Hi,

this is really annoying, but a good opportunity to learn something useful.

I have an old Urei Power Amp that needs its DPDT 10A speaker output relay
replacing.
It's annoying because the relay fitted has a totally non conventional pin
configuration, so the usual generic cheap replacement is going to involve
drilling holes in the PCB and isolating pads and using glue and stuff
because some solder pads will have to go etc.

So I thought about maybe using Solid State relays, which should be
physically smaller and lighter, and could be mounted in little patches of
available free space.


I've never seen a solid state relay in a Power Amp. Maybe there's a good
reason for that - AC transmission, Inductive loads, back emf etc.
A quick look at Farnell shows you don't generally get DPDT ones, so you need
2 for a stereo amp, and they are not that cheap.


Any experience welcome.



Cheers,


Gareth.

I have some NOS relays around. Can you post the specs on the bad one?
I will check to see if I have one.

Dan

In article ,
Gareth Magennis wrote:


I've never seen a solid state relay in a Power Amp. Maybe there's a
good reason for that - AC transmission, Inductive loads, back emf etc.
A quick look at Farnell shows you don't generally get DPDT ones, so you need
2 for a stereo amp, and they are not that cheap.

SSRs which can handle reasonable-to-high currents are typically triac
designs, I believe (or possibly back-to-back SCRs in some cases). I
don't think they're going to be able to handle speaker-level audio
without introducing a great deal of noise and distortion, associated
with the switching on and off of the triac at the zero-crossing
points.

Before you try doing this "for real", try an experiment with an
external SSR first (between an amp's speaker outputs and a speaker).
Probably best to use throw-away components all around. I doubt you'll
like how it sounds.

Also, remember that a typical SSR won't switch off (open) anywhere but
at the zero crossing. If your amp's relay-drive circuit is part of a
speaker-protection circuit (to turn off the relay if DC is detected at
the output), using an SSR would defeat this protection. If an output
transistor shorts to the + or - rail, you'd end up dumping DC into
your woofer with no cutoff and probably destroy the woofer.

I'd strongly suggest using a real relay. If necessary, build a small
interposer board to convert the original relay's pinouts to those of a
high-quality commodity relay.

On 2016-01-25, Gareth Magennis wrote:
Hi,

this is really annoying, but a good opportunity to learn something useful.

I have an old Urei Power Amp that needs its DPDT 10A speaker output relay
replacing.
It's annoying because the relay fitted has a totally non conventional pin
configuration, so the usual generic cheap replacement is going to involve
drilling holes in the PCB and isolating pads and using glue and stuff
because some solder pads will have to go etc.

You could make a small PCB for the relay, and mount that somewhere.
(E.g. standoffs rising from main PCB.) Then connect that to the original
pads with hookup wires.

So I thought about maybe using Solid State relays, which should be
physically smaller and lighter, and could be mounted in little patches of
available free space.


I've never seen a solid state relay in a Power Amp. Maybe there's a good
reason for that - AC transmission, Inductive loads, back emf etc.

Possibly also: distortion.

On 2016-01-25, John Heath wrote:
On Monday, January 25, 2016 at 5:55:29 PM UTC-5, wrote:
I have some NOS relays around. Can you post the specs on the bad one?
I will check to see if I have one.

Dan

Golden rule never put the original factory part in if possible. If the
original factory part failed then why repeat the same mistake?

Golden rule of break-ups: this time it will be different, I promise!

Gareth Magennis wrote:


This really annoying, but a good opportunity to learn something useful.

I have an old Urei Power Amp that needs its DPDT 10A speaker output relay
replacing.
It's annoying because the relay fitted has a totally non conventional pin
configuration, so the usual generic cheap replacement is going to involve
drilling holes in the PCB and isolating pads and using glue and stuff
because some solder pads will have to go etc.

So I thought about maybe using Solid State relays, which should be
physically smaller and lighter, and could be mounted in little patches of
available free space.


I've never seen a solid state relay in a Power Amp. Maybe there's a good
reason for that - AC transmission, Inductive loads, back emf etc.
A quick look at Farnell shows you don't generally get DPDT ones, so you need
2 for a stereo amp, and they are not that cheap.


Any experience welcome.


** Don't let the name fool you, SSRs are not replacements for regular relays.

SSRs use triacs or SCRs and are intended for AC supply switching and the like - where voltages are high and fixed and a discontinuity around zero is not a big problem.

Simply will not work with speakers.


..... Phil

John Heath wrote:



Golden rule never put the original factory part in if possible.
If the original factory part failed then why repeat the same mistake?


** Very true, but you must be sure you have something better available.

Not too hard with transistors where you can sub American or European brands like Motorola, Philips or ST. But ICs, mechanical parts and wound components are harder to substitute successfully.

My parts bins are stocked with what I have found to be the best available in each category, so they will cover a huge range of jobs.

It is only as the very last resort that I go to the maker or importer for a spare part.


..... Phil

On 25/01/2016 22:13, Gareth Magennis wrote:
Hi,

this is really annoying, but a good opportunity to learn something useful.

I have an old Urei Power Amp that needs its DPDT 10A speaker output
relay replacing.
It's annoying because the relay fitted has a totally non conventional
pin configuration, so the usual generic cheap replacement is going to
involve drilling holes in the PCB and isolating pads and using glue and
stuff because some solder pads will have to go etc.

So I thought about maybe using Solid State relays, which should be
physically smaller and lighter, and could be mounted in little patches
of available free space.


I've never seen a solid state relay in a Power Amp. Maybe there's a
good reason for that - AC transmission, Inductive loads, back emf etc.
A quick look at Farnell shows you don't generally get DPDT ones, so you
need 2 for a stereo amp, and they are not that cheap.


Any experience welcome.



Cheers,


Gareth.




hard wiring a big relay or two, to wherever there is space in the amp?
its not as though it is switching RF

On 1/25/2016 6:30 PM, Dave Platt wrote:
In article ,
Gareth Magennis wrote:

I'd strongly suggest using a real relay. If necessary, build a small
interposer board to convert the original relay's pinouts to those of a
high-quality commodity relay.


This was my thought.
Standard relay with a DIY PCB to make the pins match.
Mikek

On Mon, 25 Jan 2016 22:13:35 -0000, "Gareth Magennis"
wrote:

Hi,

this is really annoying, but a good opportunity to learn something useful.

I have an old Urei Power Amp that needs its DPDT 10A speaker output relay
replacing.

Surprised you need DPDT. DPST should seve this purpose, if the amp has
internal Zobel termination.

It's annoying because the relay fitted has a totally non conventional pin
configuration, so the usual generic cheap replacement is going to involve
drilling holes in the PCB and isolating pads and using glue and stuff
because some solder pads will have to go etc.

So I thought about maybe using Solid State relays, which should be
physically smaller and lighter, and could be mounted in little patches of
available free space.

SSRs will have an objectionable voltage drop, introducing distortion
whether or not the drives are compatible.

Make and model of original?

RL

legg wrote:



Surprised you need DPDT. DPST should seve this purpose, if the amp has
internal Zobel termination.



** Some amps use all the contacts on a change-over relay.

The speaker output connects to the moving contact and is grounded when unpowered. On power up, the speakers connect to the amp output.

This arrangement is far better at protecting speakers from DC faults as few relays can break the arc that forms when opening under load at high DC voltage.

Most relays are rated at 24VDC max and that is where thee begin to arc badly.


..... Phil