First three bars? 😜
Mystery of the whistling amplifier
I replaced the manufacturer-supplied low-power tubes (two 12AU7 in the pre-amp section; four 12AT7 in the amp section) in my VTL integrated amp with NOS Telefunkens from Vintage Tube Services. After a few months I started hearing hissing and whistling through the speakers. It happens regardless of the source (DAC or the phono preamp).
I read here and elsewhere that this was probably caused by about-to-fail preamp tubes.
Here're the things I've tried to address this:
1. I took the 12AU7s out and switched them between their sockets. I also reseated them in their original positions. These measures made the problem go away for a while. Then it came back.
2. I put the manufacturer-supplied tubes (JJ Elec ECC81) back in, and that "solved" the problem for a day or two; then it didn't.
3. A Youtube video recommended scraping the pins shiny with an x-Acto knife blade. I did this, and it worked for a while. Doing it again, perhaps more thoroughly, also worked for a while, and seems to have reduced the overall level of the sound. I also hit the pins with Deoxit after scraping.
I listen to this setup several hours a day. Sometimes, like right now, there's no unwanted noise. When it is happening, you can't hear it through loud passages at all. But of course I want to fix this.
I'd welcome any suggestions or diagnoses before bringing this to the dealer.
1. I took the 12AU7s out and switched them between their sockets. I also reseated them in their original positions. These measures made the problem go away for a while. Then it came back.
2. I put the manufacturer-supplied tubes (JJ Elec ECC81) back in, and that "solved" the problem for a day or two; then it didn't.
3. A Youtube video recommended scraping the pins shiny with an x-Acto knife blade. I did this, and it worked for a while. Doing it again, perhaps more thoroughly, also worked for a while, and seems to have reduced the overall level of the sound. I also hit the pins with Deoxit after scraping.
I listen to this setup several hours a day. Sometimes, like right now, there's no unwanted noise. When it is happening, you can't hear it through loud passages at all. But of course I want to fix this.
I'd welcome any suggestions or diagnoses before bringing this to the dealer.
27 responses Add your response
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I thought more along the lines of applied physics that geoffkait indulges in. Cute discussion starts on page 2. (from paragraph 2.2) http://www.physics.princeton.edu/~mcdonald/examples/tirepump.pdf |
I'd buy another set of tubes and try them. If they don't fix it, no worries, tubes don't last forever. This sounds like it will be a trial and error fix since a lot of things can cause this. Cracked solder joints can do this, so a reflow of the affected circuity is in order. Check out the capacitors in the local area, as those are suspect given the symptoms. Let's call that Plan A, Plan B is to take it to a reputable dealer or, better yet, back to the factory for a fix. |
Thanks to all who responded. The problem is "solved." I tried yet another set of J&J tubes in the pre-amp section and still had hissing and popping. So I decided to take the thing back to the dealer, and replaced all six NOS Telefunkens (two 12AU7 in the pre-amp and four 12AT7 in the amp section) with the original J&J tubes the unit had been delivered with. Hissing and popping went away, and I now have six rather expensive tubes on the shelf. In truth I noticed a subtle improvement in sound with the original tubes. Not sure what to make of all this but again I'm grateful for the help and suggestions here. |