Loudspeaker Relays

[Harry3]

Some where I have read that using one contact is not advisable as the contact material can act like a diode. Using two contacts in parallel eliminates this effect?? Don't know if this is true. Perhaps some one that can measure distortion can varify.

 

[Burnedfingers]

quote:

I personally subscribe to the "dragster" protection approach!

That's nitro fuel and big tires, thousand or so horsepower, drop the hammer when the light turns green!

If the engine blows up halfway down the strip... oh well... take it into the shop and rebuild it

Thats fine when it comes to amplifiers but what about the speakers ?

Quote:

You folks can tell me if any of these various protection schemes have saved your speakers or not? Perhaps they do these days, but the last time I was in a position to have big amps, playing big speakers loud, no protection circuit could do anything other than prevent fires... seriously. Like closing the barn door after the critters are out...

Its logic like this that doesn't help further the cause.

I've personally had my speakers saved a number of times when a amplifier went to rail delivering 90 volts DC to the speaker. The speakers were saved because the protection circuit did its job.

On the job I incorporate adequate protection so that the costly speakers and drivers will have a long life.

So its my humble opinion that relay protection circuits do provide ample protection when designed correctly. This protection outweighs any so called audio differences that may or may not be caused by having a relay in the circuit.

Not an authority either but do have many years experience servicing the big systems and numerous brands and models of amplifiers. Maybe its the pro sound experience that tells me to design and or repair something correctly the first time so that I don't need to go back a second time to do it right. I carry this attitude onto my home systems also.

 

[peranders]

Some where I have read that using one contact is not advisable as the contact material can act like a diode. Using two contacts in parallel eliminates this effect?? Don't know if this is true. Perhaps some one that can measure distortion can varify.

There are relays with forked contacts of one reason, more long term reliable contact properties.

... so if you have two contacts, use them in parallel and in series if the voltage is high or the current is high.

 

[jan.didden]

There are relays with forked contacts of one reason, more long term reliable contact properties.

... so if you have two contacts, use them in parallel and in series if the voltage is high or the current is high.

Putting contacts in series is a no-no. You never know which one is going to close/open first so its in the end still a single contact that has to do the work. And you get twice the resistance when closed.

Jan Didden

 

[john_ellis]

Hi Bonsai

Maybe damping factor isn't so important, but overall resistance is.
SUppose you have a 100 mohm speaker wire resistance for an 8 ohm speaker, which uses a woofer and tweeter. A high frequency signal of a certain voltage could drive the tweeter with a given voltage. If the same signal appeared later together with a large low frequency one, the low frequency side could cause a significant voltage drop (0.4V at 4A) which then affects the power in the tweeter. So the sound could change ("get duller") depending on the output frequency content.

No surprise that audible effects might be perceived. Hence my concern about relay resistance...and why some people say bi-amping is useful.

But the problem is that some people sell oxygen-free copper wire at very high price when all that is required is a low resistance.


cheers
John

 

[nigelwright7557]

I would like to learn what experiences people here have had with relays in the output path of a power amplifier, and what recommendations anyone might have for a very good-performing PC-mountable loudspeaker relay.

When I built my listening comparison AB switch box, I spent quite a bit of time making distortion measurements on relays as candidate for use in that application, and found substantial differences among different relays. Most of those relays were large, high-current relays that were not PC-mountable. Some were automotive relays. PC mountability and size were not an issue in that application.

Cheers,
Bob

I have a microcontroller on the output of my amps thats monitors for DC and gives a 3 second anti thump delay on power up.
I just used a 24 volt automotive relay and it seems to be fine.
The relay is a 30amp jobby but switches pretty much nothing at power up and so should last forever.

 

[jacco vermeulen]

should last forever.

At least you can't do worse than a V23234.
A Bosch car relay is three times as slow as a decent one, is not sealed and has (pure) silver contacts.
Say bye-bye to the already poor contact resistance within a couple of months in an acid environment.

(you'd almost think some folks fooled around with 5 dollar spdt relays ages ago)

 

[405man]

Has anyone tried mercury relays, the kind with the tube of mercury and the tilting mechanism, these have thick flexible leads and a very low on resistance

Stuart

 

[Bonsai]

John,
clearly you understand why I use 3 relays in parallel . . . .

 

[john_ellis]

Bonsai

Only three?

cheers
John

 

[nigelwright7557]

Some where I have read that using one contact is not advisable as the contact material can act like a diode. Using two contacts in parallel eliminates this effect?? Don't know if this is true. Perhaps some one that can measure distortion can varify.

I have had no problems with the automotive relay I used.
It was a 30 amp type so is pretty hefty.

I did loads of tests with a sig gen and a scope and it works fine.

I did use an enclosed relay.

I have used the amp for many months now and it still sounds great.

In my amp the relay never switches anything anyway unless an output transistor goes which hasnt happened yet at a gig so the contacts shouldnt get burnt.

 

[bear]

Mr. Boindfangers...

No prob - I think in a pro sound environment I'd want protection too...

On ur typical speakers, ur only gonna fry the woofies, everything else is cap coupled, unless you do the electronic x-over, I suppose...

Guess everyone need to determine their tolerance for big faults vs. "sonic purity"?

I'm ok with that... my opinion is that if you must use the evil relay, then make sure you have multiple contacts in parallel. I guess you'll have to live with the possibility that someone is going to turn on the system with the levels set to full clipping and the relay is going to drop in at full bore??

Consider a multi-pole several HP (horsepower) industrial AC contactor?

Ya getz a nice KER-THUNK when it kicks in!

Quite authoritative! Manly too...

_-_-bear

 

[nigelwright7557]

Mr. Boindfangers...
I guess you'll have to live with the possibility that someone is going to turn on the system with the levels set to full clipping and the relay is going to drop in at full bore??

_-_-bear

That wont happen with my system as the dual cd player and/or MP3 player default to no sound on power up.

Someone mentioned resistance in the contacts.
Given that quite often there is 0r1 in series with the MOSFET sources then the relay makes little difference. On top of that the MOSFET itself has a full on resistance.

 

[jacco vermeulen]

Given that quite often there is 0r1 in series with the MOSFET sources then the relay makes little difference. On top of that the MOSFET itself has a full on resistance.

Only relevant for peak output current/voltage.
For amplifier functioning, that line is the equivalent to dropping your pants in public.
Plus, the relay contact resistance is not constant, it wiggles.

 

[Mooly]

The relay is not within the global feedback loop, any source resistors, emmiter resistors etc are. Personally I don't believe contact resistance is a major issue here, but had this idea, the small glass sealed relay will include any non linearity of the main relay within the global feedback. Thoughts anyone.

 

[jacco vermeulen]

Next step is to include the LSP and the cable works in the feedback loop, which has been done before in commercial products.

 

[Mooly]

Absolutely You could use 3 wires to speaker or , do something similar lifting the earthy end of the feedback network and use 4 wires. Erm, interesting that one.

 

[nigelwright7557]

The relay is not within the global feedback loop, any source resistors, emmiter resistors etc are. Personally I don't believe contact resistance is a major issue here, but had this idea, the small glass sealed relay will include any non linearity of the main relay within the global feedback. Thoughts anyone.

I think the relay simply makes a negligible difference and I certainly cant hear the difference. But the benefits of having the relay there far outweigh any slight problems. I built an amp and missed a soldered joint in a previous design, the output went to 48 volts and fried 2 speakers !!! So a relay compared to the cost of 2 speakers is a very big saving.

 

[bear]

That's why you ought to use fuses when testing, and before you are confident that your amp/speaker combo is stable over time...

Or have an outboard "protection" scheme, if that is what you prefer...

I still prefer big CONTACTORS that have a manly KER-THUNK on pull in... no tiny "tink" sounds here!



_-_-bear

 

[Burnedfingers]

I think the relay simply makes a negligible difference and I certainly cant hear the difference. But the benefits of having the relay there far outweigh any slight problems. I built an amp and missed a soldered joint in a previous design, the output went to 48 volts and fried 2 speakers !!! So a relay compared to the cost of 2 speakers is a very big saving.

I'll have to agree with you 100% Nigel