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
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
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.
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
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
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:
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 70°C 20.4V to 33.5V.
coil resistance 900 ohm
Ambient temperature 20 to 70°C
Convenient for power amplifiers of 5 to 200W
They are from Amplimo, so I guess they are not available everywhere:
An externally hosted image should be here but it was not working when we last tested it.
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 70°C 20.4V to 33.5V.
coil resistance 900 ohm
Ambient temperature 20 to 70°C
Convenient for power amplifiers of 5 to 200W
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
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
Carlmart,
Amplimo is our suplier of high quality toroidal transformers.
See: http://www.amplimo.nl/
You can pick also another language on this site.
You can compare these with the Plitron transformers (have I red on the forum).
Cheers.
Amplimo is our suplier of high quality toroidal transformers.
See: http://www.amplimo.nl/
You can pick also another language on this site.
You can compare these with the Plitron transformers (have I red on the forum).
Cheers.
To protect the speakers from DC, you could also use big MOS-FET's to short the rails to ground and force rail fuses to blow.carlmart said:
To avoid power up thumps, you could use a relay which shortens the output to ground (so it's not in the signal path), together with bases/gates of output transistors. Watch out not to destroy the driver transistors though when doing it this way.
carlmart said:
Some good information from Dimitri (although for line level relays):
http://www.diyhifi.org/forums/viewtopic.php?p=5779#5779
Ciao, Tino
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