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Charred resistor on speaker output
Charred resistor on speaker output
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Old 5th July 2020, 05:36 AM   #11
JMFahey is online now JMFahey  Argentina
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Quote:
Originally Posted by Rundmaus View Post
The buzzing noise is gone now, although I can not imagine how this could be caused by the inoperative Zobel network...
Oh, that one is easy.
Zobel is a *stability* network, so not having it often accounts for problems.

The buzing you hear may be the audible artifacts of a supersonic (inaudible) oscillation.
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Old 5th July 2020, 10:26 AM   #12
Rundmaus is offline Rundmaus  Germany
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Lots of different ideas, thanks for the input.

1. The amp is a commercial one, an Arcam Alpha 3.

2. The unit is quite old, I think I bought it 14 years ago in used condition. It was old even back then.

3. Besides the resistors R43, R44, R143, R144 yesterday, no parts were changed yet. The rail caps are still the original ones.

4. Electrolytic capacitors: I suspected those too, but with the replaced resistors, the amp is completely quiet, apart from some random noise. I would expect to hear 50Hz or 100Hz hum if the rail caps are at the end of their useful life (and capacity).

Regards,
Rundmaus

PS. Ordered a NAD 316 BEE V2 yesterday as a replacement, but I am willing to get the Arcam back to useful operation.
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Old 5th July 2020, 12:10 PM   #13
Ian Finch is offline Ian Finch  Australia
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Alpha 3? That's almost 30 years old. Assuming it hasn't had a previous recap of the electrolytic caps, how about making a list of suitable replacements and doing a proper service job?
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Old 5th July 2020, 08:31 PM   #14
Rundmaus is offline Rundmaus  Germany
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Originally Posted by Ian Finch View Post
Alpha 3? That's almost 30 years old. Assuming it hasn't had a previous recap of the electrolytic caps, how about making a list of suitable replacements and doing a proper service job?
Yes, I think that's the way to go. Now that a replacement is on its way, I got enough time, there's no rush to get it back to service.

Anything else besides electrolytics that might not age well? I think there are a few film capacitors which should fine. But I also spotted a few small, wound polystyrene caps. Do they have any negative aging effects? And what about the carbon film resistors the manufacturer used in many places, probably due to the price? Does it make sense to replace them all by metal films?

Kind regards,
Andreas
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Old 6th July 2020, 08:19 AM   #15
Ian Finch is offline Ian Finch  Australia
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Polystyrene film caps are generally very long lasting and stable for precision applications. In fact all modern types of film caps will last a lifetime if they aren't subject to abuse. If there were problems they would most likely be visible as discolouring through the clear plastic film and measurable as incorrect or unstable capacitance readings.

However, I suggest that you don't try to unsolder them unless you intend to replace them. The polystyrene film melts very easily and the leads then pull out of the plastic as if they were not attached at all. If you still want to replace or remove and refit them for some reason, solder once only and allow them to cool and harden before trying again. Do it quickly and cleanly without stressing the leads, which isn't so easy to do.
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Old 6th July 2020, 04:22 PM   #16
Rundmaus is offline Rundmaus  Germany
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I won't touch anything that doesn't degrade with age. So only the electrolytics as it seems.

Still unsure about those carbon film resistors.
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