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Hum issues - Zkit 4+ Zkit 5 (Read 2086 times)
testingthevalves
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Posts: 2
Hum issues - Zkit 4+ Zkit 5
05/24/11 at 02:56:20
 
Hi,
I'm a valve first timer who's trying to get the most out of this beautiful kit.

I bought two of them (2* zkit 4 each with it's zkit 5 power supply) and I have the same problem: everything works, but hum is beyond what I'd think acceptable. I know I'm doing something wrong. Thank you for pointing me in the right direction.


If I  am not using a pot and directly wiring it to any solid state amp I've tried, I get a loud buzz. I NEED to attenuate the output to be able to make use of the preamp. Too bad.


One of the kits is in a grounded case.
The other one, is sitting on my bench. No difference.
Both hum too much.

As a valve, I am using the Electro-Harmonix 12au7
I had to buy some sockets as I have found two seven pin valve sockets in each kit inappopriately - not a big issue btw.

I've wired the power supply in air, followign carefully the schematics, with a couple of 20cm wires going to pins 2 and 5 of the rectifyer tube, which looks like starting up after 10 seconds of power.

I am using 220 and the primary mains series wired.
Voltage output from the power supply looks correct.

All voltage wires sit away from signal path.
Should I post some photos?
Is there something I should check beyond voltages and evident shorts?

Thank you so much
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« Last Edit: 05/24/11 at 02:57:12 by testingthevalves »  
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Hajj
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Posts: 33
Re: Hum issues - Zkit 4+ Zkit 5
Reply #1 - 06/07/11 at 08:45:38
 
Posting some pics will definitely help.
Regards
Nick
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speakerfritz
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Posts: 13
Re: Hum issues - Zkit 4+ Zkit 5
Reply #2 - 02/20/12 at 18:28:24
 
may have nothing to do with your hum/buzz problems, but it doesn't hurt to check.  I had a buzz/hum problem with a zbox.  did all the usally testing of parts and everything checked out.  then I did some cable maintenance moving and re-bundling wires. found a few cold solder joints but the problem was still there.  Someone on the DIYAUDIO forum told me to check pin 9 to see if it was grounded.  pin 9 is the center tap of the heaters.  in the zbox, the heater circut is AC and floating with no ground.  so I tried it.  The box is dead quiet now.  I sent steve and email asking if there was a reason why I shouldn't do this and never got a reply.  The grounding of the center tap gives the AC circut a DC ground reference.  It worked and was pretty easy to implement.  It can't be done if the AC heater circut already has a ground.  One other thing I was looking into that I decided I could not do was the common practice of adding 100 ohm resisters to each leg of the heater circut.  I decided against this since the current draw would be .1 amps and it looks like the supply only has .3 available.

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