Aleph 1.2 transformers buzzing

[daly2k]

Hello, I am trying to solve a problem with my Plitron 2kva power transformers that I am using in my Pass labs 1.2 amps that I built 5 years ago from the Pass Labs web site. I have moved due to a job assignment and now have my amps in the same room as the speakers and at low volumes I can now hear the "mechanical buzzing and whinning" of the torrodial xformers.
There is no humming from the speakers as the amps are dead silent from an audio pt. Plitron admits that their standard xformer line products will make noise. They now have a new line of silent xformers for sale.

I have addes noise filters to the amp ac inputs and sound deadening material under the xformer. But it looks like I need to pot the transformer in a can to get it to quiet down. Does anybody know where I can get potting materials and who may sell off the shelf xformer cans? I have not contacted Pass labs to see if they have these materials but I can do that as well. thanks

[Nelson Pass]

Could be some DC on the AC power line. Try using a blocking
capacitor to take it out. (Big electrolytics, back to back, with
diodes)

[daly2k]

Just checked my home outlets. Found out I have 12volts dc coming in from the main fuse box. AC line is 118volts with 58hz.
I don't understand this but as Mr. Pass says I will build a filter to get rid of the dc before the primary of the transformers. What is a mystery to me is why my Monster 7000 which has an isolation transformer in it for low level power uses is still passing the dc. My amps are not plugged into this. I used my radio shack digital meter. The readings between ground and nuetral were small-a few millivolts. daly2k

[wuffwaff]

Hi,

I don´t think you can measure AC-line DC content with a multimeter. Normaly it is way below one Volt wich still is enough to make torroids buzz.

If you are a s unlucky as I am the DC filter won´t help

William

[vit]

Check out P-A's DC-cure

http://home.swipnet.se/~w-50719/hifi/dct01/index.html

// Vit

[daly2k]

vit thanks for the information, this weekend I will measure with my scope etc what is actually happening. I have mono amps so I assume that I will need two boards. I will locate the boards after the power switch and as close to the transformer primary as possible. I have a variac so I can check the boards at low voltage. I am in the US so we have 60hz but your design should work for this. saludos, daly2k

[Clarkcr]

Same amp, 1.5K Piltron, same problem too. Mine actually started making oscillating/throbbing sounds on one power up. The only thing I could think of was that I had an AC unit outside and a window unit keeping me cool in this Texas heat.

I will try this cap filter soution.

C

[daly2k]

Clarkcr--just for your information, I contacted Plitron. They said at the time that I built my amps (2000-the year the world was supposed to end and I wanted to go out with the best amp) their 2kva off the shelf transformers could buzz underload and I should put the amps in a different room. I did that for a few years and all was well. Now I am forced to put them in the same big room. The engineering manager at Pllitron says they now make a "quiet line" of audio power transformer designed for low noise. The pictures on their web site show them as potted transformers. They only go to 1.5kva off the shelf. Plitron would not build me some custom 2kva types since I am not a manufacturer nor would they supply me with the cans they use now. I am taking Nelson Pass's suggestion and build a filter. I will locate it after the power switch on each mono amp. The trick is to fit these parts in neatly inside the chasis for safety. saludos, daly2k

[Clarkcr]

Good luck dude. That's what I have 1.5 KVA. How close are you to completion?

[daly2k]

Give me a few weeks, I have a vacation that I "must" go on to the SF area. When I return, I will begin in earnest. Will report when I am finished. One thing that I may experiement with is removing the 6Amp chasis mount line filter (from fair radio) that I installed before the primary of the xformers. I did this because I have long AC power cords and with the extremely large 1.2kva C-L-C (8-15kuf caps per mono amp) and being single ended class A amp with a constant current draw from the socket that these wouldn't choke the amps. Maybe I am wrong. dave