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Old 25th June 2004, 03:51 AM   #1
jj69 is offline jj69  United States
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Default NEWBIE needs help-static in one channel of preamp

Hello all,

I'm new here. I believe I've followed all the forum rules with this first post, but have mercy if I've missed something. I think I'm in the proper forum. The preamp in question uses a tube in the output stage, but the problem I'm having is not necessarily with the tube. The preamp is also a commercial unit, but the repair will (hopefully) be DIY.

My problem is with a newly acquired (used) Audio Note M-Zero preamp. There is a scratchy sounding static-like noise coming out of the right channel. The noise does not shift channels, even if I turn the balance control all the way to left. It does get louder when I turn up the volume. The sound is generally constant not just when I touch the volume control. I also notice that the right channel is slightly louder than the left channel, requiring adjustment of the balance control to an off-center position. The former owner never had a problem, so this could have occurred in transit. The unit looks mint and unabused, and cannot be more than a few years old.

I have tried the unit with different amplifiers, with different cables, and using different source components, so I have isolated the problem to the preamp itself. I have also tried setting up the unit in different rooms in the house, so I don't believe this is an interaction with an external component. The static does shift channels if I reverse the Left and Right interconnect cables to the amplifier.

While I am not technically inclined, my guess is that something is wrong with the volume control pot. However, I am not sure whether this is something that can be cured with simple contact cleaner. Does the fact the static is in only one channel (and does not move even when the balance control is adjusted) indicate that there is a problem with something other than the volume control?

For those who aren't familiar, the M-Zero is a fairly simple affair using one tube in the output stage. I have since dropped in my old Antique Sound Lab Wave Line 1 preamp, which is a very similar single-tube design. Not only is the static gone, but I noticed that there is less background hiss in both channels with the ASL when the volume is turned up.

I guess my questions are as follows:

[1] Do you think the problem is indeed with the volume control pot?

[2] If it is the volume control, is it something that basic contact cleaner can remedy?

[3] If replacement of the pot is absolutely necessary, I will have to pay someone to do the work. I am not skilled at soldering, and I don't have the necessary tools. If I must pay for service, should I have it replaced with an actual attenuator, and if so, is there a suitable drop-in replacement for the M-Zero? I would think the M-One or M-Two use a better attenuator, so I'm hoping there's a direct drop in part. I have e-mailed Audio Note UK on this, but so far no response.

I apologize for the long post, but I wanted to cover all bases. If anyone has any advice or input, I would greatly appreciate it.

Thanks in advance,
Joe
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Old 27th June 2004, 11:54 AM   #2
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Hi Joe

Sorry to hear of your problem. Do I think its the volume control? No, my opinion is that it could be the coupling cap that is causing the noise. I built a line stage one time that had the same problem and changing the coupling cap took care of the noise.

Best of luck,
Joe(burnedfingers)
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Old 27th June 2004, 02:03 PM   #3
benny is offline benny  Australia
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i was once probing one of my amps, and when i touched the meter probe to the amp, i could sudenly hear the radio through it!!!! only faintly, but i could still hear it!!! weird as hey??? maybe you got some wire or something in there that's just the right length to be picking up some sort of interfearance in your area? far fetched i know...
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Old 27th June 2004, 02:35 PM   #4
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Since the noise changes with volume, the culprit will most probably be between your preamps input(s) and the input to your volume pot. Have you tried swapping between different inputs? If that doesn't change it, start looking for bad components/solder joints from your selector switch to your vol pot.
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Old 27th June 2004, 10:32 PM   #5
jj69 is offline jj69  United States
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Hey guys,

Thanks for the responses. I actually heard back from Peter at Audio Note. He's almost positive the problem is, in fact, a bad 6111WA tube. It just needs to be replaced. Normally, that would pose no problem for me, but it turns out these 6111WA tubes need to be soldered directly to the board. I think they have leads attached to the bottom rather than pins. Unfortunately, this is something I'm not comfortable doing at my skill level. I can't even determine the right way to disassemble this preamp.

Does anyone here have experience "operating" on an Audio Note M-Zero or similar unit?

- Joe
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Old 27th June 2004, 10:49 PM   #6
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Hi,

Quote:
6111WA tubes need to be soldered directly to the board. I think they have leads attached to the bottom rather than pins.
Actually, that's not so hard to do.
You just need to unsolder the leads one by one untill you can pull the tube from the PCB.
Just be careful not to damage the board.
Once you have the new tube soldered in the excess lead lenghts can simply be cut flush with the PCB.

Here's a link with pinout and datasheets:

6111WA

Cheers,
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Frank
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