Relay Bypass - "full" or "half"?

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haima
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Location: Melbourne, Australia

Relay Bypass - "full" or "half"?

Post by haima »

hey guys - just looking for a bit of advice:

when doing a relay bypass for a modern (10k or more input impedance) line level device - do you think there's much point doing a "full" two relay bypass (ALA roger's old bypass boards)? or should i just save myself the extra relay and just swich the reference point for the output XLRs between the input XLRs and the output of the device PCB? - ALA the pico comp.

i can see how a full bypass might be good on a lower impedance device to remove the possible effect of loading - but that shouldn't be a problem with the more common high impedance inputs - or am i missing something here?

i'm finishing off a GSSL right now, and it will be used for that initially - but i thought i'd keep the question more general, in case others are wondering similar things...

thanks mateys
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mediatechnology
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Re: Relay Bypass - "full" or "half"?

Post by mediatechnology »

haima - On Roger's original stereo prototype he did full bypass and later changed it to half bypass. It saved a lot of board space and cost.

I've seen stuff occasionally load outputs when turned off but very rarely. The one I immediately recall was a -10 consumer item. I think that with modern bridging circuits its probably better and simpler to do half bypass. With the 1246 we use in the Pico the internal input resistors are 12K in each leg before they hit the 1246's op amp. With the pico off I don't think it would load much. The GSSL has similar differential inputs.
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haima
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Location: Melbourne, Australia

Re: Relay Bypass - "full" or "half"?

Post by haima »

thanks for the confirmation - i'll give it a go half bypass!

i didn't really consider that i might want the bypass to work when the unit is powered OFF - although i love that feature, and when i work live it has saved my ass more than once! it IS nice to be able to have something in the chain and just turn it off and the whole signal path keeps going.

in the studio i imagine i would just keep the unit on but in bypass if the loading got too high with it powered off...

thanks for joging my brain!
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