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Just wondering what experience other members have with small-signal (line level) switching through relays? I've located some small relays with gold-plated contacts, and I've been thinking how much easier it would be to use this for functions like source (input) selection, preamp output delay, etc. I do remember seeing problems with relays of this type in Phase Linear preamps back in the late '70s, but that might have been due to a bad run of relays. Is anyone else doing this in their DIY gear, or heard of problems in commercial tube equipment?
In addition to empirical results, relay specifications are a little out of my field. Below is an excerpt from the relay I'm considering. I've added an arrow at each item I think might be the most important for this application.
Note that the contacts are AgNi. Digikey publishes a guide to relay definitions in which they say contacts for low-level work should be AgPd. Is this a significant difference? All the other numbers, such as contact resistance and minimum switching voltage, seem to fall in line with the Digikey guide.
Any advice from those more knowledgeable on this subject would be appreciated.
Relay is this type (different mfg/model)
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Buy Chinese. Bury freedom.
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I have used DIP style relays for low level signals for 30 years now and they always work fine. Just your generic sealed DIP relay is all you really need. Mercury wetted is of course better but I think it's overkill for line level audio. If switching tape heads or phono cartridges, I might be inclined to use wetted contacts.Be careful with using power relays to switch low level signals such as line level audio. Higher current relays often rely on the arc to clean the contact. I once used big latching relays for analog video (1v across 75ohms) and they turned intermittent after a few months.
Edits: 08/07/17
Two things I see.
The switching contacts are gold plated silver. I believe silver nickle alone is adequate. They hold up well as witnessed by many years as the "gold" standard on relay pads.
Also think about putting a diode in parallel with the coil. It helps to save the coil.
Personally, I'm not a big fan of those compact relays. This is borne out because of many years of dealing with them in industrial applications. Low voltage, low current with minimal switching action they work fine.
I prefer the "ice cube" type and feel they are more robust. If you use the octal base type you can steal one for a 6sn7 front end in a pinch!
I thought the free-wheeling diode was to save what ever is switching the coil.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
I recently had the unfortunate opportunity to witness this exact thing in the process of repairing a piece of non-audio equipment. The spike that's generated when the voltage source of a 12V relay coil is suddenly disconnected can exceed 200V.
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Buy Chinese. Bury freedom.
If you use relays to switch sources, consider the mercury wetted contact variety. IIRC, Thorsten Lösch used the Hg wetted parts.
Eli D.
That's probably what I'll do. The dry relays are attractive because they can be mounted in any position. Most now also offer really good specifications and pricing. After reviewing my project again, I realize the relays will be mounted on a vertical PCB. It won't be a problem to use the mercury-wetted type.
More on this subject, I wonder if there's really much difference in contact resistance and reliability between a dry relay with gold-plated contacts and the usual rotary or push switch? I remember Pioneer and Sansui receivers in the '70s and '80s with push switches that failed in droves. Even Deoxit didn't help for long, and the factories eventually provided new inserts (the push shaft with contacts) at no cost as an extended warranty item. My company must have replaced thousands of them.
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Buy Chinese. Bury freedom.
I think one of the biggest advantages of using relays for switching line level inputs is that the relay board can be placed near the inputs eliminating all those long runs of wires running to a front mounted selector switch. Only one set of inputs need to go to the preamp board. That can be done with a shielded cable.
There are a few boards on Ebay that look interesting. I picked up a VTA SP9 tube preamp that was already built with the relay switching option, very impressed with it's performance. I have a Aikido octal tube kit that I'm considering using relay switching in.
BillWojo
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