Can you describe the ruckus? Anyone care to guess this?

[radardoug]

Disconnect the summing amp from the bus. Is it clean? Then its a bus problem or a module problem. Remove all modules and add them in  slowly. Does the noise increase as you do so? Its a bus problem.

 

[pucho812]

Here is an ap test measurement...

The specs on the aux is bad. This is the most offending one, aux master #1.
None -28dBu noise floor and 2%thd.

The other auxes are all around -40dBu
With around .5% thd. Specs are atrocious  compared to channel direct out and multitrack busses.

Direct out noise floor is about -70dBu and .03% thd, while multitrack busses are around -65dBu noise and .03% thd.

 

[pucho812]

And here is a comparison between aux masters 1-2, ch1 is aux master 1 ch 2 is aux master 2....

 

[radardoug]

Have you done the test I suggested to you where you isolate from the bus? I presume all the aux bus amps are in a module together. Have you verified this module is correctly grounded and supplied with power?

 

[pucho812]

Have you done the test I suggested to you where you isolate from the bus? I presume all the aux bus amps are in a module together. Have you verified this module is correctly grounded and supplied with power?

The aux masters and buss amps for the auxes are in 5  separate modules, 2 aux masters per module.
So when I measure aux master 1/2 it was in the same module and same pcb.
I have taken measurements using various channels on the desk  to get sound to the aux buss masters with the ap and they measure around the same.

 

[radardoug]

You need to disconnect the bus from the bus amp, and see if it is clean. That way you can tell if the problem is on the bus, or in the module. Then add an input resistor to ground which is bus resistor divided by number of channels. That will force the bus amp to its normal gain. If its still clean, your problem is in the buses.

 

[jdurango]

You need to disconnect the bus from the bus amp, and see if it is clean. That way you can tell if the problem is on the bus, or in the module. Then add an input resistor to ground which is bus resistor divided by number of channels. That will force the bus amp to its normal gain. If its still clean, your problem is in the buses.

Shouldn't that be multiplied by # of channels? To simulate the load with channels connected?

 

[radardoug]

No, divided, the resistors are effectively in parallel. So, 20K resistors, 20 channels, 1K test resistor.

 

[pucho812]

You need to disconnect the bus from the bus amp, and see if it is clean. That way you can tell if the problem is on the bus, or in the module. Then add an input resistor to ground which is bus resistor divided by number of channels. That will force the bus amp to its normal gain. If its still clean, your problem is in the buses.

wait I am confused here, so speakiung generically each channel should have a buffer for each aux send. From there It leaves the channel down the buss to the master where there would be another buffer and an amp before it leaves the console correct. there may also be a buffer in the master module to drive metering and such.

are you suggesting taking as measurement post buffer pre bus amp?

 

[JohnRoberts]

wait I am confused here, so speakiung generically each channel should have a buffer for each aux send. From there It leaves the channel down the buss to the master where there would be another buffer and an amp before it leaves the console correct. there may also be a buffer in the master module to drive metering and such.

are you suggesting taking as measurement post buffer pre bus amp?

"bus"

He is suggesting you isolate the bus gain stage from the physical bus....  I suggested earlier that an impedance from the bus to ground can cause elevated noise gain in the bus amp, making even a normal bus amp seem noisy.  An appropriate  resistor to ground from the VE input to ground can simulate a properly loaded bus.

JR