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https://www.decware.com/cgi-bin/yabb22/YaBB.pl SUPPORT FORUMS FOR ZKITS >> ZKIT 4 Support forum >> Hum issues - Zkit 4+ Zkit 5 https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1306202180 Message started by testingthevalves on 05/24/11 at 02:56:20 |
Title: Hum issues - Zkit 4+ Zkit 5 Post by testingthevalves on 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 |
Title: Re: Hum issues - Zkit 4+ Zkit 5 Post by Hajj on 06/07/11 at 08:45:38 Posting some pics will definitely help. Regards Nick |
Title: Re: Hum issues - Zkit 4+ Zkit 5 Post by speakerfritz on 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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