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Taming Hum on two pre-owned Aleph Mini's
Taming Hum on two pre-owned Aleph Mini's
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Old 28th January 2019, 03:36 PM   #21
mpmarino is offline mpmarino  United States
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Me thinks that either you'r drawing too much current for the Hammonds, or there is substantial DC in your mains making the EIs buzz. Usually EIs don't do this badly.

Have you tried halving the current only running one channel?

Maybe drag the whole thing to a friend's house and see if they buzz there? Find a friend in a remote cabin with only incandescent lamps running

I hate mechanical buzzing, and usually have the same problems -so much that I avoid using toroids at my house. I wish you luck with this annoyance.
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Old 29th January 2019, 04:25 PM   #22
rhthatcher is offline rhthatcher  United States
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I tried the single channel only test to drop the current, great idea!



Unfortunately the trannies still buzz. I swapped secondaries. Same story.
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Old 30th January 2019, 05:37 PM   #23
rhthatcher is offline rhthatcher  United States
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I'm going to go on the working assumption that the Hammonds are not going to work no matter what I try.


I contacted Plitron. US$1,200 minimum order and 10-12 week lead time. Nope.


Next call was to Avel Lindberg. 2 transformers are on the way.
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Old 30th January 2019, 06:17 PM   #24
Dennis Hui is offline Dennis Hui  Canada
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Taming Hum on two pre-owned Aleph Mini's
Holy cow! I guess I'm never ordering from Plitron again.
They used to have a $200 min order and had a webshop. Since
they got acquired, that's all gone.

I was going to ask what happens if neither channel is attached to
the power supply (ie, no load)
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Old 30th January 2019, 07:29 PM   #25
rhthatcher is offline rhthatcher  United States
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Dennis,


I disconnected the secondaries. No rectifiers, CRC, or amp boards. Simple as can be. Buzz....


I'm glad I'm using quick disconnects, not solder on transformer and bridges. It makes these tests go quite fast.
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Old 31st January 2019, 02:19 AM   #26
mpmarino is offline mpmarino  United States
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Quote:
Originally Posted by rhthatcher View Post
Dennis,


I disconnected the secondaries. No rectifiers, CRC, or amp boards. Simple as can be. Buzz....
Well then, that's never gonna work!

~~~~~~~~~~~~~~~~~~~~~~~~~

In case you haven't seen....

Mains DC and Transformers

Rod talks about mains DC, how to test for it, and how to block it.
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Old 31st January 2019, 02:36 PM   #27
Eric is offline Eric  United States
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Taming Hum on two pre-owned Aleph Mini's
I've had good luck with Antek Transformers. Plenty to choose from, no minimum and fast shipping.

Another possibility is adding a snubber network to the transformer secondaries. This can be added across the terminals of your rectifiers. Given what you have, this will be a somewhat random "try it and see" approach. Usually something like 10R-100R 1/4w resistor paralleled with a 0.1-0.47uF 65v film cap across each diode. I've had good success with this approach taming a noisy transformer, but you have to play around with values and sometimes it just doesn't work.

For more room in your chassis, do your CRC boards fit the back panel if you mount them standing up? Then, you have more room inside for the transformer...
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Old 31st January 2019, 02:47 PM   #28
6L6 is offline 6L6  United States
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Taming Hum on two pre-owned Aleph Mini's
Quote:
Originally Posted by rhthatcher View Post
Any other ideas on transformers? I'm assuming these won't work, so I'm looking for a "one and done" solution. 2x 15V or 16V or 18V @ 200VA-ish

AS-2215 - 200VA 15V Transformer - AnTek Products Corp

The AS-series have a shielding band wrapped around the transformer and in my experience that greatly helps with magnetic AND mechanical hum. I've had great luck with them.
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Old 4th February 2019, 11:44 AM   #29
rhthatcher is offline rhthatcher  United States
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It was a good weekend! My transformers arrived. I got Avel Lindberg 230VA 15+15V (model Y236607) transfomers.


I tested the with a temporary wire-nut hookup on the bench with the transformer out of the chassis. Hum is fixed from speakers, and no transformer buzz! Excellent. I got some L-Brackets at home depot hoping I wouldn't need to put a bolt through the amp's faceplate. With a little drilling on the bracket, and drill/tap on the chassis bottom I got the transformer in. It's a hair off center because there was a preexisting tapped hole next to where I would have drilled. I took advantage. The top will actually fit on the amp and not touch the transformer. Whew!


I'm getting +/- 19.9V rails.

DC offset is 22mV on one channel, 23.3mV on the other.


Help me make sure I get this one right.

Bias voltage = .553V
current = .553/0.47 = 1.176A
Mosfet is burning 1.176A x 19.9V = 23.4W Within papa's range. (22-25W?)
I ran the amp for about a half hour and the bias settled in the .553 range. It was .565 when cold.



Right now pots are in to set DC offset and bias. I'm thinking I leave the bias alone and replace with a fixed resistor.


Any recommendations on how much I should work to fiddle with the DC offset? I know zero is the goal. I think I've read 20mV is acceptable. How much effort should I put into chasing zero?


I've learned a ton on this amp. The "Tallboy" amp should go a lot faster after learning so much on this one!
Attached Images
File Type: jpg Avel Trans Test.jpg (984.1 KB, 68 views)
File Type: jpg Avel mounted.jpg (990.6 KB, 66 views)
File Type: jpg Avel wired.jpg (997.0 KB, 65 views)
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Old 4th February 2019, 12:06 PM   #30
6L6 is offline 6L6  United States
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Taming Hum on two pre-owned Aleph Mini's
Looking good! Congratulations on your success!

20mV is fine. You'll find that to will move around with air currents when the lid is off, so you'll never get it exactly to zero.
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