fancy programs... :)

my comment "right of the diode" was cc that older layout - not: in general.

In general: the most silent point in the circuit is at minuspole of C20
(using Gaussmarkovs numeration in his last layout...);
this is where both the plus and the minus of the battery ought to be soldered;
this is where the single ground connection to the chassis ought to be (later on);
this is where R1 & R3 & R4 ought to "sit", as well as C2 & C3 and gainpot ccw-lug.
(if its not possible to have them all together physically,
connect these 6 parts through one trace, which then goes to C20 without having
anything else hooked to it to it.
(this can be regarded as one ray/branch of a "star-grounding").

The same goals for C22: its groundpoint  ought to be physically close to R8 & R9 & R11
& C8 (that groundplane you got there is fine, but it ought not to return to C20 through the sensitive input circuit`s ground-trace...

Similarly, trim1 cw-lug ought to run directly to C20 pluspole,
withought "picking up" other supply currents ("dirt") along the way.
(I love to use the word: "star-supply")...

got it!  thanks everyone for helping me.  ton, i don't need to tell you how helpful you have been.  your explanation for this example has taught us a lot.  thank you.  i will revise according to these comments.

gm

So like this?
With the exception of the Ground being moved closer to the PSU "big" cap.Thanks Puretube!

(http://www.mrdwab.com/john/tornbeta4edit.jpg)

Interesting layout Gauss, it wraps around a bit but the output is pretty far from the input all in all.

EDIT

I was just going to post this and Gauss posted. Well maybe this will confirm the revisions at least...?

John

Thanks Ton, superb :D
Gauss - this is pretty close to how my power/ground is connected other than after
filtering, they are almost 4cm apart !!
But the parts Ton has pointed out are connected to power / ground in that same way.
I'm also used to laying out in a "linear" way   :icon_redface:
Peace,
Marty.

hope it helps  :icon_smile:

So is the layout i hacked two posts above about what you were thinking putetube?
I didn't move the ground of the Gain pot closer to the source but...

To make things slightly nore complex:
Pulling the first FET does nothing for background noise. Pulling FET one and two Lowers it to just about the right level (sheesh) .

Sometimes there is a pot betwen the first and second, and the second and third stages in high gain amps.
I wired up a dual gang 500KLog pot with the first side as in the schematic. Then the second half of the pot between the 820K after Q2 then the wiper to the top of the 180K  (Lug one ground, Lug two to the top of 180K, and Lug 3 to the right side of the 820K.

Here what it sounds like.

www.mrdwab.com/john/Tornadodualvolume.mp3

HB Neck pickup for the single note stuff and the bridge for the chordal stuff.
Gets pretty clean and all the way up to meltdown.

There is still a little bit of hiss with the dual 500K volume turned all the way down... Also the tone knob was set almost all the way down on this recording. I'll try so more fitering at the end an re do the tone stack possibly which should take the hiss down as well as alow me to have the tone pot centered more. The amp is pretty mellow sounding so it's not just a bright amp. I used an Electrovoice RE20 as well which is a pretty flat responce mic.

Watta you think?

John

Quote from: Basicaudio on March 07, 2007, 12:07:41 PM
Alright! Looks like we have somefeedback (literally and figuratively)  to work with. I need to check out Gauss's post in detail but I have this clip for comic relief. Marty, seems my built has way more gain than yours. This is with the voltage at 6 volts across the board. I can get singing feedback with out plucking notes...

www.mrdwab.com/john/tornadonoise.mp3 

This is the newest board with the parts spaced out.

Gain full up, humbucker bridge, after I stop playing I turn down the gain all the way and that's the noise I get.The static varies. The underlying rushing noise is consistant with all the 3 builds.

EDIT: Almost forgot that I disconnected the Feedback when the clip was recorded. I couldn't hear much difference and wanted to see it it affected the noise at hand...

I need to go over the posts above with the original layouts. I just wanted to post this so you know i'm not crazy and to let you hear what's going on.
Thanks for the pics marty!. I need to study those now as well. Your clip is much more tame than mine. If I didn't know better I'd say it's not the same circuit!

Marty. No hard feelings obviously. Just strange that we have such different behaving builds. It does sound great. Just need to tame this beast.

John

My Dr. Boogie makes that same noise so I look forward to someone figuring it out(because I've failed too). I almost have to think that this is a downfall of JFet circuits that have many cascaded stages.

RDV

Do you get the static as well as the wooshing noise RDV?
Try the trim pot thing by replacing the trimmers with fixed resistors. Worked for me.
My Dr Boog is pretty quiet actually. Maybe I'll replace the trimmers on it and see if it gets even better!

Use shielded wiring (in/out and to the switch and back) keep the wires short and uncrossed and you should be fine.

John

here's another draft.  C22 has moved so that it has a different ground on the star, per ton's suggestions.
the input section up to and including the gain pot has it's own arm.  and for good measure, i put the "output"
section on it's own star arm as well.  well, except for R22.  any idea how important that is?

i also made sure that all of the components would fit this time and made the gain connections a little more
spaced out.

john commented:

QuoteInteresting layout Gauss, it wraps around a bit but the output is pretty far from the input all in all.

i think i know what you mean so let me tell you my thinking and maybe i can get some more feedback.  if you
follow my signal path you will see that no components are next to each other.  in all of our previous layouts,
there are some instances where two components in series are positioned right beside each other in a sort of
doubleback.  i thought of that as not linear.  so i did not do this anywhere.  at worst components in the signal
path are at right angles to each other.  the path goes straight up the left side, stair steps down from the upper
left-hand corner to the lower right-hand corner and then shoots straight up the right side.  my guess was that
this is practically very linear.  and, of course, it enables me to keep the width of the board smaller.

that said, i could easily expand sideways and we would still have enough room to put this into a 1590BB.  :icon_cool:

all the best, gm

(http://i41.photobucket.com/albums/e270/gaussmarkov/Forum%20Posts/linear06a.png)

Gauss

That looks good. My only concern is the grounding.
Form how I usnderstand it you want the first stages to have the cleanest ground. Which would be right at the ground point by the 100uf cap.
Then the higher current/gain areas are at the other end...down the line. You can look at it like, the cleanest signal get s the cleanest grounding.

If you cut the connection to the right of the diode and then fill in that plane on the far right (or cut it out making the board a tiny bit smaller then the ground path cleanest to dirtiest. (you need to connect the to left section to the top right as well) The ground path then goes from the bottom up the left side, over the top and then down the right side...clockwise.  Does this make sence? Simple to do with your layout now.

Thanks for working on this more!
Any thoughts on the clip folks. Not my horrid playing but the dual volume idea.

John

The clip sounded like mine when I had the 2m2 pot in there, more cleaner tones
but mine was "sucking gain" !
I have it back to "schem" values now and it is a BEAST !
I still dont have that noise though, I think it's all to do with layout, Gauss is onto that now
so let's see if a new version fix's the issue ..... finally  :D

MM.

Marty
Gauss's new layout makes sense to me with the star grounding points.
Not much hum issue with mine but clean grounding can help with a few issues.

Did your noise go up at all with the gain increase? I have mainly hiss now proportionate to the gain level
it seems tolerable, but less noise is always good. If you get a few minutes could you make a maxed gain clip? 

Getting closer...

John

john got me thinking (again).  one more suggestion-- and even closer to the star ground ideal--how about a jumper direct to C20 for the Q2 ground branch like this:

(http://i41.photobucket.com/albums/e270/gaussmarkov/Forum%20Posts/tornadoscrap.png)

Surprise...it's me...

That looks better gauss. More direct and will clean up the trace going up the side and over the top.
Plus it will make the board a couple millimeters smaller!

John

 I gotta say, I really have to admire your determination and patience with solving this problem!

Quote from: Basicaudio on March 08, 2007, 09:06:11 PM

Did your noise go up at all with the gain increase? I have mainly hiss now proportionate to the gain level
it seems tolerable, but less noise is always good. If you get a few minutes could you make a maxed gain clip? 

I posted that answer a few steps back ! ( It's getting complex - I know :D )

I have no decernable change in hiss having gone back to "stock" with it.
There's some and a touch of earth hum, but I'm not going to get this HUGE version
in a box, it would be silly to try.
At some point, I'll remake a smaller one, though I also have a Thor/LA screamer/BBE/Q&D comp
and a few other things to get in enclosures first !!!
If this PCB is sorted, perhaps one of you could etch an extra one for me ? that would be V- cool.
This is good work and in the true DIY spirit chaps  :icon_mrgreen:

MM.

Quote from: RDV on March 08, 2007, 04:27:19 PM
My Dr. Boogie makes that same noise so I look forward to someone figuring it out(because I've failed too). I almost have to think that this is a downfall of JFet circuits that have many cascaded stages.

the rushing noise has nothing to do with layout I'm afraid ...

Marty, you've got cap bypassing on every gain stage, giving lots of gain but increasing noise gain everywhere at the same time - which is already poor in jFET's running at 9v ... then you throw away a bunch of signal between gain stages using resistive voltage dividers between each stage ...

Dude!   :icon_wink:

the combination of both will give you poor S/N ... that poor S/N will sound proportionally hissy if you're using relatively small caps to bypass Sources along the signal path ...

compare this to the Thor ... no bypass caps, no signal throw away with dividers ...

you can always try shaving off some Treble/Hiss by paralleling the drain loads with 0.001uF to 0.003uF caps on every stage, not a perfect solution by any stretch ... still, I think you're asking for trouble here ...

it's easy fix to remove Source caps and dividers, but there's the obvious potential loss of voicing ... that's shitty !

maybe a good compromise is to remove all Source caps, and voltage dividers, then stick the one Source bypass cap that best defines the current voicing and re-bias Drain loads carefully ...

g'd luck ...

That's great information JC - Bless you !! :icon_cool:
I see exactly what you're saying, I can probably compensate for the changed "voicing" by
adjusting the interstage caps from the fet drains and roll off caps/RC network etc.
I have to repeat that I DONT have a real hiss/hash problem with mine, perhaps I
just got lucky if it's not a layout issue.
I think it's time for a Tornado Version 2.0  !!!
My dilemma will be that if it sounds this good AND is quiet, I may not want to post it up !!

Good man !
MM.

Quote from: MartyMart on March 09, 2007, 06:47:22 AM
just got lucky if it's not a layout issue.
I think it's time for a Tornado Version 2.0  !!!
My dilemma will be that if it sounds this good AND is quiet, I may not want to post it up !!

... your call n'est-ce pas ?!

the first BSIAB I built sounded dark and muddy, to the point of being unusable ... everything biased right but it seems that channel capacitance must have been xtra high for some of the devices I was using then ... this is very possibly another one of those high-variance jFET issues ...

I thought about this and forgot to mention, yeah, could be that your devices are perfect for the circuit as you've arrived to it ... it's something that's almost to be expected with FETs ... I wouldn't say it's luck on your part, more so that you adjusted the circuit to work correctly with your starting ingredients ... like any competent chef would  :D

just going back to the cap thing for a minute - old school purists in high end hi-fi circuit design land avoid Source/Emitter/Cathode bypass caps like the plague (... well, almost) ... the idea that the more you can achieve your (gain) goals without it the more you stand a chance of maintaining a certain level of transient "accuracy" (for lack of a better word) ... "focus" perhaps ... in a distortion circuit that can matter even though the definition of fidelity goes out the window ...

some interesting set of design constraints this music stuff ...

Makes me wonder why almost all Tube amps have quite large cathode bypass caps  !!
.... probably they dont suffer the same noise issues from those and the resistor dividers ( answers own question )
Yup, fets can be a real "bugger" sometimes !

MM.

triodes have about the same device noise as transistors but the signal swing in a typical HV app is way higher leading to better S/N

Nice insight JC!
The dividers were kind of nagging on my mind as well. The resistive dividers are throwing away signal to ground but removing them will cause the gain to increase correct? I know how they work I just was wondering about where to go once they are removed or lessened.

Removing source bypass caps will lesten the gain as well as some tone shapping as well. What is a better way to reduce the gain outside of the divider and removing source bypass caps? Rasing the the voltage to the drains?

Some Engle high gain amps have 10uf bypass caps on all the stages!

Marty
It does seem our builds are very different gain wise. Initially I thought it was more of a layout issue which is was to a point, but I have screaming gain to the point oscillation and my wiring isn't cluttered and the layout seems pretty close to ideal with the exception of grounding..but no hum on mine either... Plus I used shielded wiring on all the ins ans outs to the switch and back.
Getting tired of this i'm sure...

John

No, not tired I'm learning a LOT from this thread !!

I'm onto Version 2.0 as we speak :D
Schemo adjusted and I'm trying things out, most bypass caps have gone
and divider resistors adjusted down :D also more power filtering too !
May take me 'til next week - but this WILL be right :D

MM

john,

i think that's right.  i believe i read somewhere that raising the voltage supply to these circuits helps.  as a caution to others:  if you try this, be sure to respect the ratings on your caps and resistors.

we are moving on, but just for the record, here's a final version of the star-grounded tornado v1 beta:

(http://i41.photobucket.com/albums/e270/gaussmarkov/Forum%20Posts/perf-2.png)

OK, here's some "adjustments" to the Tornado, sorry I have not redrawn the
complete schem yet but this should make sense, schem comes v soon :
-----Tornado V 2.0-----

Q1 :
MPF102 bypassed with 2k2 and 680n cap, from the 22n drain cap output direct to 1M log pot.
470k r at gate to ground from Q2
Removed the 3m3/6n8 link
Q2 :
MPF102 bypassed with 3k3 and 470n cap, from the drain cap output ( now 10n), divider of 470k/470k ground
into the Muamp section.
Muamp :
2N5457's As before but with 680Ohm bypass r, from C11 (now 22n ) a 180k/180k divider to Q5's gate.
Q5 :
J201 Bypassed with 3k3 r no cap ! drain cap output now 22n then 470k/470k divider into Q6 gate
Q6 :
J201 Setup as a source/follower, 9v to drain source bypassed with a 10k which is the output to the 1uf
C16 to tone stack - as normel here.
Getting good tones from this with minimal noise, not quite as much "clean" range but this is about
gain here !!
Anything else not mentioned, such as gate to ground pf caps remain.
My layout is smaller and required a second ground and 9v strip, so I'm double filtering the 9v rail
one that feeds Q1/Q6 and one that feeds Q2/Q3&4/Q5 both use 100uf and 100n caps from 9v to ground.
The feedback loop was causing a touch of "howling" and also a wierd "compression" in this version
so was removed ( see above )
Not 100% there yet but getting closer ! it sounds a touch "thicker" so may well use more of the 10n and
smaller caps from drains between stages.
Thanks to all for the useful contributions BTW
MM

http://aronnelson.com/gallery/Martys-layouts-and-photos/Tornado_V_2_0?full=1

Schematic - bit ragged but readable !!  sorry Gauss  :icon_wink:

MM

Marty,  C2 (120pF) to source of Q1 instead of ground?  The older schem went to ground and we changed that, right?  gm

... and the output of the mu amp is the source of Q4?  :icon_biggrin:  sorry, another blem on my first schem. :icon_twisted:

how's this?  i marked it up to show the separate +9v power rails, now VA and VB, adding nominal 100 ohm resistors to distinguish them.  the  components are relabelled to follow the schem.  C2 is a "miller-capacitance-sim cap" across the gate and source of Q1.  and the output of the mu-amp is the source of Q4.

(http://i41.photobucket.com/albums/e270/gaussmarkov/Forum%20Posts/ver20_schem.png)

Marty

You said "2N5457s as before" for the Mu amp. Is this correct? On the schamtic and all gauss's schems the Mu amp has been J201s.
A possible sourse of why my gain was way more?

I've been reading over the Fetzer valve material over at ROG. There is a lot of good material there.
Some points I've been thinking about and need to try.

Biasing and determining the operating points of the stages.
Getting a good amont of gain but not so much as to need to throw away gain with resistive dividers.
Adjusting the source resistors bassed on the gain of the FETs. ROG mentions much smaller values.

What is the difference between gate caps tro ground and gate to source caps? (simulating miller capacitance)

Source bypass caps and the idea that unbypassed source resistors run closer to tube triode curves.

Running at more than 9v to get more current strength.

Marty
Thanks for posting your reworked Tornado here.
A dual 1Mpot could be added easily here to get more clean range. After C7 in the v2 schem posted above.
Replacing R10 with the second half of the pot.

John

Chaps, thanks for jumping back in :D

So, John, my mistake the first version MU was indeed J201's !
I've gone with 5457's now- seems to help and may help you on the gain front Too !
The dual 1M or pair of 1M pot idea is sound, I'll implement that on monday.
Gauss, schem looks right, though I now have all the 120pf's gate to ground and not "millered"
Not sure how much change this is, could be loosing some high end, so the 2n2 at end with the
10k possibly not required at all.
I had a touch of your problem john, it came on intermitantly but was solved with a re-bias and
fresh 9v battery !
It's failry quiet now, about the same as V 1.0  :D
It's much smaller, perhaps half the size, with no "ill" effects, so I'm pleased.
I recommend a possible reduction of drain cap size, all 10n and off Q2 at 4n7 sounds real nice
too.
Ditch the bypass cap at Q2 also works fine and reduces gain some, could be on the edge of
"howl" at full tilt still !
Still some experimenting to do but it's 90% there I think.

Marty.

thanks, marty.  shall we leave our schems as they are for now, given the fluid nature of things just now?

also, i wonder whether everyone should measure Vgs for their transistors and report those, perhaps using R.G.'s JFET measuring circuit (http://www.geofex.com/Article_Folders/fetmatch/fetmatch.htm)?  might be good to match the mu-amp transistors, too.  both would be helpful for keeping the supply under 9V, per John's comment.

i will be lower profile for the next coupla weeks.  pls don't interpret that as a lack of enthusiasm on my part.  i'm just slammed with other stuff.  :icon_neutral:

all the best, gm

Quote from: gaussmarkov on March 16, 2007, 04:33:29 PM
thanks, marty.  shall we leave our schems as they are for now, given the fluid nature of things just now?

also, i wonder whether everyone should measure Vgs for their transistors and report those, perhaps using R.G.'s JFET measuring circuit (http://www.geofex.com/Article_Folders/fetmatch/fetmatch.htm)?  might be good to match the mu-amp transistors, too.  both would be helpful for keeping the supply under 9V, per John's comment.

i will be lower profile for the next coupla weeks.  pls don't interpret that as a lack of enthusiasm on my part.  i'm just slammed with other stuff.  :icon_neutral:

all the best, gm

Gauss, no problem at all, I'm going to do some final tweaking during the next few days and post an updated
schem, V 2.1 !
I'll implement some changes including John's "dual/pair" of gain pots, for better overall range and some gain/tone
changes, as it's very close to GREAT now !!
The dual pots remain in my original and I like how that works for the cleaner settings.
I think this should end up as a Marty/John/Gauss design, given the number of suggestions and input !
This is all much appreciated BTW :D
More in a few day's people, so be patient !  I'll sort out a new post for it and include perhaps a vero layout
also, as mine is quite a decent size now, about 8cmX5cm it will go "sideways" in a 1590BB

MM.

Marty, wow; you really got that vero sized down! This new build has the same amount of parts pretty much, doesn't it?
I'm going to tackle Gauss's New PCB layout for it and see how that goes. I don't have any vero & haven't used it before.
What's the gain like now on yours marty? Still a fire breather with the lowered gain FET type?


Gauss
The Fet Matcher would be a good idea. I bit of a pain but once you get it up and running it would be simple.
Especially if you use FETs a lot.
I think there is one layed out in the Gallery if I'm not mistaken.

Maybe a new thread topic but I was thinking of trying Parallel FETs as in some Matchelss, marshall etc type circuits.
If the FETs were not matches how would this affect things such as bias? I'd have to average the bias setting of the trimmer but I wonder how the parallel FET thing would translate from a tube triode pair?

John

It's still a fire breather but a wee bit more tame than my V 1  !!
I could make a vero version for you John, just main parts and trimmers with
wires ready for pots and I/O if you like ?
Could be interesting to compare direct to a PCB version ?
I'd appreciate a PCB also .... :icon_wink:

Parallel Fets !!!  would that work like BJT's ?
Lowering gain then right ?

MM

Marty

If you can send me a vero layout and a piece of vero I'll give it a shot.
I can make you a PCB in trade. Only one thing, we need to get a PCB hammered out with the newest revisions.
Shipping will be cheaper without the parts and the layout is the main thing.

With the parallel fets I guess it would lower the gain. I was thinking the opposite though, as in the marshal amps with parallel stages.
Grids, plates and cathodes (gates, sources and drains) are paralleled.
I have a matchelss chieftain clone I made and it gets a good amount of gain.
Thought I'd try to make a FET pedal version of it.

I bread boarded it up and when I pulled one of the FETs from each pair there was no real difference...!?
I guess I need to fool with it some more and start another thread...

John

OK, give me a few day's for a final revision and I'll draw up a layout and send
you the vero, perhaps half layed out ?
Good luck with the parallel idea, sounds interesting !


MM

How is it going Marty? I was following this topic because your tornado sounds so incredible! Any updates?

I don't mean to speake for marty but here's the scoop:

Marty has been redoing the circuit to get the noise down and Gaussmarlov has the layout pretty much squared away.
Marty says his new version sounds very close to the original.
With any luck we can get this thing fired up and tamed as far as noise.
I built the new schematic values version on Gaussmorkov's layout but I need to finish it still.
I'm sure marty will post in the next day or so with some refinements. 

John

Still chewing on this one folks !
My V2 was getting close but has developed a nasty "hard edge" to it, with almost a
"sharp clip" to the front of every note - seems way too compressed also !!  :icon_eek:

More work to be done I'm afraid ....

MM

Bummer! I was thinking you were getting close. I listened to my clips of it and listened to your initial clips and they sound great, noise or not.
This one has to see the light of day at some point.

John

Yeah those V1 clips are great, little noise or not !!
Even though it's not perfect with all the gain boost and dividers, it has MAGIC :D
At this point, V2 isn't even half as good a tone, could be several things but the way
each boosted/eq'd stage HITS the next is making a huge difference, jfet variations
also comming into play !
Perhaps there's a reason for limited commercial jfet circuits ???

MM.