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Very hot U5 and no sound
Posted:
Sat Sep 20, 2008 8:14 amby mikikiki
I have built 2 N72 (very fine) and 2 A12
One A12 has this problem: when I rise the gain nothing happens (no noise floor too). Only if I tap on the microfone capsule I can heard the sound . The sound is clipping immediately. So I get only clipping sound or nothing
Touchin g U5 I feel it's very hot, even after 1 minute
What can I check?
I've also noticed that if I take the op-amp off (sc10) U5 doesn't get warm
Posted:
Sat Sep 20, 2008 8:52 amby tpryan
Can you adjust the power supply voltages correctly, say to +/-18V?
What happens if you swap op-amps from your other A12?
Posted:
Sat Sep 20, 2008 10:13 amby mikikiki
I'm measuring very stange numbers...
Is this correct? Setting the DMM like this
Between pin 3 and 4 I get -30V
Between pin 4 and 5 I get +48V
on both a12
I've turned all the 3 potentiometer fully counter clockwise
Posted:
Sat Sep 20, 2008 10:55 amby tpryan
You need to measure voltages at U1, not the power connector.
Posted:
Sun Sep 21, 2008 3:54 amby mikikiki
ok sorry
On the right a12 I get correct voltages and I can also adjust the potentiometer to get 18V
On the other a12 I get +14,4V between 4 and 3
-10,5V between 4 and 5
Posted:
Sun Sep 21, 2008 8:02 amby tpryan
With or without the SC25 installed?
Posted:
Sun Sep 21, 2008 10:05 amby mikikiki
without sc10
Posted:
Mon Sep 22, 2008 3:01 pmby tpryan
Make sure C4 and C5 are installed the right way round.
Make sure you haven't swapped U4 and U5 by mistake.
Posted:
Tue Sep 23, 2008 1:02 amby mikikiki
This elements are correct, they are in the same position as the working a12...
Maybe some component broken? How can I find the broken one?
Posted:
Tue Sep 23, 2008 7:07 amby tpryan
Measure the resistance of C4 and C5 directly across the capacitor leads. Measure each capacitor twice, once with normal polarity and once with reverse polarity. What do you find?
Posted:
Tue Sep 23, 2008 11:24 amby mikikiki
I always get same values for normal and reverse polarity;
----------------------
On the right A12 I get
2k01 on C5
1k63 on C4
-------------------------
On the broken a12 i get
1k37 on C5
1k32 on C4
Posted:
Tue Sep 23, 2008 12:13 pmby mikikiki
The only different between the U4 and U5 in the two a12s I've done is that in one the screws are mounted like the tutorial (in the correct one), in the other are in the opposite position, but I don't think this can be a problem...
correct a12
wrong a12
sorry for the photos...
Posted:
Thu Sep 25, 2008 1:07 amby mikikiki
what should I do?
Posted:
Thu Sep 25, 2008 3:47 pmby tpryan
What happens if you swap op-amps between modules?
Posted:
Thu Sep 25, 2008 11:09 pmby mikikiki
One works and one no as usual.
The problem is not the op-amp