[sdiy] clickless muting

Tom Wiltshire tom at electricdruid.net
Mon Oct 29 15:22:38 CET 2012


Hi Neil,

>> I wouldn't say there's any problem with running audio through a panel switch, but it won't get you anywhere close to silent switches, and I'd avoid relays for the same reason. Anything with bouncy bits of metal banging together.
> 
> Look up Teledyne relays, and mercury-wetted relay technology.  Used
> extensively in RF and ATE.  As always, quality costs.

Fair enough. Budget is always an issue though, isn't it. And we're only on audio here, not RF, so I'd seriously doubt it's worth it.

> Irrespective of any mechanical issues, relays will "click" in the
> audio path simply due to the abrupt change in amplitude.

True enough, and in my view this makes an electronic "switch" that can be slowly faded from one to the other over several milliseconds much the preferred solution. Even if your switch contacts have no bounce at all and you've achieved mechanical nirvana ("toggle on, toggle off, ohmmm"?) if you switch the signal at a peak you'll get a good click - hardly ideal.

>  They were OK for PFL switching in older desks before FET switches became cheap
> enough.  The late Jim Williams recommended them for wideband precision
> switching when multiplexers and OTAs and other analogue trickery just
> won't cut it.

I can see that you'd want to stay away from OTAs, and perhaps away from multiplexers too for some applications, but there are definitely plenty of devices that are good enough for audio. There are even plenty of video crosspoint switches out there, so they at least must have some reasonable bandwidth.

Incidentally, David, you should look at some of the old stompbox stuff. It used to be the case that people aspired to have stompboxes that switched on silently, and FETs or analog switches were the way to do that (and where I learned about it). Nowadays, everyone (apparently) wants "true bypass" switching where a mechanical switch totally removes the circuit and any associated loading from the guitar. This mostly came about because of several famous but crap designs that had a fairly low input impedance and would drag a guitar down - the Crybaby being one. Ultimately it's a fashion though. Modern clones usually dump the FET switching, but I think it'll have a renaissance in due course. These things go around and come around.

Regards,
Tom




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