Dynacomp Debug

[svstee]

Built a Dynacomp from this Vero layout http://www.aronnelson.com/gallery/main.php/v/ibodog/other/dynacomp+with+clean+blend+vero+verified+v1_1.gif.html?g2_imageViewsIndex=1

I'm having problems with it. I get a little sound with the volume all the way up, but it is hardly audible. Voltages:
IC1
1 4.62
2 4.62
3 4.52
4 0.00
5 4.52
6 5.16
7 4.62
8 9.23

IC2
1 8.96
2 9.08
3 9.08
4 0.00
5 0.62
6 2.58
7 9.23
8 0.00

Q1
c 9.23
b 9.08
e 8.47

Q2
c 6.77
b 2.58
e 2.40

Q3
c 8.48
b 0.01
e 0.00

Q4
c 0.00
b 0.52
e 8.46

Q5
c 0.00
b 8.48
e 7.47

Any idea what could be wrong? I checked the backside for bad trace cuts or solder bridges, nothing.

[jdub]

Looks like Q5c is off since on the layout it's connected directly to +9v; Q4c looks odd too.  I'll check my voltages later & post if I get a chance...

[svstee]

I'll check that. Thanks!

[svstee]

User error, I measured that voltage wrong.

The collector on Q5 is 9.23.

[jkokura]

I was going to ask - are 4 and 5 in backwards? The other three have collectors at around 9 and the emitters lower voltage, but those two are backwards to that. Could it be you have them oriented wrong?

I don't have much experience, and need a lot of help debugging projects of my own, so that's the best I can get is just observing.

Jacob

[svstee]

Their orientation matches the layout. The layout is verified, so I don't think that's the problem.

[jdub]

I didn't notice before that the layout you used is for a modded dynacomp- mine's a standard (no TL072) so I'm not sure if my voltages will help...glad to post if you like, though.  BTW, on mine Q4c and Q5c are both close to +V...

[jdub]

OK, here they are- bear in mind that I used 2N3904s for the trannies, V+ is down to about 8V, no signal (used a dummy plug) and all voltages are with reference to sleeve lug of input jack...

IC (CA3080):
1: 1.8 mV
2: 3.94V
3: 3.94V
4: 0
5: .62V
6: 2.38V
7: 7.9V
8: 4.3 mV

Q1
e 1.6V
b 1.99V
c 7.9V

Q2
e 1.85V
b 2.37V
c 6.05V

Q3
e 0
b 0
c 7.74V

Q4
e 0
b 0
c 7.85V

Q5
e 7.3
b 7.8
c 7.9

Not sure if these are "correct" for the Dynacomp, but mine sounds pretty good.  Hope this helps! 

[svstee]

Wow, there are some major differences there! I honestly don't understand the circuit well enough to hazard a guess why. Can someone clue me in to what my problem could be?

[svstee]

Any thoughts? I'm drawing a blank here... 

[jdub]

I'd definitely look at pin one of the 3080- should be no connection there and you've got +V- maybe a missed trace cut (e.g. the one under R9 in the layout)? Also the voltages on pins 2 & 3, related to those on Q1e- seems like there's a prob there.  I'd also take a look at the orientation of Q4, as yer voltages are close to mine, but E & C are switched.  Apart from those, I'm not sure- mine's a standard Dyna & is done on perf, so I can't say much more... good luck, though- hope you get it workin'!

[svstee]

Haha, stupid alert! I missed the trace cut under R9! 
This has happened to me before, but I was sure I got all the ones on this build. I should know by now that my "sure" doesn't mean a thing!

One other question, the 2K trimpot (VR1). What does it do, and how do I set it?\


Thanks for the help and putting up with my ridiculous mistake!

[jdub]

No prob, man.  As for the trim, do a quick search on the forum for "dynacomp" and "trimpot" and you should turn up some threads discussing setting of the trim.  Happy 2010!