Switching Noise Between Preamps

[bassnkeys]

I use two preamps.

I have a high quality selector to choose which pre I'm listening to.

I feed a single source to the selector and then use the selector to choose which pre.

If both preamps are on there is a pop when switching.

If only one pre is on, no pop when switching.

If both preamps are off - no pop when switching.

What's up?

 

[DF96]

DC level changes. One or both preamps probably lacks a ground resistor at the input or output (on the outboard side of the coupling capacitor).

 

[AndrewT]

Those grounding resistors can be of very high resistance value.
When the interconnects are in place and the source is selected/active, the very high resistance has a virtually zero effect on proper circuit operation.
I habitually use 2M2 at the output and input of all my interconnected equipment.

 

[jan.didden]

I have a high quality selector to choose which pre I'm listening to.

I feed a single source to the selector and then use the selector to choose which pre.

Just so I understand you: you mean to feed a single source to both preamps and then select the output of the preamp you want to listen to?

jan

 

[bassnkeys]

jan.didden,
You are correct... I was not clear.
I am taking the output from a DAC that has two sets of outs.
One set of outs to each pre.
Each pre always has signal available.
Source to DAC.
DAC to each pre.
Pre 1 to A and Pre 2 to B of an A/B switch.
Output from A/B switch to power amp.

 

[bassnkeys]

Also, one pre is actually a B1 buffer built from the Pass board.

 

[AndrewT]

The B1 has a DC blocking cap on the output.
Have you fitted a ground referencing resistor after that cap?
What about the output of the other pre?

 

[bassnkeys]

I have not made any additions to the Pass design.
I am going to open the other pre this afternoon for a look.
30°f and 6" of new snow in central MN.