Author Topic: Help diagnose: Sunking ver 2, IC voltages included  (Read 1335 times)

knd

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Help diagnose: Sunking ver 2, IC voltages included
« on: December 09, 2010, 11:27:20 PM »
Hi All:

Wired up using ver 2.  Used a .47uf instead of a .390uf.  All caps are +25v rated.

Here's my issue:
Everything works, but it sounds really thin and there is a huge volume drop.

With that said, I have included some images and here are the voltages of the IC.
IC1 pin 3(+ input) is off, and IC3 pin 7(to + supply) is off.

Doesn't hum.  The pictures showf the .47uf cap almost touching the ic pins, but it doesn't when in place.

IC1
1 - 4.45v
2 - 4.46v
3 - 1.2v ****
4 - 0v
5 - 4.4v
6 - 4.4v
7 - 4.6v
8 - 9v

IC2
1 - 4.6v
2 - 4.6v
3 - 4.6v
4 - -8.7v
5 - 4.5v
6 - 4.6v
7 - 4.6v
8 - 16.9v

IC3
1 - 9.3v
2 - 4.5v
3 - 0
4 - -4.7v
5 - -9.1v
6 - 4.5v
7 - 0v  *****
8 - 9v









Please advise.

Thanks!

« Last Edit: December 09, 2010, 11:49:20 PM by knd »

madbean

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Re: Help diagnose: Sunking ver 2, IC voltages included
« Reply #1 on: December 10, 2010, 07:23:47 AM »
The two voltages you highlighted are off a bit. Pin3 of IC1 should be closer to 3-4v. I don't remember what pin7 of IC3 should be off the top of my head but I don't think it's 0. I think you have a solder bridge to the ground plane there.

How about when it' bypassed (in buffer mode). Do you get a volume drop that way, too?
I own madbeanpedals (duh). I am part owner of Function F(X).

knd

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Re: Help diagnose: Sunking ver 2, IC voltages included
« Reply #2 on: December 10, 2010, 11:33:27 AM »
The two voltages you highlighted are off a bit. Pin3 of IC1 should be closer to 3-4v. I don't remember what pin7 of IC3 should be off the top of my head but I don't think it's 0. I think you have a solder bridge to the ground plane there.

How about when it' bypassed (in buffer mode). Do you get a volume drop that way, too?


Here are the proper voltages:



No volume drop at all when it is bypassed.  Would it be grounding with pin 3 of IC 3?

I will check that tonight.

Thanks

knd

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Re: Help diagnose: Sunking ver 2, IC voltages included
« Reply #3 on: December 13, 2010, 04:21:17 PM »
Any suggestion guys?

IC1 pin 3 is still at 1.3v(supposed to be around 3.4v).  IC3 is good now.

Still have huge volume drop.  Sounds thin.  Bypassed, sounds normal.

Thanks!

madbean

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Re: Help diagnose: Sunking ver 2, IC voltages included
« Reply #4 on: December 13, 2010, 06:27:32 PM »
Have you tried probing at pin3? I think probing several test points is the key to finding the volume drop here. Particularly I'm interested in what's coming off pin7 of IC1 (where the clipping occurs) and just before and after the tone control. 

There is not much going on there at pin3. You have an input cap and a resistor that sets bias at the input of that op-amp. Could be 1M is too high for your build. Or, there could be something funky with the input cap.

Anyway, a somewhat lower voltage there isn't necessarily the cause of the volume drop.
I own madbeanpedals (duh). I am part owner of Function F(X).

knd

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Re: Help diagnose: Sunking ver 2, IC voltages included
« Reply #5 on: December 13, 2010, 06:38:38 PM »
IC1 pin 7 - 4.6v.

Which points should I probe around the tone control?

Thanks!