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How to cure buzzing chokes/transformers?
How to cure buzzing chokes/transformers?
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Old 15th October 2018, 08:52 PM   #101
maxhifi is offline maxhifi  Canada
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I do make a better than decent living as an electrical engineer, however I mostly work with power systems, and industrial controls. I think microelectronics has become a real niche market, with not so much opportunity locally. It is definitely one of the most interesting parts of electrical engineering, but with so much globalization I don't see it being cost effective any time soon to do it in locations where the cost of living is high. I will keep going as a hobby though, it does keep the brain cells firing and I find it always engaging.

One aspect which I find a constant limiting factor, both in hobby activities and also to a lesser extent professionally, is I think I have an inadequate knowledge of chemistry and materials. I don't have any education in chemistry beyond the first year organic and inorganic university courses which all engineers need to take, and it bothers me that I have no intuition about what sort of reaction will be exothermic or endothermic, what will need oxygen to react - what solvents are compatible with what solutes. If I could take myself back to school, I would focus on materials and chemistry, since they're the basis of almost everything we do. Even this process of encapsulating the transformer, I had to regard the chemistry portion as black magic, instead of really understanding it. For example, when to apply heat, if I should dilute something, etc. It could have been more methodical if I knew more about how varnish works.

I really appreciate all the advice and encouragement on the forum.
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Old 15th October 2018, 11:28 PM   #102
trobbins is offline trobbins  Australia
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Top effort maxhifi.

I notice you didn't determine the level of 'rustle' and how much that was attenuated:
http://www.extra.research.philips.co...956_57-110.pdf
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Old 15th October 2018, 11:43 PM   #103
maxhifi is offline maxhifi  Canada
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Quote:
Originally Posted by trobbins View Post
Top effort maxhifi.

I notice you didn't determine the level of 'rustle' and how much that was attenuated:
http://www.extra.research.philips.co...956_57-110.pdf
Very interesting. Rustle puts a name to the noise I've been chasing all along. It is the main quantity which has been attenuated by impregnation of the choke. I didn't measure it, but when I had the completed amplifier beside the one which was original, I could switch the finished one on, and hear a very small hum when I was up close. Then the original one would warm up, and the buzz would be right there. I would estimate the attenuation to be on the order of 15dB. It's enough to render it inaudible, whereas before it was quiet but always there.

It's also the most annoying sound - a bit of hum isn't that big of a deal, but the rustle is really annoying.

It's a bit of a strange name to apply to something which sounds more like a raspy buzz, than for example the rustle of leaves.

The only downside to all this, is I'll be more likely to forget the amplifiers are on now!
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Old 15th October 2018, 11:47 PM   #104
trobbins is offline trobbins  Australia
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'Rustle' reminds me of the microphony term that never did catch on called 'signal to clang ratio'.
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Old 15th October 2018, 11:48 PM   #105
TonyTecson is offline TonyTecson  Philippines
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How to cure buzzing chokes/transformers?
oh, another side, the traffo end bells can also vibrate causing buzz...

there are end bells that are made of thin sheets....
so in such cases, i mix epoxy on the hollow of the end bells so that about 4 to 6 mm epoxy build up is deposited...
this ensures a quieter traffo......you can include this in your bag of tricks...
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Old 15th October 2018, 11:52 PM   #106
maxhifi is offline maxhifi  Canada
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Quote:
Originally Posted by TonyTecson View Post
oh, another side, the traffo end bells can also vibrate causing buzz...

there are end bells that are made of thin sheets....
so in such cases, i mix epoxy on the hollow of the end bells so that about 4 to 6 mm epoxy build up is deposited...
this ensures a quieter traffo......you can include this in your bag of tricks...
On these transformers, the end bells are sturdy stamped steel. When I was initially troubleshooting the issue, I tried squeezing them, and cupping my hands around them. The only way I could reduce "rustle", was to hold my thumb over the choke's air gap. I think the varnish has done a great job of sealing this up, and preventing noise from escaping.

I'm going to try that if I ever have this issue again though. I think these old RCA amps are the worst case I've encountered.
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Old 15th October 2018, 11:56 PM   #107
TonyTecson is offline TonyTecson  Philippines
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How to cure buzzing chokes/transformers?
yes, there are end bells that are made from thick sheets....
so they may not need the epoxy treatment...
in other cases that i encountered, an aluminum sheet sized enough to fit the hollow of the end bells, 4 mm thick was used using strong adhesives...

anyway, most of this are encountered using end bells for 1 3/4 in cores, although i had one case with a 1 1/4 inch core, so it is a case by case basis...

clamping chokes harder btw, increases their inductance more than you realise...
so the varnish treatment works best if you want the inductance stay the same while reducing the noise..
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Old 16th October 2018, 02:37 AM   #108
maxhifi is offline maxhifi  Canada
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Quote:
Originally Posted by trobbins View Post
'Rustle' reminds me of the microphony term that never did catch on called 'signal to clang ratio'.
Hah that's even better than rustle!
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Old 16th October 2018, 02:39 AM   #109
maxhifi is offline maxhifi  Canada
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Quote:
Originally Posted by TonyTecson View Post
yes, there are end bells that are made from thick sheets....
so they may not need the epoxy treatment...
in other cases that i encountered, an aluminum sheet sized enough to fit the hollow of the end bells, 4 mm thick was used using strong adhesives...

anyway, most of this are encountered using end bells for 1 3/4 in cores, although i had one case with a 1 1/4 inch core, so it is a case by case basis...

clamping chokes harder btw, increases their inductance more than you realise...
so the varnish treatment works best if you want the inductance stay the same while reducing the noise..
That's a very big transformer! Do you varnish output transformers too, or just power TX?
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Old 16th October 2018, 03:07 AM   #110
TonyTecson is offline TonyTecson  Philippines
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How to cure buzzing chokes/transformers?
both power and OPT's get dunked in varnish...

but for OPT's not so elaborate as with power traffos...
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