Loudspeaker Relays

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
 
Bob Cordell said:
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.

The problem with all these relays is that they are designed to switch a load. Typically relays for speaker output are switched without a load (dry). This is a more like a low-power, signal application.

So a good speaker relay is a high-power signal relay, which is not very common, to say the least ...

For me, the best (but expensive) compromise is a Matsushita (Nais, Panasonic, SDS ...) S Relay. Minimum switchable current is 100uA, max. is 4A (which makes it unsuitable for high power amps). I am using two contacts in parallel.

Thomas
 
Bob Cordell said:
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

This is from my long experience with P.A. power amplifiers such Peavey.
Peavey in all models of the old good series CS used a type of relay named AROMAT. After an extensive research i discovered that those relays was direct similar with the NAIS (Matsushita) "JTN 1aS-PA-f-xxV. Concretelly these relays are of type 1 Form A which means SPNO with a switch capability of 30A. If its contact material which is Silver alloy it is not a problem for you, then i am in position to confirm that these relays are very strong and never presented any problem in their operation. The price it is about 2,23Euros per piece.

Fotios
 
Re: Re: Loudspeaker Relays

mat02ah said:


The problem with all these relays is that they are designed to switch a load. Typically relays for speaker output are switched without a load (dry). This is a more like a low-power, signal application.

So a good speaker relay is a high-power signal relay, which is not very common, to say the least ...

For me, the best (but expensive) compromise is a Matsushita (Nais, Panasonic, SDS ...) S Relay. Minimum switchable current is 100uA, max. is 4A (which makes it unsuitable for high power amps). I am using two contacts in parallel.

Thomas

Hi Thomas

For the record only, i had a bad experience with the paralleled contacts, because the precision of activation mechanism to close the contacts. Some times, the one was closed faster from the other contact and thus all the load passed through one contact. I have seen in practice this as such: the one contact was damaged
instead the second was very clean. The synchronisation of moving the contacts in such type arrangements it is very critical. For this reason exactly i prefer the single contact relays.

Fotios
 
Re: Re: Loudspeaker Relays

fotios said:


This is from my long experience with P.A. power amplifiers such Peavey.
Peavey in all models of the old good series CS used a type of relay named AROMAT. After an extensive research i discovered that those relays was direct similar with the NAIS (Matsushita) "JTN 1aS-PA-f-xxV. Concretelly these relays are of type 1 Form A which means SPNO with a switch capability of 30A. If its contact material which is Silver alloy it is not a problem for you, then i am in position to confirm that these relays are very strong and never presented any problem in their operation. The price it is about 2,23Euros per piece.

Fotios


Thanks for the tip. I'll try to get hold of some of these and measure them for distortion.

Cheers,
Bob
 
Re: Re: Re: Loudspeaker Relays

For the record only, i had a bad experience with the paralleled contacts, because the precision of activation mechanism to close the contacts. Some times, the one was closed faster from the other contact and thus all the load passed through one contact. I have seen in practice this as such: the one contact was damaged
instead the second was very clean. The synchronisation of moving the contacts in such type arrangements it is very critical.
Parallel contacts are used everywhere in consumer audio...why do we care if one relay closes a few mS before the other one? It is not an issue...
 
Re: Re: Re: Loudspeaker Relays

fotios said:

For the record only, i had a bad experience with the paralleled contacts, because the precision of activation mechanism to close the contacts. Some times, the one was closed faster from the other contact and thus all the load passed through one contact. I have seen in practice this as such: the one contact was damaged
instead the second was very clean. The synchronisation of moving the contacts in such type arrangements it is very critical. For this reason exactly i prefer the single contact relays.

Good point, but this only applies if you switch the load. In this case paralleling contacts won't help for the reason you described. So if you want to use a relay to switch from speaker 'A' to 'B', make sure that a single contact is rated for the load.

But typically speaker relays are used for muting after turning on the amp and will be switched 'dry'. In this case paralleling helps to reduce the contact resistance.

You are right again if you want to use the relay for protection (e.g. DC protection). In this case the spec of one contact counts. But for DC protection relays are close to useless anyway, because you won't find relays for DC >40V and high-current apps. All you can do is to use a change-over contact, short circuit the speaker to ground. The relay will be defective after that.

Thomas
 
Re: Re: Re: Re: Loudspeaker Relays

EchoWars said:
Parallel contacts are used everywhere in consumer audio...why do we care if one relay closes a few mS before the other one? It is not an issue...

Under normal conditions of load of course it is not an issue because the existence only of the little iddle current throwing to the load. These conditions are: 1) During powering up the amplifier there is not signal in its input (i.e. the input it is grounded via the vol. pot. in its minimum place) so there is not a high current throwing to load. 2) During operation at high power levels, there is not any triggering of relay from the protection circuit (i.e. false detection between input and output due to large V.I. phase shifts caused from the reactive components of the load) 3) There is not any heavy shorting of output in the case of signal presented in input (and thus current flow to load). 4) There is not frequently presented failures of the output due to shorted power transistors which activates the DC protection circuit and then if the main fuses are not blown (a usual phenomenon in many amplifiers) then all the current pass through the contacts of relay during its deactivation which is the worst case for damaging the contacts (when the coil armature try to open the contacts under loading condition, the power it is by 30% bigger than of the case of closing the contacts).
Finally, why so many verbosity about relays with single or double contacts? The common thought says that if the price it is the same between a relay with single pole single touch (SPST) with a current rating of 30A why we must use a double pole single touch (DPST) with a current rating of 15A per contact?
One more remark it is that, the same relay when formed as 1A (SPST or SP N.O.) it has a current rating of 30A, and when formed as 1C (SPDT or SP C.O.) it has 20A.
To not misunderstand me (and thus to we not start a tiring debate without sense as usual happens in this forum) my thought is formed under my occupation with big power amplifiers (from +/-60Vcc up to +/-100Vcc) for 25 years and i can to confirm you that this is an issue in such devices. I have replaced enough relays with sticked contacts after a short circuit of their outputs; this related by 90% with relays of two or more contacts.

Regards

Fotios
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Use a "double mute" arrangement whereby the input to the power amp is muted as well. This second muting relay operates after the speaker is connected so that there is no possibility of the L/S relay contacts operating when there is a large signal present. Similarly on switch off this second relay removes the signal to the power amp first. I think there is more of a problem if the relay has to work for real, the inductance of the speaker will draw a large arc, many relays would fail under these conditions. I have thought about designing a protection circuit that does away with the usual time constant of traditional D.C. offset protection, along the lines of a comparator that would track the input and output's of the power amp and react if there were any difference. If it could be made 100% foolproof a triac as used in the old Quad 405 may be another posibility to include along with the relays. Maybe we could devise a "test network", lowish wattage resistors or perhaps a small filament bulb in order to test protection circuits. It's to late when a few thousand pounds worth of speaker goes up in smoke.
Regards Karl
 
Dave said:
Why do some relays specify a minimum switching voltage say 100uV for example or minimum switching current?

Typically you get a very thin isolating (single-atom) layer on the contacts. Upon closing the contacts the electrical current has to break this layer in order to make contact.

What can be done to faciltiate this?

1) put the contacts in a sealed environment with protective gas (N, He, ...) in order to avoid oxidation or for example formation of AgS.

2) make the contacts from Au, AgPd, ...

3) ensure some whiping action when contacts are closed

Relays where this is done are signal relays. They need only little voltage and/or current to break the insulating layer.

Unfortunately this does not work for higher currents where you will inevitably get arcing when contacts are opened (and closed). This arcing causes slight damages to the contacts and together with the environment (the arcing also contaminates the environment of the contacts so that sealing and protective gas won't help anymore) helps forming a insulating layer.

So first of all for higher currents you need contacts that can stand the arcing (Ag, AgCd, ...). But these contacts form insulating layers that are harder to break, which means that you need a minimum voltage/current in order to break it.

For a brand-new relay the required load is not very high. But once the contacts got used (switched under load) and/or where exposed to the environment they need to be switched under load in order to get closed properly (= low contact resistance).

A typical defect you find in old equipment: One (or both ...) channel is missing until you crank up the volume until proper contact in the speaker relay is made. Then you can reduce the volume again but output is still there. Replacing the relay fixes it.

Thomas
 
Dave said:
Why do some relays specify a minimum switching voltage say 100uV for example or minimum switching current?

Maybe this related with the resistance (or better impedance? because a contact is a contact join and not a solder join and thus maybe it has and a little capacitance) which presented when the contacts joined between them. Also in the data sheets except the min voltage or current it also reffered and the resistance of contacts.
I haven't examine this subject never, thus my thought it is formed this moment due to this question; please correct me if i am wrong.

Fotios
 
mat02ah said:


Typically you get a very thin isolating (single-atom) layer on the contacts. Upon closing the contacts the electrical current has to break this layer in order to make contact.

What can be done to faciltiate this?

1) put the contacts in a sealed environment with protective gas (N, He, ...) in order to avoid oxidation or for example formation of AgS.

2) make the contacts from Au, AgPd, ...

3) ensure some whiping action when contacts are closed

Relays were this is done are signal relays. They need only little voltage and/or current to break the insulating layer.

Unfortunately this does not work for higher currents where you will inevitably get arcing when contacts are opened (and closed). This arcing causes slight damages to the contacts and together with the environment (the arcing also contaminates the environment of the contacts so that sealing and protective gas won't help anymore) helps forming a insulating layer.

So first of all for higher currents you need contacts that can stand the arcing (Ag, AgCd, ...). But these contacts form insulating layers that are harder to break, which means that you need a minimum voltage/current in order to break it.

For a brand-new relay the required load is not very high. But once the contacts got used (switched under load) and/or where exposed to the environment they need to be switched under load in order to get closed properly (= low contact resistance).

A typical defect you find in old equipment: One (or both ...) channel is missing until you crank up the volume until proper contact in the speaker relay is made. Then you can reduce the volume again but output is still there. Replacing the relay fixes it.

Thomas

You anticipate me with one by far much better and detailed explanation from mine. Many thanks for these precious informations.

Regards
Fotios
 
For many years now I have been using a specific Amplimo relay that has two parallel contact. At closure, a 100A (!) tungsten contact closes first, followed by a gold plated shunt across the main contact. At opening, the reverse takes place.

It's not a very well known relay but has been specially designed for audio power amps. I've used dozens of them , never had any problem.

I did some THD measurements with/without the relay in the chain and couldn't detect any differences.

I anyone is interested I can get the details; last time I looked it cost about 4 euro's from Amplimo, the tube transformer people.

Jan Didden
 
Re: Re: Re: Re: Re: Loudspeaker Relays

fotios said:


Under normal conditions of load of course it is not an issue because the existence only of the little iddle current throwing to the load. These conditions are: 1) During powering up the amplifier there is not signal in its input (i.e. the input it is grounded via the vol. pot. in its minimum place) so there is not a high current throwing to load. 2) During operation at high power levels, there is not any triggering of relay from the protection circuit (i.e. false detection between input and output due to large V.I. phase shifts caused from the reactive components of the load) 3) There is not any heavy shorting of output in the case of signal presented in input (and thus current flow to load). 4) There is not frequently presented failures of the output due to shorted power transistors which activates the DC protection circuit and then if the main fuses are not blown (a usual phenomenon in many amplifiers) then all the current pass through the contacts of relay during its deactivation which is the worst case for damaging the contacts (when the coil armature try to open the contacts under loading condition, the power it is by 30% bigger than of the case of closing the contacts).
Finally, why so many verbosity about relays with single or double contacts? The common thought says that if the price it is the same between a relay with single pole single touch (SPST) with a current rating of 30A why we must use a double pole single touch (DPST) with a current rating of 15A per contact?
One more remark it is that, the same relay when formed as 1A (SPST or SP N.O.) it has a current rating of 30A, and when formed as 1C (SPDT or SP C.O.) it has 20A.
To not misunderstand me (and thus to we not start a tiring debate without sense as usual happens in this forum) my thought is formed under my occupation with big power amplifiers (from +/-60Vcc up to +/-100Vcc) for 25 years and i can to confirm you that this is an issue in such devices. I have replaced enough relays with sticked contacts after a short circuit of their outputs; this related by 90% with relays of two or more contacts.

Regards

Fotios
NOW you're describing something totally different from your original statement. You were talking about relay contacts closing a few mS apart was a serious issue. Now you're describing fault conditions which are unrelated to your first statement, as far as I can tell.

I've worked on hundreds of amps too, and I find fused (burned closed) relay contacts to be a rare thing. Worn and pitted contacts are common, but not 'stuck' ones.

Paralleling relay contacts is very common on amps with 'ice-cube' type relays (such as the Omron 'MY' and 'LY' series relays). I don't see a thing wrong with the practice, and your above reply to my first post does nothing to convince me otherwise. Your comments above go more to amp and protection scheme designs than the choice of relay.

Lastly, I do very little new design. Mostly I fix old amps (70's and 80's stuff). Rarely do I have an opportunity to even contemplate changing the style of relay...it is what it is, and that's what I have to go with. But I'd also say that there's nothing wrong with the choice of relays in most of the equipment I work on.

...sorry for the thread detour. Carry on, gentlemen. :smash:
 
Re: Re: Re: Re: Re: Re: Loudspeaker Relays

EchoWars said:
NOW you're describing something totally different from your original statement. You were talking about relay contacts closing a few mS apart was a serious issue. Now you're describing fault conditions which are unrelated to your first statement, as far as I can tell.

I've worked on hundreds of amps too, and I find fused (burned closed) relay contacts to be a rare thing. Worn and pitted contacts are common, but not 'stuck' ones.

Paralleling relay contacts is very common on amps with 'ice-cube' type relays (such as the Omron 'MY' and 'LY' series relays). I don't see a thing wrong with the practice, and your above reply to my first post does nothing to convince me otherwise. Your comments above go more to amp and protection scheme designs than the choice of relay.

Lastly, I do very little new design. Mostly I fix old amps (70's and 80's stuff). Rarely do I have an opportunity to even contemplate changing the style of relay...it is what it is, and that's what I have to go with. But I'd also say that there's nothing wrong with the choice of relays in most of the equipment I work on.

...sorry for the thread detour. Carry on, gentlemen. :smash:

Come on my friend, please avoid the misunderstanding

Moreover also me never i have found relay stucked contacts in any P.A. amplifier originated from your country. Instead in amplifiers of European origin many times. As you can see i am not sovinist (nationalist) and for 25 years i advocate that the P.A. amplifiers of USA origin are by far supperior from any other country originated amplifiers. You are pioneers in this kind of audio (included speakers) and the 90% of my theoretical knoweledge it comes from books writen in your country (BTW these are by far most comprehensible, for example, from any U.K. origin book because their spread and clear scientistic forming of speech). Tell me now how much European amplifiers have passed from your workbench? From mine have passed many of them, and mainly from this formed my place and my thought. I ask the forgiveness of my European fellowmens for this, but the true it is true.

Regards
Fotios
 
Ask yourself if you want your amplifier's output running through a single point contact or not. I don't.

Do you want your amp running through 20ga wire or smaller?
There are wires used in relays...

Paralleled contacts are better than any single contact that I know of.

Jan's special relay sounds like some sort of improvement over standard contact arrangements.

Crosspoint and wiping contacts are clearly better, but have their own issues and are not terribly commonly available - or I've never seen them used in a power amp context...

Parallel contacts if you must use them.
Use the best contact arrangement & materials you can find for the job, and then parallel them.
Use larger contacts rated higher than you need.
Investigate the low power level behavior of the set up too...

Avoid relays if you can is my advice.

_-_-bear