Humming Zen V4

[Diomedian]

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]

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.

 

[jh6you]

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]

!

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]

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