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carlmart 18th August 2005 12:24 PM

Looking for the best relay
 
Relays seem like a necessary evil on power-amp outputs if you want to prevent on/off thumps and protect the speakers from destructive DC off-set. Right? Or not right?

The right type to use, in my mind, would seem to be normally-open-contacts type. Then they would start open and only close when the time-constant is through and no DC is sensed.

Then the quality of the contact's metal and plating seems to be essential. I have never seen any article reviewing relays brands or types, which I think would be more important than resistors, capacitors, diodes or even cables.

Does that metal & plating affect sound quality? Which is best?

Most do not specify what they use, and many of them look dangerously like nickel plated metal, probably copper.

Silver, gold-plate and silver cadmium-oxide are also popular on those that do specify the contacts. Which would be best or what sould we look for?



Carlos

Leolabs 18th August 2005 02:51 PM

Most branded stuff will do the job:)

analog_sa 18th August 2005 03:19 PM

Quote:

I have never seen any article reviewing relays brands or types
There was a refence to a German magazine article comparing low signal relays once. A search within the relay attenuators thread will probably locate it.

High current relays seem even more problematic. It will be very interesting to compile some info on commercial high end amps - what percentage do use relays and what brands.

As far as i am concerned any effort to avoid a relay along the speaker output is justified.

carlmart 18th August 2005 03:21 PM

Quote:

Originally posted by Leolabs
Most branded stuff will do the job:)

Doing the job is not enough. It has to be done properly, and by that I mean with as much quality as possible.

People care for nickel-plating on an RCA connector, and don't think on the metal to metal contact of a relay.


Carlos

peranders 18th August 2005 03:22 PM

Avoid AgCdO because they are intended for hard loads and not small current.

Avoid also goldplated because the gold is thin and torn away rather fast.

Hardsilver is good, AgNi.

jcx 18th August 2005 05:02 PM

sequenced/rate controlled power supply turn on could eliminate the need for a relay in some amps

another option might be for most of the feedback to come from the speaker side of the relay - only enough to establish the dc operaing point would be connected when the relay is open - this gives high dc gain when the relay is open so the offset would need trimming or servoing

jdoorn 18th August 2005 05:23 PM

I used this one in my amplifier, two in parallel per channel to be sure.
They are from Amplimo, so I guess they are not available everywhere:
http://www.amplimo.nl/contents/media/t_LRZ.jpg

This high quality relay can be used in combination with all the Amplimo power amplifiers. (1 relay per module is needed)
The module and loudspeaker will only be protected against overheating, high-frequency oscillations and DC on the output when a loudspeaker relay is used.

This unique AMPLIMO relay has been designed for switching loudspeakers. It contains a tungsten leading contact which can switch 100A (at 50V) loudspeaker current.
After closing, this contact is bridged by a gold plated silver contact, giving negligible contact resistance even at small currents.

When switching off the loudspeaker the silver contact opens before the tungsten contact.

The silver contact is protected by the tungsten contact, it never switches high currents, so it will not burn in. The gold-plating prevents oxidizing of the silver contact, so even years later the contact resistance is very low.
Coil voltage 24VDC nominal, at 70C 20.4V to 33.5V.
coil resistance 900 ohm
Ambient temperature 20 to 70C
Convenient for power amplifiers of 5 to 200W

Bensen 18th August 2005 05:23 PM

Hi there,

Have you seen this relais:
http://www.vego.nl/amplimo/07/07.htm

It's a relais with a 100A rating NO contact, and right after is closes there closes a second smaller contact made of silver. This relais only costs 8.15 here in Belgium.

Greetz

Bensen 18th August 2005 05:24 PM

jdoorn,

You've beaten me.

jdoorn 18th August 2005 05:28 PM

Quote:

Originally posted by Bensen
jdoorn,

You've beaten me.


But I forgot to add the URL !

Regards, Jan


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