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SSR for speaker protection?
SSR for speaker protection?
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Old 17th February 2018, 01:41 PM   #1
fvzeppelin is offline fvzeppelin  Germany
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Default SSR for speaker protection?

Hello,

I'm modifying an old power amp, which has a very sophisticated speaker protection circuitry To make things easy with my modifications, I would like to place a relay at the amplifier output.

Now, I have found a pair of S202S01 SSRs among my parts and I'm wondering if it would be reasonable to use these

Does anyone have experience with SSRs as speaker on/off switch?
Or do you see any problems using these (apart from heat dissipation)?

Best gegards,
Frank
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Old 17th February 2018, 01:55 PM   #2
Mooly is offline Mooly  United Kingdom
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SSR for speaker protection?
The SSR such as you mention use triacs and are unsuitable for use as a speaker relay because they would generate massive non linear distortion around the zero crossing point.

SSR's made using two power FET's and a floating photovoltaic coupler are the way to go and many have used these successfully. I would never go back to mechanical relays now.

This long thread has all the details:
Output Relays
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Old 17th February 2018, 02:34 PM   #3
fvzeppelin is offline fvzeppelin  Germany
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Thank you, Mooly - this was VERY quick
In the last pages of the thread you mentioned, they use PVI1050A optos to drive a pair of IRFB3077PBF MOSFETs. This actually makes things easier for me, as the circuitry of my old amp is already designed to drive 4N35 optos
Do you think, I can use the 4N35 right away or would you recommend to replace them with the PVI1050A optos?
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Old 17th February 2018, 04:10 PM   #4
fvzeppelin is offline fvzeppelin  Germany
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Quote:
Originally Posted by fvzeppelin View Post
Thank you, Mooly - this was VERY quick
In the last pages of the thread you mentioned, they use PVI1050A optos to drive a pair of IRFB3077PBF MOSFETs. This actually makes things easier for me, as the circuitry of my old amp is already designed to drive 4N35 optos
Do you think, I can use the 4N35 right away or would you recommend to replace them with the PVI1050A optos?
This one was stupid - sorry
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Old 17th February 2018, 04:52 PM   #5
Mooly is offline Mooly  United Kingdom
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SSR for speaker protection?
No problem

If you are unsure of anything then just ask.
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Old 17th February 2018, 05:43 PM   #6
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by fvzeppelin View Post
Hello,

Does anyone have experience with SSRs as speaker on/off switch?
Or do you see any problems using these (apart from heat dissipation)?

Best gegards,
Frank
I would have thought they might introduce some cross over distortion as the phase changes as one transistor turns off and the other on.
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Old 17th February 2018, 06:56 PM   #7
LKA is offline LKA  Europe
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Quote:
Originally Posted by nigelwright7557 View Post
I would have thought they might introduce some cross over distortion as the phase changes as one transistor turns off and the other on.
amplifier measurement at 55W@4R5
first picture - no protection at all
second picture - SSR protection
RED trace - optocouplers in serial
YELLOW trace - optocouplers in parallel

no_protect.png

SSR RED-SER YELLOW-PAR 2.png
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Old 17th February 2018, 08:02 PM   #8
fvzeppelin is offline fvzeppelin  Germany
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You mean, the red trace in the second picture corresponds to a circuit like posted here ?
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Old 18th February 2018, 01:18 PM   #9
LKA is offline LKA  Europe
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yes, red and yellow traces on second picture show amp distortion when SSR was in the signal path. below is schematic and populated pcb (on the right is the last version with jumpers)

ProtectSSR-schema.JPG

ProtectSSR-v1.1-front1.jpg
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Old 18th February 2018, 02:31 PM   #10
fvzeppelin is offline fvzeppelin  Germany
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Quote:
Originally Posted by LKA View Post
yes, red and yellow traces on second picture show amp distortion when SSR was in the signal path. below is schematic and populated pcb (on the right is the last version with jumpers)

Attachment 663301

Attachment 663302
Thank you, LKA, for sharing this information!

But how to interpret these measurements? With my naive perspective, I'd say: There is no difference between parallel and serial optos.

As I already have a fault detection circuit in place which provides an open collector driver, I will only need the optos, the two MOSFETs, and a serial resistor to adjust the LED current - less is more And for the optos, I will probably go for the serial configuration to be on the very safe side with the voltage.

Or did I miss something with the interpretation of the measurements?
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