DIY Preamp switch.

[TOOLGUY]

Looking to build a a/b preamp output switch box for my 2101 and pre.

I have a good schematic for a buffered relay switched a/b box that I built (works great) but this box switches the input through two outputs (non used output goes to a 50k resistor-to ground thus grounding the preamp input cable so it wont hum).
What I want to do is build a reverse one with four inputs and two outputs so I can a/b 2101/ mesa pre preamp outputs into my poweramp.

The question I have is should I resistor ground the mesa pre and 2101 outputs (thus giving those outputs a load). Or can I just relay switch the pre/2101 outputs to "open" (sort of like pulling the cable out of the poweramp) when that preamp is switched "off". The inputs to both pre amps will be "hot" (y-cable) all the time.
Does it damage anything in the pre if there is an input signal/volume-gain with the a-b outputs not going into anything?

I know...buy a gcx.. I just don't want to spend $$ on anything I think I can make.
Thanks for the help.

 

[kiff]

from what I understand, preamps don't requiere a load. I don't think you'll have a problem

 

[TOOLGUY]

It can't be that easy..Got to be missing something here.

 

[kiff]

looks right except you'd need to swap the 2101/mesa on one side, since in the default "de-energized condition" you'll be getting 2101's B and the mesa's A. but that's a small detail.

you might want to just goto radioshack and pick up a dpdt toggle switch to test it out for ground loops/buzzing and to prove to yourself that it works before going all out.

another thing to note. many true bypass circuits ground the output when bypassed, not to provide a load, but to prevent the open circuit buzzing and to drain coupling caps to avoid the pops when they become active. not having it may or may not be an issue for your rig, try it out and see what happens

 

[TOOLGUY]

I have a way to do that too but I need to use two relays. one "side" will go through a resistor to ground. Guess I can give it a shot without and see how it goes. It' just solder. :wink: