Build Your Own Clone Message Board

Hi, I recently built the mimosa jr kit (I really enjoyed putting it together). Unfortunately, there's a rhythmic thumping sound coming from the compressor.
The amplified signal is 'ok' (that is - when the blend is all the way to the left, so compression is turned off); there is very little thumping in the pure amplified signal. However, the moment I turn the blend on a little (adding the compressed signal). I get a thumping sound. The thumps decrease in frequency as I turn the blend up.

Any ideas of how to fix this? I tried reheating each solder to make sure the components were all well-connected, and I cleaned the solder side with rubbing alcohol; this affected the thumps slightly, but didn't get rid of them.

Here are images of the circuitry:
https://www.dropbox.com/s/damgngfvo9rgv23/IMG_3320.JPG?dl=0
https://www.dropbox.com/s/432yf6rnjuelt72/IMG_3321.JPG?dl=0
And here are the voltages around the IC:
https://www.dropbox.com/s/0voo01qpok3fsqz/IMG_3320%20voltage.JPG?dl=0

Let's see some pics please. And voltage readings of the IC. https://youtu.be/XRFtlUn4eBg here's a demo on how to do that if you need it.

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*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

Also, make sure you've dialed in your trimpot according to the instructions. In my case, I got some motorboating sound when the trimpot was turned up too high.

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Scott

My band, Austin Hollow

@Keith, thanks: I've posted images here to the forum and also sent you an email (whichever you prefer). I appreciate all the help.
@Scott: Thanks for the tip: I have a voltage of 1.56 on the middle pin of the transistor to the left of the trim pot; so I don't think that's the issue. I did find it quite challenging to trim it to that value - it was extremely sensitive (in case that info helps diagnose the problem).

FWIW, I had to bias mine lower to get rid of the noise. I think I settled in at about 1.25. (I know the instructions indicate 1.5–1.7, so it's possible there is also a problem with my build too.)

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Scott

My band, Austin Hollow

I don't see any parts out of place and your voltages look good. Is there any change you have C4/2n2 mixed up with one of the other caps? Is there any point in the trimpot rotation where there isn't the thumping?

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

Hi Keith
Thanks so much for your help! As you suggested, I had swapped a 4.7µF capacitor with the 47µF capacitor. Now that I have them in the right place, the pedal plays extremely cleanly! There is absolutely no oscillating thumping anymore, and I can feel the compression as I play.

There is an audible volume bump when I switch the pedal on and again when I switch it off - I'm not sure if that is normal.

@Scott - thanks for your suggestions. I played with the trim pot a little after I fixed the build; I wasn't getting any noise through the pedal, and adjusting the trim pot didn't add any noise (I didn't turn it up to extremely high levels though - I kept it below 2 the whole time).

OMG I just checked my build, and I did the exact same thing. See, even us old timers still make rookie mistakes on occasion. Thanks for posting this thread so I could discover my own mistake!

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Scott

My band, Austin Hollow

It wasn't the cap I though, but I figured something was letting too much signal in to cause the self-oscillation.

I'm not sure what you are describing. There should be a slight pop or click when you turn the pedal on or off. This is normal with true mechanical bypass. Comrpessors are the worst about this.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

Just to close off this thread, I fixed the volume spike that would occur when engaging the footswitch: it was caused by a bad solder join on the footswitch; reflowing those fixed it. I now have a very transparent and warm compressor, which I am extremely pleased with. Thanks for all your help!