[toddc2]

I installed some NOS RCA VT-231's in my LS100 yesterday. The first thing I noticed was a low level tone that would rise in volume with the music. It sounds like a test tone and is in the right channel only.

I decided to let the tubes run in and hooked up a DAC to play continuously via the XLR inputs. The right channel tone went away. Now the left channel is clipping with strong bass notes, but that's an issue for another thread...

Getting back to the test tone issue, I looked up the output impedance of my Zesto Andros phono stage and it seems pretty high at 10k. The input impedance of the LS100 is listed at 39k, which seems pretty low. I have read that that the general rule of thumb is 1:10 (output:input) so I suspect I've just created an expensive compatibility problem.

I haven't tried any trouble shooting yet (swapping tube positions, swapping tubes, etc) although I can say the tone was not present with the Russian current production tubes that came with the used LS100.

Does anyone have experience with the Zesto/LS100 combo or suggestions on what to try?

Todd

[dminches]

I installed some NOS RCA VT-321's in my LS100 yesterday. The first thing I noticed was a low level tone that would rise in volume with the music. It sounds like a test tone and is in the right channel only.

I decided to let the tubes run in and hooked up a DAC to play continuously via the XLR inputs. The right channel tone went away. Now the left channel is clipping with strong bass notes, but that's an issue for another thread...

Getting back to the test tone issue, I looked up the output impedance of my Zesto Andros phono stage and it seems pretty high at 10k. The input impedance of the LS100 is listed at 39k, which seems pretty low. I have read that that the general rule of thumb is 1:10 (output:input) so I suspect I've just created an expensive compatibility problem.

I haven't tried any trouble shooting yet (swapping tube positions, swapping tubes, etc) although I can say the tone was not present with the Russian current production tubes that came with the used LS100.

Does anyone have experience with the Zesto/LS100 combo or suggestions on what to try?

Todd

Have you tried listening to another source?  I doubt you would have an impedance mismatch with one set of tubes and not another.

I would do 2 things:

1) Try listening to another source to see if the test tone and clipping issue is still there.
2) I would swap the 6SN7s from left to right, etc. and see if the issue changes channels.

[toddc2]

Thanks! Yes I tried different sources. The first source was my turntable via the Zesto and the second source was my DAC.

I will try swapping tube positions after I run them in for awhile.

[vinyl_lady]

I ran a Zesto Andros with a ModWright 36.5 DM pre amp without any problems. So at least with the 36.5 there were no compatibility issues with the Andros.

[toddc2]

Thanks, that's a good data point!

UPDATE on the clipping: I use Amarra Symphony with room correction for my digital playback. I didn't retake the measurements after swapping preamps. I turned off the room correction and the clipping is gone.

[toddc2]

UPDATE on the tone issue: The tone went away after about 50 hours of burn in (both my turntable and DAC are now OK as sources). However, the same tube is now ringing, my guess is that it's gone microphonic on me. Too bad because it sounds great when it's not ringing like a church bell.

Oh well, back to the dealer with that tube. I'll have him check the replacement tube for microphonics before sending it out.

[sunnydaze]

I installed some NOS RCA VT-321's in my LS100 yesterday. The first thing I noticed was a low level tone that would rise in volume with the music. It sounds like a test tone and is in the........

Hmmmmmm........

Maybe the problem is that you are using the VT-321 tube instead of VT-231?

 

[toddc2]

Hmmmmmm........

Maybe the problem is that you are using the VT-321 tube instead of VT-231?

 

Oops, fixed the typo. Thanks...