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.


128x128ramtubes
@ramtubes

You wrote the following regarding ARC:

Im sorry, but you asked. I'm sorry to be so negative about ARC, but I was a dealer for them from 1975 to 1980. If you have not heard about the "pink papers" thats a story in itself. ARC treats dealers with a heavy hammer, large opening order and threats if you do not follow the party line. Bill called us up one day because he heard we were doing A/B comparisons for our customers. He said "stop immediately or I will pull the line"

Of course I respect your technical experience and ARC anecdotes, but let me just weigh in on ARC.  Perhaps I have been crazy lucky, but I have owned ARC gear for quite awhile and my anecdotal experiences are quite different than yours.  

In particular, as far as linestages go, I've owned the Ref 3, Ref 5, Ref 5SE and now currently, the Ref 6.  As far as amps go, I've  owned the VS110, the VS 115, the Ref 150 and now the Ref 150SE.  My CDP is the Ref CD-8 and my phone pre is the PH-8.    

To date, I have had only one problem; namely:  blown bias resisters in my older amps.  Other than that, no other problems whatsoever.  In the case of my Ref 150SE, I am running KT-150s. So far, … fingers crossed, ... no problems with arc'ing or blown bias resisters.

As far as bench tests are concerned JA tested the Ref 150 amp, an earlier version of the Ref 150SE.  Here is his report:    https://www.stereophile.com/content/audio-research-reference-150-power-amplifier

Notably, JA reported that "Fig.1 indicates that the Ref150 has a wide bandwidth, particularly into loads higher than the nominal tap value, which correlates with a well-defined 10kHz squarewave (fig.2). While this graph reveals a small but critically damped overshoot on the leading edges of the waveform, presumably due to an ultrasonic transformer resonance, no ringing is visible."  By comparison, the Ref 75 did not test as well.  And you noted the same in your prior post.  

I can't speak to whether the circuits in my ARC gear are elegantly simplistic or labyrinthically complex .  I am not a EE.  But so far, my gear is holding up pretty well.

As far as SQ is concerned, … no comment.  I have not had an opportunity to A/B ARC gear against any other brands.  But to my untrained ears, my gear seems to sound OK.

Perhaps your views about ARC might change if you road tested some of their current models.  I understand that ARC opted to simplify the circuits in its latest offering, the Ref 160 mono blocks.  Haven't heard them, but it doesn't matter.  I am not going to drop $30K on mono blocks.

Btw, I owe you two quads of KT-150s for matching.  The 3rd party vendor from whom I purchase the tubes didn't match the tubes to ARC spec.

Regards,

Bruce
Roger,

This has been a great and informative thread. Thank you for sharing your time, knowledge, and insight. I've learned a lot.

A question for you: any further thoughts on ARC's M300 monoblocks? They're a fairly...unique design and perhaps the best evidence of your view that WZJ's ARC designs were often over-complicated. That said, I enjoy them, and they've only blown up a couple times over the years. Any further comment?

(As to your point about the reliability of ARC products, I also have a pair of Ref 600s and pray every time I switch them on that they don't go up in flames.) 

One other question: for those of us with super-inefficient speakers like Magnepans, what should we be looking for in an amplifier? 
VAC seems to be doing some good work these days. I have worked on one of their big preamps, it was nice but picked up hum from a power amp 2 feet away. We were surprised.

Yes, we were! Hey Roger. Great thread!
Bill

Ralph,
Thanks.
I didn't totally follow all that, but that's due to my level of ignorance. 
Clio09
I am curious how you settled on the 60 Hz cutoff and what other levels you may have experimented with.


Clio09
atter much experimentation I found the 57's positioned the way they are in my space to be the most room filling and linear top to bottom - down to about 50-55 hz. Still, to get the bottom octave and bass impact (it's a large room) I needed to add subs. I used to have a big HSU set up in nearfield next to me. It was fine as long as you were sitting in one spot. But if one uses the room - walks around, and sits in different spots around the room;  multiple subs are the answer to eliminate the bass nodes. Adding the two 12" Dynaudio subs improved on the single large HSU. Keeping the HSU as a slave would have been interesting, but my son took it. 8^0
The lowest crossover point on the Dynaudio BM12s is 60 hz. So that is where they are set. I have tried higher settings in the past with other subs and felt it interfered with the 57's bass too much.