Thumb Sucker Compressor distorts instead

[Kevin Mitchell]

Conflicting voltages or unstable power supply?
Hmmm....

I don't know. I use a Truetone 1 Spot CS12 or CS6. And I feel it has been stable. Then I have used the wall wart I got from some pedal purchase in some cases, one from EHS and another small I think from Source Audio.
Is it strange? Yes.
I will rebuild and then re-measure again. And hope to be brave enough to present whatever readings I get.
Got me thinking of
"...then whatever remains, however improbable, must be the truth"
But if all this gets to "said and done" most likely there is some error on my side.

When I see things like this the first thing I try is pull all ICs to see if the power supply stabilizes.
Then install IC1, check VR and the main supply again...
Continue forward until you find a possible problematic IC that's mucking things up.
Otherwise, you've got a noisy supply and probably shouldn't be dismissed.

But I could very well be drawing your attention further from *the real problem*.

I'm kind of itching to hop on the ET Comp train. Breadboard it again to try and help solve some of these riddles...
It's been years and I'm pretty sure it failed using a CA3080 - either error on my part or I too suffered the same result as few others. Sadly the success of others had me dismiss it as user error or a naughty breadboard.
I can put up some oscilloscope shots if it's of any use.

[DrAlx]

I downloaded a bit of motopotato's soundcloud file and opened it in audacity to see what the distortion looked like.
The picture is cut from about 13 seconds into the original recording where a note was dying down yet there was still buzz distortion on it.
I notice two things:

1) The buzz sound comes from a high frequency ripple on the wave form.
2) That ripple is mostly on the bottom part of the waveform. e.g. 0.007s , 0.027s, 0.047s  etc

To me, it doesn't suggest an op-amp limit is being reached.
It does suggest there is some sort of asymmetry at play.

[matopotato]

Thanks DrAlx, really cool. Unfortunately that distortion is now definitely like a fuzz right now.

So I re-boarded it. That is went through each connection to verify connectivity.
Then I tested. after a tip, to use the other unused "Side" of the LM13700. I got the pinout so I could separate the buffer from the rest. Kept the buffer connected "as is" and for the other connectors I switched sides. There was no difference to the problem though.

I then went on to measure. Some parts stay stable, others keep rising or falling. And when I get around to the PNP, the pins 6 and 7 on the IC2.2 have moved again in values, so my values do not quite make sense. I tried at one stage to wait it out. And when I thought it settled, went to other places, got back and it had snuck up again, only to fall when I measure.
So "what are the voltages"? Well, when do you want to know? Feels really odd.
Anyway, I try to be a good bot and measure anyway and paste in the schema.
I had signal chain connected, strummed once in a while, but that did not seem to affect the readings.
I could try with only the DC power connected and see if that makes it more stable or not.

I'm wondering if the fluctuations and instability could be part of the problem...
I had background noise a while until I found a cable that had jumped. Even with my ignorance I felt the values had been off, and then measured again. Some went better, but IC2 fluctuate a lot.
IC1 is quite stable but pins 6&7 vary slightly.
PNP takes a beating from IC2 I suppose, or they tease each other. The LM13700 seems the more stable one at this point.

[PRR]

........leads me to think that there are more than one ways to present readings......

This struggle has gone on for a week in multiple threads. What you are doing clearly is not working.

The idea that you can modify or rip-up your breadboard is very distressing. If you can not trust your connections, take-up another hobby.

You did take Merlin's advice. A very funny thing stands out on schematic rather than as text list.


HTH can you have 4V one stage and 2V another stage? Yes, we could design it that way, and there are some 0.6V drops, but a little 1k resistor with an "infinite" (TL072) load will not lose voltage like that.

Busted pot wires? (K.I.S.S.: Wire fixed resistors until it works good.)

Shorted caps? (Normally you can remove caps and not affect DC levels, but this may be an exception.)

Bad chips? Stray wire scraps? Termites?

[PRR]

...So I re-boarded it. That is went through each connection to verify connectivity.

Thanks: but now you have "impossible" readings.

I marked some arrows in Red- these pairs of points are on the SAME wire and would have to be equal. Why aren't they?

The Base-Emitter voltage can only be zero to <1V. When working happy (this may not work at idle) we expect 0.6V. Not 2.1V. Bad transistor? Wrong transistor? Mistaken pinout? A breadboard so goofy that the two ends of the wire IC2.2 to Q1 change connection moment to moment?

[matopotato]

Conflicting voltages or unstable power supply?
Hmmm....

I don't know. I use a Truetone 1 Spot CS12 or CS6. And I feel it has been stable. Then I have used the wall wart I got from some pedal purchase in some cases, one from EHS and another small I think from Source Audio.
Is it strange? Yes.
I will rebuild and then re-measure again. And hope to be brave enough to present whatever readings I get.
Got me thinking of
"...then whatever remains, however improbable, must be the truth"
But if all this gets to "said and done" most likely there is some error on my side.

When I see things like this the first thing I try is pull all ICs to see if the power supply stabilizes.
Then install IC1, check VR and the main supply again...
Continue forward until you find a possible problematic IC that's mucking things up.
Otherwise, you've got a noisy supply and probably shouldn't be dismissed.

But I could very well be drawing your attention further from *the real problem*.

I'm kind of itching to hop on the ET Comp train. Breadboard it again to try and help solve some of these riddles...
It's been years and I'm pretty sure it failed using a CA3080 - either error on my part or I too suffered the same result as few others. Sadly the success of others had me dismiss it as user error or a naughty breadboard.
I can put up some oscilloscope shots if it's of any use.

I think IC1 is central for Vref at least. And VCC is stable at 9.29 this time. And they have been in and out earlier during swap testing with a third TL072. So put that in the mix and rotated around. No change.
The supply has not been an issue in other cases, and I used 3 different ones. Home appliances have not complained either so the base power in the house feels ok.
I appreciate the "make sure you start from the right base and work yourself up" well, forward perhaps. And I subscribe to it in many troubleshooting scenarios, but I honestly feel I have no reason to distrust my power supply.

About the ET in general. I wish I had more example experiences to compare with. The circuit and its implementations get overall very high praise, so I too think it is something I've done wrong. Or perhaps my first case of faulty component.
Because others have them working fine. OK some extreme settings might cause a little bit of distortion, but I think that is understood and expected. And using all extremes or some specific "bad" settings can cause the circuit to chase itself I think I read somewhere.
But having now two copies. Swapped everything else around, tested two different LM13700's (but only in the build though) I can no longer see any part or component that if identified would make me go "Yes, of course, now it makes sense and fits together" because I feel I have changed everything.
Unless it is some evil component conspiracy where several individuals in combination take turns causing the problem. But then the probability is at zero IMHO.

Might try another round of measures again tomorrow. Perhaps another sound sample since it now sounds really bad.
Unless anyone is interested in a Dying Battery Fuzz with Random Bypass. 5 knob version.

[matopotato]

...So I re-boarded it. That is went through each connection to verify connectivity.

Thanks: but now you have "impossible" readings.

I marked some arrows in Red- these pairs of points are on the SAME wire and would have to be equal. Why aren't they?

The Base-Emitter voltage can only be zero to <1V. When working happy (this may not work at idle) we expect 0.6V. Not 2.1V. Bad transistor? Wrong transistor? Mistaken pinout? A breadboard so goofy that the two ends of the wire IC2.2 to Q1 change connection moment to moment?

Yes, I know they are impossible readings.
I tried to say that some keep varying. How long to wait? Until they reach zero? When are they to be regarded as stable?
I measure, come back for other reason like you mention impossible values and they have changed.
I don't think I have fried the DMM (yet).

So I could make up values to calm things down, but that would be counterproductive and useless.
I feel that I am the messenger rather than the message.
Yes, I should probably take up some other hobby. Leave you guys to it and stop disturbing this forum. Last thing I want is to be regarded as a negative guy causing distress.
But effects, pedals is my passion too. Sorry, can't really help it. It has only been a year since I started with this and I feel I am learning, but far from know it all yet. (Probably never will).
I also have a strong drive on troubleshooting, logic and "customer focus" from other walks in my life.
And I felt that my pedal problem would be "solvable" with some help. Especially since two other members had the same or very similar problem.
But now it seems to be more of a nuisance than of interest.

[eh la bas ma]

But now it seems to be more of a nuisance than of interest.

What ? PRR is only trying to help, with is own original style. I am following this thread with great interest !

The fact that there are four active threads about the Engineer's Thumb  is easily and perfectly understandable :

There's an old one,with a similar issue from reply #31, with some possible leads.

There are three Engineer's Thumb builds that don't work correctly.

I even suspect there are more builds showing the exact same issue, and their users don't know there is something wrong with their compressor... I suspect it because I was one of them...see reply #2. We are most probably doing something that will be useful for the next builds.

I am sure Merlin the Valve Wizard is proud of his compressor, and happy to see people struggling to make them work, instead of throwing them away without a second thought.

So thank you Matopotato for bringing this distortion issue to my attention.

Without you and Wook22, I would have thought this compressor was quite weak and easily distorting the signal. I am no engineer or scientist, I studied letters, foreign languages, and I started building circuits because I play music. I didn't suspect there was an issue with my build... I built it carefully, just like I did with 40 or 50 stompbox kits before, and I can't find any obvious issue, at least not on my own.

So far you have been really contributing, at least from my point of view.

...please take it easy...breath...where is your "jacket" ? Think about the Common Good... we may get to the bottom of it...hopefully.

[puretube]

Another theoretical thought try from my side, before starting to breadboard this circuit:
what happens to the "fuzz", when the inverting OTA-input (pin4) is not directly connected to Vref (4.5V) as in the original schemo, but through a 220R resistor?
(before trying a 500R trimpot pot across the +/- inputs with wiper to Vref, as another possibility to check whether the whole case is an offset-/symmetry-issue; or even AC-coupling the OTA).

[duck_arse]

Yes, I should probably take up some other hobby. Leave you guys to it and stop disturbing this forum. Last thing I want is to be regarded as a negative guy causing distress.
But now it seems to be more of a nuisance than of interest.

no. your prose style is too interesting, you'd better stick at it.


I had a go at the rectifier section on the breadboard today, cause I wasn't sure about what to expect. now, I can honestly say I have no idea what or how it is doing, but do know what to expect. about your measures - there is a process.

no audio, no looper, no signal in, not to start with. build the thing on the breadboard, neatness counts. we even like photos of that stage, just to make sure of things you tell us. [and yes, thanks for the pics.] build the circuit, power on, measure all the voltages. just measure them and write them down - if you have to wait for a moving voltage when there is no input signal [which is rule number one, just quoted], then the voltage [or the measure method] is wrong.

if you have a full build doc with a complete circuit diagram with all IC references and pin numbers included on same, [and your breadboard follows same exactly] then yes, text form voltage postings is fine, because you will obviously have included all those critical docs in the first post of the thread. and - writing the voltages on the circuit is a useful diagnostic tool, as we have seen.

my partial breader showed that there should be half supply volts on all the IC2 pins [on your pedalpcb circuit] from the thresh pot wiper thru to the transistor base pin. give or take a few hundred millivolts, but nothing less than 4V. I also found that when I whacked it with signal, those voltages didn't move by more than 100mV at the R9//C5 point, and it went down.

but that did make the transistor do stuff, pass current into a resistor as load which varied with the input signal level, so I call that a success.

stick at it.

[eh la bas ma]

This is probably nothing but I 'd like to make sure...

According to PedalPCB values (your R10 corresponds to my R11 and vice-versa),

Do you have continuity between both R11 (1M) pads and E, B and C (BC327) ?

I also have continuity between D4- , one R11 pad and both R10 pads (still with PPCB nomenclature).

According to our schematics, I wouldn't expect that, is it the same on your build ?

[PRR]

.....effects, pedals is my passion...

So get passionate about figuring why your build and readings are not making sense.

I'm just pointing out places _I_ think you should be looking. Don't take it as criticism.

[eh la bas ma]

This is probably nothing but I 'd like to make sure...

According to PedalPCB values (your R10 corresponds to my R11 and vice-versa),

Do you have continuity between both R11 (1M) pads and E, B and C (BC327) ?

I also have continuity between D4- , one R11 pad and both R10 pads (still with PPCB nomenclature).

According to our schematics, I wouldn't expect that, is it the same on your build ?

I am a bit puzzled now...  When the power jack is inserted, I have theses strange connections as described above, but not when the 9V power jack is unplugged...then I have continuity as shown on schematics...

Edit : I thought I was dreaming or something, so I reflowed the pads in this aera, looked for shorts, but still...
Same behavior with sockets once I took off the transistor.

Edit 2 : I might need to borrow your straitjacket... is it available ?

[matopotato]

Sorry. Life and work happend. Will buy components, and do measurements, and photos during weekend.

[ElectricDruid]

Life and work happend.

Reality is so damn thoughtless like that! Doesn't it realise I have more important stuff to do?!? 

[matopotato]

I managed to get another B1M pot plus some trimmers. I will try the trimmer suggestions tomorrow I hope @puretube.
For what it is worth, the PCB build I restored and it sounds as at the outset. Distorts much "sooner" than my friend's ET. His only begins to distort a little with Ratio full CW and Threshold full CCW. As I have understood this is normal behavior considering how the parts interact, so no issue there. When he rolls on a little bit of threshold the noise is gone.
In my case at 3 and 9 respectively, it is still there, even at noon. Of course guitar volume, pedal volume, pickups etc influence this, but the distortion/scrapy sound is remarkably consistent on my Thumb Sucker PCB version.
The breadboard now has all its onw parts except the ICs and PNP. And it distorts quite a bit worse, like a dying battery fuzz at times. But it did sound the same as the PCB build at the outset, so it should be possible to use as experimentation.

I measured both and found IC2, pin1 on breadboard to be 0.0V. So I swapped out the D1, D2 and D5 (for good measure) to fresh 1N4148's. But still the same.
Also the breadboard circuit showed a lot more fluctuations, mostly rising values. I marked with * the ones that kept changing. So forgive me if they come out impossible. E.g. IC2 pin7 and PNP Base went from 5.70-ish to 7.60. In tandem though, so they did learn a lesson from last. I could they were afraid I would tell them off, but rising they went.

No cables, In or Out from guitar or any other signal were involved during the measurements.

Anyway, here are the readings:
Breadboard, Graphical:
NB: I missed the 4.79 on IC3 pin4. It is included properly below though. In the txt version



Breadboard, txt:

Power in 9.84
VCC 9.62 - 9.60

IC1
4.60   9.61
4.79   4.80
4.37   4.80
0.00   4.76

IC2
0.00   9.62
4.80   5.80-7.60
4.69   6.75 (at some point)
0.00   4.72

PNP
C 1.10
B 5.70-7.60
E 6.78 (at some point when B was high)

IC3
1.10   0.00
0.55   0.00
4.59   0.00
4.79   0.00
4.79   0.00
0.00   9.60
0.00   0.00
0.00   0.00


PCB build
Graphical. Again * is for fluctuating values I think all were on the rise.



PCB Build, txt:

Power in 9.85
VCC 9.65

IC1
5.00   9.64
4.84   4.70*
4.41   4.81*
0.00   4.70*

IC2
4.76   9.64
4.82   4.33
4.77   4.82
0.00   4.67

PNP
C 1.12
B 4.32
E 4.82

IC3
1.12   0.00
0.20   0.00
4.82   0.00
4.82   0.00*
4.83   0.00*
0.00   9.64
0.00   0.00
0.00   0.00


Some uninitiated observations: The PBC looks better, more stable values and seem to be "better", but the original problem is still present very much. I don't see this a pedal I would give to anyone else as a compressor, let alone charge money for it.

Why the breadboard (re-continuity checked again today) sounds much worse is also a mystery. Might have to rebuild it from scratch to have both on par to test some of the remaining suggestions.

@duck_arse: Here is the breadboard, but it is not for the faint-hearted.
I tried to translate "neatness" to Swedish, but google gave up on me, so... I'm gonna guess "amount"...

[matopotato]

This is probably nothing but I 'd like to make sure...

According to PedalPCB values (your R10 corresponds to my R11 and vice-versa),

Do you have continuity between both R11 (1M) pads and E, B and C (BC327) ?

I also have continuity between D4- , one R11 pad and both R10 pads (still with PPCB nomenclature).

According to our schematics, I wouldn't expect that, is it the same on your build ?

I am a bit puzzled now...  When the power jack is inserted, I have theses strange connections as described above, but not when the 9V power jack is unplugged...then I have continuity as shown on schematics...

Edit : I thought I was dreaming or something, so I reflowed the pads in this aera, looked for shorts, but still...
Same behavior with sockets once I took off the transistor.

Edit 2 : I might need to borrow your straitjacket... is it available ?

Just for completeness and the digital archeologists: It was sorted in this thread https://www.diystompboxes.com/smfforum/index.php?topic=129237.20 that measuring continuity and other stuff while pushing signal through can cause unexpected effects.

Mi Straightjacket, Tu Straightjacket. I think it is 9XXXL so it will fit us both. You can even stay in France and me in Sweden I think. There is room for everyone.

[matopotato]

Another theoretical thought try from my side, before starting to breadboard this circuit:
what happens to the "fuzz", when the inverting OTA-input (pin4) is not directly connected to Vref (4.5V) as in the original schemo, but through a 220R resistor?
(before trying a 500R trimpot pot across the +/- inputs with wiper to Vref, as another possibility to check whether the whole case is an offset-/symmetry-issue; or even AC-coupling the OTA).

I plan to try this tomorrow.
I like the idea of the signal being offset as a possible source for problems. When I used a scope a few weeks back it seemed that when dialing up so the problem appeared, it first showed as a flat top on the tonegenerator wave, but the bottom was fine and sinus-y. Until I pushed harder of course. And if there is an offset issue, that can be softened or pushed further down the line so to speak, then that might be enough to keep the good sound until you hit the extremes, where it distorts anyway and also is sort of bad territory. At least it would make sense IMHO. And if I ever sort this out I think I would like to understand what was the cause.

[eh la bas ma]

Priority should be to get voltages that make sense.

If you did a lot of trials, unsoldering then soldering parts back on the board, etc. it wouldn't be very surprising that there are some scraps, some remains of solder on the soldering side.

You might want to clean everything with your iron and a dry toothbrush, reflow all suspicious pads (and those that look good), hunt for shorts, perform a ritual sacrifice to the diy goddess (while listening to The Bloods), and then try to check those voltages. Finally compare them with your friend's compressor (give him your blueshift, he will agree i am sure). See if anything stands out. (Edit : remember IC and transistors are heat-sensitive, remove them if you clean the board with your iron)

Duck_Arse helped me verify if the sidechain was working on my build. There are three points of interest :


Blue circle is C3/R9 junction,  Voltage here should be sensitive to the Release control. If you turn it, the voltage in the blue circle changes.

Red circle on your schematics corresponds to pin 10 of the TL74 on my board, for you it's IC2 pin 5. Voltage here should follow the value at C3/R9 junction.

Finally green circle :

but that did make the transistor do stuff, pass current into a resistor as load which varied with the input signal level, so I call that a success.

stick at it.

I notice something happens At R10/BC237 junction when I strum.

Ratio = 2'  Threshold = 9' Attack= 9' Release= 12' -->> 1.118 V. switching on : 1.117 V and if i strum it goes up to 1.268 V and goes down gradually to 1.117 V

Does it do the same on your build ? Measure voltage in the green circle first with no signal, then try again while strumming your guitar (no looper, a real guitar, full volume). Circuit powered and switched on.

[matopotato]

Priority should be to get voltages that make sense.

If you did a lot of trials, unsoldering then soldering parts back on the board, etc. it wouldn't be very surprising that there are some scraps, some remains of solder on the soldering side.

You might want to clean everything with your iron and a dry toothbrush, reflow all suspicious pads (and those that look good), hunt for shorts, perform a ritual sacrifice to the diy goddess (while listening to The Bloods), and then try to check those voltages. Finally compare them with your friend's compressor (give him your blueshift, he will agree i am sure). See if anything stands out. (Edit : remember IC and transistors are heat-sensitive, remove them if you clean the board with your iron)

Duck_Arse helped me verify if the sidechain was working on my build. There are three points of interest :


Blue circle is C3/R9 junction,  Voltage here should be sensitive to the Release control. If you turn it, the voltage in the blue circle changes.

Red circle on your schematics corresponds to pin 10 of the TL74 on my board, for you it's IC2 pin 5. Voltage here should follow the value at C3/R9 junction.

Finally green circle :

but that did make the transistor do stuff, pass current into a resistor as load which varied with the input signal level, so I call that a success.

stick at it.

I notice something happens At R10/BC237 junction when I strum.

Ratio = 2'  Threshold = 9' Attack= 9' Release= 12' -->> 1.118 V. switching on : 1.117 V and if i strum it goes up to 1.268 V and goes down gradually to 1.117 V

Does it do the same on your build ? Measure voltage in the green circle first with no signal, then try again while strumming your guitar (no looper, a real guitar, full volume). Circuit powered and switched on.

Thanks. Will add to list of tests for sure.
Actually the pcb board is the one behaving best and more consistent during my trials and despite changing things on it, it still is as from the outset.
The breadboard vetsion is a different beast though.
Plan is to build up again on a new breadboard. This one can be a bit wobbly in some holes.
Then
try @puretube suggestions around signal offset adjustments.
Then go through the test from above.
What did it make you find or discover or adjust?