Postby YoungDave » Wed Jan 03, 2018 1:59 am

This issue of the audible hum reminds me of a phenomenon I recently encountered. My old phono preamp uses DC for the tube filament heaters, and its power supply box recently began to give out a mechanical hum - not unlike a refrigerator in the next room. I could place my hand on the power supply box and feel the hum or buzz. I suspected a failing transformer, where the laminations were separating or something like that.

Long story short, and thanks to Manley Labs support, it was due to the monolithic full-wave rectifier for the tube heater circuit - a $3 part. This rectifier had not failed in the usual way, that is, one diode opening or shorting, resulting in a blown fuse or no preamp operation. It failed by permitting leakage current that was seen as a heavy load to the transformer, causing that transformer to behave as though it was working too hard - making a mechanical buzz. I replaced the rectifier myself and once again have silent operation.

Now I know that the ADS does not use tubes, but it obviously uses a transformer and at least one rectifier - I wonder if the problems might be caused by a bad rectifier loading down the transformer? There are a lot of different rectifiers out there - maybe a bad lot or maybe just trying a heavier-duty one...

Of course, the issue is largely academic as the ADS is new and they must surely still be under warranty - but a buzzing transformer is not necessarily a failing transformer - one should investigate downstream components, too.
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Postby Marc » Wed Jan 03, 2018 10:46 am

glide wrote:
Marc wrote:I would suggest to reach out to your dealership and they would be able to help you out and get you back up and running!

How? Have VPI actually addressed the issue yet?

Yes, we completely switched transformers for the ADS and they now go through additional screening before shipping. It has been quite some time since we have had anyone contact us about a hum in the current version of the ADS.
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Postby JimTimP » Wed Jan 03, 2018 7:06 pm

What makes it more difficult is not every (older) unit exhibits the hum issue. I've had mine for almost a year, and never heard any hum. Even before I got the PS Audio P5 this past November. It was connected to a rather ordinary surge strip.

I'm still convinced the hum issue is related to dirty power. But who knows. Anyone having a hum issue with the ADS connected to a power regenerator like a P5 or P10???
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