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.
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.
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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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...
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...
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.
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!
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!
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Jim 6L6 - Tallboy is the same as Shorty LxW (I don't have the numbers handy) and it's 1" taller. So I'll simply do another L bracket and put a little more air above and below the transformer.
When that's done, my buddy has 4 monoblocs that will need CRC power supplies and who knows what on the boards. He said there are toroids in already, so that's a good start. I'll be picking up 2 of the monoblocs from him.
Picture attached is the end goal.
When that's done, my buddy has 4 monoblocs that will need CRC power supplies and who knows what on the boards. He said there are toroids in already, so that's a good start. I'll be picking up 2 of the monoblocs from him.
Picture attached is the end goal.
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I'm surprised too. Back up a little: the original diagnosis was spikes at 60Hz, 120Hz, 240Hz, 360Hz, something like that, so: rectifier current ground loop stuff. For sure this is not fixed by the new transformer; it has been fixed by changing the wiring loop, especially for the rectifier and capacitor returns.
Still, nice and congrats that it is fixed, but anybody else out there thinking they can fix their hum with a new transformer - think again
Jan
Jan, you're right. The fix was much more than the tranny. I have all new CRC power supply boards, proper grounding, changed from single to dual rectifier bridges, and a new transfomer. Plus some work on the boards. It's just my Hammonds weren't getting the job done, so I switched to the Avel Lindberg. That was the final thing, and it did the trick.
Tallboy is done. 2nd one moved a lot faster since I knew what I was doing!
DC offset is <5mV
Bias is set to get me about 23W per MOSFET.
When I hook it all back up into the horn setup, I can tell this made a nice difference!
However... I can still hear a little bit of noise. I'm hearing it when I get close to my unpadded JBL 375 compression drivers - very efficient speakers.
Would playing with a CRCRC power supply potentially make a difference?
Next up - rework 4 monoblocs I'm picking up at a friend's house tonight. That will keep me busy the next few weeks!
DC offset is <5mV
Bias is set to get me about 23W per MOSFET.
When I hook it all back up into the horn setup, I can tell this made a nice difference!
However... I can still hear a little bit of noise. I'm hearing it when I get close to my unpadded JBL 375 compression drivers - very efficient speakers.
Would playing with a CRCRC power supply potentially make a difference?
Next up - rework 4 monoblocs I'm picking up at a friend's house tonight. That will keep me busy the next few weeks!
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