IC muff hiss/whine?

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IC muff hiss/whine?

Postby BakedAlaskan » 10 Jan 2015, 01:14

Excuse me if overlooked any similar threads while searching for an answer here. I recently built an IC Muff using the tagboard FX vero layout (seen below). While it sounds just as good if not better than my original IC muff, it has a strange quirk in that it starts to create a sustained whistle when no notes are being played, when the tone and sustain controls are dimed with the tone stack engaged in the circuit. When I back up off the tone and sustain controls a bit to 3 o'clock each, the whistling goes away and it sounds fine. When I bypass the tone stack, it goes away completely and acts just like it does on all settings like the original. I double checked everything and it all seems to be in its right place (it initially didn't work because of a bridge I forgot so its been well troubleshot). If it matters, the IC's I used are for IC1: RC4558P and for IC2: LM471CN. Has anyone encountered a similar problem before and know what went wrong and what to do about it? Or where I should start investigating on the circuit board? Any help would be much appreciated!

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Re: IC muff hiss/whine?

Postby phatt » 12 Jan 2015, 03:26

Not sure I follow all of the board labels but looks like "Volume 3, Sw1, SW2 and Input" are all side by side which is a sure bet for oscillation. Induced positive feedback as the input is High Z which will pickup any stray magnetic field floating nearby and if it happens to be the output then,,, well you now know why lead dress is so important. :blackeye
I'd be looking at a rethink of the layout and keep input well away from Output. :thumbsup
HTH,
Phil.
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Re: IC muff hiss/whine?

Postby mictester » 12 Jan 2015, 07:33

Exactly right, Phil. That Vero layout is very compact, but is sure to be unstable. It also demands the use of the smallest electrolytics you could find! I'll do another layout (I've always wanted to make one of these) and put it up here in the next few days.
"Why is it humming?" "Because it doesn't know the words!"
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