HELP!!! DynaComp problem!~!!~!

[Willthebold]

I put together my Dynacomp and there's a lot of gain.  I think I've determined that the first place it appears is after the IC. (Pin 6 to be exact).  Any ideas what could be causing this?  Everything seems to working ok but there's just a lot of gain.  I wonder if somehow this is the wrong IC.  I got it from SmallBear.  

Will

[R.G.]

You are not getting the signal into the transistors to back the gain off.

The IC (which is probably the right one) should show a lot of gain at pin 6 with no signal. As signal is introduced, it should back down the voltage that appears at the 10uF cap that connects to the collectors of two of the transistors and the base of the one that feeds the sustain pot.

Check the pinout on your transistors, then your soldering and wiring. If that does not help, measure the voltages on each pin of the IC and every transistor, and post it back here.

By the way, that is the generic way to debug *every* effect.

[Willthebold]

Here are my Tranny voltages:

Q1: e-4.94  b-5.2, c-8.8
Q2: e-4.28, b-4.9, c-4.55
Q3: e-0, b-0, c-8.36
Q4: e-0, b-0, c-8.8
Q5: e-7.8, b-8.36, c-8.8

[Paul Perry (Frostwave)]

3 and 4 CAN'T be right!! maybe they are pinned wrong & melted??

[Willthebold]

I'm still getting a signal coming out of the effect, so I don't know if the transistors are blown or not.  Still lots of gain though.  Any ideas?

Will

[Paul Perry (Frostwave)]

If you run a continuous tone into it, or a more or less continuous signal, it should show some voltage at the base of Q4 and Q3, because that is how it works, together they do the detecting of the envelope.
The 3080 shouldn't blow out, if it has the resistor going to pin 5, that is the 'danger!' pin....

[Willthebold]

As I turn up the sustain pot the gain increases, and up to maybe halfway the signal is still clean, though not as loud as it should be I don't think.  So I think there is signal getting to the IC to regulate the gain, but I'm still not sure why it's so distorted.  When the signal output is clean, I think it should be louder.  It's not even as loud as a straight signal from guitar.  Maybe there is a problem with how the last three transistors are affecting the signal.  I don't know.  Please help!!!

Will

[R.G.]

As I turn up the sustain pot the gain increases

Then the IC is working correctly. The sustain pot is a resistor in series with the control voltage that appears on the emitter of Q5. The IC works by having a gain that depends on the current into pin 5, and that pot plus one resistor is in series between Q5E and pin 5.

What's going on is that the voltage on the base of Q5 is not going down with signal peaks like it should. Q3 and Q4 are set up to pull down on the base of Q5 with their collectors. Their bases are held at ground except for signals coupled in through capacitors from the collector and emitter of Q2.

If you look at Q2, you find a problem. The base is about 0.6V higher than the emitter, so that's OK, but the collector is actually at a voltage between the base and emitter. This transistor is in hard saturation. It appears that the base of Q2 should be at about 2.6 to 2.8V. Its base should not be at 4.9V.  I can't tell from your voltages why that should be. I would bet on a bad connection or incorrect part value in the bias supply circuit (56K/27K) or a bad connection somewhere leading to the base of Q2.

[Willthebold]

Thanks for all of your help everybody.  I was looking over the voltage bias part of the circuit when I caught what was causing the problem: A short between two solder points that I had apparently kept overlooking.  What it was effectively doing was bypassing the 150k resistor to Q2 so it was getting too much juice I suppose.  Now the circuit seems to be working fine.  I do have one more question about this effect: How clean does it stay when fully cranked?  I still get a little distortion/fuzz when I crank both controls  all the way, but I kind of assumed that's normal.  There's a little low-end fuzziness even when the sustain isn't cranked, but only when you push the control past 6 or 7.   Thanks again for all your help.  This site has probably single-handedly kept me in the DIY world.

Will

[Willthebold]

Also, at first the effect seemed to be wanting to jump an octave down at times, but after adjusting the trimpot, it seemed to go away.

Thanks again
Will

[Willthebold]

Anybody know how clean the DynaComp stays when cranked?

Will

[brett]

Hi Will
the dynacomp is far from distortion-free.  At the very least, you'll get a little "ripple" or "fuzz" from the signal control section because no rectifier is perfect (this one is in the ok, but not fantastic, category).  I seem to recall that when the ca3080 is used in other circuits (such as a vca), distortion measurements usually indicate that very low (<200Hz) and high (>5kHz) frequencies are the most distorted (often at up to several % THD, which would be fairly noticable).
For some reason my dynacomp "overshoots" when I first pick a string (the compressor takes a fraction of a second too long to reduce the gain, so the pick noise can be annoying in sparse playing).  Would you count that as distortion?
Someone else might be able to be more definative about distortion from the Dyna.
cheers