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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@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?

Thanks for answering me. I noticed that the continuous bias VAC 200IQ sounds better than the manual bias predecessor Phi-200. The improvement is claimed on the continuous bias. I also own a backup amp, the 70 watt EAR 890 which runs really hot in Class A with autobias. It is not sonically in the VAC ballpark. It doesn’t control 3-12" woofers in my main system with 2.8 ohm low impedance but sounds fine in my second system controlling 3-10" woofers with a 3.7 ohm low impedance.

I now remember my own experiences with an ARC SP-14 preamp where the central cap melted in the middle of the circuit board and the need to replace output tubes after maybe 1000-1500 hours in a pair of Classic 60s. That’s also what worries me about the VAC 200IQ as they get 100w 8 ohms out of a pair of KT88s. Based on your lecture, it appears they are being driven too hard. The worst tube life experience I’ve had were the Dynaco Mark IIIs. 9 months and I had to replace the output tubes-bad design.
@bdp24 .. I had an older CJ preamp, a PV-8, which sounded as you describe. I replaced that with this one, a Rogue Perseus Magnum. It improved on the sound I was getting from the PV-8 in some areas, but I also felt like there was something missing when playing LPs. I didn’t realize it at the time, but discovered that the Rogue uses a ss phono stage, rather than tube... the tubes were only in the linestage. I don’t know if that was the difference in the sound, or some other area of its performance. The Rogue sounded a bit clearer and had better sounding bass, but after I got used to that improvement, I sensed that the LP playback was a bit veiled. When I tried the inexpensive phono preamp, a schiit mani, there was an obvious improvement in every parameter... like the cleaning of a window to the sound. I want more of that ;)
Clio09
@ct0517 - thanks for the response. With the subs in place are you still running the Quads full range, the using the sub fior 60 Hz and under, or are the Quads completely cutoff at 60 Hz?

Hi Clio09
The 57's are full out on the RM10 and in parallel to the subs. The preamp I am using in that room has two direct outputs. One output set going to the L and R 57, the other set going to the L & R sub. The subs are on each side of the listening couch, the opposite room side to the 57's. The Quads are seven feet from the front wall. So they are about a third of the way into the room. 
   
I realize that the way I have set up the Quads (see virtual system pics) and the subs is, well, unorthodox. But that is just one of the aspects of a dedicated room, that allows you to manipulate speaker placement, and affect the way the speaker output and the room gel. The hell with aesthetics. Hey, anyone with Quad 57's isn't into aesthetics anyway - 8^0.  

Room A is my main room, it pressurizes easily due to its shape and the speakers used in there; but Room B is a better room for entertaining due to its size. It's been a lot of fun when people visit and if any are interested in audio, watching them get a grasp that the Quad 57 is actually a speaker. Equally entertaining is when I tell them there are two subs in the room and to tell me where they are as music with a lot of bass plays. They start looking over at the 57's across the room, looking in the corners nearby. When I tell them they are on each side of the couch they are sitting on, one right next to them on the left - they are in disbelief.
Cheers

@krelldreams, the "cleaning of a window" is the transparency I was speaking of above. It’s the opposite of the veiled, opaque, translucent sound (a layer of "scrim", as J. Gordon Holt called it) you are trying to rise above. Transparency can and has been achieved via both tubes and transistors, being more a matter of the talent of the design engineer. For instance, though Roger uses primarily tubes, he felt transistors would work better as the input stage of his RM-200 power amp to achieve the performance he was after.