[sdiy] Relays or reed switches for routing?

Mike Bryant mbryant at futurehorizons.com
Mon May 31 23:57:50 CEST 2021


The DG series are excellent, and I sometimes use them for setting mic preamp gains.  But some applications such as automated patch panels need to switch low impedance line level signals into pretty capacitive loads without loss and they're not so good at that.  And if you're running a 48 or 100 volt supply to provide more headroom, then CMOS switches definitely aren't a solution.  There the choice is MOSFETs or relays, and I've used both over the years.


-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of David G Dixon via Synth-diy
Sent: 31 May 2021 22:05
To: 'Tom Wiltshire'; 'cheater cheater'
Cc: 'synth-diy'
Subject: Re: [sdiy] Relays or reed switches for routing?

For audio switching, why would anyone today use anything other than a CMOS switch?  The DG series are excellent, and there are lots of configurations to choose from (although, like everything else, a bunch of them were just made obsolete in DIP format, like the excellent DG333 quad SPDT -- luckily, I found a pile of them at a very good price).


-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Tom Wiltshire
Sent: Monday, May 31, 2021 1:48 PM
To: cheater cheater
Cc: synth-diy
Subject: Re: [sdiy] Relays or reed switches for routing?

[CAUTION: Non-UBC Email]

It's not that they cause distortion. If there is a problem with relays, it would be contact bounce. The acoustic noise they make is not the issue so much as the electrical noise. They switch fast, so any non-zero signal causes a click. Obviously some are much worse than others. Some may be good enough. Silent switching generally means "slow switching" - it's a crossfade in a few tens of msecs, not a hard jump from one to another.

In stompbox-world, a lot of people are currently hung up on "true bypass switching" which is (mostly) taken to mean a solid path of metal from input to output when the effect is out of circuit. This is the current holy grail because having extra buffers in your signal path is taken to be clearly wrong (despite highly-thought-of mixing desks having dozens between the signal coming in and going out). In an attempt to meet this demand whilst providing silent switching (and also to avoid expensive and failure-prone 3PDT footswitches), some manufacturers have moved to relays, but these are often (mostly) accompanied by some type of short-to-ground element to silence the output while the relay switches. This makes up for the instantaneous switching and contact bounce of the metal-on-metal relay switching. The previous pedal generation used FETs to provide this switching action, and they could be ramped on softly, unlike relays. But for pedalworld, switching FETs in the signal path and the buffers that go with them are now often regarded as not the right answer, so other solutions have been found that hit the current marketing buzzword.

HTH,
Tom

==================
       Electric Druid
Synth & Stompbox DIY
==================



> On 31 May 2021, at 13:57, cheater cheater via Synth-diy
<synth-diy at synth-diy.org> wrote:
> 
> Why would relays introduce distortion? Aren't they just a conductor 
> that gets mechanically moved back and forth. What's the nonlinearity?
> 
> On Mon, May 31, 2021 at 2:10 PM Gordonjcp <gordonjcp at gjcp.net> wrote:
>> 
>> On Sun, May 30, 2021 at 11:22:38AM +0200, cheater cheater wrote:
>>> Why can I not use relays to switch audio? What's wrong with relays?
>>> 
>>> BTW, I was thinking of acoustically dampening relays. EG use sound 
>>> proofing foam.
>> 
>> They're electrically noisy as well as mechanically noisy.  They're
unreliable when you use them for switching tiny currents.  They introduce a lot of distortion.
>> 
>> Literally nothing sane uses relays in the audio path.
>> 
>> --
>> Gordonjcp
>> 
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