darlington pair... base to base?

Started by skrunk, January 21, 2011, 05:21:40 PM

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skrunk

I was just mucking around with a buzzaround circuit on my breadboard and it sounded really good.
then I noticed I actually had the bases of Q1 and Q2 connected, instead of Q1E to Q2B, like a regular darlington pair.
so I switched it the right way, but it just added a layer of spitting and crackling at the top end (common enough for this circuit).

connecting the bases (as well as the collectors) of Q1 and Q2 didn't effect the tone in any other way that I could tell, apart from cleaning up all that gunk at the top.
so I'm wondering if it's ok to leave it like that and if it's a configuration that's ever used?

with the bases connected, the voltage at Q2C is -4.32v.
connected the correct way, it is -3.96v.
the voltage at Q3 changed only by 0.01v or so.
I tried swapping out the 10k at Q1C for a 9.1k (with the correct orientation of the trannys) to match the -4.5v or so that I got when the bases were connected
and the gunk was still there,
switched the bases back together, and it cleaned up again.

PRR

> wondering if it's ok to leave it like that

Yes. If it was gonna die, it wudda died instantly.

> and if it's a configuration that's ever used?

You gave no link, no as-built diagram, no observed voltages, and your description is not clear enough. On Q1 you swapped Base and... which, E or C?

In any case, I don't see any "common" connection here. In fact I can't see how signal passes at all, ass-uming ideal transistors. If you got signal, it's probably because Germanium transistors are very non-ideal. And inconsistent, meaning what worked with your pair may not work the same with another pair.

You found a happy accident. Enjoy it.

> spitting and crackling at the top end (common enough for this circuit).

It's a funky circuit.

You could (on a built-right version) insert 470 to 2K in series with the cap bypassing Q2 Emitter to make it less violent. Try 0.01uFd from Q2 Collector to ground to get less spit-sizzle.
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skrunk

thanks PRR.
here's a link to the schematic:
http://3.bp.blogspot.com/_y4AYtND8Hz8/SO00F7to5oI/AAAAAAAAAMo/zK5PHOBMnYY/s1600-h/BURNS+BUZZAROUND.GIF

apologies for not being clearer.
I had it set up as per the schematic, except the bases of Q1 and Q2 were connected (instead of Q1 E to Q2 B).
hfes were something like 60, 65, 135 each with moderate leakage.
I just found the attack of the notes comes through clearer without all the spit and sizzle they produced when the circuit is set up correctly
had a look around for darlington pair info and came across 'piggy-backing' transistors (emitters and collectors connected) but not the bases, and was just curious if connecting them E-E and B-B wasn't bad electronic practice or something.
my grasp of the theory at work is pretty thin on the ground here.