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Old 04-24-2008, 08:50 AM
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Question What causes hum in vintage receiver??

I have an old Electro-Voice receiver that will hum after being on for a short while. It's not very loud as you can only notice it when the music stops.
Turning the receiver off for just a few seconds will make the hum go away but it comes back in a minute or two.

What would be a likely cause?
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Old 04-24-2008, 10:14 AM
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The power filter caps are probably starting to age and are not up to spec. When the caps get older they aren't able to 'smooth' out the power as effectively so you get ripple in the power thats feeding your amp, that is probably what you are hearing. Luckily they are relatively cheap and easy to replace.
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Old 04-24-2008, 11:59 AM
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Question What causes hum in vintage receiver??
Answer: Vintage receiver forgot the words to the music?
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Old 04-24-2008, 12:28 PM
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Quote:
Originally Posted by Mattwizz3 View Post
The power filter caps are probably starting to age and are not up to spec. When the caps get older they aren't able to 'smooth' out the power as effectively so you get ripple in the power thats feeding your amp, that is probably what you are hearing. Luckily they are relatively cheap and easy to replace.
I agree with the above. Failing electrolytic capacitors are the most likely cause of hum in vintage receivers. Another cause of hum is ground loops causes by poor design. Not that common, however, I have run across this a few times.
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Old 04-24-2008, 06:25 PM
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Quote:
Originally Posted by Mattwizz3 View Post
The power filter caps are probably starting to age and are not up to spec. When the caps get older they aren't able to 'smooth' out the power as effectively so you get ripple in the power thats feeding your amp, that is probably what you are hearing. Luckily they are relatively cheap and easy to replace.
This is what I suspected. I hope I can find a cap that will fit inside this receiver! It's a 22000uF cap and it fits into metal spring clips so the new cap will have to be nearly the same size physically. There is no room to relocate the cap.
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Old 04-24-2008, 06:31 PM
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Quote:
Originally Posted by Chazb11 View Post
This is what I suspected. I hope I can find a cap that will fit inside this receiver! It's a 22000uF cap and it fits into metal spring clips so the new cap will have to be nearly the same size physically. There is no room to relocate the cap.
Modern caps tend to be physically smaller than older ones, sometimes very much so. For a power supply cap, if the modern 22000uF ones you find in the original voltage are too small to fit, go to a higher voltage - that won't cause any operating problems, and won't affect the sound. You might also go to a higher uF value - some people find that improves the sound (tighter bass), but it can put more strain on the transformer, and/or cause fuses to blow from start up surges. Personally, I'd be willing to try a bigger cap, but no bigger than 150% of the original uF value.
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Old 04-24-2008, 06:53 PM
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Use self adhesive foam weatherstripping to increase the effective diameter of caps that are physically smaller than the originals, just wrap it around the cap where the clamp encompasses it.

Something I picked up from a Yamaha tech
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Old 04-25-2008, 08:14 AM
myrgatroyd myrgatroyd is offline
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Hmm. My english is not such as good...
Does "hum" definitly means "electrical low frequenced sound" or just "low frequenced sound"?

That means: Can you hear the hum in the speakers or is it the receiver itself?
Once had a Tannhauser with a terribly transformer, gave it away, my wife could not stand the sounds the trans made. Problem was caused by vibrating iron plates.

Then: Is the hum present only at one source (TT, TD) or present at all? Then you could have a problem with your connection.

Otherwise I would change the caps like the folks here do advise.
You should do it, because you will have that problem in nearer future anyway, even if your caps are actually in good condition.
Last tip: Turn the power plug 180 degree. (Not in the oven. Left to right.)

Yours
Alex
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Old 04-25-2008, 08:55 AM
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Quote:
Originally Posted by myrgatroyd View Post
Last tip: Turn the power plug 180 degree. (Not in the oven. Left to right.)

Yours
Alex
Now that's funny right there!

Also going to add a little more info here...the hum gets more noticeable the longer the unit is on. No hum at all when first turned on and everything is cool. In short it seems to be related to operating temp, the cooler it is the less hum. Does this still sound like just a cap failing? (the unit is not overheating at all, just warming up normally)

I'm going to replace the cap anyway. There is only one and it's 2000uf, not 22000 as I said in the first post. (i don't type so well). I think I have found a suitable replacement at Mouser > 2100uF 150v and the size is right. (CGS212U150RC3 is the mfg. number, if you're interested)
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Last edited by Chazb11; 04-25-2008 at 09:04 AM. Reason: added part number
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Old 04-26-2008, 07:41 AM
myrgatroyd myrgatroyd is offline
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Is the hum in the speakers or does it come from the unit itself?
That transformer in my Tannhauser acted similar. The sound got worse when the radio played some minutes, got then to a certain level.
It was the iron plates vibrating due magnetical fields in the coil.
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