EQUIPMENT FORUMS >> ZBOX >> zBox buzzes like a barbers clipper

Message started by speakerfritz on 02/15/12 at 02:57:05

Title: zBox buzzes like a barbers clipper
Post by speakerfritz on 02/15/12 at 02:57:05

So I got a used zbox today.  My system is dead quiet with out the box.  Real loud buzz with the box.  I'm installing it after my DAC.  switched to a few known and tested tubes but still have the problem.  I'm thinking it's a diode in the power supply since the buzz is in both channels.  anyone been down this road and find the problem.  I saw a post by someone who reported he got a buzz after three weeks but decided to unload the box rather than fix it.  the CIrcut looks pretty simple so im sure it's one of the dozen 10 cent parts.  thanks.

Title: Re: zBox buzzes like a barbers clipper
Post by Lon on 02/15/12 at 04:13:38

I don't know what it is with the ZBOX. That one reported was one I sold to Don, and I bought/buying it back from him, put it in both of my systems briefly. . . and no buzz. I've had hum with the unit before that always turned out to be a tube problem.

I put mine back in the closet, will probably put it into one of the systems soon and see if it stays quiet. Mine was rebuilt 13 months ago by Steve, and was one of the first several dozen built I think. Maybe you should contact Steve and see if he has any light to shed on these situations.

Title: Re: zBox buzzes like a barbers clipper
Post by speakerfritz on 02/15/12 at 04:23:09

I'll test the zbox this weekend.  My money is on the power supply diodes.  One is probally leaking.

I noticed the earlier ones have lower temp rated caps that the newer ones.  got a cap testers so I' go thru the power supply cap as well.

Title: Re: zBox buzzes like a barbers clipper
Post by speakerfritz on 02/17/12 at 16:54:04

Update.  All parts checked out.  No diode problems, cap problems, or resistor problems.  

All grounds check out

I taped all power wires to run right against the case.  repositioned signal lines, etc.

I have to admit, the buzz is less noticeable if I use a 4 watt per channel SE amp.  If I use 50WPC to 350WPC tube amps, the buzz is haunting.  If I use the Zbox on 130WPC to 160WPC SS gear, is just as haunting.

So things to try next.
-using two 100 ohm resistors to ground each leg of the heater supply
-reversing the phase of the heater supply
-converting heater supply to DC
-choke addition to power supply
-add more capacitance to power supply
-scrap the Zbox and clean up the wiring rats nest by using a PCB board for a Zkit4 or maybe Zkit5 and just keep the box around as a buffer (I was more interested in the Zbox, but can't spend too much more time on chasing this ghost).


Title: Re: zBox buzzes like a barbers clipper
Post by speakerfritz on 02/18/12 at 20:18:01

ok, I took this problem over to DIYAUDIO forum and the guys dove right into it.  In trying to improve the wiring lay out, 4 cold solder joints were found. two wires popped out as soon as I moved the POT.  Resolder those.  while in there I rotated the tube socket so that the AC heater lines was no longer right in the middle of the tube circuit components.  I moved the turns on the AC heater lines as far close to the tube circut as I could.  I hot glued the AC heater lines right to the case.  I bundled tied the in and out lines and moved them away from DA and AC power lines.  I relocated and hot glued the B+ line so that it was not near signal lines or AC lines and hot glued it in place.   I tested the unit out and the loud buzz hum is gone.  Now all I get is the faint backgound noise of the AC heaters and thats only if I crank everything up with no signal.

So hats off to the guys on the DIYAUDIO forum for talking me into addressing the wiring layout.  I was going to dive right into an AC to DC heater conversion and a few other things.  And probally would never have found the cold solder joints.  Pic's are up at the DIYAUDIO link I posted.  Cant figure out how to post pictures here.  

OK, edit, the system will not let me post a link to the DIYAUDIO thread.  You can do a search and find my pic's.  Best wishes.

edit: about the faint background noise that remained.  One of the DIYAUDIO forum members suggested that I ground pin 9 which is center tap for the heaters.  Grounding of the heater center tap would give the AC circut a DC ground reference.   There was a faint background hum remaining but only noticeable a full volume with no signal. I checked pin 9 and it's not grounded. I confirmed that the whole AC heater circut is floating with no grounds. I grounded pin 9 and the system when totally dead quiet. No noise at all. Awesome.


Title: Re: zBox buzzes like a barbers clipper
Post by speakerfritz on 02/18/12 at 20:21:43

just noticed I have 5 posts, so lets try the link again.  If you have the buzz problem, check this thread out. Pic's and great discussions

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