DIY HiFi Forum

Posted by OzMikeH (A) on April 26, 2008 at 00:50:32

Here is what I did.

replaced the B+ diodes with Ultra fast soft recovery diodes.
replaced the Bias pots with some Bourns 10 turn wirewound ones. (because I was having problems with the originals)
make a bridge rectifier for the Bias with 1N4934 Fast switching diodes.
replaced the 220 uF Bias capacitors with low ESR 470uF.
Bias was set for 0.43V with Valve Art EL34.

There is now a soft hum from both speakers, can be heard 1 meter away.
Both channels the hum is the same so I made the same mistake on both or I made an incorrect parts choice.

There is also a bleed redidtor on each B+ supply of 330k, these were fitted a long time ago so I don't think they matter.

Where should I look for the hum? did I use noisy diodes for the Bias bridge rectifiers?

Edits: 04/26/08   04/26/08

• "Both channels the hum is the same so I made the same mistake on both" - Goneill 19:58:09 04/27/08 (6)
  • RE: "Both channels the hum is the same so I made the same mistake on both" - OzMikeH 00:58:39 04/28/08 (5)
    • Sorry...don't know about the Signature (Brian!) - Goneill 20:57:46 04/28/08 (4)
      • Hum almost gone now - OzMikeH 02:54:58 05/03/08 (3)
        • RE: Hum almost gone now - Goneill 04:10:35 05/03/08 (2)
          • RE: Hum almost gone now - OzMikeH 18:27:24 05/03/08 (1)
            • RE: Hum almost gone now - mccormick 12:36:10 05/07/08 (0)
• RE: Ella, Implemented most of Graham's mods and it hums - RHone 10:15:54 04/27/08 (1)
  • RE: Ella, Implemented most of Graham's mods and it hums - OzMikeH 06:37:45 06/25/08 (0)

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