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  1. #1
    Linear Guy
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    tube preamp hum and pop

    I recently put a tube pre-amp in my system that I had on a shelf for a while. It is a generic looking 7 tube 3 stage model from Bancock. I've had the thing for 2 years now and finally got to some serious listening. I am noticing a low level hum during operation. Noticeable but not irritating yet. Also, there is a low amplitude pop in the right channel after shutting the unit down. Any suggestions on things I might do to minimize these noises would help. No board level modification suggestions please.
    Oh, btw, reason for not using much, it is just not superior to my ss pre-amp. Thanks dk

  2. #2
    Do What? jrhymeammo's Avatar
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    You may want to switch out your tubes. What tubes do you have? I've been real curious about GrooveTubes. If all of your tubes are securely placed, try tapping on your tubes with an eraser on the back of your pencil. Maybe you can figure out which tube is the cause. I'm assuming hum is coming from your speakers?

    I have to think it's your power supply though.... You got it from Bancock, but it;s designed for USA, right? just assuming you are using this in the states.

  3. #3
    Linear Guy
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    in response.....

    5 of the 7 tubes are mullard,sylvania and rca nos. The remaining two are new russian. Tapping on the tubes with an earaser is possible but how can I tell if it is the transformer? , The hum is coming from the speakers and Yes, I am here in the good old US of A.

  4. #4
    Do What? jrhymeammo's Avatar
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    If you can somehow isolate that from your tubes. Do you know any ways to significantly shield transformer from your tubes?
    My VTL phono stage doesnt have external power supply, but I havent experienced any issues with it though.

  5. #5
    Audio Enthusiast
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    Your hum may be a simple case of grounding.
    You may want to try running a ground wire from your preamp casing to your amplifier casing. Sometimes that solves the low hum. That's the least expensive alternative.


    However, I've had errant tubes cause the conditions you describe.

    My preamp was based on 12AU7 tubes. But similar rated tubes from other manufacturers would sometimes cause more hum and noise compared to others. I had a pair of ElectroHarmonics that would sound nice but had a low frequency buzz. In contrast, a pair of Phillips tubes would be more silent but did not sound as nice.

    I also had a pair of GEs that seemed to make noise and pop on one channel. I switched them from left to right and determined that the noise was coming from the tube rather than something board level.

  6. #6
    Linear Guy
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    thanks for suggestions

    I will see what I can do. It does seem worth saving . The tube preamp has its moments, particularly on vocal tracks and small combo where ther voice appears to be more dynamic and lifelike than the ss model.

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