Humming Zen V4

Diomedian · 21st April 2006, 04:05 PM

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

Diomedian · 21st April 2006, 05:40 PM

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. :-)

jh6you · 21st April 2006, 05:49 PM

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

Diomedian · 23rd April 2006, 04:21 AM

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

Szyderca · 26th April 2006, 08:30 AM

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

21st April 2006, 05:40 PM	#2
Diomedian diyAudio Member Join Date: Nov 2004 Location: Halifax, N.S.	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. :-)

23rd April 2006, 04:21 AM	#4
Diomedian diyAudio Member Join Date: Nov 2004 Location: Halifax, N.S.	! 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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21st April 2006, 05:49 PM	#3
jh6you Account Disabled 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

26th April 2006, 08:30 AM	#5
Szyderca diyAudio Member 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