BOSOZ balanced connectio

[BBB]

I am running the A75 and BOSOZ in the balanced configuration.
Is it typical to see a 30mv DC offset shift at the output side of the A75 when you connect the two together?
With no input connection on the A75 the DC offset is stable at 7mv when I connect the BOSOZ it jumps approximately 30mv and is unstable going from 30mv to -10mv over a five minute period.
This is after both units have been running for several hours.
Thanks in advance for any help on this.

 

[jewilson]

Offset problems

I don't feel that 30mv of offset in the amp in a power amp is a big deal. However, you should
check the amp out.

The problem could be in the driver section or an output MOSFET. Since it changing with over time and temperature you most likely you have a components with temperature related leakage. However, offset can be the product of almost any stage of amplifier. This includes the Diff amp to the output stage.

If you don't have offset in non balanced mode you may have a component in the inverting-negative side of the amp that has a gain, bias, and temperature or leakage problem.

1. Get a can of freeze spray, then with the amp while running. Freeze each component one at a time. Check the out put each outset each time.

2. Check the DC bias on all amp stages and make sure that P1 and P2 are adjusted correctly. Since the amp is a balanced design, the bias currents on the plus side of the amp should be close to the negative side.


JW

 

[BBB]

I will be able to verify your suggestions this weekend,
should have the results posted Monday morning.
I agree that the 30mv is not much to be concerned about but the drifting is a concern and would be great to isolate it so that I can get my mind back on to the music.

Thanks,
BBB

 

[PassFan]

I will be able to verify your suggestions this weekend,
should have the results posted Monday morning.
I agree that the 30mv is not much to be concerned about but the drifting is a concern and would be great to isolate it so that I can get my mind back on to the music.

Thanks,
BBB

What is the offset out of the BOSOZ? When you set the offset on the A75 did you use a ground plug on the input? Just checking.

 

[BBB]

Hello,
On the BOSOZ would the offset be checked from each phase of the balanced line out to ground if yes then the offset is 0VDC.
For the A75 would that be grounding the -phase of the balanced input before I set the offset value?

Thanks,

BBB

 

[PassFan]

Hello,
On the BOSOZ would the offset be checked from each phase of the balanced line out to ground if yes then the offset is 0VDC.
For the A75 would that be grounding the -phase of the balanced input before I set the offset value?

Thanks,

BBB

I set my offset on my A75 in unbalanced mode using shorting plugs wired + to ground. I assumed once set it would be fine for balanced operation as well. I don't know about setting the offset in balanced mode


Good Luck