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Do-it-yourself pedal building

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Re: Debugging (success!)

Thu Mar 14, 2019 7:58 am

I consulted the comments under the layout and changed the oscillation pot from 100K to 2K and for a bit more "spittiness" suggested in another comment, swapped Q2 from an MPSA18 to a 2N2222, which appears to have made a fairly subtle difference.

Much more usable as a consequence, so I'm going to consider it "done for now" and box it up when I have a minute.

Hurrah!

Re: Debugging (success!)

Thu Mar 14, 2019 9:07 am

That's what it does. The oscillation thing is just a ground starve. I didn't care for it.

Good job, it's almost always a cut or a row ;)

Re: Debugging (success!)

Thu Mar 14, 2019 9:19 am

Yes, the oscillation isn't essential, but it might come in handy as something I can put at the beginning of my chain and chop up and mess around with - or even as a sound generator for debugging other circuits :)

I still want to return to the first layout I tried at some point, I'm sure I will learn something by getting it working.

Re: Debugging (success!)

Sun Apr 21, 2019 12:25 am

if you have a circuit that is oscillating with no input you can do the opposite of a audio probe. you can just plug the output into an amp and start shorting caps to ground in between gain stages. the old russian big muff when in bypass is neither grounded input nor is it grounded output. it is in fact actually grounding the signal path between Q2 and Q3. since there are 4 stages (4 transistors), this is basically half way between the input and the output. for a broken pedal that will not be quiet you can start right before the output transistor and work backwards towards the input. noise can not pass through a shorted (shunted) ac coupling cap. it is %100 impossible. in this way you can at least target a specific gain stage which is in almost every case one transistor or one opamp.
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