relays and switching noise

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Freddy G

Well-known member
Joined
Jun 4, 2004
Messages
463
Location
Canada
Hi,
I built a DIY mic pre and I used Omron low signal relays for phantom, pad and polarity.
I tried installing some 1uf caps across them and it did help a lot to tame down switching noise.
I'm wondering....would installing diodes help as well? Or are there already diodes built into the relays?
Thanks,
Freddy G
 
The diodes are a must - the caps are optional.

Best regards,

Mikkel C. Simonsen
 
You may also want to make sure that you are not having the current from the relay running through your board. Ideally you want it returned directly to the power supply hookup.
 
Is it really that critical to have a separate supply for the relays?? I'm only wondering becuase for say, a phantom power and polarity relay, they are only used occasionally and never while tape would be rolling. In other wordss what about an idle relay makes it bad to have it on the same supply as audio??

Ian
 
[quote author="Ian MacGregor"]Is it really that critical to have a separate supply for the relays??[/quote]
No, I have never used seperate supplies for relays - and I have never had any problems.

Best regards,

Mikkel C. Simonsen
 
The best trick with relays is to drive them from your +ve and -ve rails as opposed to say +ve and gnd. This way any relay noise is common to both rails, and the op-amps will have a chance of rejecting it via PSRR.

Another trick is switch your relays from your pre-regulated DC voltage, that way the regulatorwill attempt to suck out the relay noise.

Cheers,

Kris
 
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