1100a2 bias question

[mnhiphop101]

yes. thats how i got it to produce any signal at all

 

[Perry Babin]

Are you using a signal source with a grounded shield?

I had 2 diagrams marked as an 1100A2. The attached one is for this amp.

 

[mnhiphop101]

Yes.
What would cause the output on both channels to be less than a volt?

 

[Perry Babin]

You need to follow the signal from the RCAs through the circuit to see where it is lost.

 

[mnhiphop101]

I dont think the voltages on the op amps are correct.

Pin 4: -17.5vdc
Pin 8: -11.79vdc

 

[Perry Babin]

Negative voltage on pin 8 is definitely wrong. What is the voltage on all terminals of the LM317 regulator?

I wouldn't expect the bias to work without positive voltage on pin 8.

 

[mnhiphop101]

pin 1 17.56 vdc

pin 2 18.81 vdc

pin 3 26.56 vdc

 

[Perry Babin]

What's the resistance from the center leg of the regulator to pin 8 of the op-amps?

It should be near 20 ohms.

 

[mnhiphop101]

7.3k ohms

 

[mnhiphop101]

whats in between pin 8 and the regulator?

 

[Perry Babin]

20 ohm resistors. R146 and R148.

The diagram is posted in #22.

 

[mnhiphop101]

ok now the voltages are
pin 4 -17.5v
pin 8 18.2v

for all the op amps except for U106. on that
pin 4 17.5v
pin 8 18.2v

 

[mnhiphop101]

still less than 1v output

 

[mnhiphop101]

The diagram is posted in #22.

i did look at it. i just dont know how to read them very well.

 

[Perry Babin]

Are you saying that U106 pin 4 is different from pin 4 on U103?

 

[mnhiphop101]

Yes

 

[Perry Babin]

What's the resistance between those two terminals?

Is any trace burned in that area? Check top and bottom.

 

[mnhiphop101]

ok so u103 and u106 have the same voltages. all of the op amps on one side have neg voltage on pin 4 and on the other side they have pos voltage on pin 4

 

[Perry Babin]

Check the resistors R147 and R149.

 

[mnhiphop101]

Ok audio is coming through but the output is very low and sounds distorted