Leach amp - need suggestions for output relays

[velicko]

A friend of mine, much better in audio electronics than myself, finally finished a leach amp for me.

Even there is no mentionable DC voltage on output, just for case I have decided that speaker protection with relays on output should be implemented, to protect my expensive speakers.

The easiest way for me to buy relays is through Farnell, but almost all I have found, with higher current (30,40Amp) has contact resistance of 0.1 OHM, which is too large I suppose and can affect output impedance.

Would someone experienced propose which relays I should use to make the least effect on sound, and that could preferably could obtain through Farnell.

[djk]

I'm sure it is much less than 0.1 ohm.

A 10A relay should be adequate.

I use a 3P relay, the third pole is part of the inrush limiter circuit.

TYCO ELECTRONICS / POTTER & BRUMFIELD|KUMP-14D18-24|POWER RELAY, 3PDT, 24VDC, 15A | Newark.com

[AndrewT]

if a 30A relay had 0r1 resistance across the contacts and the lead outs, then that relay would drop 3V before you get outside.

You will be unlucky if you can measure >300mV Vdrop across the relay @ 30A, indicating ~10milliohm sum of the maximum resistances.

Imagine dropping 3V supplying a pair of 12V car headlamp filaments!!!!!

[djk]

30A across 0R1 is 90W!

The relay would burst into flames.

[tryonziess]

Velicko,
You could just try this little item from Vellemen electronics
Velleman Speaker Protection Circuit Kit | Parts-Express.com
It is the entire output protection circuit, relay and all.

Tad

[Original Burnedfingers]

Ebay has a speaker protection circuit for $9.90 plus shipping or I have seen the same one that is put together for $11.00 I bought two of the kit ones and they sense DC disconnect immediately upon turn off and take 2.5 seconds to latch up. They have a 15A relays.

[velicko]

Originally Posted by 6BG6GA

Ebay has a speaker protection circuit for $9.90 plus shipping or I have seen the same one that is put together for $11.00 I bought two of the kit ones and they sense DC disconnect immediately upon turn off and take 2.5 seconds to latch up. They have a 15A relays.

Since I have decided to ruin the sound with relays, I hope that if I pay more, I will get relays with better contacts that will modify the sound less..

I do not have confidence in complete kit with relays for such low amount of money...

What worries me is contact pressure, contact material and contact size (area). Why am I investing in very expensive connectors, expensive cords when I have relay with loose contact of only few square mm....

[Original Burnedfingers]

Quote:
Since I have decided to ruin the sound with relays, I hope that if I pay more, I will get relays with better contacts that will modify the sound less..

I do not have confidence in complete kit with relays for such low amount of money...

What worries me is contact pressure, contact material and contact size (area). Why am I investing in very expensive connectors, expensive cords when I have relay with loose contact of only few square mm....

Well, a simple response of none would have been far better. If you believe that relays modify the sound then so be it. Buy the most expensive relays that you can afford by all means. I've already tested these cheap relays that you want no part of and found them to be ok and suited for MY application.

[tryonziess]

Velicko,
you can always use output capacitors and fuses.
Many more knowledgeable than me claim you will not hear the capacitors. That is a debate I wish not to get into. There also is the output transformer for protection. You could also add in a servo. All of these fixes have there drawbacks.
I do not use any protection other than a set of fuses on my Leach amps. I constructed my own speakers and would rather not loose them if at all possible, but, things do happen. The latching time of the relay is a pretty long. Is it something you trust to work effectively when called upon?

Good luck, Tad

[Preamp]

You could simply put several contacts in parallel to minimize resistance and add some reliability to the whole thing.