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Old 21st April 2006, 05:05 PM   #1
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Join Date: Nov 2004
Location: Halifax, N.S.
Default Humming Zen V4

Hi all,

I've had my Zen V4 running for a while now with only one remaining problem (thanks to those who helped me with the last ones! :-). The amp exhibits a fairly loud hum.

I've constructed it dual-mono in the same chassis (two IEC AC connectors and everything), so I didn't put two rectifier bridges on each channel as depicted in the schematic. My simple grounding scheme is depicted below (if I can figure out how to attach a picture). If you're familiar with the V4 board from Pass DIY, you'll know that the left-bottom bolt hole is connected to PCB ground, which is then supposed to be connected to chassis. But when I was tapping the holes in the heatsink, of course I broke a tap in that hole, so I re-routed the ground to another PCB bolt. Chassis ground is the heatsink, because the rest of my case is made of wood.

I've tried a couple of things so far - basically making sure that both channels were separate. This seems to be the case now.

When I was testing the amp on my test speaker, I didn't notice any hum, but I assumed this was just due to really poor frequency response on my test speaker ($20... new). But it turns out that I get the hum when the inputs for both channels are connected - I would only test one channel at a time.

I have a passive pre-amp and sure enough, when I crack open the case, all four ground lugs on the RCAs are connected by one big wire. Could this be the problem, or do I need to bust out the second rectifier bridges?

thanks,
Jeremy
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Old 21st April 2006, 06:40 PM   #2
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Join Date: Nov 2004
Location: Halifax, N.S.
Default Second Rectifier Bridge

Well, it would seem I didn't search hard enough:

http://www.diyaudio.com/forums/showthread/t-25662.html

In this thread (which I ran across looking for something else), Mr. Pass recommends using the second rectifier even in mono.

Just a couple of questions about this before I go ahead with it. Does the isolating bridge really need to be 35A? I've got some spare 25A bridges sitting around which I could use...

Also, do these need to be mounted on the sinks? This would be a real pain in the neck - removing the sinks at this point would require some major effort. :-)
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Old 21st April 2006, 06:49 PM   #3
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Join Date: Aug 2002
Location: Near to the Pacific Ocean
25A is acceptable, IMHO.
No current would flow through it in normal woring condition.
Only when there is a problem, the bridge will work as a current bride to the life protective earth, but in short time till the fuse blows off. I think that using the right size of fuse is essential for overall safety.

Regards
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Old 23rd April 2006, 05:21 AM   #4
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Join Date: Nov 2004
Location: Halifax, N.S.
Default !

Thanks for the help again jh6you. :-)

Well it works! The hum is gone - after nearly two years of off-and-on work on this thing, my Zen V4 is finally working as well as I'd hoped. The next one will probably be an EL84 PP UL. :-)

I'll get to posting some pictures at some point. Maybe after this album. hehe

- Jeremy
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Old 26th April 2006, 09:30 AM   #5
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Join Date: May 2004
Location: TONGEREN
Hi,

I'm buisy with building an Aleph 3 now :-) small remark on you next project I've a home made EL84 but i've have changed it into triode setting it has more control over the bass driver but u reduce the outputpower but u have a better sound. So if you have some high rendement speakers you should go for the triode setting for the PP 84 :-) with no feedback


Greetz and good luck with your tube project
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