# Thumb Sucker Compressor "scrapy" sound



## Matopotato (Feb 6, 2022)

Hi,
I just "finished" building a Thumb Sucker Compressor. Sounds very cool, more impressed than I had expected.
But..
1. There is an element of distorted scratchy sound. More with humbuckers than single coils. It is not distortion as you would like from a distortion pedal. More scratchy. It is all in the box so I doubt there is some loose cable or joint (famous last...). I am not very used to the controls yet, but it seems to vary with very low setting on release but maybe not. More so with (higher) ratio above 12 and (lower) threshold below 10-12...
(2. The attack and release knobs. Checked connection and that seems to be all good at least in that vicinity of the board. But they do not change things much. Is it because they are that subtle? Or do they only come in play with other settings? (CORRECTION: Asked this here as well: https://forum.pedalpcb.com/threads/thumb-sucker.6769/ post #6 I think. sorry for double posting))


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## Matopotato (Feb 6, 2022)

__
		https://soundcloud.com/user-558594533%2Fthumbsuckerscrapy

Soundclip example (my first, hope it worked)
And knob setting picture


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## Matopotato (Feb 7, 2022)

Since pictures are always wanted, although I doubt it matter at this point for either of my questions above.


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## xefned (Feb 7, 2022)

That's bizarre. I wish I could help, but I've never heard anything like it. It sounds like something is rattling acoustically.

Are there any knob settings that make it go away?


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## Matopotato (Feb 8, 2022)

Yes, I agree. As if something was loose, not any  "normal distortion".
It is most prominent with high Rate and low Threshold. The others don't affect it as far as I can make out.


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## xefned (Feb 8, 2022)

I'm hoping someone more knowledgeable than me can jump in cuz I'm at a loss. Visually everything looks correct.

If the LM13700 came from Tayda or Futurlec you might try a known good one. But that's just a stab in the dark. Good luck.


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## Matopotato (Feb 8, 2022)

xefned said:


> I'm hoping someone more knowledgeable than me can jump in cuz I'm at a loss. Visually everything looks correct.
> 
> If the LM13700 came from Tayda or Futurlec you might try a known good one. But that's just a stab in the dark. Good luck.


Thanks, Well honestly I am just happy someone reacted to my post. Feels better  
I got it from Das Musikding, but not sure where they source from.
I tried with (Trio +) looper and audio probe, but it gets very high pitchy noisy, so I went for guitar instead. Downside is that your hands are no longer very free...
But for sure the audio at the in jack is clean, and on the out jack it has the crackly thing. So something happens "in between", just a matter of tracing until I can figure out where the problem begins and then either re-solder or swap that component. I tried swapping the TL072s but could not say if that mattered. Also the 2N3906 felt a bit wobbly in its socket, but I could actually pull it out of the socket with no clear impact.
So thanks for cheering me on, and I hope someone who might know this build will find this thread eventually.


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## Matopotato (Feb 8, 2022)

Not sure if this means anything, but I probed to the green point which still sounds "clean". I assume this makes sense since this seams to be the clean signal route.
The red junction is where it sounds sh*t. But this does not have to mean that this is the problem. There is signal, but much more scrapy than the out result. Still I will try to swap the TL072CP for a spare one, and resolder the socket legs and D1 and D2. And yes, I also doublechecked that the diodes are facing according to pcb layout.


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## JamieJ (Feb 8, 2022)

I would try and trace the signal across the audio path first -


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## Matopotato (Feb 8, 2022)

Thanks @JamieJ . It traces to the out. I did not unbox it just yet, so I couldn't verify each side of C4, but since the signal passes through all the way to the output, I take that as the red path checks out.
I have been swapping the two TL072CPs with each other and at some point it felt as if that made a difference, but now I am kind of back on square one. Actually pin 1 on IC2.1 has the stronger signal and it sounds really broken.


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## JamieJ (Feb 8, 2022)

No I would go through the red signal path to see if you can detect if there is a point that reproduces the noise.


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## Matopotato (Feb 8, 2022)

Thanks
One problem is that the audio is at one level coming in and until pin3 on IC1.1 TCL072 then on pin1 it gets amplified (of course) making it hard to distinguish between any scraping vs just very loud, it is not until Level knob I can get back to some more unity level, and then for sure the scraping is there.
I would say the noise is about the same on R8 (1) going in as on  R7 (2) down side, so I doubt the C4 is dodgy.
Considering it is loud I would still say C2 (1) and IC1.1 pin 1 junction is noisy, but pin 3 seems fine. But again not easy to separate the variation in volume there...
But would that be pointing at the TL072? Or more likely a badly soldered socket leg?
I can always re-solder the legs of that socket, or re-wet them at least.
Now I switched the TL072s and there is no change so I would rule out them being faulty.
Listened on pin 5 on the LM13700 and pin2 on TL072 and it is pretty noisy there...
I guess resolder the socket is about what I can come up with. Unless of course this is some sort of built in aspect: High ratio, low threshold, will be noisy...


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## Matopotato (Feb 9, 2022)

OK, I went through and re-heated and re-soldered as needed the sockets, including the 16-pin one for good measure. Q1 was a bit wobbly in its socket, so I soldered it to another socket and stacked them. I reheated and reflowed the Release and Attack.
It still has that scraping noise. Right now it sounds perhaps slightly worse than before. More with humbuckers than SCs, and more on Marshall DSL40 than solid state practice amp.
Chatted with Origin Effects and it might be an inherent thing with compressors on full Ratio and very low threshold that you get distortion, so that might be a factor in this case as well.
But the noise I get does not sound like any distortion-y sound I get from other pedals. It is just scrapy as if something was loose (as per sound example).


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## Chuck D. Bones (Feb 9, 2022)

It's supposed to sound like crap at the red node, that's the peak detector.  If it's good at the green node and dirty at the output, that narrows the problem down to IC1's socket, C4, R8, the LEVEL control, the switch or the output jack.  And all of the associated solder joints.  INSPECT the solder side before reflowing.


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## Matopotato (Feb 10, 2022)

Thanks a lot! New hope...
I might have placed the green in the wrong spot (pin 1), it is more like pin 3, the plus going in to IC1.
At 1 and 2 pins it is noisy.
I will inspect as you suggested anyway.

Is there a way to verify that ATTACK and RELEASE does something? If they do it is very subtle.


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## Chuck D. Bones (Feb 10, 2022)

Matopotato said:


> Yes, I agree. As if something was loose, not any  "normal distortion".
> It is most prominent with high Rate and low Threshold. The others don't affect it as far as I can make out.


I assume you meant "RATIO."
RATIO sets the max gain.  Turning RATIO up increases the maximum available gain.
THRESHOLD sets the sensitivity of the peak detector.  The peak detector measures the loudness and uses that information to turn down the gain.  Turning THRESHOLD down makes the peak detector less sensitive and it is therefore not going to reduce the gain as much.

Bottom line: setting THRESHOLD low and RATIO high is not a good combination.  You are causing the pedal to overdrive itself.  Your pedal is working as it should.  

Another effect of setting THRESHOLD low is it causes the ATTACK and RELEASE knobs to have little effect.


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## zgrav (Feb 10, 2022)

Does the distortion go away if you back off on the humbucker volume?  CDB's suggestion that you may be setting it to overdrive its circuit would show up more with higher input levels.


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## Chuck D. Bones (Feb 10, 2022)

As luck would have it, I breadboarded a Thumbsucker yesterday.  This is the input (green) & output (blue) with these settings:

RATIO 2:00
THRESHOLD 8:00
ATTACK 9:00
RELEASE 9:00
VOLUME 5:00

IC1-1 is being driven to the rails.  The input is from a sig-gen.  350mVp-p is a moderate Humbucker output.


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## zgrav (Feb 10, 2022)

Thanks Chuck.  Easy to see the flattening of the signal at that input level with those settings.


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## Matopotato (Feb 10, 2022)

Thanks a lot. Yes, I meant RATIO. My bad. Too many recent builds and this my first compressor.
I tried to ask early on if low THRESHOLD and high RATIO were inherent (?) to cause distortion. Now I know. Thanks.
Humbuckers pronounce the "problem" more, but with RATIO at 03:00 and THRESHOLD at 09:00 a Single Coil is much affected as well.
I have many distortion pedals and feel that they have some commonality in how they sound. I mean, I think I can pick out distortion among other sounds.
And the sound sample I send at the beginning of the thread does not sound as I expected it. IMHO sounds more like something almost mechanical broke.

I will try with higher THRESHOLD to see it ATTACK and RELEASE will yield som effect. I think I already did, but will try again. 

@zgrav : I didn't try around much with guitar volume on either one in an organized fashion, but as far as I remember, the noise trails off a little bit with instrument volume down, but less effect than the knobs give.

I now understand that my settings is pushing it too much in this case.
Still when I yesterday had both RATIO and THRESHOLD at noon, there is still noise.
So my thought was that it is a bit waste of knob turn to have around half of each as useful. I understand compression is a bit sublte, and I am more "all in" than subtle, but as I learn my pedals, subtle is making progress. 
I had always shied away from compression before due to this, but decided to try out a diy to see what it is like. And at some more pushed settings got my Strat to sound much more thick and alive(?) So I naturally wanted more of the same. And then I soon reach disappointment when the distortion got so prominent so soon. 
So a huge thanks for setting me straight and taking your time in doing so.
If you have time over, please confirm that my sound clip indeed is due to what you have explained. I would appreciate it.
2 questions remaining from me:
1. Do you know of any other build where the RATIO/THRESHOLD "wrong way" distortion is much less pronounced?
2. Or any pedal on the maket known to have that quality? (Cali76, Keeley plus, ThorpyFX,....)
Many thanks in advance


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## Matopotato (Feb 6, 2022)

Hi,
I just "finished" building a Thumb Sucker Compressor. Sounds very cool, more impressed than I had expected.
But..
1. There is an element of distorted scratchy sound. More with humbuckers than single coils. It is not distortion as you would like from a distortion pedal. More scratchy. It is all in the box so I doubt there is some loose cable or joint (famous last...). I am not very used to the controls yet, but it seems to vary with very low setting on release but maybe not. More so with (higher) ratio above 12 and (lower) threshold below 10-12...
(2. The attack and release knobs. Checked connection and that seems to be all good at least in that vicinity of the board. But they do not change things much. Is it because they are that subtle? Or do they only come in play with other settings? (CORRECTION: Asked this here as well: https://forum.pedalpcb.com/threads/thumb-sucker.6769/ post #6 I think. sorry for double posting))


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## Matopotato (Feb 10, 2022)

Settings I moved around a bit with, but about:
RATIO 1:30
THRESHOLD 2:00
ATTACK 10:00
RELEASE 2:30
VOLUME 2:00
Bright: On

As I let a chord ring out, it is clearly suppressed at the beginning, but it gets more and more "released and increased".
There is an oscillation in there and at the end distortion. I would guess this distortion is the same nature as discussed above and as you showed @Chuck D. Bones in your graph due to the compressor pushing harder with the diminishing signal, so my settings are probably not optimal for keeping things clean.
Still curious if this is much less or much more the case with ThumbSucker.

Can Irun it at 12 or 18 volts to increase the headroom? Or is that not going to help out with my issue...

Some sound samples. I felt SC were more prone to the distortion and less reduced when dialing down guitar volume (not really in the clip) than the Humbucker.

Single Coil into Marshall DSL (You hear the slight oscillation, and at 0:10 the scraping)
EDIT: Better sample

__
		https://soundcloud.com/user-558594533%2Fthumbsucker-sc-2


Humbuckers

__
		https://soundcloud.com/user-558594533%2Fthumbsucker-hum


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## Matopotato (Feb 10, 2022)

It seems the electrolyte caps are 25V or more, The LM13700 can take 36V and the TL072 more. The film caps take 100. The diodes and 3mm LEDs and a 100pF ceramic I don’t know...
Will await confirmation or educated guesses before trying to fry anything
EDIT: And 2N3906 should manage 60V it seems, ar least 18V


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## Chuck D. Bones (Feb 10, 2022)

I think you will find this enlightening: http://www.valvewizard.co.uk/engineersthumb4.html

The Thumbsucker is a slightly earlier version of the Engineer's Thumb v4.

Try setting RELEASE below noon.

It looks to me that you can run this on 12V or 18V.  YMMV.


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## Matopotato (Feb 10, 2022)

Many thanks. Yes, I saw that page.
Couldn't figure out what the 3mm LEDs can take, but they seem to be where I am wild guessing, 18V wouldn't hit them too hard?
Would you think engineer's thumb is a less distortion prone build? IMHO, they seem to be very similar in schematics though...

Would the RELEASE below noon reduce the slightly wobbly oscillation aspect?


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## Chuck D. Bones (Feb 10, 2022)

18V power won't stress the LEDs.  You might want to increase R100 so that the ON/OFF LED isn't blinding.  I recommend increasing R10 to 1.8K-2.2K for 18V operation. 

Try the lower RELEASE setting.  I think the wobbly decay you're hearing may be caused in part by feedback from speakers to strings.  Try headphones with the speakers off and see if the wobble is still there.


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## Matopotato (Feb 11, 2022)

Many thanks!


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## Matopotato (Feb 11, 2022)

What would be the negative impact of having R10 on 1k while trying 18V?
And would say 2k cause provlems for 9V?
Thinking of having some switch or similar or just setting it to either fixed value


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## Chuck D. Bones (Feb 11, 2022)

R10 and Vref determine the max current thru Q1 and into the control pin on IC3.  We know the existing combination works with 9V power.  If we increase the voltage, Vref goes up too because Vref = 1/2 Vcc.  When Vref goes up, the max control current goes up.  At that point, we're sailing off the edge of the map and we don't know if the result will be good or bad.  I'm not convinced that raising the power supply voltage is necessary, so I don't plan on testing or analyzing the high voltage case.  After I spend some time with my breadboard, I might change my mind.  My working assumption is that Valve Wizard knows what he's doing and the design is sound.  

If you want to run it on 12V or 18V, feel free, you're not going to break anything.  Leave R10 alone for the time being.


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## Matopotato (Feb 11, 2022)

Great, thanks. I got the idea from Jacob at Origin Effects where he mentioned that more headroom could alleviate one of the two main distortions:
"Either you run out of headroom and you're causing a clipping style distortion, or you have really aggressive compression settings and the compressor starts to fight itself."
My case might be woth the latter, but you graph got me thinking of clipping.
So I am willing to try. And will share any findings.


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## zgrav (Feb 11, 2022)

it is also possible that you have different kind of compressor in your mind.  Something that squeezes the signal more to give a lot of sustain without necessarily killing the dynamic range of the incoming signal.  Some compressors let you blend in a clean channel with the compressed sound to give you the benefit of the dynamic range plus sustain.


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## Matopotato (Feb 11, 2022)

zgrav said:


> it is also possible that you have different kind of compressor in your mind.  Something that squeezes the signal more to give a lot of sustain without necessarily killing the dynamic range of the incoming signal.  Some compressors let you blend in a clean channel with the compressed sound to give you the benefit of the dynamic range plus sustain.


Yes, the talk with Origin was around their Cali76 CD vs Stacked, and if distortion is inherit in compression when you dial in extremes (IMHO, it is)


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## Matopotato (Feb 11, 2022)

Findings:
I put on headphones, and turned off the speaker. There is still that sort of oscillation. Like a tremolo on low depth and mid to slow rate. I flipped the speaker on and off but it had no impact as far as I can tell. I am quite untrained in compression though (still can't hear ATTACK knob effect, but I am getting there...)

9V I have already written about the noise issue. 18V and it was gone. Like really gone. I had RATIO maxed and THRESHOLD "minned". Then I discovered I had left some reverb on. Turned that off and, yes there is still some distortion on 18V, but when going back to say RATIO 03:00 and up with THRESHOLD to 09:00 it was very hard to hear, if any.
Flipping between 9 and 18V was very telling.
Only downside with 18V is that the volume dropped quite a bit, so I had to compensate more with LEVEL, which just adds a touch of distortion but not nearly as much as with same "output level feeling of sound" as with 9V.
The 3mm LEDs inside didn't react. And the 5mm on/off led is the same brightness regardless of DC input voltage.

So I have learned I have to get to know compression more and then use it wisely. It is not like any other kind of pedal where the extremes and all combos "work", but more delicate and interaction and dependencies has a bigger role. 
And 18V will probably be what I use until I understand the nuances better.

Plans:
I like to tweak. Even my first kit build I could not help changing it. The big upside with DIY is price of course, but in my case maybe even more the control of adding stuff I would like.
(I made my own distortion based on a Brian Wampler video on how to build your own distortion. I ended up putting 17 diodes for clipping in different constellations, using two rotary switches that eventually got so "thick" with all cables and soldering that I could not close the lid without quite a bit of force. But I got what I wanted...)
So all that said, I will most likely go ahead and add some R10 option even if @Chuck D. Bones advised me to leave it alone. I am thinking a socket and then I can swap in and out 1k or ~2k if I flip between 9 and 18V in a sort of semi-flexible way...

Is there something else I ought to change if running on 18V, especially to bring up some more volume? Or better to just turn LEVEL knob as needed?


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## Matopotato (Feb 11, 2022)

This might be interesting:





						AMZ-Compressor Pedals
					

Measuring the Characteristics of Compressor Pedals. Written by Jack Orman.




					www.muzique.com


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## zgrav (Feb 11, 2022)

Does the level drop at 18v even if you have the compression set to minimum?   I would not have expected any drop in signal level when you switched to 18v.


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## zgrav (Feb 11, 2022)

Matopotato said:


> This might be interesting:
> 
> 
> 
> ...


Biggest surprise for me is seeing that Jack Orman is still putting up new articles on his site.  Very good to know.  Thanks.


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## Matopotato (Feb 11, 2022)

zgrav said:


> Biggest surprise for me is seeing that Jack Orman is still putting up new articles on his site.  Very good to know.  Thanks.


Made me happy 😀
Planning on doing his take on mxr dist + with all the variants on clipping, and if ok, take the ones I like into another crazy build

EDIT: He posted on DIYstompboxes.com under Pictures where he linked it.


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## Matopotato (Feb 11, 2022)

zgrav said:


> Does the level drop at 18v even if you have the compression set to minimum?   I would not have expected any drop in signal level when you switched to 18v.


I have to check. How do I set compression to minimum? Is that THRESHOLD at max? ATTACK, RELEASE?


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## Matopotato (Feb 11, 2022)

So with THRESHOLD on minimum setting, there is not a whole big difference between 9 and 18V. At noon, there is nothing to think about, 18V drops in volume in comparison. I A/B with same settings and on/off.
Strat
Bright on
ATTACK min
RELEASE 10:00
LEVEL 01:30
RATIO 12:00

I am also surprised, I thought 18V meant "more"... I run OCD and MXR Clean Boost on 18V and they are "more loud"


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## Matopotato (Feb 11, 2022)

Chuck D. Bones said:


> R10 and Vref determine the max current thru Q1 and into the control pin on IC3.  We know the existing combination works with 9V power.  If we increase the voltage, Vref goes up too because Vref = 1/2 Vcc.  When Vref goes up, the max control current goes up.  At that point, we're sailing off the edge of the map and we don't know if the result will be good or bad.  I'm not convinced that raising the power supply voltage is necessary, so I don't plan on testing or analyzing the high voltage case.  After I spend some time with my breadboard, I might change my mind.  My working assumption is that Valve Wizard knows what he's doing and the design is sound.
> 
> If you want to run it on 12V or 18V, feel free, you're not going to break anything.  Leave R10 alone for the time being.


I heard the sound clip and there was similar oscillation at the end. So nothing wrong with my build, it is part of the deal.


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## princeofyams (Feb 11, 2022)

Matopotato said:


> Findings:
> I put on headphones, and turned off the speaker. There is still that sort of oscillation. Like a tremolo on low depth and mid to slow rate. I flipped the speaker on and off but it had no impact as far as I can tell. I am quite untrained in compression though (still can't hear ATTACK knob effect, but I am getting there...)
> 
> 9V I have already written about the noise issue. 18V and it was gone. Like really gone. I had RATIO maxed and THRESHOLD "minned". Then I discovered I had left some reverb on. Turned that off and, yes there is still some distortion on 18V, but when going back to say RATIO 03:00 and up with THRESHOLD to 09:00 it was very hard to hear, if any.
> ...


Did you run it at 12V? Just wondering if that makes any difference with respect to the Threshold?

Just wondering if the extra power affects that.


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## Matopotato (Feb 6, 2022)

Hi,
I just "finished" building a Thumb Sucker Compressor. Sounds very cool, more impressed than I had expected.
But..
1. There is an element of distorted scratchy sound. More with humbuckers than single coils. It is not distortion as you would like from a distortion pedal. More scratchy. It is all in the box so I doubt there is some loose cable or joint (famous last...). I am not very used to the controls yet, but it seems to vary with very low setting on release but maybe not. More so with (higher) ratio above 12 and (lower) threshold below 10-12...
(2. The attack and release knobs. Checked connection and that seems to be all good at least in that vicinity of the board. But they do not change things much. Is it because they are that subtle? Or do they only come in play with other settings? (CORRECTION: Asked this here as well: https://forum.pedalpcb.com/threads/thumb-sucker.6769/ post #6 I think. sorry for double posting))


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## Matopotato (Feb 11, 2022)

princeofyams said:


> Did you run it at 12V? Just wondering if that makes any difference with respect to the Threshold?
> 
> Just wondering if the extra power affects that.


Not yet. Will try but it takes some tweaking first...


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## Matopotato (Feb 11, 2022)

So I did the most unscientific test, Friday late night, but hey...
I ran with 18, 12 and 9 volts. There might be all kinds of objections, but my take on all this is to run at 18V, learn how to dial in the pedal and look for subtle but good. I am closing in on  the first...
Oh, almost forgot, now that I am beginning to accept this build and pedal, it deserves a nice decal print. Compressor to me is an Atlas Copco yellow smooth-cornered machine from the 70's so I plan on using that somehow...

Here are my settings:




Single coil, A Fender Strat

__
		https://soundcloud.com/user-558594533%2Fsinglecoil-18-12-9volts

Humbucker, LP Classic

__
		https://soundcloud.com/user-558594533%2Fhumbucker18-12-9volts


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## Matopotato (Feb 12, 2022)

I took out R10, put sockets in.
Tested with 18V.
1k gives less distortion when on 18V vs 9V
2k sort of bring back some distortion.
So I tried with 470R and the distrortion is basically gone.
But it sounds as "less compression pedal" being the cost.
Is that an accurate observation? (@Chuck D. Bones ?)


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## Matopotato (Feb 15, 2022)

I think I can slightly almost sense something happening with ATTACK if I tamper a lot with RELEASE. But (in my case) not enough to have the knob in the first place.
Low RELEASE seems to be lifting the sound more than natural as it rings out. So it acts like an after-boost, sort of as if the pedal forgot do do its work gradually, got reminded and rushes it. Almost an oscillating thing. Not so musical IMHO.
The scraping distortion is still there, and I can appreciate that extreme settings and low strings will produce it, but to have to swap resistors etc while on noon settings feels as if I am not getting the right effect out of the pedal compared to what ought to be possible and what I was expecting/hoping for. I am no compressor wizard, let alone any decent player, but feels as if something is missing still.
I plan to put in a 2k trimpot for the R10 and try to dial in some unicorn sweet spot of high compression effect and low scrapiness, but my hopes are not very high. It feels as if something is wrong in the build, but since the extremes cause the negative effect mostly, there might not be any more advice to get. 
I might try to randomly step through the "non-clean" side of the path, but I wont know what to look for, so right now this pedal stands out as the first among some 40+ that does not make it to any board... Sad...
I will try to build a different compressor kit that emulates Diamond Compressor. Hope that works better. Else I will just have to buy some real deal compressor, because despite my problems, there was enough effect with the Strat at least to make me want to pursuit some better version of it.


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## Matopotato (Feb 21, 2022)

I got a 2k trimpot for R10 today. With 18V, Ratio on 3 o'clock and Threshold on 9, I had to dial it down to about 340 ohms. And at that point I am not able to hear as much of compression as with 1k or recommended 2k.
So I tend to think that there is something else wrong, not just pushing the boundaries (which I do not feel that I am doing anymore).
Any ideas of how to trace the compressed part of the circuit, or how to test the LM13700 would be much appreciated.


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## Chuck D. Bones (Feb 21, 2022)

I do not recommend less than 1K for R10.  The LM13700 is spec'ed for Iabc (current into pin 1 or 16) 1mA or less.  If you go above that, performance is undefined.  My Thumbsucker does not do what yours is doing.  I'm using an LM13700 I bought on Amazon, of all places.

One interesting thing I found out on my Thumbsucker breadboard is that C5 and C6 should be 1uF film capacitors.  Aluminum electrolytic is too leaky.  Even tantalum is unacceptable at longer RELEASE settings.  The swell you hear during the note decay is normal.  The high freq content tapers off more quickly than the fundamental as the guitar signal decays.  When the compressor turns the gain up as the note decays, there will be more and more fundamental content. This is particularly noticeable at high RATIO settings.  Mine sounds best with ATTACK & RELEASE below 10:00, RATIO below 2:00, THRESHOLD above noon.


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## Matopotato (Feb 21, 2022)

Chuck D. Bones said:


> I do not recommend less than 1K for R10.  The LM13700 is spec'ed for Iabc (current into pin 1 or 16) 1mA or less.  If you go above that, performance is undefined.  My Thumbsucker does not do what yours is doing.  I'm using an LM13700 I bought on Amazon, of all places.
> 
> One interesting thing I found out on my Thumbsucker breadboard is that C5 and C6 should be 1uF film capacitors.  Aluminum electrolytic is too leaky.  Even tantalum is unacceptable at longer RELEASE settings.  The swell you hear during the note decay is normal.  The high freq content tapers off more quickly than the fundamental as the guitar signal decays.  When the compressor turns the gain up as the note decays, there will be more and more fundamental content. This is particularly noticeable at high RATIO settings.  Mine sounds best with ATTACK & RELEASE below 10:00, RATIO below 2:00, THRESHOLD above noon.


Thanks for coming back to me. Felt a bit lonely there for a bit...
I will keep it at 1k for R10. Makes sense. I assume this is for 18V.
I got the LM13700 from Das Musikding as part of the kit. I will see if there is a way to test it to see that it is OK or not, but not quite sure how.

C5 and C6 are 1uF electrolytes, and have polarity marks on the pcb. I might get a chance to swap them out later on for "film box" MKT (?), would that be something to try?

Any hints on how to "trace" the compression side for anomalies? And/Or the LM13700...

Thanks


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## Chuck D. Bones (Feb 21, 2022)

No need to quote me message in your replies.

Power supply voltage doesn't matter.  1K is the max recommended value for 9V, 12V or 18V.
Das Musikding does not have the best reputation for parts quality.
Testing the LM13700 is not easy and I would use a scope and sig gen to do it.  I'll see if I can come up with a simple test circuit and get back to you. Might take a while. Do you have a breadboard?

Does turning RELEASE down below noon make the _scrapy _noise go away?

I do not have any other troubleshooting suggestions at this time.


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## Matopotato (Feb 21, 2022)

Sorry,...

OK, I felt a clear difference as to my issue being lot less prominent on 18V compared with 9V. I also assume that 18 would raise the headroom (from what I read) and possibly result in less clipping problem in my (previously) more extreme settings.

Yes I have a breadboard (with a Dist + on it to try out Jack Orman's Saturation variations and some asymmetrical clipping, but it is easy enough to disassemble again). No hurry at all. If you find the time I am grateful.

Will try RELEASE down later on, but with my previous settings of RATIO at 3 and THRESHOLD at 9, it had no impact on the scrapy stuff IMHO. (I thought scrapy was a word in English... Might have been wrong all along.) 

Your recommended settings are fine, not much scraping there, although a little bit less "compression effect" than what I was trying to find. 
I am not very subtle with my playing and gear, more all in, for better or for worse. So I liked the first feel of the compressor but I suppose I set it  quite "hard". With more subtle settings I struggle as of now to hear and feel much difference from clean tone. I guess there is a learning curve to compression and I built the kit because I was sceptic if compression would be to my "taste".
But the first impression with this build was "Wow, my tone just got more lively and fatter" and I liked that! Then scrapy...


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## Chuck D. Bones (Feb 21, 2022)

I have no problem with headroom at 9V as long as I keep THRESHOLD above noon.  I don't think the scrapy sound is from overdriving IC1.1 because the scrapy sound doesn't happen during the attack, it happens during the release.  Make sure Q1 is tight in the socket.  I don't recommend socketing transistors in those SIP strips because the leads are too small for the socket.


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## Matopotato (Feb 21, 2022)

Yes, I  have noticed sometimes how SIP sockets are not tight enough.
What alternatives are there/do you use?

EDIT: I actually soldered it into another SIP and stacked them to keep things tighter.


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## Chuck D. Bones (Feb 21, 2022)

I solder transistors.  Sometimes I'll socket ICs.  I used to socket germanium transistors, but these days I audition them on a breadboard then solder 'em in.  Sockets are just one more thing to go wrong.


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## Matopotato (Mar 2, 2022)

I did change the 1uF electrolytes, C5 and C6 to Film Caps. I has been a while since I tested, but spontaneous feeling was that the scrapy sound got less scrapy, but more present. I mean even with previously unaffected settings, it was now audible. It could well also be in my mind only, and the knobs were not on so I could not tell for sure what positions I had dialed in. 
Since I had unboxed it, I tried to take some shots, although I am not very good at that. Still it might be helpful if someone has sharper eyes and more experience than I do.

I am still trying to figure out how to possibly test the LM13700 on a breadboard. I googled a bit, but couldn't quite understand how to set it up.


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## Chuck D. Bones (Mar 2, 2022)

I think your LM13700 is working fine.  Something I noticed when I monitored IC2-1 on a scope was a tendency toward oscillation.  That might be what we're hearing in your first sound clip.  I ended up installing a 47pF cap in parallel with D1 and that fixed it.  I have some other mods in mind, but they're not ready for prime-time just yet.

There's a lot of flux on the board.  I recommend cleaning it off because when exposed to humidity, flux becomes conductive and can upset the circuitry.


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## Matopotato (Mar 3, 2022)

Thanks, will try.
I am not adding any flux myself, must be part of the solder then. Thought that was conservatively included. Will figure out something to clean with and make it a habit.
Thanks for checking and I assume that the solders looked reasonably ok apart from solder.
47pF can be ceramic I suppose.


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## Matopotato (Mar 3, 2022)

It was not easy getting to the D1, but I kind of managed to have contact and strum a string, but with the occasional touching the wrong thing. Pop and gradual come back. I first thought that was effect of the cap, but got wiser.
In the end I could not tell much difference. I tried 47pF, 82pF (felt a tiny bit better, but not sure) and 120pF (no difference). Seems some hiss or similar goes away though, but with the pedal in the open it is sensitive to the surroundings. I used 18V, but that has been better than 9V for me from the start, so I doubt 9V would make it better.
I really hoped this was the fix, but could not get it to happen. I used slightly pushed settings to tell if the noise goes away.
Good point that it might not actually be distortion per se, but possibly something else like oscillation. I'd be eager to try any of tour other ideas and appreciate your patience in this.


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## Matopotato (Mar 8, 2022)

My friend came over with his Engineer's Thumb and it did not have the scrapy noise. With RATIO max and THRESHOLD min there was some noise as expected, but it disappeared quite soon.
We tested my Thumb Sucker with 47, 82 and 120pF in parallel with D1 and it seemed to get better occasionally but once the caps settled in it was back to bad. Not all that easy to test even being 2, but no solution unfortunarely.


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## Matopotato (Mar 22, 2022)

We should have swapped LM13700's just to rule that out during the comparison, but weren't too clever about it...

@Chuck D. Bones : "I have some other mods in mind, but they're not ready for prime-time just yet."
Did you manage to try out any other of those mods you were thinking of?


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## Matopotato (May 18, 2022)

Hi again,
It's been sitting around for a bit while other projects were completed. 
Now I managed to re-flow every solder. Flux used to make it flow nicely. Felt that everything went well.
Disappointingly the scrapy sound remains and worse than I had remembered.
I already swapped places with the TL072s and I also tested with a 2N5087 for the 2N3906. Even removed the transistor all together. No change .(Wonder what that transistor is contributing with...)
So besides swapping each resistor for a new one, each cap for a new one etc etc, there is only the LM13700 remaining that is easy enough to test.
So that'll be the last thing to do. As mentioned above, my friend has an LM13700 in his Engineer's Thumb and his sounds as it should and could be expected, so the test should be easy enough.
If that is not the cause, then I will most likely give up on the Thumb Sucker project.


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## Matopotato (May 18, 2022)

Chuck D. Bones said:


> <snip>  I have some other mods in mind, but they're not ready for prime-time just yet. <snip>


Any of those ideas that you could share? Thanks.


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