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Synth clips awfully on speakers/soundcards but NOT on headphones? Halp, Impedance or some other sorcery? Electronics-savvy advice much-needed
db1989
post Apr 22 2014, 19:18
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QUOTE (KMD @ Apr 22 2014, 19:08) *
on the face of it its highly unlightly that a solid state NPN tansitor is a "highly sensitive device"
And yet here we are, with these specific transistors having failed 3 times, whilst absolutely everything else in the circuit continues to work flawlessly.

Hence why I thought it could only be either a slight ripple/overload from the PSU that only stresses these, or some kind of stress from the jack physically being plugged in and out nearby.

What would your alternative hypothesis be?

QUOTE
Did you check the voltages against the data sheet, available from serching google
Voltages from the PSU? I don’t have a voltmeter at the moment. And I know how to Google, but er, thanks!

QUOTE
and , and also on the face of it, before it blows it would need to get hot

are you sure they are blown, because if they blew without getting hot that would be odd. They are not cmos chips after all.
I never said “blown” specifically. But they have definitely failed every time. The only thing that ever fixed the issue was to replace both (not just one channel).

Again, if you have any alternative ideas or clarifications, rather than just vague doubts, that’d be handy.

This post has been edited by db1989: Apr 22 2014, 19:19
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KMD
post Apr 22 2014, 19:22
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One thing that can cause odd clipping sounds or total input "swamping", that is hard to identify without a 'scope, is ultrasonics. Steady waves or spikes.

This post has been edited by KMD: Apr 22 2014, 19:22
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db1989
post Apr 22 2014, 19:25
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And what’s your theory for how that might, specifically and 3 times, have caused irreversible loss of the proper functionality of this single part number?
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KMD
post Apr 22 2014, 19:28
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so what are you driving there is it a Brian Eno hand me down or a contemporary DSP in a box job
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db1989
post Apr 22 2014, 19:40
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not relevant and not a tenable attempt at deflection!
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KMD
post Apr 22 2014, 20:04
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OK just saw your comment at 18.:18 .

If you did have a meter you could see if the voltages at the pins to the transistor were in spec.

This post has been edited by KMD: Apr 22 2014, 20:12
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Rotareneg
post Apr 22 2014, 21:19
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Is there a schematic for this thing available anywhere? This site says those muting transistors often fail from ESD damage, perhaps that's what's killing yours.

This post has been edited by Rotareneg: Apr 22 2014, 21:21
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db1989
post Apr 22 2014, 21:33
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Eh, somewhere. That page I’d already found and seems to be one of the few places actually discussing muting circuits and particularly the 2878! And I believe that was where I got my idea that maybe dodgy cabling might be the issue. But something that makes me heavily suspect the PSU is that – for some completely unfathomable reason… – I decided it would be experimentally useful to swap it into a working other unit of the same synth, whose 2878s promptly died. wacko.gif
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