Weird thing in a Klon clone: clipping diodes, sound "choking out"

[KarenColumbo]

Yeah well ... I soldered in new Ge-diodes and, whoda thunk, it works as intended. Weird stuff going on when you blow one in a pair of diodes, it seems.
Thanks @ all!

Amazing.  I wonder if everyone that has that problem has damaged the Ge diodes!

I wonder ... since there's obviously one or the other problem with the circuit itself (under specific circumstances, I mean), as you kindly pointed out, maybe a blown-out diode just triggers a chain of events. It just makes me wonder, because the Centaur (TM) is, if there is any, a very well thought-out circuit - I mean Mr. Finnegan and his advisor sure took their time to develop this bit of technology.

Well, you gave me some hints to probable "choke-traps" in this thread, I have another board for a Refractor build and I'm pretty sure I have all the needed Parts in abundance, so I will go ahead and do a "fail-safe" variant. Who knows, it might even sound a lot better.

[Rob Strand]

I wonder ... since there's obviously one or the other problem with the circuit itself (under specific circumstances, I mean), as you kindly pointed out, maybe a blown-out diode just triggers a chain of events.

It's quite possible.

It's also possible there's some other equally obscure behaviour that keeps the problem in check.  For example IC2A isn't always in the clipped state.   

It just makes me wonder, because the Centaur (TM) is, if there is any, a very well thought-out circuit - I mean Mr. Finnegan and his advisor sure took their time to develop this bit of technology.

A problem like that could get under the radar.    When you get weird behaviour in products like this you need to get your hands on a unit which has the problem.  Then you spend whatever hours trying to decipher what's going on.  In this case it's the builders who are seeing the problem.

To me the best proof of the feedback idea would be to see the problem in a unit then lift either or both of R7 and R19.  If the problem goes away then there's a lot going for the low frequency oscillation theory.

Well, you gave me some hints to probable "choke-traps" in this thread, I have another board for a Refractor build and I'm pretty sure I have all the needed Parts in abundance, so I will go ahead and do a "fail-safe" variant. Who knows, it might even sound a lot better.

The fixes I mentioned are really only good for proving the cause of the problem.   Some may work but they aren't the best way to go about it.   Adding LEDs to across R20 may work but then we have to judge whether they change to sound!

The *best* solution would be to connect R7 to it's own cap to the output of IC1A.  That stops the positive feedback because the signal coming back through R7 stops at IC1A and cannot get back around the loop.
However we can't just add the cap.   You may need to add a 1.5k resistor (or something near that) from IC1B side C3 to VB.   Even then it might not be 100% the same as before.  What I'm saying is the circuit around C3 and R7 may need to be tweaked a bit to let us connect R7 to a new point *and* not affect the behaviour of the circuit.

[PRR]

> Maybe one of the Ge diodes is bad?

Asymmetric (one good one bad) diodes after a cap will charge-up one-way and perhaps disable the following stage.

But why would this happen in the Klon more than other diode clippers? (Different next-stage?)

[willienillie]

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[Rob Strand]

Without trying to re-jig all the component values or make changes which have a small effect on the response, one solution is to use a buffer,



Of course this assumes the positive feedback problem is real - we don't really know that at the moment.

[antonis]

Weird stuff going on when you blow one in a pair of diodes, it seems.

For blown open, nothing weird other than asymmetrical clipping..
For blown shorted, nothing weird other than no sound at all..

I suspect something weird in the node of current limiting resistor and diode pair..