First Time Tube Screamer - No Audio - Debug Info. Please help!

[pgorey]

Sorry, I jumped the gun on those measurements.

The picture at the link below shows the audio probe tests.  Color coding is same as last post.

http://imgur.com/a/FrFsh

Please disregard the line going horizontal across the tone wires.  That was an errant paste.

[GibsonGM]

It would be this one, Pgory!!   http://smallbear-electronics.mybigcommerce.com/diode-1n914/

The ones you used are probably OK, but they 'turn on' at a lower voltage than 1N914.  It will likely  make your screamer distort more, but that may not be a bad thing!  1N914 are silicon, turn on about .5V, and are used ALL OVER, so get 100 of them when you buy some.

Looks like a good job on the audio probe! Take note of the cap voltage rating that you used - don't use it on anything of a higher voltage, like a tube amp (some small amps use around 50V, too).   I made mine with a cap rated 600V for that reason....the wire connected to the outer barrel of the jack gets an alligator clip on the end, and you attach it to the circuit ground.  Without this you'll have a big BUZZ when you probe the circuit.

The other end, connected to the jack tip, is your signal wire...this will take audio from the circuit and send it to your amp.  Turn it down a bit or you'll get a jump, LOL!  You start where your guitar (or other) signal comes into the circuit, be sure you hear it, then probe the chip OUT pins (don't short pins together!).    You can also check transistors where they output.    If you get signal say on the base, but nothing on the collector (or emitter depending on circuit and transistor config), it indicates a short, wrong component value or dead transistor, for ex.   This is why you look at the schematic, to find the route...

Pots: well, they will work and pass audio if wired right, but the tapers are not correct for this circuit.    You want all linear taper, I believe (been a while).  A 500K, 20K (or 25K if that's all you find), and 100K.     Set what you have now in the middle for testing.  If you feel a mistake was made, write Smallbear, he is very helpful!

[GibsonGM]

OK, you are started, but need to check the OUTS of the chip.  Some parts go to ground, won't have signal on one end, that is normal and can't say from the pic...

[pgorey]

All pins of the IC have audio except the power bus on 8 and nothing on 4.

The two collectors don't have audio but are part of the 9v buss so I'm assuming that's why.  What I can't figure out is why there is no audio at the output cap and output.  Basically from Ra to the output.  All soldering looks good. 

[GibsonGM]

Ok dude, listen to the emitter of the first transistor.  You should have signal there.    Then, the emitter of the 2nd (last) transistor.   Those are the first and last stages of the circuit.

Do you notice if the signal is louder at the output pins than the inputs?  After the 1st stage you should also be able to hear 'dirt' (distortion) when you adjust the drive control.     This is helpful if someone else gently picks notes for you, or if you use a signal generator, CD player, etc....

Should have gotten this for you before...note the signal path...

[pgorey]

Thanks Gibson!  That drawing does help show the signal path nicely.  Both emitters have signal.  Unfortunately, the emitter at Q2 doesn't seem to be any louder than at Q1.  Additionally, if I test from the 1k resistor after the drive circuit, no additional dirt is heard from adjustments on the drive pot.  Tone and volume pots both affect the output at emitter off Q2 as expected.  My brain is hurting a bit 

[duck_arse]

I dunno why I stopped looking at Ra last night - your Rb shows 10k fitted, while the tonepad docs show it as 100k. if you have 100k at Ra and 10k at Rb it will matter much more than if you have 100R at Ra and either 10k or 100k at Rb. but 100k will allow more signal out, as determined by the ratio of Ra : (Ra + Rb). which is probably not helpful.

if you have signal at the Q2 emitter, but not the output, the problem has to be Ra, the 10uF cap or Rb - or the wiring to the outside world. this assumes you have effected signal on the transistor, if it is clean, the problem is futher forward. can you measure the voltages on those three parts please?

about your W taper pot - that is the usually specified type for that tone-control application. and about those diodes - don't sweat it if they work, but the mojo runs out of the leads if they are not bent neatly with needle nose pliers.

and your pliers become handy clamps if you wrap an elastic band around the handles.

[GibsonGM]

^^ Yes.   If your vol and tone controls work, you are getting there!   

The emitter signals will not be much greater than that input to the transistor, they are buffers rather than amplifiers ("emitter follower"). 

I can't get the Tonepad version of the schematic to come up.  using mine up there: the drive pot works with the 51K resistor to set the gain of that opamp stage, which is where your dirt will come from.     Signal must pass thru the cap and the 4.7k to Vr (bias voltage), which is the same as if it went to ground.  If that network is not wired right, you won't amplify...so IMO, you might start right there, being sure the drive pot is connected the right way, that the 51K is the right value, and going to Vr (4.5v), etc.     You should hear the results at the 1k at the output.  Short circuits in there, by solder or other, will result in little to no amplification.   

"Amplification" can mean clipping too - not much louder, but dirty. The diodes cut the signal off which results in clipping.  Check that they are opposed - cathodes going in opposite directions.  If you can get that 1st stage working, you'll have proven the chip is still OK and the rest should go easy!   

[pgorey]

Guys, thanks for sticking with me on this.  Here's what I have done.

I didn't have the right combination of resistors in my bin for Ra and Rb for the 808 config.  I thought the new resistor I found at my office was 100R, turned out to be 10.  It was a larger 5 band and I assumed the Brown, Black, Brown Gold meant 100R but since there was a white band at the end, I think this actually means it's 10.  It was also a 1/2watt and not 1/4watt so I didn't like that it didn't match.  I have a really limited supply of components at the moment because I just relocated from cross country and sold off everything I had before moving.  Also, the local radio shack was closed yesterday because we got 7" of snow - I found this to be hilarious coming from a place that received 21' of snow in Dec alone
Long story short, I did have the right resistors for the TS-9 so Rb is now 100k and Ra is now 470R.

The good news is now I have audio at the guitar jack output.  The bad news is that the drive control still does nothing - not at the 1k resistor as Gibson mentioned and if it doesn't work there, we're not going to hear it further down the line right?

Duck, I have listed measurements from those components below.  I'm not sure how much more tidy I can make those leads for the diodes since the length of the component already exceeds the distance between the holes.  Hopefully don't lose too much mojo as is but I'll try to crimp the leads a bit more tightly.

9v Battery Voltage for Reference:  8.65v
Rb: 0v - uh oh
Ra:  3.03v
10uF:  3.03v on positive side (coming from Ra).  0v on negative side

Gibson, here are some measurements from the drive network you mentioned:
4.7k to Vr:  4.25v
51k Resistor is right value:  green, brown, orange gold

I'm having a little trouble confirming my 51pf cap - it reads SL51J which I think translates to the right cap value but I'm not sure.

[GibsonGM]

Lemme get this straight: Rb is the 100k below output (pink), and Ra is now the 470R (turquoise)?  If so, ok, leave that.  If Rb IS that 100k, DC is blocked by the 10u cap, and that is good.

The 51 pF does nothing regarding the opamp stage operating; it trims some (very) high freq. content in use.  As long as it is not a short, no worry for now.

If you get no drive there, we must find out WHY.  I'd use my multimeter on its continuity setting, power removed, to be sure there is no short thru that diode network, from output back to IN -   .    Assure that the drive pot is wired up as shown, as a variable resistor.   If the chip has power, and is wired that way, it WILL amplify and clip with those diodes...

If you were to put your meter leads on the output at 1K resistor, and  51K/51p junction, I would expect to read something like ".315" or so on a diode Vf test, if your meter has that.   And the same again if you reverse your leads.    Just a quick test to see what's up with those monsters...

And then with power on....signal is present at the "+" pin when you play, right?

Sadly, this is stuff I/we do quickly once we know to do it - I fee like we're telling you to hunt all over, but eventually this will take you 10 mins. to run thru!!

[pgorey]

Rb is the 100k below output (pink)
Yes
and Ra is now the 470R (turquoise)
Yes

The 51 pF does nothing regarding the op-amp stage operating; it trims some (very) high freq. content in use.  As long as it is not a short, no worry for now.

Tested continuity and no short.

If you get no drive there, we must find out WHY.  I'd use my multimeter on its continuity setting, power removed, to be sure there is no short thru that diode network, from output back to IN. 

I tested continuity and have it from the through the diode part of the circuit.

Assure that the drive pot is wired up as shown, as a variable resistor.   If the chip has power, and is wired that way, it WILL amplify and clip with those diodes...
looking at how tonepad shows this pot wiring in the drawing (maybe you can see it at the link below), the wiring appears to be correct - the order from left to right goes 3,2,1 as printed on the top of the board - this goes 3,2,1 from left to right looking at the top of the pot.  I'm going to try swtiching the leads just in case there is an issue with the numbering as labeled on the board.  Perhaps pins 1 and 3 need to be swapped.

Pics of the circuit and my actual pot wiring here:
http://imgur.com/8E2qnIc

If you were to put your meter leads on the output at 1K resistor, and  51K/51p junction, I would expect to read something like ".315" or so on a diode Vf test, if your meter has that. 

I unfortunately don't have a diode mode on my meter.  I could borrow one from the office tomorrow - they have flukes there.

And then with power on....signal is present at the "+" pin when you play, right?

+ pin on what component? The output?  I have signal all the way through to the 1/4" mono output.

Sadly, this is stuff I/we do quickly once we know to do it - I fee like we're telling you to hunt all over, but eventually this will take you 10 mins. to run thru!!

No worries at all.  I have already learned so much in just a few short days.  I really appreciate all of the follow up and input from you guys!

[GibsonGM]

TRUE continuity in the feedback loop is bad IF your pot is set to say, halfway. You should always have about 51k between in and out, and in parallel with whatever the diode's dynamic resistance is if your meter turns one on....you don't need a special meter, it's ok.

Can you measure the actual resistance between "IN - "and output?  My instinct says that you have a short somewhere right there...next thing would be lifting one end of those diodes (they're not really twisted, right? That was a joke...).   I'm talking about the chip output here, not all the way to the circuit output.   "Out1".

I can use pin numbers, and hope they have not put the 2nd opamp section first, LOL.....

<<<<So - you want to know what's going on between pins 1 (out) and 2 (IN - ).  The 'notch' in the chip is 'up', and you count pins starting on left side, going down, around to R side then going up, like a U>>>  http://www.ti.com/lit/ds/symlink/tl072a.pdf refer to this data sheet, save for your "library"....3rd page, right side top is your TL072

The pot wiring appears right, won't matter if it's "1 and 3" or "3 and 1", as long as an end and middle (the 'wiper') are connected...just that the pot would work backwards.

Put short - a last resistance test between pins 1 and 2, and then maybe you lift one end of each diode to remove them from the circuit.  If all is well, this should be amplifying, controllable with the drive pot, not just 'present' to the output.   If not, the chip is dead or at least has something shorted that needs to be fixed...usually a magnifying glass will help find solder bridges across chip pins and so on....

[pgorey]

Thanks Gibson.  Had a late night at work so getting just a little done here tonight - also ran out of solder and will get more tomorrow after work and will re-solder all pots with stranded wire. I used some solid core and they have broken off a few times so I want to remove that variable.

I have an RC4558P chip as per the Tonepad parts list.  I did however order a few other ICs and the TL072 was one of them.  The chip I have does not have a indent but a small circle at the bottom left that aligns with a matching graphic on the board that I think typically shows the 1st pin.  Measuring resistance between pins 1 and 2, I am getting 1.2k resistance with the diodes pulled.  That's no where near your recommended 51k when the drive pot is at half way.  However, with the diodes completely removed, I have proven that the IC is in good shape because It amplifies via the drive pot control all the way to the circuit out 1 (1/4") out.  The solder points all look really clean to me even under a large mag glass  and I had audio on all pins of my diodes when they were installed so I'm curious if there is some issue with using the NOS GE1N91 847 diodes with this particular chip.  Anyway, this last test also proved my wiring to be correct on all pots though I will be replacing that wiring for the reason mentioned above.  I'm going to see if my local radio shack has the 1N914 diodes in stock as my small bear order wont get here for a week or so and I feel like I'm so close and I want to try using what is specified by the schematic to remove that variable as well.  Thanks again for all of your assistance and knowledge.

[GibsonGM]

No problem, it sounds like it's starting to come together!  Sorry it takes so long to get an idea like debugging across, ugh.

Actually, with your drive pot 1/2way, you should see 1/2 its value plus 51K!  Make SURE that resistor actually measures 51K or thereabouts, and that your pot is actually 500k (I know, I know, you already have!).  Might be because the chip is in socket. (?)
4558 and TL072 are generally interchangeable, '72 being a 'higher performance' version. Some think it's more sterile than the 4558...no worries. 

If you are getting VERY noticeable amplification at output, as in this sounds like a BOOSTER, then you've probably got it and the diodes have a good chance of being the issue. Don't know why, but sometimes it's like that...perhaps there was a short in your soldering, called a solder bridge...

[pgorey]

Thanks Gibson.  Yes, definitely sounds like a booster now.  I'm hoping the local radio shack has three diodes and solder as I think I'll be golden after those.  Will also clean up the wiring to pots and add the switch / led as soon as I confirm the board is good to go.

[GibsonGM]

Great!  Next one will go faster, ha ha 

[duck_arse]

the diodes, huh? anything you have at hand, 1N400x, BAT4x, 1N47xx (the schottky's), red leds, green leds, yellow leds even, 1N914, 1N4148, any of those weird 1SS japanese, or MAsomething ...... just about any diode you have at hand will do to prove/disprove the oppy is actually boosting enough for the diodes to do good work. tack in any two diodes back-to-back, what happpens?

when I say any two, any but those black power top-hats you have, cause they're shonky.

[GibsonGM]

You might find you PREFER LEDs - I do!  Grittier, and leaves you with a louder signal since they clip at a higher voltage.

[pgorey]

Interesting regarding the leds!  Any particular color / brand etc?  I wouldn't mind something more on the grittier side. 
Got 3 1N419s in place as I'm running the asymmetrical version and guess what?

It works!!!!

Those top hat diodes were the issue.  Oh well, I got to learn a lot more about the circuit and some basics on the debugging thanks to you guys.  There's still so much for me to learn within this pedal let alone all the infinite options and mods out there.  I like how it sounds as-is but I think I'll add another switch to toggle between asymmetrical and symmetrical configurations.  I imagine trying out different ICs would be a cool experience too - I know they mostly do the same thing but I'm sure they affect the overall sound too.  Anyway, time to wire back in the switch and led and clean up the pots and I/O wiring before stuffing into an enclosure.  I have a fuzz to finish up and then will button up the screamer after and of course share some pics.  Thanks again guys.  Really thankful to be part of this community / knowledge base.  You'll be seeing a lot of me on here.  Screamer and fuzz were the first two.  Next up will be a compressor, then octave, then analog delay or a verb and an envelope filter of some sort.

[GibsonGM]

Sweet!!  I'm glad that was the problem!  I have no idea why those diodes wouldn't work, but there must be 'something' about them...too high a forward voltage, maybe (?), called "Vf".   
Now that it works, maybe make this one cherry and build ANOTHER with all those options   Just an idea.

Ok - using "search", you could probably find 400 topics on "clipping diodes", and discussions on why they differ.   However, the big point is the voltage they turn on at (Vf).   Germanium diodes are around .3V, silicon .5V, and LEDs run into a couple of volts; they vary.   

The higher the Vf, the more 'gritty' the distortion, the more signal you need to hit them with to clip, resulting in a louder, "hotter" signal (hard rock, blues).  More dynamics.   BUT - early clipping, like with Ge's, distorts the WHOLE signal, like a square wave, and is much more clipped (metal...).  Lower output, but much more distortion, all being equal.   Best thing is to breadboard a basic gain stage and try many types!!   One application may make you choose Ge and a midscooped tone section...another may be 2x1 LEDs, mid hump....

I think you'll hear this best on a gain stage where the LEDs are on the output, NOT in the feedback loop like the TS...look up "MXR Distortion +" to see this type.  Mod to your heart's content!   (note, the gain pot on that is so big that it distorts the opamp too, may wish to lower from 1Meg)

I like red LEDs...but not the new 'super bright' - the old school 3mm ones.  By experimenting, you find many combos that sound good...