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

Actually, the talk of switchers raises another question I'd like to direct to Robert:

I have more than one amp I like to use for my system.  It's a minor pain to switch the cables, but it sure would be nice to have a switcher where I could switch between amplifiers to the main stereo speakers.  (So interconnects would lead from one output of my preamp to my main amplifiers, and out the other output to a second amp.  Depending on which amp I wanted to use I'd just flip a switch.


At one point I did a bit of research and saw some candidates, but for the most part they looked awfully cheap, which left me hesitant.

Would you say a fully transparent switcher of the type I'm describing could be built?

@clio09, I suspect (and hope!) that clio09 (and Roger) x/o from the Quads to the subs at 60Hz using high pass (on the Quads) and low pass (on the subs) filters. But the point I want to convey to you is that such a filter (a x/o) is not absolutely at the specified frequency, but rather that frequency is where the x/o slope has dropped by 3dB, I believe it is. The slope can be 6dB/octave (1sr order filter), 12dB (2nd order), 18dB (3rd order), 24dB (4th order), or even steeper. The Quads are not "completely cutoff" at 60Hz, still putting out some sound below 60Hz, at increasingly reduced output as frequency drops due to the filter.

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?