Seventh Circle Audio

by **mikikiki** » Sat Sep 20, 2008 8:14 am

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

by **tpryan** » Sat Sep 20, 2008 8:52 am

Can you adjust the power supply voltages correctly, say to +/-18V?

What happens if you swap op-amps from your other A12?

by **mikikiki** » Sat Sep 20, 2008 10:13 am

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

by **tpryan** » Sat Sep 20, 2008 10:55 am

You need to measure voltages at U1, not the power connector.

by **mikikiki** » Sun Sep 21, 2008 3:54 am

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

by **tpryan** » Sun Sep 21, 2008 8:02 am

With or without the SC25 installed?

by **mikikiki** » Sun Sep 21, 2008 10:05 am

without sc10

by **tpryan** » Mon Sep 22, 2008 3:01 pm

Make sure C4 and C5 are installed the right way round.

Make sure you haven't swapped U4 and U5 by mistake.

by **mikikiki** » Tue Sep 23, 2008 1:02 am

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?

by **tpryan** » Tue Sep 23, 2008 7:07 am

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?

by **mikikiki** » Tue Sep 23, 2008 11:24 am

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

by **mikikiki** » Tue Sep 23, 2008 12:13 pm

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...

by **mikikiki** » Thu Sep 25, 2008 1:07 am

what should I do?

by **tpryan** » Thu Sep 25, 2008 3:47 pm

What happens if you swap op-amps between modules?

by **mikikiki** » Thu Sep 25, 2008 11:09 pm

One works and one no as usual.

The problem is not the op-amp

Seventh Circle Audio

Very hot U5 and no sound

Very hot U5 and no sound

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