Strange noise problem

[warioblast]

Hi,
I have a strange problem with my new build, a Blues Breaker.
The pedal alone in the chain is fine; it's almost dead quiet, whether I powered it with an AC adapter or a battery.
But when I put it my chain the pedal gets noisy when stacked after any other non engaged effect. And when the pedal is 1st in the chain, all gets quiet again.
I'm lost 
Any help would be greatly appreciated.
Cheers,
Fabrice

[GibsonGM]

Sounds weird, man!  I can only tell you where I would start if it was me:

I'm assuming the pedal is in an enclosure.  Maybe check the output of the Breaker, test it for DC (could be a bad cap there?).  Could also be a bad input cap, or a short somewhere.  The 'non engaged' thing makes me wonder...they are all true bypass?  Shouldn't cause any noise, unless the extra capacitance of the cables is doing something inside the Breaker.   Is the breaker star grounded?

Are you running all these from the same PSU? That could be an issue, maybe decoupling or something?  Anything running from a positive ground supply?

It'll get figured out 

[sfx1999]

Sounds like a ground loop. Try putting a battery in it while it is in your loop. If it goes away, you have a ground loop. You can solve the problem by putting it on a different power supply.

[warioblast]

"Sounds weird, man!  I can only tell you where I would start if it was me:

I'm assuming the pedal is in an enclosure."
yes it is.

"Maybe check the output of the Breaker, test it for DC (could be a bad cap there?)."
I don't know what this means, could you enlighten me ?

"Could also be a bad input cap, or a short somewhere."
As the pedal worked right away, I didn't look for shorts or other mistakes. Will do.

"The 'non engaged' thing makes me wonder...they are all true bypass?"
Yes there are all TB

"Shouldn't cause any noise, unless the extra capacitance of the cables is doing something inside the Breaker.   Is the breaker star grounded?"
All ground points (jacks & board) are connected together if this is what you mean.

"Are you running all these from the same PSU? That could be an issue, maybe decoupling or something?  Anything running from a positive ground supply?"
I was in a Hendrix mood so my chain was at first: guitar > sweet sound mojovibe > modded wah > analogman sunface > roger mayer octavia > my BB clone > amp
sunface, octavia & wah on battery, the mojovibe and the BB on their own PSU.
Like you mentionned, my first thought was that I had problem with the + ground of the sunface. At this moment I made tests stacking only one pedal with the BB, but it was all the same. My last try was to put the BB first and everything went fine.

"It'll get figured out  "
I hope so. Or else I maybe buy the real thing. I've seen some good deals (45 € = $50). For once, I really like how it sounds without any mods. I mean as a booster it outcomes my expectations.

[GibsonGM]

I haven't built that one...is it Rangemaster-ish?

I check my pedals for shorts etc. by just measuring any DC voltage across the output, output wire to ground.  Once in a rare while, I actually find that I have a volt or 2 DC at the output (shorted output cap, etc, letting Vbias thru or something).  Better to find it that way than throw it into the amp!  I asked since it wreaks havoc 'down the line' when that happens.   
Having a look at the schematic:

Pulldown resistor in place at the output?  And the 2.2M and 1M at the + input?  How about putting in a different TL072?  Did you mount the output cap right on the 100K pot at the ckt output? That's caused me troubles before....

I really can't think of much else that could be causing the noise!  Maybe you could open it up, put it in the chain where it makes noise, and start listening inside it with an audio probe to see where it starts....

[warioblast]

I haven't built that one...is it Rangemaster-ish?

I check my pedals for shorts etc. by just measuring any DC voltage across the output, output wire to ground.  Once in a rare while, I actually find that I have a volt or 2 DC at the output (shorted output cap, etc, letting Vbias thru or something).  Better to find it that way than throw it into the amp!  I asked since it wreaks havoc 'down the line' when that happens.   
Having a look at the schematic:

Pulldown resistor in place at the output?  And the 2.2M and 1M at the + input?  How about putting in a different TL072?  Did you mount the output cap right on the 100K pot at the ckt output? That's caused me troubles before....

I really can't think of much else that could be causing the noise!  Maybe you could open it up, put it in the chain where it makes noise, and start listening inside it with an audio probe to see where it starts....

Well it's a well balanced mild OD, I'd say it's more tubey than the TS, as a booster it's fat, creamy, and it doesn't cut bass. My old trusty TS sounds so thin in comparison.

I measured 4.25V at the ouput. Is it good or not ?

2.2M & 1M at the input right.

I didn't use the TL072, I used 2 single OPamps; a TL071 & a TL081. I also subbed some parts:
6k8 R subbed with 5k6 & 1k2 in series
220k          "          180k &  39k in series
3k3            "          3k9 & 22k in parallel
Up to now it's fine but you made me realise that I miserably screwed my caps subs. I replaced the 2* .01 uF caps at the end of the circuit with 2 couple of 0.022 uF caps wired in ... parallel  that should have been in series. So I'm gonna fix this and see what it does.

The .1 uF output cap is on my board.

I don't have an audio probe but it looks like it can be fixed http://www.diystompboxes.com/wiki/index.php?title=Debugging

GibsonGM, thanks for your support

[GibsonGM]

I'm glad some light is shining on the subject, Wario )  Look how much info you came up with, lol.

The 4.5 DC on the output - BADDDD!!!  Something is shorted, check your output cap!  That is enough to create the problem right there.  I always check that before I plug into my beloved amp...check also that 'ground' is ground, 0V, and hasn't been accidentally shorted to 1/2VCC, which is....4.5V.  Do that by measuring voltage between battery - and your enclosure. 

Don't know if the TL081 will cause any problems, if it is functioning ok, worry about that later. 

Your resistor subs look OK.
The .02uF cap would've been alright until you could get a single .01, just a little bassier...chances are good that there is a short right there between them, causing the 4.5V getting thru to the output - check it out ;o)

An audio probe is really easy to make and use, and well worth the time to put together.  Helps to learn what's going on in a circuit, too.  You can find out about it in the DIY FAQ link up top.

Hope it comes out nice and helps you kick some @ss!

[warioblast]

OK I did another mistake, I measured the wrong side of the ouput cap which leads to volume2.
Output is measured at 0V 

from the PSU I measured 9.08V
right after the 1n4001 diode it falls to 8.4V
Vcc is 4.2V
and ground is 0V

I removed a cap from my duos of 0.02uF, which normally made the sound brighter. Sadly it didn't solve my problem. And to add to my growing frustration, the LED is now very dimmed 

I'll look into the audio probe.

[GibsonGM]

Well, 0 VDC at output is good, and you should get some reading at AC (mV to low V).   Are you using Gus Smalley's hand-drawn schematic, or the nice one from the 'schematics' link above?   Post your IC voltages, that would help, too...the LED getting dim, weird, it's supposed to be independent.  That can happen if your - and + are shorted....try hooking up a battery, and with your meter on + and - watch the voltage...if it goes down quickly and/or battery gets warm, there's definitely a PS short! 


Probably a solder short in there, man.  You wouldn't believe how often that is the #1 reason things get screwy or don't work at all.   I just did a TS, and it didn't sound very good - short! And I've built tons of effects.  Keep patient, and go back over the whole thing.  The audio probe will help, remember to include a cap (.22uF or greater is good) with it so no DC gets thru to whatever amp you use to hear what you're probing.

[warioblast]

I'm working with tonepad's schematic http://tonepad.com/getFile.asp?id=75
I don't know what happened with the LED, I changed it and it's fine, though I miss the yellow LED, it looked good with the gold paintjob  ... now it's green.

My voltage readings:

IC1 (TL071)
pin 1: 0.15
pin 2: 4.20
pin 3: 2.08
pin 4: 0
pin 5: 0.14
pin 6: 4.20
pin 7: 8.40
pin 8: 0

IC2 (TL081)
pin 1: 0.14
pin 2: 4.28
pin 3: 4.13
pin 4: 0
pin 5: 0.14
pin 6: 4.20
pin 7: 8.41
pin 8: 0

That makes me think I didn't try to swap the ICs, it's worth the try.

I made a quick attempt with the DIY audio probe, but I didn't really know what to look for. It seemed like I got audio signals except for ground, V+ & Vcc (Vb in tonepad schemo) places.
My DIY day is over. It's 10:30 P.M. here in France.  Don't miss tomorrow's episode 
Cheers,
Fabrice

EDIT: I'm reading a topic about the audio probe; in which you appear to be :-)
http://www.diystompboxes.com/smfforum/index.php?topic=54011.0
Using the boss DD-20 to make a loop is a brilliant idea.

[GibsonGM]

Hey Fabrice,

Here are my voltages, I just built a BB to see what it sounds like...not high gain, huh?  Mine sounds like...the blues...sparkly and rich, but no grit or distortion (hope I wired mine right, LOL). My drive pot does little in terms of gain, but acts like a 'brightness' control.   My battery was at 7.56, rather low:

1.  3.78    8. 7.56
2.  3.78   7.  3.78
3.  3.3     6. 3.78
4.  0        5. 3.78

Your voltages don't seem too much different, so that end of things is probably ok.
I used a TL072.  You might try putting in 2 TL071's, if you have an extra lying around; could be the replacement IC causing trouble.

[warioblast]

Yes it's not a high gain pedal for sure. My drive pot acts like yours; after many readings it seems like the majority of the owners of the BB (clone) uses the pedal with the drive pot set to max.

While investigating on the BB, I found a "grit pot" mod you might want to try. http://www.diystompboxes.com/smfforum/index.php?topic=49272.0

Unfortunately I do not have others TL071. I built the BB from parts I already had, hence my substitutions. The TL071 & TL081 were originally intended to put in an output wah buffer but it wasn't successful.
The only single ICs I have are a LM741 & a LM308.

And once again, I want to thank you for all the time you took to drive me through this kind of debug. This noise/hum problem is slightly driving me crazy. I'be less pissed if the pedal did not work at all or if it was always noisy.

[GibsonGM]

No problem, man!  Hey, you turned me onto the pedal by my trying to help you...karma!! I like the circuit...might try some mods, but I see a lot of potential.  Very 70's, AC/DCish.   My .1 cap before the diodes was bad; I subbed it out, and now the drive is better )   

I killed my last TL072; I put a 4558 in there, and it's doing ok - so, why don't you put in the 741 for testing?  Just a generic opamp, it's 1/2 of the 4558, and has the same pinout as the '71.  Might get you closer...

[warioblast]

I've just tried to swap the ICs, tried the LM741. The problem is still there. As soon as the BB is not 1st in the chain, it starts humming. It's not a huge hum but it bugs me cause the pedal itself (or when it's the 1st pedal of the chain) is really quiet, I can only hear a light white noise.

[warioblast]

My latest mods:
_ replacing the input cap which was the most likely to be damaged since it's an old cap from a dunlop wah.
_ messing with the ground.
_ raising the cap from the feedback loop (I had sockets in there so that was quick).
Nada - Nothing - Que dalle - Niet...

I'm gonna make a last try with the audio probe. Could you give me a quick rundown, like in which places should I hear audio signals or not ? This would be the last favour I'll ask from you. I swear 

[GibsonGM]

So, there must be some interaction somewhere!  It is possible that it's one of the OTHER pedals causing this...other than retracing the entire BB, there isn't much else I can think of to do!  It would be simpler if the problem occurred all the time, and not just when used with other pedals.  I think you need to ask a guru like R.G. or Mark Hammer, Wario!  If there is a solution, those guys will find it...I still think there's a bug in your assembly, which is entirely normal, common, and nearly unavoidable.   The last thing I can think of is perhaps an electrolytic capacitor is in backwards?  Or a ground loop in there somewhere. 

I like this circuit - I'm going to box mine up, with the 'grit' mod )  Thanks for the link to that!  I'm going away this weekend so won't be around until Monday - good luck, and keep trying!   
---------------------------------
Check at the input .01uF cap...after it....pin 3 of the 1st opamp (+input),  pin 6 (out), all 3 tabs of the gain pot,  all through the clipping network, - input of the 2nd opamp, output of 2nd opamp,  all thru the tone control caps and pot,  and at the output jack.   Do that while the hum is happening, and you might find the area where it starts! 
)

[GibsonGM]

FWIW, do make sure it's not a bad patch cord somewhere down the line - and see if it's traceable to only 1 other of your pedals causing the hum to happen!   Should've brought that up earlier, LOL....