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Loud pop when I shut down ASR-444?

N

nyindallas

Well-Known Member
I have really been enjoying my Stromberg Carlson ASR-444. I have noticed when I power it down I get a loud pop from 1 or both speakers.

Is there an easy solution?

Can that cause damage to the amp or speakers?

Thanks
 
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Is there a cap across the primary of the transformer (or across the power switch?

Sounds a bit like an inductive spike... many amps have a .01uf 1400v or 2000v ceramic cap across the primary of the power supply transformer... which, among other things, might well be capable of "snubbing" this sort of transient noise...

Fortunately, such caps are readily available... Mouser, DigiKey and other electronics houses have plenty of 'em...

Regards,
Gordon.
 
Can you post a picture of the inside of the amp, with the bottom cover removed? We need to see the area near the power transformer and the wiring going to the power switch, primarily. With that, we might be able to see if there's one of these caps there already... or where to add it, if not...

Regards,
Gordon.
 
The schematic doesn't show any snubbing capacitor on primary or secondary. A 130V MOV would be ideal, and could go across the terminals of the switched AC outlet, which puts in in parallel with the primary. Here's one from (believe it or not...) Radio Shack... http://www.radioshack.com/product/i...tures&origkw=MOV&support=support&tab=features

I'd use a smaller one myself (but then I have some lying around already...) 20 cents each from Mouser...
 
I've noticed the same issue with my ASR-433...

Would the same fix work? I was planning to go to the Rat Shack tomorrow anyway for some odds and ends....:thmbsp:
 
I doubt you'll find the MOVs in a Radio Shack store... except inside surge protectors... a quick test might be to plug a 60-100 W lamp into the switched outlet. If the pop is gone when you turn it off, the MOV or a (high voltage!) cap will take care of it.
 
I did the lamp test. The pop went from a very loud pop to a very low click. I found an old huge lamp to do the test. I am not sure how to install a MOV. Other than the lamp is there any other external solution? Is there a power strip or plug that lowers the voltage a bit? Thanks again


Tom Bavis said:
I doubt you'll find the MOVs in a Radio Shack store... except inside surge protectors... a quick test might be to plug a 60-100 W lamp into the switched outlet. If the pop is gone when you turn it off, the MOV or a (high voltage!) cap will take care of it.
Click to expand...
 
SC, as good as there stuff is, used pretty crummy slide switches. The good news is that they have exact replacements at RS. I changed mine out and added a cap which solved the problem. The PAS and PAT Dynaco preamps usually need the same treatment (same slide switch too).:dunno:
 
Here's what they have at the local store....

Tom Bavis said:
I doubt you'll find the MOVs in a Radio Shack store... except inside surge protectors... a quick test might be to plug a 60-100 W lamp into the switched outlet. If the pop is gone when you turn it off, the MOV or a (high voltage!) cap will take care of it.
Click to expand...

pRS1C-2160484t98.jpg


* Heavy-Duty Metal-Oxide Varistor
* Provides transient voltage spike protection for 120VAC circuits
* Replaces V130LA20A MOV
* Max RMS Voltage = 130VAC, Max DC Voltage = 175VAC
* Peak Current = 6500A (8 x 20uS)

So it's $2....Still cheaper than paying the shipping from Mouser or Digikey. Too bad my big Mouser shipment came in today.....:tears:

Anyway, just strap it across the terminals of the switched AC outlet? Almost sounds too easy.......
 
So let me get this straight: I get the mov and solder each end to the internal terminals of the switched AC. Do the sides matter? Does sound too ez.

analog addict said:
pRS1C-2160484t98.jpg


* Heavy-Duty Metal-Oxide Varistor
* Provides transient voltage spike protection for 120VAC circuits
* Replaces V130LA20A MOV
* Max RMS Voltage = 130VAC, Max DC Voltage = 175VAC
* Peak Current = 6500A (8 x 20uS)

So it's $2....Still cheaper than paying the shipping from Mouser or Digikey. Too bad my big Mouser shipment came in today.....:tears:

Anyway, just strap it across the terminals of the switched AC outlet? Almost sounds too easy.......
Click to expand...
 
nyindallas said:
So let me get this straight: I get the mov and solder each end to the internal terminals of the switched AC. Do the sides matter? Does sound too ez.
Click to expand...

Yep, across the terminals of the switched AC outlet (the one that turns on and off with the power switch).

These things aren't polarized... so there's no matter which side goes to which terminal. One lead from the MOV on each outlet terminal of one switched outlet... that's all you gotta worry about.

Regards,
Gordon.
 
GordonW said:
Yep, across the terminals of the switched AC outlet (the one that turns on and off with the power switch).

These things aren't polarized... so there's no matter which side goes to which terminal. One lead from the MOV on each outlet terminal of one switched outlet... that's all you gotta worry about.

Regards,
Gordon.
Click to expand...


Great. My ASR-333 suffers the same condition.

Could this be done at the power on switch?

Thanks gentlemen,
Craig
 
Yes, it would work there as well, but I think it will be more effective across the primary - across the terminals of the switched outlet.
 
Tom Bavis said:
Yes, it would work there as well, but I think it will be more effective across the primary - across the terminals of the switched outlet.
Click to expand...

Thanks Tom, and thanks for the part #. Just picked one up. I need to re-cord this little amp so it all works out well.

I just can't seem to find a nice straight across fit though for the volume pot. I was running the amp just last week to see how it matched up with a speaker project I'd just finished. I already was aware of the popping but wasn't going to address it until I found a volume pot. One trip in and out. Figured I'd just power down by unplugging, NOT the case. Pop is as bad or worse as it is with the switch. No issues on start up or operation other than worn out pot. Tying in this MOV is only a few minute task with this little amp. Will be very nice if it clears all of this malady up. :yes:

Anyone have any NOS pots, please let me know. I need a dual gang Stereo, 1meg, Audio taper.

Thanks,
Craig
 
No improvement, still have a nasty transient "pop" on power down.

I still can't visualize how the MOV offers any help on the primary, on power DOWN. I can see it helping there with in rush and surge on power UP.

It was worth the gamble for 2 bucks. At least it got a fresh cord while I was at it.

Thanks,
Craig
 
I still have not tried it yet. I had great success getting rid of the pop by plugging in the 60w bulb into the switched power. I will post the results.

Question: could I do a test by plugging the mov directly into the switched output socket before messing with solder?
 
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