Does anyone care to ask an amplifier designer a technical question? My door is open.

I closed the cable and fuse thread because the trolls were making a mess of things. I hope they dont find me here.

I design Tube and Solid State power amps and preamps for Music Reference. I have a degree in Electrical Engineering, have trained my ears keenly to hear frequency response differences, distortion and pretty good at guessing SPL. Ive spent 40 years doing that as a tech, store owner, and designer.
Perhaps someone would like to ask a question about how one designs a successfull amplifier? What determines damping factor and what damping factor does besides damping the woofer. There is an entirely different, I feel better way to look at damping and call it Regulation , which is 1/damping.

I like to tell true stories of my experience with others in this industry.

I have started a school which you can visit at There you can see some of my presentations.

On YouTube go to the Music Reference channel to see how to design and build your own tube linestage. The series has over 200,000 views. You have to hit the video tab to see all.

I am not here to advertise for MR. Soon I will be making and posting more videos on YouTube. I don’t make any money off the videos, I just want to share knowledge and I hope others will share knowledge. Asking a good question is actually a display of your knowledge because you know enough to formulate a decent question.

Starting in January I plan to make these videos and post them on the HiFi school site and hosted on a new YouTube channel belonging to the school.

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Roger and George,
Thanks for the insights into the 6SN7 tubes in preamps.  I have a tube preamp that uses 4 of these tubes, along with a rectifier, and have upgraded from NOS Sylvania and GE tubes to both the Psvane CV181-T and the Shuguang CV 181-z tubes.  The new tubes are simply remarkable, far better than the NOS tubes (other than a handful of the Holy Grail tubes) and with good longevity.  I will admit that they are microphonic.  Thanks again for your information and furthermore for you taking the time to participate in this forum.  Your insights are most enlightening.  
I recall that in a thread here a while back Kevin Deal of Upscale Audio also mentioned very emphatically that 6SN7s are often microphonic.

FWIW, though, during the approximately seven years in which I owned a VAC Renaissance 70/70 MkIII, which uses four of those tubes, at various times I used a total of about 20 of them. All of them were the GTB version, with the majority being NOS tubes of various makes from the 1950s and 1960s, and the rest being current production. None were microphonic initially, as determined by lightly tapping on them with a pencil eraser. Two of them eventually became severely microphonic, however.

Best regards,
-- Al


I will measure the Axiom with a meter. Actually, after considering your comments regarding my experience with the passive, I reinstalled it in my system. This time I reduced the gain of my phono preamp, and I’m giving it another go ‘round. I’m using a variety of albums by a variety of artists in a variety of genres. I made my judgement in haste the first time, because the first LP I played sounded bright. I know better than to make a judgement so quickly without giving the component in question some time. I’m glad you questioned my impressions! This passive was never intended to take up residence in my main system, but I’m beginning to think a higher quality passive unit may indeed be a good fit. As to the phono preamp, I would actually prefer to used a tubed unit if possible. I appreciate you taking the time to discuss the details of these things. Clio gave me a contact email for getting information about products, which is outside the scope of this thread. I will continue to evaluate this passive in my system for awhile to get a handle on its strengths and weaknesses. It is sounding quite nice. Maybe it was revealing a bright recording that the preamp was taming..? Anyway, I’ll keep at it. Thank you again 
None were microphonic initially, as determined by lightly tapping on them with a pencil eraser. Two of them eventually became severely microphonic, however.

Yes Al there are so many that are and owners don’t even know they have them, they think it’s "euphonics" but in fact echo.
I test "every tube" not just 6SN7’s that come by me, with a tap of the fingernail and watching the oscilloscope.
Or in the listening system turn the volume up to normal and get someone to listen in front of the speaker/s while you flick gently with the finger nail.
A "bonk" microphonic, with a "tinkle" can be loose/shaky heater filaments as well.
A "runway" bonk (rotating feedback) that just gets louder and louder, a severely microphonic tube have your spare hand on the poweramp power switch.

Cheers George

 I’ve tried power cords from Shunyata and XLO and have not heard any difference.  Shunyata one was there flag ship that was selling used for almost 2K. Nada. 
 That was before I really got into the hobby and started building some things and learned a little bit about how this stuff works. I thought there was something wrong with me that everybody could hear these drastic changes and I couldn’t!