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.
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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 http://berkeleyhifischool.com/ 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,
I recall you saying at Burning Amp a year ago that you did not like 6SN7 tubes in preamps.  I have a preamp that uses these tubes and it is the best I have ever heard in my system.  What is the problem with these tubes from a designer's standpoint?  Thank you. 
Oops, clio09, I meant to say ct0517 above. I keep conflating you two!
@ramtubes. Thank you for your reply to my questions.

You asked: “If you have a good preamp, why change?”. I’ll list a few things that have me looking elsewhere. 

1.) I bought this preamp new, and after about two years it developed an issue. Every few times I switched sources, the left channel would fail to output sound. After cycling the selector the sound would return to normal. I called the manufacturer for advice. They told me to spray the switch with contact cleaner, which I thought shouldn’t be necessary for a two year old unit, but I did as they suggested. While it was open, I noticed that there was a screw missing from the vertical board that the selector switch was attached to. When I rotated the switch, the board moved around. I installed a screw in the corner of the board where it had been missing, and it no longer moved when I rotated the switch knob. That seems to have solved the problem, but made me wonder what else could have been overlooked. 

2.) I recently bought an inexpensive, but well-reviewed phono preamp for another system. I decided to see how this stand alone phono pre compared to the built-in phono stage of my main preamp. The inexpensive phono preamp, through the tube linestage of my main preamp, sounded noticeably better. I asked the manufacturer, as diplomatically as possible, why this might be. They told me that the tube line section of the preamp is much better than the built in ss phono stage. Why include a phono stage that you know is inferior to the rest of the unit?

3.) I’ve read that the 12au7 is not the best tube to use in a preamp circuit. My preamp uses all 12au7 tubes (4 of them), and I’d like to try something that is designed around a different tube type. 

4.) This preamp is made by one of the manufacturers whose amplifiers left you “not impressed”.

I like the way my system sounds, but for the reasons listed above, I’m feeling like replacing this preamp could allow the whole system to sound better... especially after the surprising phono preamp experiment. A system can only be as good as its weakest link, right?
@bdp24, well that makes more sense. We are not crossing over the Quad in the test set up. However, in our respective RM-3s both Roger and I use 4th order Linkwitz/Riley crossovers, 24 dB slope cut at 100 Hz for high and low pass. Roger also adds some EQ to the low pass board that I believe he explained here or perhaps in another thread. In any event I have used the Quads with the RM-3 and my bass array in a biamp set up and like that arrangement, which I also do with my modified Acoustats. I don't run the satellites full range.

@krelldreams, Conrad-Johnson uses the 12AU7 in their pre-amps, so I’ll guess that’s what you have. CJ products are considered to have a "warmer" sonic character than those of other companies. Some like and want that in their system, others want a different sound from their electronics.

The 12AX7 and 12AT7 are used by many other designers, both of them by Keith Herron in his well-regarded VTPH-2 phono stage. I have no doubt that unit would provide a considerable improvement over the C-J, with a more "modern" (less colored---"added" warmth is a coloration, like a filter on a camera lens, more transparent and detailed) tube sound. Roger Modjeski (@ramtubes) prefers the 6DJ8 for pre-amp use, but I don’t know that he currently offers a phono amp. Roger or clio09?