Engineer's Thumb - distortion problems RESOLVED

  • Hi everyone,

    I recently started making some of the kits from Musikding and until now had some pretty good success. I'm still learning but I've had some trouble with my latest project and am looking for any insight as to what might be going wrong. Yesterday I built the Engineer's Thumb and it seems to be working properly except for a strange distortion or fizzing sound when the compressor is active. At first I was wondering if maybe I had put the LEDs in backwards, but I don't think that's the issue.

    Here's a sound sample for the moment, and I'll post photos shortly.

    Compressor Problems
    Listen to Compressor Problems by East Coast Disaster Complex #np on #SoundCloud
    soundcloud.app.goo.gl

    The E major chord is with the effect off, when I play the E minor the compressor is on and you can hear the chord sustaining and that is when you can hear the distortion. The effect also 'pops' a little bit more than I'd like, but maybe that's normal. My main issue is the distortion/fizzing sound you hear as the chord rings out.

    Thanks for any advice!

    C

    2 Mal editiert, zuletzt von Christiaan27 (10. September 2022 um 20:07)

  • Hi Christian,

    welcome to the forum. To give you any useful advice, a link to the building documentation would be helpful. And detailed pictures of your build including the solder joints, switches, jacks etc. The next step would be measurements, DC voltages to ground from all pins of the ICs and transistors.

    Imagine being asked a question like that:
    "Hey Chris, a car is not working correctly...I guess, but maybe that's normal. Please tell me what's wrong."

    Could you be of any help in this scenario? I don't think so - because you needed more details, right? Same here. :S

    But don't worry, we will help you and get your thumb running!

    Cheers, Max :saint:

    "Perfektion ist nicht dann erreicht, wenn es nichts mehr hinzuzufügen gibt, sondern wenn man nichts mehr weglassen kann."
    - Antoine de Saint-Exupéry

  • Thanks! I guess to follow the metaphor, I came to say my car is making a strange sound. I tried banging on the engine with a wrench, but that didn't work.

    Here are some photos. (Please tell me I don't have to remove the pots to show all the solder joints beneath them!) I'll take some measurements next.

    Thanks for the quick response.

  • Engineers Thumb schematic

    https://www.musikding.de/docs/musikding/engineer/engineer_schalt.pdf

    IC1 LM13700

    1: 1.09v

    2: 0

    3: 4.60

    4: 4.60

    5: 4.62

    6: 0

    7: 0

    8: 0

    9: 0.07 and quickly drops to 0.03

    10: 0

    11: 9.19

    Pins 12-16: 0

    IC2 TL074

    1: 4.61

    2: 4.61

    3: 3.07

    4: 9.18

    5: 4.59

    6: 4.59

    7: 4.49

    8: 4.16

    9: 4.59

    10: 4.15

    11: 0

    12: 2.26

    13: 4.60

    14: 4.60

    Transistor BC327

    C: 1.08

    B: 4.22

    E: 4.67

    I hope that's helpful info. I'm adding photos of the jacks and switch, but I get a perfectly good clean signal so I don't think it's the jacks. I was quick to solder the pots and they all seem to work except for the strange fizzy distortion.

  • I found some time to double-check all the components and found that all four 10k resistors (R6, R7, R12, R13) and are reading as 5k despite having the colour code for 10k. I suspect that's the source of my problem.

    I hope it's just me and there isn't a big batch of mislabelled resistors being sent it with too many kits!

  • Thanks. You're right. R12 and R13 are indeed 1M.

    But I feel extra foolish since I pulled out the resistors and measured them correctly, out of the circuit. Lesson learned: parallel resistors within a circuit affect how they read on a multimeter.

    So I still can't figure out what is causing the distorted fizzing sound. The mystery continues!

  • Thanks for that link. I read through that whole thread and a few others that were linked and it seems like you might be right that it's "normal." It's strange that some people don't seem to have any distortion issue while others do, based on sound samples I've heard.

    I find it really hard to believe that a project so popular would have such an obvious problem that, in my opinion, makes the pedal unusable. I might try replacing the IC to see what happens if no one else has any better suggestions before I give up.

  • Hi there,

    Honestly, sounds strange to me as well. If one reads through the original article https://www.valvewizard.co.uk/engineersthumb2.html it's stated that the Thumb has an input headroom of 5 Vpp. No guitar can put out such a high signal, not even a metal axe with active pickups. Yes, one might be able to set the controls up so badly that distortion occurs but honestly, this is (imo) the best DIY compressor out there - by far - and I personally have to come across a better one on the market as well. The controls are thought through and the ranges limited with care so that it is really hard to mess up the settings.

    My Thumb doesn't distort even with my EMG guitar.

    Your recording doesn't sound like the input is clipping. There is distortion right after the initial attack, when the level is coming back. Moreover it sounds to me that your settings are extremely aggressive, low attack time, low threshold, high ratio.

    Does the sound change with different settings?

    Cheers,

    Max

    "Perfektion ist nicht dann erreicht, wenn es nichts mehr hinzuzufügen gibt, sondern wenn man nichts mehr weglassen kann."
    - Antoine de Saint-Exupéry

    Einmal editiert, zuletzt von Moonshine (11. September 2022 um 09:32)

  • Yes it does change to some degree with different settings, but the only way to totally remove the distortion is to essentially have compression ratio at or near zero. There's always at least a little fizz as the signal sustains and it's enough that I could never use it live or on record.

    I know my recording has some exaggerated settings but this was my attempt to make it clear when the distortion begins.

    Reading that section of the Valve Wizard article initially made me suspect it was a problem with the LEDs, but like you said, the signal is clean until after the initial attack, so I think the LEDs seem to be doing their job.

  • Thanks for the suggestion Hendrixianer. I reflowed the solder joints and added a little where I thought necessary but hear no change. There always some amount of distortion. I've ordered another LM13700 and am hoping that will solve the problem.

  • Good news: problem resolved! I replaced the chip with a new LM137000 from a different supplier and it seems to have resolved my problems.

    I still get distortion with more extreme settings but it doesn't have the same kind of 'fizzing' sound and I can easily reproduce the overdrive sounds demonstrated in the other thread (Hendrixianer, thanks for that link!) at those extreme settings. Perhaps the pots in my kit are not the ideal values but that's a problem for another day.

    Thanks to everyone for your assistance trying to isolate my problems. I now have a working compressor!

  • Christiaan27 26. September 2022 um 19:48

    Hat den Titel des Themas von „Engineer's Thumb Compressor - distortion problems“ zu „Engineer's Thumb - distortion problems RESOLVED“ geändert.
  • I know this is an old thread, but I was reading it anyway and also the diystompboxes thread linked by Hendrixianer. eh la bas ma wrote here:

    "Finally, Theshold fully CCW, Ratio fully CW, Release fully CCW . These are the settings with the worse distorted signal possible with my build."

    When I go to these settings I get a distortion, too. It's actually not a bad sounding distortion, but this is not my point :)

    I just would like to point out that if you look at the schematic provided by Valve Wizard and you want to build a 2 knob version with Ratio and Level only, then you'd use 1 M for Threshold, 470k for Release and 0R for Attack.

    When you translate that to the knob positions of the 5 knob ET you get:

    Threshold pot: fully CW

    Release pot: ~7 (on a scale of 1 to 10) (because there's 100k in front of the 500k pot the pot should be set to 370k)
    Attack pot: fully CCW

    So this is pretty much the opposite of what was suggested to get the most distortion.

    I just dial in my 5 knob ET as if it was the Valve Wizard 2 knob version and then I just set Level and Ratio how I like them.

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