Speaker Protection Question.

[~misfit~]

Hi. I've recently bought some second-hand speakers that are a lot more
power-hungry than my previous speakers so am in the process of refurbishing
and tuning a 'Playmster Pro Series Three Power Amplifier', a kitset amp
designed by Electronics Australia with kits put together by DSE and Jaycar.
The guy who built it was a bit... agricultural and I can see how to make it
sound better. I'm also upgrading and replacing the filter capacitors in the
power supplies (it's dual mono construction with two 300VA toroidial
trannies).

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.

Thoughts?

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~ wrote:

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

Hi. I've recently bought some second-hand speakers that are a lot more
power-hungry than my previous speakers so am in the process of refurbishing
and tuning a 'Playmster Pro Series Three Power Amplifier', a kitset amp
designed by Electronics Australia with kits put together by DSE and Jaycar.
The guy who built it was a bit... agricultural and I can see how to make it
sound better. I'm also upgrading and replacing the filter capacitors in the
power supplies (it's dual mono construction with two 300VA toroidial
trannies).

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.

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

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.

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.

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.


...... Phil

 

[~misfit~]

Once upon a time on usenet Phil Allison wrote:

~misfit~ wrote:

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

Hi. I've recently bought some second-hand speakers that are a lot
more power-hungry than my previous speakers so am in the process of
refurbishing and tuning a 'Playmster Pro Series Three Power
Amplifier', a kitset amp designed by Electronics Australia with kits
put together by DSE and Jaycar. The guy who built it was a bit...
agricultural and I can see how to make it sound better. I'm also
upgrading and replacing the filter capacitors in the power supplies
(it's dual mono construction with two 300VA toroidial trannies).

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.

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;
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.)

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?

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?

The speakers cost me more than the amp (not counting 8 x 10,000uF / 100V
filter caps and time sepnt on it since then) and I *would* prefer to have
the amp blow rather than the speakers. I dare say I can source some 2SJ162
and 2SK1058 MOSFETs if I need to whereas it's unlikely I could source
replacement speakers (even if I could afford to).

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)?

Thanks again for the reply, I appreciate it. I have a lot to learn.
--
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:

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

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.

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.

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.

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.


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.


..... Phil

 

[Trevor Wilson]

On 18/06/2017 2:47 PM, ~misfit~ wrote:

Once upon a time on usenet Phil Allison wrote:
~misfit~ wrote:

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

Hi. I've recently bought some second-hand speakers that are a lot
more power-hungry than my previous speakers so am in the process of
refurbishing and tuning a 'Playmster Pro Series Three Power
Amplifier', a kitset amp designed by Electronics Australia with kits
put together by DSE and Jaycar. The guy who built it was a bit...
agricultural and I can see how to make it sound better. I'm also
upgrading and replacing the filter capacitors in the power supplies
(it's dual mono construction with two 300VA toroidial trannies).

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.

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;
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.)

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?

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?

The speakers cost me more than the amp (not counting 8 x 10,000uF / 100V
filter caps and time sepnt on it since then) and I *would* prefer to have
the amp blow rather than the speakers. I dare say I can source some 2SJ162
and 2SK1058 MOSFETs if I need to whereas it's unlikely I could source
replacement speakers (even if I could afford to).

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)?

Thanks again for the reply, I appreciate it. I have a lot to learn.

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

BTW: What are the speakers?

--
Trevor Wilson
www.rageaudio.com.au

 

[~misfit~]

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,
--
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)

 

[Computer Nerd Kev]

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

Once upon a time on usenet Phil Allison wrote:

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.

It shouldn't be hard to replace the relays.

--
__ __
#_ < |\| |< _#

 

[~misfit~]

Once upon a time on usenet Computer Nerd Kev wrote:

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Phil Allison wrote:

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.

It shouldn't be hard to replace the relays.

It doesn't seem easy. I have no idea how to source relays like these and the
PCBs are made for them - there are no other holes for any other type. It's
bloody annoying frankly, I thought I was doing the right thing buying these
as the amp doesn't have any speaker protection, not even fuses. I'll add
fuses (not sure of values to use) and throw these things in a drawer I
guess.

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~ wrote:

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

** 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.

** So they are 4 pin types ???



...... Phil

 

[~misfit~]

Once upon a time on usenet Phil Allison wrote:

~misfit~ wrote:

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



** 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.



** So they are 4 pin types ???

Yes, as I said in my reply to you when you asked before.

The negative connection to the speaker passes through unswitched, the
positive goes to pins on the relay and there are two other pins at the other
end of the relay which appear to be for the coil.

They aren't powered up and there is no continuity between the pins connected
to the positive speaker rail.
--
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:

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

** So they are 4 pin types ???

Yes, as I said in my reply to you when you asked before.

** I somehow missed that line.

Similar relays ( with 5 pins) are available from Element 14 and RS Components.



...... Phil


..... Phil

The negative connection to the speaker passes through unswitched, the
positive goes to pins on the relay and there are two other pins at the other
end of the relay which appear to be for the coil.

They aren't powered up and there is no continuity between the pins connected
to the positive speaker rail.
--
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 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.

 

[Computer Nerd Kev]

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:

Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Phil Allison wrote:

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.

It shouldn't be hard to replace the relays.

It doesn't seem easy. I have no idea how to source relays like these

They don't need to be exact matches. Key parameters are operating
voltage, maximum switching current/voltage, number of poles (greater
than two apparantly) and, in this case, switching time. With these
conditions met, most normal relays will be suitable substitutes for
the ones you have. You should be able to find some suitable ones
on Ebay/Aliexpress, as well as the major suppliers like RS.

and the
PCBs are made for them - there are no other holes for any other type.

The board has PCB mounted relays, but you can desolder them and just
solder wires to a relay glued beside the board in the case. Many
relays have large contacts suitable for soldering wires to, and even
a PCB relay can be connected in this way if you're careful.

I rarely have relays mounted on-board for hobby projects.

It's
bloody annoying frankly, I thought I was doing the right thing buying these
as the amp doesn't have any speaker protection, not even fuses. I'll add
fuses (not sure of values to use) and throw these things in a drawer I
guess.

I've never had anything to do with speaker protection, but I doubt a fuse
would be quick enough - especially if the arcing in a relay goes on long
enough to cause trouble.

--
__ __
#_ < |\| |< _#

 

[Computer Nerd Kev]

Computer Nerd Kev <not@telling.you.invalid> wrote:

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Phil Allison wrote:

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.

It shouldn't be hard to replace the relays.

It doesn't seem easy. I have no idea how to source relays like these

number of poles (greater than two apparantly) and,

Actually I might have misunderstood that. Thinking about it, I think
Phill must mean you need Double Throw relays instead of Single Throw
relays.

So you want an arrangement like this where when the relay (just shown
as a switch) switches, the two speaker lines are shorted together and
any arc just flows straight back to the amplifier:

|
_* /*----|AMP OUT 1
| / |
| / |
| *-----|SPK IN 1
| |
| |
|--------------|AMP OUT 2
| |
--------
SPK IN 2

--
__ __
#_ < |\| |< _#

 

[~misfit~]

Once upon a time on usenet Computer Nerd Kev wrote:

~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Phil Allison wrote:

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.

It shouldn't be hard to replace the relays.

It doesn't seem easy. I have no idea how to source relays like these

They don't need to be exact matches. Key parameters are operating
voltage, maximum switching current/voltage, number of poles (greater
than two apparantly) and, in this case, switching time. With these
conditions met, most normal relays will be suitable substitutes for
the ones you have. You should be able to find some suitable ones
on Ebay/Aliexpress, as well as the major suppliers like RS.

and the
PCBs are made for them - there are no other holes for any other type.

The board has PCB mounted relays, but you can desolder them and just
solder wires to a relay glued beside the board in the case. Many
relays have large contacts suitable for soldering wires to, and even
a PCB relay can be connected in this way if you're careful.

I rarely have relays mounted on-board for hobby projects.

It's
bloody annoying frankly, I thought I was doing the right thing
buying these as the amp doesn't have any speaker protection, not
even fuses. I'll add fuses (not sure of values to use) and throw
these things in a drawer I guess.

I've never had anything to do with speaker protection, but I doubt a
fuse would be quick enough - especially if the arcing in a relay goes
on long enough to cause trouble.

Thanks for this Kev. I'm considering my options and appreciate all info.

Running relays off-board might be the answer. I'm in the process of
rebuilding the power amp at the moment but am thinking about the speaker
protection issue and will decide what to do when I've finished the amp.

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)

 

[~misfit~]

Once upon a time on usenet Computer Nerd Kev wrote:

Computer Nerd Kev <not@telling.you.invalid> wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Computer Nerd Kev wrote:
~misfit~ <shaun.at.pukekohe@gmail.com> wrote:
Once upon a time on usenet Phil Allison wrote:

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.

It shouldn't be hard to replace the relays.

It doesn't seem easy. I have no idea how to source relays like these

number of poles (greater than two apparantly) and,

Actually I might have misunderstood that. Thinking about it, I think
Phill must mean you need Double Throw relays instead of Single Throw
relays.

So you want an arrangement like this where when the relay (just shown
as a switch) switches, the two speaker lines are shorted together and
any arc just flows straight back to the amplifier:

|
_* /*----|AMP OUT 1
/ |
/ |
*-----|SPK IN 1
|
|
--------------|AMP OUT 2
|
--------
SPK IN 2

That could be what he means, using a SPDT relay (instead of the SPST type
fitted) with the NC contacts shorting the speaker - I'll ask him (then try
to get my head around it and work out how to wire it up using the existing
uPC1237 based protection boards).

FWIW here's a blog of a guy making his own speaker protection boards using
the uPC1237 and he's just using SPST relays...
http://blog.audioworkshop.org/upc1237-amplifierspeaker-protection-module/
I wanted to avoid having to make my own so, after reading up on them on
several DIY audo sites decided these modules were the answer. However if I
have to modify them to improve them further I will.

The uPC1237 is quite nifty, it has a built-in delay so that when it's
powered up it doesn't connect the speakers for a couple seconds to stop
'thump'.
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)

 

[~misfit~]

Once upon a time on usenet Phil Allison wrote:

~misfit~ wrote:

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




** So they are 4 pin types ???

Yes, as I said in my reply to you when you asked before.


** I somehow missed that line.

Similar relays ( with 5 pins) are available from Element 14 and RS
Components.

Thanks Phil. So exactly what type of relay do you suggest using? Do you mean
to use a SPDT relay and wire it so that in it's non-energised position the
speaker is shorted?

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)

 

[~misfit~]

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.

I'm bloody annoyed actually, should have done this 'research' first as these
speaker protection circuits were far more expensive than others using the
same uPC1237 IC and from what I could see the added expense was mainly
because of the heavy-duty relays used.
--
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 Trevor Wilson wrote:

On 18/06/2017 2:47 PM, ~misfit~ wrote:
Once upon a time on usenet Phil Allison wrote:
~misfit~ wrote:

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

Hi. I've recently bought some second-hand speakers that are a lot
more power-hungry than my previous speakers so am in the process of
refurbishing and tuning a 'Playmster Pro Series Three Power
Amplifier', a kitset amp designed by Electronics Australia with
kits put together by DSE and Jaycar. The guy who built it was a
bit... agricultural and I can see how to make it sound better. I'm
also upgrading and replacing the filter capacitors in the power
supplies (it's dual mono construction with two 300VA toroidial
trannies). 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.
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;
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.)

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?

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?

The speakers cost me more than the amp (not counting 8 x 10,000uF /
100V filter caps and time sepnt on it since then) and I *would*
prefer to have the amp blow rather than the speakers. I dare say I
can source some 2SJ162 and 2SK1058 MOSFETs if I need to whereas it's
unlikely I could source replacement speakers (even if I could afford
to). 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)?

Thanks again for the reply, I appreciate it. I have a lot to learn.

**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.

I had some Jamo speakers that never sounded very good despite having what
appeared to be high quality drivers (and of course the Jamo name). After a
while I decided to check the crossovers with an eye to re-capping them if
they didn't use good quality caps. That's when I saw the polyswitches. I did
some research at the time and found these is almost universal condemnation
for having polyswitches in crossover circuits - unless you're happy with
'mid-fi'.

I wasn't (and am not) and so sold the Jamos.
--
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 29/06/2017 12:17 PM, ~misfit~ wrote:

Once upon a time on usenet Trevor Wilson wrote:
On 18/06/2017 2:47 PM, ~misfit~ wrote:
Once upon a time on usenet Phil Allison wrote:
~misfit~ wrote:

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

Hi. I've recently bought some second-hand speakers that are a lot
more power-hungry than my previous speakers so am in the process of
refurbishing and tuning a 'Playmster Pro Series Three Power
Amplifier', a kitset amp designed by Electronics Australia with
kits put together by DSE and Jaycar. The guy who built it was a
bit... agricultural and I can see how to make it sound better. I'm
also upgrading and replacing the filter capacitors in the power
supplies (it's dual mono construction with two 300VA toroidial
trannies). 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.
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;
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.)

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?

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?

The speakers cost me more than the amp (not counting 8 x 10,000uF /
100V filter caps and time sepnt on it since then) and I *would*
prefer to have the amp blow rather than the speakers. I dare say I
can source some 2SJ162 and 2SK1058 MOSFETs if I need to whereas it's
unlikely I could source replacement speakers (even if I could afford
to). 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)?

Thanks again for the reply, I appreciate it. I have a lot to learn.

**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.

I had some Jamo speakers that never sounded very good despite having what
appeared to be high quality drivers (and of course the Jamo name). After a
while I decided to check the crossovers with an eye to re-capping them if
they didn't use good quality caps. That's when I saw the polyswitches. I did
some research at the time and found these is almost universal condemnation
for having polyswitches in crossover circuits - unless you're happy with
'mid-fi'.

I wasn't (and am not) and so sold the Jamos.

**I would suggest that your dislike of the Jamos may not have been down
to the Polyswitches. I've fitted LOTS of Polyswitches to all manner of
speakers over the years (from a couple of hundred Dollars to
$20,000.00). Mostly when there was a risk of damage to mid and HF
drivers by the owner (or drunk friends). NOT ONCE has there been a
complaint about the sound quality. Now, I realise that is not conclusive
proof, but it is strong anecdotal evidence. That said, I don't see the
big deal. Buy a couple of Polyswitches and see for yourself. Total cost
- $10.00 and 20 minutes of your time. I doubt you can hear a difference.
All that being said, a Polyswitch will always introduce a small loss
into any system. I would argue that, under anything but extreme
circumstances, the sound quality change will be insignificant.

--
Trevor Wilson
www.rageaudio.com.au