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SSR Hum
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Old 26th October 2020, 07:09 PM   #1
tvrgeek is offline tvrgeek  United States
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Default SSR Hum

Ai do not remember having this issue before. But, seems I am on a roll.

Bought a nifty 40A SSR off the WEB. Hooked it up so USB controls the rest of the stereo. Serious hum in the transformers. Load dependent. Now before, I just had a very light load on a 10A SSR, but did not notice any hum.

So, swapped in the 10A. Still hum, but only when load over an amp.

Drug out the scope. I can just barely tell a switching glitch for the triac, but nothing I woudl think upset the transformers. Anyway, guess I am looking for a relay. I wanted the SSR as it pulls so little from the USB. Best relay I found is 70mA.

Anyone else have this?
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Old 26th October 2020, 08:27 PM   #2
Vovk Z is offline Vovk Z  Ukraine
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SSR may be non-symmetrical device and it may distort sine non-simmetrically, so it may do something like additional dc-bias to the transformer.
It is better to use usual relay.
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Old 27th October 2020, 01:38 PM   #3
tvrgeek is offline tvrgeek  United States
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Ordered some relays boards. Guess the best tool for putting in a nail is still a hammer.

Odd, the waveform out of the output here looks a bit distorted, but it may be my cheap probes at that scale. I should still have an old P6106 somewhere. Hope it is not my old Tek scope going off, but it is 30 years old.

I want to test further just to understand. The possible DC bias I had not thought of, but it makes sense. I still have an old huge line filter I might play with. Don't have an isolation transformer, just a big autotransformer from back when I built amps. Yesterday was a very frustrating day, so I need to chill a little.
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Old 27th October 2020, 03:38 PM   #4
nigelwright7557 is offline nigelwright7557  United Kingdom
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There are two types of SSR, triac and mosfet.
The triac ones cause distortion of audio signal at crossover, the mosfets dont.
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Old 27th October 2020, 06:22 PM   #5
tvrgeek is offline tvrgeek  United States
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I can guarantee the $10 E-bay are triac. For that matter, the $40 ones look to be the same device with a different sticker. Could you point me to a MOSFET device?
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Old 29th October 2020, 08:31 PM   #6
tvrgeek is offline tvrgeek  United States
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Been reading up on DC blockers. "Sounds" like that was in fact the problem. It was so bad my e-core in my DAC supply hummed, but not like the toroid in the Creek.

My solution is a relay, but I may just incorporate one along with a basic line filter in my buss bar. Seems like good practice.
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