Audio Power Amplifier Solid State Relay

[Gareth Magennis]

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.

[dansabr...@yahoo.com]

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

[John Heath]

Golden rule never put the original factory part in if possible. If the original factory part failed then why repeat the same mistake? Most of the time the factory part is over priced as that company can not stay in business on product alone so they resort to over priced non generic replacement parts that should not have failed in the first place. In fairness they should apologize for your need to replace the part and offer the part for free. The real world is not fair but do not add to it by giving them money they not deserve. I will now get off my soap box.

I would put in the cheap generic sub with wires going the the PC board and tie wrap it to the nearest post hole or what ever. This amp is headed for the garbage bin within the next ten years so who cares is it is meat ball fix. This amp is to be used and enjoyed not line the pockets of some manufacturer who put a non generic parts in to make money in the service after market.

[Dave Platt]

In article <k6xpy.305540$Mi6....@fx35.am4>,

Gareth Magennis <sound....@btconnect.com> 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.

[Kaz Kylheku]

On 2016-01-25, Gareth Magennis <sound....@btconnect.com> 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.

[Kaz Kylheku]

On 2016-01-25, John Heath <heath...@gmail.com> wrote:
> On Monday, January 25, 2016 at 5:55:29 PM UTC-5, dansabr...@yahoo.com 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!

[Phil Allison]

Gareth Magennis wrote:
>
>
> This really annoying, but a good opportunity to learn something useful.

** 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

[Phil Allison]

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

[N_Cook]

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

[amdx]

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

[legg]

On Mon, 25 Jan 2016 22:13:35 -0000, "Gareth Magennis"
<sound....@btconnect.com> 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

[Phil Allison]

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