Speaker Protection Question.

[Phil Allison]

Trevor Wilson wrote:

-------------------------

**Following on from PA's comments, you should consider fitting
PolyswitchesT to the HF and mids (if fitted), as these will work quite
well to protect these drivers from excessive PDiss.

** It is bad practice to install Polyswitches ( or fuses) in series with drivers where a passive crossover is involved.

Typical 12dB and 18dB crossover filters must be loaded with the intended impedance or they become *series tuned circuits* with a deep notch in the impedance - down to near zero ohms. The notch frequency is fairly close to the filter's 3dB down frequency.

Also and maybe worse, the output voltage from the filter goes sky high at the notch frequency, many times higher than the input level and exceed the 60V or so rating of the Polyswitch.

The correct procedure is to install the device PRIOR to the crossover filter - so it isolates the filter or filters and the driver.

As Polyswitchs trip when an amplifier is being played loudly, the last thing you need is short on the amp at the same time.


..... Phil

 

[Chris Jones]

On 29/06/2017 12:11, ~misfit~ wrote:

Once upon a time on usenet Chris Jones wrote:
On 19/06/2017 16:51, ~misfit~ wrote:
Once upon a time on usenet Phil Allison wrote:
~misfit~ wrote:

------------------


The issue I have is that it has no speaker protection and my
speakers are irreplaceable (rarity and my budget considered). I
have two speaker protection PCBs sourced from AliExpress that
look up to the task, well designed with heavy duty relays and
thick signal traces made thicker by having the solder mask
removed and solder added. My problem is that I can't fit them
and their power supply into the amplifier case.

So I'm planning on putting them in a box between the amp and
speakers with speakers in and out connectors on the back. Just
checking to see if anybody thinks this isn't worth doing for any
reason? From what little I know they should work fine like this,
it's just a little fiddly.


** Having the speaker relay and drive circuit outboard and with
its own PSU is a good idea - then it can be used with any amp you
like.

Cool - and thanks for the reply.

But a word of warning, the Playmaster amp has DC rails of about
60V right?

This is the "III" model which uses TO-3P trasistors and has 75V
rails.


** Worse than I thought then.


Even relays rated for 10amps at 240VAC cannot switch off that much
DC - an arc forms across the contacts and will burn the relay and
you speakers to destruction.

These are apparently 30A but that can be taken with a pinch of
salt;

** But rated at only 30VDC.

These relays come in single pole and changeover versions.

Single pole types have 4 pins on the bottom, changeover ones have 5.

It has 4.

https://www.aliexpress.com/item/upc1237-large-current-speaker-protection-board/32809522760.html


There are a couple of ways to fix this but the best is to use the
normally closed contacts of the relay the SHORT the speaker line
rather than opening the connection.

Ahh this is the 'crowbar' method of speaker protection?


** Not a crowbar, the speaker is shorted but NOT the amplifier.

Ok got ya.

In this scheme the speaker connects to the moving contact and the
normally closed one is grounded. The amp output connects to the
normally open contact.

If an arc ever does develop when the relay opens, the speaker is
protected by being shorted.

... which usually blows the output devices of the amp correct?


** Not normally cos is NOT a crowbar.


Understood.

However I have these protection devices already and surely they're
better than running the amp with no speaker protection at all (as
it has been for the last 30 odd years)?

** If those relays are single pole it's good as worthless.

If changeover types, you need to wire them the way I described or it
is still worthless.

People have been selling WORTHLESS relay protection systems for
decades.

Ok I won't bother then, just run the amp straight into the speakers.

BTW:

the relay PCBs must NOT power up before the amp does or it is
worthless.

That's why installing them in the case is actually better.

Thanks but as they're worthless I won't bother going to the trouble
of mounting them in a box, hooking up a power supply and connectors.

Cheers,


IIRC Phil posted something about finding that a capacitor across the
relay contacts generally stopped them from arcing. Phil, can you
remind us of the result of your experiment? Perhaps it would not be
ideal (e.g. if the amp went into high frequency oscillation), but may
be better than nothing at all.

That could be good if it works. A lot easier than running outboard relays on
these modules.

FYI a link to Phil's post:
https://groups.google.com/d/msg/sci.electronics.repair/nwWqmrjKEsU/A1SGGVcCbj8J

Full Text:
** I have just been experimenting with a PCB mount, 240VAC/12amp relay
made by "Schrack" and a variable PSU - consisting of a 300VA tranny,
bridge rectifier and 10,000uf cap. The tranny was fed from a Variac.

The relay, when energised, connected a 4ohm high power load to the PSU
and tried to disconnect it when de-energised. With no cap across the
contacts, serious flash arcing occurred at 30VDC. With 50VDC, you can
normally expect the arc to become continuous, first shot. The maker's
rating for DC switching is 24V at 10 amps max.

However, with a 20uF film cap across the contacts, all signs of arcing
at switch off disappeared. Amazingly, this was still the case when tried
with 6, 3 & 1uF instead. When I tried 0.22uF, flash arcs appeared on
about 1 out of 3 tries.

To simulate a *bad* inductive speaker load, I added a 5mH air core choke
in series with the 4 ohm load and saw slight flash arcing with a 1uF cap
but none with 3uF.

With a 8 ohm load and 100VDC, 6uF was enough to reduce arcing to minor
flashes.

So, a film cap across the relay contacts made a huge difference when
breaking DC current at voltages well above the relay's ratings.

FYI: the film cap delays the voltage rise across the relay's contacts
for the first 10 to 50 *microseconds* after opening - which is when the
arc forms. Delay that rise enough and there is no arc.

 

[Phil Allison]

Chris Jones wrote:

FYI a link to Phil's post:
https://groups.google.com/d/msg/sci.electronics.repair/nwWqmrjKEsU/A1SGGVcCbj8J

Full Text:
** I have just been experimenting with a PCB mount, 240VAC/12amp relay
made by "Schrack" and a variable PSU - consisting of a 300VA tranny,
bridge rectifier and 10,000uf cap. The tranny was fed from a Variac.

The relay, when energised, connected a 4ohm high power load to the PSU
and tried to disconnect it when de-energised. With no cap across the
contacts, serious flash arcing occurred at 30VDC. With 50VDC, you can
normally expect the arc to become continuous, first shot. The maker's
rating for DC switching is 24V at 10 amps max.

However, with a 20uF film cap across the contacts, all signs of arcing
at switch off disappeared. Amazingly, this was still the case when tried
with 6, 3 & 1uF instead. When I tried 0.22uF, flash arcs appeared on
about 1 out of 3 tries.

To simulate a *bad* inductive speaker load, I added a 5mH air core choke
in series with the 4 ohm load and saw slight flash arcing with a 1uF cap
but none with 3uF.

With a 8 ohm load and 100VDC, 6uF was enough to reduce arcing to minor
flashes.

So, a film cap across the relay contacts made a huge difference when
breaking DC current at voltages well above the relay's ratings.

FYI: the film cap delays the voltage rise across the relay's contacts
for the first 10 to 50 *microseconds* after opening - which is when the
arc forms. Delay that rise enough and there is no arc.

** Yep, that was posted my me some time back.

A 10uF, 200V or better film cap would do the job very nicely.

But there is a problem:

Speaker relays are mainly used to STOP switch on noises - like loud cracks, squeals and thuds.

Having a 10uF cap across the contacts lets a lot of it through - certainly to the mids and tweeters in a system.



...... Phil

 

[~misfit~]

Once upon a time on usenet Chris Jones wrote:

On 29/06/2017 12:11, ~misfit~ wrote:
Once upon a time on usenet Chris Jones wrote:
On 19/06/2017 16:51, ~misfit~ wrote:
Once upon a time on usenet Phil Allison wrote:
~misfit~ wrote:

------------------


The issue I have is that it has no speaker protection and my
speakers are irreplaceable (rarity and my budget considered). I
have two speaker protection PCBs sourced from AliExpress that
look up to the task, well designed with heavy duty relays and
thick signal traces made thicker by having the solder mask
removed and solder added. My problem is that I can't fit them
and their power supply into the amplifier case.

So I'm planning on putting them in a box between the amp and
speakers with speakers in and out connectors on the back. Just
checking to see if anybody thinks this isn't worth doing for
any reason? From what little I know they should work fine like
this, it's just a little fiddly.


** Having the speaker relay and drive circuit outboard and
with its own PSU is a good idea - then it can be used with any
amp you like.

Cool - and thanks for the reply.

But a word of warning, the Playmaster amp has DC rails of about
60V right?

This is the "III" model which uses TO-3P trasistors and has 75V
rails.


** Worse than I thought then.


Even relays rated for 10amps at 240VAC cannot switch off that
much DC - an arc forms across the contacts and will burn the
relay and you speakers to destruction.

These are apparently 30A but that can be taken with a pinch of
salt;

** But rated at only 30VDC.

These relays come in single pole and changeover versions.

Single pole types have 4 pins on the bottom, changeover ones have
5.

It has 4.

https://www.aliexpress.com/item/upc1237-large-current-speaker-protection-board/32809522760.html


There are a couple of ways to fix this but the best is to use
the normally closed contacts of the relay the SHORT the speaker
line rather than opening the connection.

Ahh this is the 'crowbar' method of speaker protection?


** Not a crowbar, the speaker is shorted but NOT the amplifier.

Ok got ya.

In this scheme the speaker connects to the moving contact and
the normally closed one is grounded. The amp output connects to
the normally open contact.

If an arc ever does develop when the relay opens, the speaker is
protected by being shorted.

... which usually blows the output devices of the amp correct?


** Not normally cos is NOT a crowbar.


Understood.

However I have these protection devices already and surely
they're better than running the amp with no speaker protection
at all (as it has been for the last 30 odd years)?

** If those relays are single pole it's good as worthless.

If changeover types, you need to wire them the way I described or
it is still worthless.

People have been selling WORTHLESS relay protection systems for
decades.

Ok I won't bother then, just run the amp straight into the
speakers.
BTW:

the relay PCBs must NOT power up before the amp does or it is
worthless.

That's why installing them in the case is actually better.

Thanks but as they're worthless I won't bother going to the trouble
of mounting them in a box, hooking up a power supply and
connectors. Cheers,


IIRC Phil posted something about finding that a capacitor across the
relay contacts generally stopped them from arcing. Phil, can you
remind us of the result of your experiment? Perhaps it would not be
ideal (e.g. if the amp went into high frequency oscillation), but
may be better than nothing at all.

That could be good if it works. A lot easier than running outboard
relays on these modules.

FYI a link to Phil's post:
https://groups.google.com/d/msg/sci.electronics.repair/nwWqmrjKEsU/A1SGGVcCbj8J

Full Text:
** I have just been experimenting with a PCB mount, 240VAC/12amp relay
made by "Schrack" and a variable PSU - consisting of a 300VA tranny,
bridge rectifier and 10,000uf cap. The tranny was fed from a Variac.

The relay, when energised, connected a 4ohm high power load to the PSU
and tried to disconnect it when de-energised. With no cap across the
contacts, serious flash arcing occurred at 30VDC. With 50VDC, you can
normally expect the arc to become continuous, first shot. The maker's
rating for DC switching is 24V at 10 amps max.

However, with a 20uF film cap across the contacts, all signs of arcing
at switch off disappeared. Amazingly, this was still the case when
tried with 6, 3 & 1uF instead. When I tried 0.22uF, flash arcs
appeared on about 1 out of 3 tries.

To simulate a *bad* inductive speaker load, I added a 5mH air core
choke in series with the 4 ohm load and saw slight flash arcing with
a 1uF cap but none with 3uF.

With a 8 ohm load and 100VDC, 6uF was enough to reduce arcing to minor
flashes.

So, a film cap across the relay contacts made a huge difference when
breaking DC current at voltages well above the relay's ratings.

FYI: the film cap delays the voltage rise across the relay's contacts
for the first 10 to 50 *microseconds* after opening - which is when
the arc forms. Delay that rise enough and there is no arc.

Thanks. I may subscribe to sci.electronics.repair.

Cheers,
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[Phil Allison]

~misfit~ fuckwit wrote:

--------------------------

Thanks. I may subscribe to sci.electronics.repair.

** That post was from *me* you dopey retard !!!

And I *deliberately* did NOT refer to the idea of using a film cap.

Cos it is NOT a good one for the actual purpose.

See my reply for the reason.

FYI:


Appear on SER and I will murder you.




...... Phil

 

[~misfit~]

Once upon a time on usenet Phil Allison wrote:

~misfit~ fuckwit wrote:

--------------------------



Thanks. I may subscribe to sci.electronics.repair.




** That post was from *me* you dopey retard !!!

I know that Phil, I'm not drunk. However it was Chris who posted it here
after you didn't reply to his question on the subject a week ago.

And I *deliberately* did NOT refer to the idea of using a film cap.

Cos it is NOT a good one for the actual purpose.

If you'd said that a week ago when Chris first reffered to the post it would
have saved him a bunch of time tracking it down

> See my reply for the reason.

I saw it and read it. Your reply doesn't change the fact that Chris went out
of his way to find it for me after you didn't reply to his question about
it.

FYI:


Appear on SER and I will murder you.

Just because it's evening and you're pissed and alone again there's no need
to try to take it out on me.

I think I'll wander over to s.e.r, introduce myself and tell them that I'm
there because of you.

As for "I will murder you" all I can say is wow! How brave of you, making
threats safe behind your keyboard. What a man!! A drunk and lonely man but
you sure seem to think that you're tough.

Perhaps maybe stick to something you might have a chance of doing - like
murdering another beer.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[Phil Allison]

~misfit~ fuckwit wrote:

--------------------------

Thanks. I may subscribe to sci.electronics.repair.




** That post was from *me* you dopey retard !!!


I know that Phil, I'm not drunk.

** Do not fucking thank people for posting stuff from me I did NOT want reposted - you total imbecile.

And I *deliberately* did NOT refer to the idea of using a film cap.

Cos it is NOT a good one for the actual purpose.


If you'd said that a week ago when Chris first reffered to the post it would
have saved him a bunch of time tracking it down

** Honestly, I never saw his post or I would have.

See my reply for the reason.

I saw it and read it. Your reply doesn't change the fact that Chris went out
of his way to find it for me after you didn't reply to his question about
it.

** See above - you stupid fuckhead.

I already gave you my *best* advice.

Wot a fucking waste of effort that was.

FYI:


Appear on SER and I will murder you.

Just because it's evening and you're pissed and alone again there's no need
to try to take it out on me.

** I am only giving you fair warning.

I have long known you are mentally defective troll.

I think I'll wander over to s.e.r, introduce myself and tell them that I'm
there because of you.

** Then it's on.

No holds barred, all bets are off.

As for "I will murder you" .....

]
** It was **figurative** you loopy, autistic, bloody tenth wit !!!!




........ Phil

 

[~misfit~]

Once upon a time on usenet Phil Allison wrote:

~misfit~ fuckwit wrote:

--------------------------




Thanks. I may subscribe to sci.electronics.repair.




** That post was from *me* you dopey retard !!!


I know that Phil, I'm not drunk.



** Do not fucking thank people for posting stuff from me I did NOT
want reposted - you total imbecile.

Once it's in the public domain then you don't own it anymore. He asked you
first and then gave you credit for it - yet you still lose your rag.

And I *deliberately* did NOT refer to the idea of using a film cap.

Cos it is NOT a good one for the actual purpose.


If you'd said that a week ago when Chris first reffered to the post
it would have saved him a bunch of time tracking it down


** Honestly, I never saw his post or I would have.

And that's my fault? Like you didn't see my reply to you about how many pins
there were on my relays?

See my reply for the reason.

I saw it and read it. Your reply doesn't change the fact that Chris
went out of his way to find it for me after you didn't reply to his
question about it.


** See above - you stupid fuckhead.

I already gave you my *best* advice.

Wot a fucking waste of effort that was.

I copied and pasted it for future reference and intend to use the system -
it wasn't a waste of time.

FYI:


Appear on SER and I will murder you.

Just because it's evening and you're pissed and alone again there's
no need to try to take it out on me.


** I am only giving you fair warning.

I have long known you are mentally defective troll.

I think you're projecting old fella.

I think I'll wander over to s.e.r, introduce myself and tell them
that I'm there because of you.

** Then it's on.

No holds barred, all bets are off.

Wow! You sound like you do this sort of thing a lot. Maybe a "mentally
defective troll"?

As for "I will murder you" .....

]
** It was **figurative** you loopy, autistic, bloody tenth wit !!!!

Going by the rest of your out-of-control ranting it certainly seems more
than figurative.

You're threatening my life over a misunderstanding (and it's *your*
misunderstanding!). I'm only glad you're in a different country to me - it
saves me getting the authorities involved over internet bullying and
threatening to murder.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[Phil Allison]

~misfit~ fuckwit wrote:

---------------------------

Thanks. I may subscribe to sci.electronics.repair.




** That post was from *me* you dopey retard !!!


I know that Phil, I'm not drunk.



** Do not fucking thank people for posting stuff from me I did NOT
want reposted - you total imbecile.

Once it's in the public domain then you don't own it anymore.

** I asked YOU not to thank him - end of story.

And I *deliberately* did NOT refer to the idea of using a film cap.

Cos it is NOT a good one for the actual purpose.


If you'd said that a week ago when Chris first reffered to the post
it would have saved him a bunch of time tracking it down


** Honestly, I never saw his post or I would have.

And that's my fault?

** It no-one's fault, just a smiple fact .

Your ridiculous fuckhead.

See my reply for the reason.

I saw it and read it. Your reply doesn't change the fact that Chris
went out of his way to find it for me after you didn't reply to his
question about it.


** See above - you stupid fuckhead.

I already gave you my *best* advice.

Wot a fucking waste of effort that was.

I copied and pasted it for future reference and intend to use the system -
it wasn't a waste of time.

** Yes it was, cos you misunderstood it and ignored it.

Like trolling fuckheads all do.

FYI:


Appear on SER and I will murder you.

Just because it's evening and you're pissed and alone again there's
no need to try to take it out on me.


** I am only giving you fair warning.

I have long known you are mentally defective troll.

I think you're projecting old fella.

** Yawwwnnnnnnnnnnnnnnnn....................

I think I'll wander over to s.e.r, introduce myself and tell them
that I'm there because of you.

** Then it's on.

No holds barred, all bets are off.

Wow! You sound like you do this sort of thing a lot.

** Crushing fuckwit trolls is one of my talents.

As for "I will murder you" .....

]
** It was **figurative** you loopy, autistic, bloody tenth wit !!!!

Going by the rest of your out-of-control ranting

** The only one ranting here is YOU - fuckhead.

Over absolutely NOTHING too.

You're threatening my life over a misunderstanding ...

** Wot insane bollocks.

FYI:

You threated to STALK me over nothing.

You are completely anonymous on usenet.

Get over your stupid self.



..... Phil

 

[~misfit~]

Once upon a time on usenet Phil Allison wrote:

~misfit~ fuckwit wrote:

---------------------------





Thanks. I may subscribe to sci.electronics.repair.




** That post was from *me* you dopey retard !!!


I know that Phil, I'm not drunk.



** Do not fucking thank people for posting stuff from me I did NOT
want reposted - you total imbecile.

Once it's in the public domain then you don't own it anymore.



** I asked YOU not to thank him - end of story.

After I did - like that's any use.

And I *deliberately* did NOT refer to the idea of using a film
cap.

Cos it is NOT a good one for the actual purpose.


If you'd said that a week ago when Chris first reffered to the post
it would have saved him a bunch of time tracking it down


** Honestly, I never saw his post or I would have.

And that's my fault?


** It no-one's fault, just a smiple fact .

Your ridiculous fuckhead.

Leave my fuckhead out of this.

See my reply for the reason.

I saw it and read it. Your reply doesn't change the fact that Chris
went out of his way to find it for me after you didn't reply to his
question about it.


** See above - you stupid fuckhead.

I already gave you my *best* advice.

Wot a fucking waste of effort that was.

I copied and pasted it for future reference and intend to use the
system - it wasn't a waste of time.


** Yes it was, cos you misunderstood it and ignored it.

No, because I couldn't use the information at the time as I didn't have the
equipment. You assume to know what's in my mind and what you come up with
only shows what's in yours.

> Like trolling fuckheads all do.

It seems you know a lot about trolling and fuckheadedness.

FYI:


Appear on SER and I will murder you.

Just because it's evening and you're pissed and alone again there's
no need to try to take it out on me.


** I am only giving you fair warning.

I have long known you are mentally defective troll.

I think you're projecting old fella.


** Yawwwnnnnnnnnnnnnnnnn....................

Yep, a few drinks too many maybe.

I think I'll wander over to s.e.r, introduce myself and tell them
that I'm there because of you.

** Then it's on.

No holds barred, all bets are off.

Wow! You sound like you do this sort of thing a lot.


** Crushing fuckwit trolls is one of my talents.

Self-hate is a terrible thing.

As for "I will murder you" .....

]
** It was **figurative** you loopy, autistic, bloody tenth wit !!!!

Going by the rest of your out-of-control ranting


** The only one ranting here is YOU - fuckhead.

Over absolutely NOTHING too.

LOL.

You're threatening my life over a misunderstanding ...


** Wot insane bollocks.

Right, can't say I blame you for backing out of that one. It was really OTT.

FYI:

You threated to STALK me over nothing.

Untrue.

> You are completely anonymous on usenet.

Untrue.

> Get over your stupid self.

One of us is most certainly stupid.

https://au.linkedin.com/in/phil-allison-61694842
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[Chris Jones]

On 29/06/2017 17:17, Phil Allison wrote:

Chris Jones wrote:


FYI a link to Phil's post:
https://groups.google.com/d/msg/sci.electronics.repair/nwWqmrjKEsU/A1SGGVcCbj8J

Full Text:
** I have just been experimenting with a PCB mount, 240VAC/12amp relay
made by "Schrack" and a variable PSU - consisting of a 300VA tranny,
bridge rectifier and 10,000uf cap. The tranny was fed from a Variac.

The relay, when energised, connected a 4ohm high power load to the PSU
and tried to disconnect it when de-energised. With no cap across the
contacts, serious flash arcing occurred at 30VDC. With 50VDC, you can
normally expect the arc to become continuous, first shot. The maker's
rating for DC switching is 24V at 10 amps max.

However, with a 20uF film cap across the contacts, all signs of arcing
at switch off disappeared. Amazingly, this was still the case when tried
with 6, 3 & 1uF instead. When I tried 0.22uF, flash arcs appeared on
about 1 out of 3 tries.

To simulate a *bad* inductive speaker load, I added a 5mH air core choke
in series with the 4 ohm load and saw slight flash arcing with a 1uF cap
but none with 3uF.

With a 8 ohm load and 100VDC, 6uF was enough to reduce arcing to minor
flashes.

So, a film cap across the relay contacts made a huge difference when
breaking DC current at voltages well above the relay's ratings.

FYI: the film cap delays the voltage rise across the relay's contacts
for the first 10 to 50 *microseconds* after opening - which is when the
arc forms. Delay that rise enough and there is no arc.



** Yep, that was posted my me some time back.

A 10uF, 200V or better film cap would do the job very nicely.

But there is a problem:

Speaker relays are mainly used to STOP switch on noises - like loud cracks, squeals and thuds.

Having a 10uF cap across the contacts lets a lot of it through - certainly to the mids and tweeters in a system.

Yes, though in the present situation with no speaker protection at all,
it is just as bad, and adding the relay with capacitor might help the
speaker to survive an amplifier failure without burning out. Perhaps
this particular amplifier does not suffer from those switch on noises
anyway, e.g. due to lucky supply sequencing.

If the relay has two sets of contacts that are able to be connected in
series, then a capacitor could be connected across just one set of
contacts. The contacts with the capacitor would be able to switch off
the speaker hopefully without arcing in the event of an amplifier fault,
and the contacts with no capacitor would stop the clicks and pops if
they occur when the relay coil is not energised.

 

[Phil Allison]

Chris Jones wrote:

-----------------------

FYI a link to Phil's post:
https://groups.google.com/d/msg/sci.electronics.repair/nwWqmrjKEsU/A1SGGVcCbj8J


** Yep, that was posted my me some time back.

A 10uF, 200V or better film cap would do the job very nicely.

But there is a problem:

Speaker relays are mainly used to STOP switch on noises - like loud
cracks, squeals and thuds.

Having a 10uF cap across the contacts lets a lot of it through
- certainly to the mids and tweeters in a system.



Yes, though in the present situation with no speaker protection at all,
it is just as bad, and adding the relay with capacitor might help the
speaker to survive an amplifier failure without burning out.

** Using a DPDT relay wired like I suggested works a treat - and is totally silent when in the rest position.

It's the only method that deserves recommendation.

Perhaps
this particular amplifier does not suffer from those switch on noises
anyway, e.g. due to lucky supply sequencing.

** When connected to a pre-amp, if both come on from the same AC switch - it almost certain to make a loud noise.

If the relay has two sets of contacts that are able to be connected in
series,

** Tolerating one iffy relay contact in series with Hi-Fi speaker is bad enough thank you.




..... Phil

 

[~misfit~]

Once upon a time on usenet ~misfit~ wrote:
[snipped]

The issue I have is that it has no speaker protection and my
speakers are irreplaceable (rarity and my budget considered). I have
two speaker protection PCBs sourced from AliExpress that look up to
the task, well designed with heavy duty relays and thick signal
traces made thicker by having the solder mask removed and solder
added. My problem is that I can't fit them and their power supply
into the amplifier case.

So I'm planning on putting them in a box between the amp and
speakers with speakers in and out connectors on the back. Just
checking to see if anybody thinks this isn't worth doing for any
reason? From what little I know they should work fine like this,
it's just a little fiddly.

These are apparently 30A but that can be taken with a pinch of salt;
https://www.aliexpress.com/item/upc1237-large-current-speaker-protection-board/32809522760.html
(I purchased what look like identical items from a different seller
who no longer has them for sale. I see that listing says maximum amp
20w - that seems as unlikey as the previous listings 600w.)

Well I finally got a transformer (EI as I didn't think a toroidal was needed
as the 'signal' is high-current) and built two of these single channel
protection PCBs into a re-puposed case. I figurd they're better than nothing
(if only for the built-in 3 second delay to avoid 'thump') until I can
rebuild a different two-channel upc1237 based PCB with remote relays to
short the speakers...

The damn thing introduces shitloads of hum! It took me a while to make back
and front panels for the case so only just got around to hooking it up with
my existing amps. (I prioritised this over finishing the refurb of the other
amp so I'd have /some/ protection ready and could use it when finished.) I
tried removing the transformer and running it oiutside the case but it still
hums.

Biugger! I don't get much low-pain 'mobile' time as it is after the
housework etc is done and I've just wasted a bunch building this thing.
Who'd have thought these would introduce so much hum? (Not me obviously.)
It's not as if I've got my stereo system laid out as I'd like it yet with
speaker wires and power cables separated AMAP and only crossing at
right-angles (I'm planning on putting it in a different place when it's all
done so...).
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[Trevor Wilson]

On 15/07/2017 2:15 PM, ~misfit~ wrote:

Once upon a time on usenet ~misfit~ wrote:
[snipped]
The issue I have is that it has no speaker protection and my
speakers are irreplaceable (rarity and my budget considered). I have
two speaker protection PCBs sourced from AliExpress that look up to
the task, well designed with heavy duty relays and thick signal
traces made thicker by having the solder mask removed and solder
added. My problem is that I can't fit them and their power supply
into the amplifier case.

So I'm planning on putting them in a box between the amp and
speakers with speakers in and out connectors on the back. Just
checking to see if anybody thinks this isn't worth doing for any
reason? From what little I know they should work fine like this,
it's just a little fiddly.

These are apparently 30A but that can be taken with a pinch of salt;
https://www.aliexpress.com/item/upc1237-large-current-speaker-protection-board/32809522760.html
(I purchased what look like identical items from a different seller
who no longer has them for sale. I see that listing says maximum amp
20w - that seems as unlikey as the previous listings 600w.)

Well I finally got a transformer (EI as I didn't think a toroidal was needed
as the 'signal' is high-current) and built two of these single channel
protection PCBs into a re-puposed case. I figurd they're better than nothing
(if only for the built-in 3 second delay to avoid 'thump') until I can
rebuild a different two-channel upc1237 based PCB with remote relays to
short the speakers...

The damn thing introduces shitloads of hum! It took me a while to make back
and front panels for the case so only just got around to hooking it up with
my existing amps. (I prioritised this over finishing the refurb of the other
amp so I'd have /some/ protection ready and could use it when finished.) I
tried removing the transformer and running it oiutside the case but it still
hums.

Biugger! I don't get much low-pain 'mobile' time as it is after the
housework etc is done and I've just wasted a bunch building this thing.
Who'd have thought these would introduce so much hum? (Not me obviously.)
It's not as if I've got my stereo system laid out as I'd like it yet with
speaker wires and power cables separated AMAP and only crossing at
right-angles (I'm planning on putting it in a different place when it's all
done so...).

**Ensure that the mains earth is isolated from the speaker earth/s.

--
Trevor Wilson
www.rageaudio.com.au

 

[Phil Allison]

Trevor Wilson wrote:

----------------------------

**Ensure that the mains earth is isolated from the speaker earth/s.

** Also ensure the speaker grounds are kept separate too.

Wanna bet "misfit" has used a metal panel with 1/4 inch jacks for the speakers ?

In any case, he has created a totally unnecessary ground loop.



..... Phil

 

[Trevor Wilson]

On 15/07/2017 5:01 PM, Phil Allison wrote:

Trevor Wilson wrote:

----------------------------


**Ensure that the mains earth is isolated from the speaker earth/s.


** Also ensure the speaker grounds are kept separate too.

Wanna bet "misfit" has used a metal panel with 1/4 inch jacks for the speakers ?

In any case, he has created a totally unnecessary ground loop.

**I ain't taking that bet. Such a fault could be very nasty if the amp
is a bridged one.


--
Trevor Wilson
www.rageaudio.com.au

 

[~misfit~]

Once upon a time on usenet Trevor Wilson wrote:

On 15/07/2017 2:15 PM, ~misfit~ wrote:
Once upon a time on usenet ~misfit~ wrote:
[snipped]
The issue I have is that it has no speaker protection and my
speakers are irreplaceable (rarity and my budget considered). I
have two speaker protection PCBs sourced from AliExpress that
look up to the task, well designed with heavy duty relays and
thick signal traces made thicker by having the solder mask
removed and solder added. My problem is that I can't fit them and
their power supply into the amplifier case.

So I'm planning on putting them in a box between the amp and
speakers with speakers in and out connectors on the back. Just
checking to see if anybody thinks this isn't worth doing for any
reason? From what little I know they should work fine like this,
it's just a little fiddly.

These are apparently 30A but that can be taken with a pinch of salt;
https://www.aliexpress.com/item/upc1237-large-current-speaker-protection-board/32809522760.html
(I purchased what look like identical items from a different seller
who no longer has them for sale. I see that listing says maximum amp
20w - that seems as unlikey as the previous listings 600w.)

Well I finally got a transformer (EI as I didn't think a toroidal
was needed as the 'signal' is high-current) and built two of these
single channel protection PCBs into a re-puposed case. I figurd
they're better than nothing (if only for the built-in 3 second delay
to avoid 'thump') until I can rebuild a different two-channel
upc1237 based PCB with remote relays to short the speakers...

The damn thing introduces shitloads of hum! It took me a while to
make back and front panels for the case so only just got around to
hooking it up with my existing amps. (I prioritised this over
finishing the refurb of the other amp so I'd have /some/ protection
ready and could use it when finished.) I tried removing the
transformer and running it oiutside the case but it still hums.

Biugger! I don't get much low-pain 'mobile' time as it is after the
housework etc is done and I've just wasted a bunch building this
thing. Who'd have thought these would introduce so much hum? (Not me
obviously.) It's not as if I've got my stereo system laid out as I'd
like it yet with speaker wires and power cables separated AMAP and
only crossing at right-angles (I'm planning on putting it in a
different place when it's all done so...).


**Ensure that the mains earth is isolated from the speaker earth/s.

Thanks. It is. In both the amplifiers and the speaker protection unit.
(Although the amp I'm rewiring curently to use soon, the Playmaster Pro III
doesn't isolate the mains and speaker earths.)
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[~misfit~]

Once upon a time on usenet Phil Allison wrote:

Trevor Wilson wrote:

----------------------------


**Ensure that the mains earth is isolated from the speaker earth/s.


** Also ensure the speaker grounds are kept separate too.

Wanna bet "misfit" has used a metal panel with 1/4 inch jacks for the
speakers ?

In any case, he has created a totally unnecessary ground loop.

I'll take the bet.

The back panel is hardboard and I have fixed 40cm wires going out the back
for 'speakers in' terminated in 3mm banana plugs. There are speaker jacks
mounted on the back panel that accept banana plugs, lugs or bare wire to the
speakers (currently using banana plugs).

Thanks.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

 

[Phil Allison]

~misfit~ wrote:

-------------------

**Ensure that the mains earth is isolated from the speaker earth/s.

Thanks. It is. In both the amplifiers and the speaker protection unit.
(Although the amp I'm rewiring curently to use soon, the Playmaster Pro III
doesn't isolate the mains and speaker earths.)

** That is not what TW meant.

He was saying not to create and EXTRA mains earth going to the speaker ground terminals - cos doing that can make a "hum loop".



...... Phil

 

[Phil Allison]

~misfit~ wrote:

--------------------

**Ensure that the mains earth is isolated from the speaker earth/s.


** Also ensure the speaker grounds are kept separate too.

Wanna bet "misfit" has used a metal panel with 1/4 inch jacks for the
speakers ?

In any case, he has created a totally unnecessary ground loop.

I'll take the bet.

The back panel is hardboard and I have fixed 40cm wires going out the back
for 'speakers in' terminated in 3mm banana plugs. There are speaker jacks
mounted on the back panel that accept banana plugs, lugs or bare wire to the
speakers (currently using banana plugs).

** Have you somehow linked the speaker grounds from each channel ?

Cos if you have kept the channels separate and insulated from ground, the new speaker wiring cannot possibly cause the system to hum.



...... Phil