Restoring a Op-Amp Muff, help needed.

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carboncomp1
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Joined: 17 May 2020, 23:23

Post by carboncomp1 »

Hi, Can anyone help, I got a Muff in a trade but the sound is really weak on just over unity with everything maxed and first thought was to check for bad caps, but they all seem to look fine before desoldering and testing thought I would ask here if the voltages on the op-amps look OK?

Image

741CN

0v (1. Offset Nul)
1.6v (2. Inverting Input)
4.8v (3. Non-Inverting input)
0v (4. V-)
0v (5. Offset Nul)
1.5v (6. Output)
9v (7. V+)
0v (8. NC)

4558N

4.5v (1.1 Out)
4.5v (2. 1In-)
4.5v (3. 1In+)
0v (4. VCC-)
4.5v (5. 2In+)
4.5v (6. 2In-)
4.5v (7. 2Out
9v (8. VCC+)

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Manfred
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Post by Manfred »

What big muff type is that, Big Muff from 1977 or from 1978 ora Little Big Muff?

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plush
Cap Cooler
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Post by plush »

carboncomp1 wrote: 17 May 2020, 23:29

741CN

0v (1. Offset Nul)
1.6v (2. Inverting Input)
4.8v (3. Non-Inverting input)
0v (4. V-)
0v (5. Offset Nul)
1.5v (6. Output)
9v (7. V+)
0v (8. NC)

Hi

Looking at opamp muff schematics, there should be roughly 4.5-5v on both inverting, non-inverting and output pins of 741.
Check coupling caps for shortages. Or maybe 741 itself is faulty.

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