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Post subject: DRRI hum?? - Help please!
Posted: Fri Jul 16, 2010 10:35 pm
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Location: Northern Calif
I'm having trouble tracking down a loud hum when at 10. I thought it was my pedal board, changed all cables, new Voodoo Lab brick, power conditioned going through a Monster Pro 2500. Tried each pedal one at a time, still hum. I plug my guitar straight into the amp (nothing in the chain), still hum. Not as loud, but still hum. Could it be tubes? I just changed to all new tubes, and set the bias on my Tung-Sol 6V6GT power tubes to 23~25. Any ideas would help!

Thanks.


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Posted: Sat Jul 17, 2010 1:15 am
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Hi,

Does it appear suddently? It is 50 Hz from AC supply? have you got a good earth?

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Posted: Sat Jul 17, 2010 7:39 am
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It does appear as soon as I turn up my amp. I'm not sure what you mean by good earth or 50Hz from the power supply, I assume clean power?? I do have a Monster Pro 2500 power conditioner that I plug everything into. It gives me a constant 121-122V. I also have a Voodoo Lab power brick with isolated 9V connections for each pedal. I took each pedal out of the chain, tried it with AC and with battery, no change. I also turn my amp up with no input cables, bare amp. It does hiss, not as loud, but still loud enough to be recorded. Thats why I'm wondering if it could be a power or rectifier tube. Even though I have all my connections going through good clean power, can I still get interference from things in the same room like my computer, wireless access point, wireless house phone, cell phone chargers? I thought that's what the Monster Pro eliminates.


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Posted: Sat Jul 17, 2010 9:21 am
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Ok, we try to find where is is located, It could be a valve, sometimes filement are very sensitive, but i'm not conviced.

Your amp has different sections:

AC/DC supply, 2 preamp, 1 reverb, 1 vib and 1 push-pull with dephaser.

Let's investigate with valves (no danger)
(Operations shall be done amp off and unpluged)

1. Remove V1 clean channel preamp --> Hum Y/N N --> Put back
2. Remove V2 Vib channel preamp --> Hum Y/N N --> Put back
3. Remove V4 reverbmixer --> Hum Y/N N --> Put back
4. Remove V5 Tremolo --> Hum Y/N N --> Put back


By the way, does the hum is affected by the volume?

Let us know your investigation.

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