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,
           Thanks for this great thread! It is one of the best threads I have ever read on this website! Your time educating us non-technical prople is greatly appreciated. I still own the original Beveridge Model 2׳s and have a couple questions after reading your earlier comments about these speakers. You mentioned in an earlier post that the perfect room for these speakers is one that is 11’ W by 24’ long. You mentioned that they needed to be at least 6 feet from the rear wall facing each other. Then you commented on their amazing imaging saying that they should be 2 times 6ft or 12 feet area for imaging. Were you just saying that both speakers were 6 feet away from the rear wall or were you saying the speakers should be pulled 12 feet from the rear wall in this perfect room?


The speaker will be 6 feet from the rear wall. 12 feet is the depth of the image which is 6 ft to the wall and 6 more for the sound to return to the speaker. a 12 mSec delay feels like 12 feet.

Very nice speaker, hold on to it. I hope visitors appreciate it.

Lastly, i have stayed away from your RM-1 (and RM-2 Power supply) Beveridge preamp because I have been told that the preamp is very hard on tubes used in it. This seems very much counter to your later works. Is this true or myth about the RM-1/2? If so, is there a later fix for this issue or should I just buy a later preamp of yours. I have used many preamps with the Beveridge 2’s. Currently I am using an old PS Audio 4 preamp in the passive mode. I obviously am
a fan of your work!


The early runs of the preamp ran hot even though I ran the tubes at one half dissipation. I reduced it to 1/4 rated dissipation. We upgraded many but there are some high current ones out there.12 tubes makes some heat so it needs free air and not in a rack or stack. Many of them come to me with Ram tubes so I can tell last time we sold the customer tubes. Its typically 3 years. Now a tube can get noisy at any time and its a very low noise preamp so people use the MM input for cartridges  0,5 mV and up.. Therefore they would run the line higher and a noisy tube would be obvious.

Lets say this. For its 1978 vintage it something few can do. Its DC coupled, no output capacitor, many features for phono lovers. Try one out. Clean or better yet, replace the 12 pin connector from the power supply. 

If people want to know about RM-1s I will write up a white paper. If it was still in production I would be sending on to Stereophile for JA to bench text. There would be no drop off in the bottom or top end at any load, even a ohm. Output impedance is 100 ohms, very rare for tubes of the day.

I would say it rivals an SP10 in many ways and perhaps more reliable. 

More about Beveridge and the company on request. He was my mentor and very out of the box.
Hello Roger, thanks again for this opportunity seeing you worked for Harold Beveridge , I have two questions, 1). I have a pair of Beveridge 2SW's with a panel that has gone south. I am looking to make a jig to tension the mylar film. Can you shed some light on how to rebuild the panels, I have some background info on the mylar but would like to know the tension techniques to properly rebuild.

Question 2), I had purchased a set of Counterpoint SA-4's about 2 years ago needing repair/restoration. One was functional one was not but found one tube had vented, I think it was due to mishandling during transportation.

Can you give info on what to check for, and possible ECO's on this amp so I can proceed with a restoration for a set of Quad 63's I am planning to use them on.

Best Regards,    
Roger,
          Thank you for the comments about Beveridge speakers. Could you also make some mention about the power transformer of these direct drive amps?  Should it be so difficult to find a source to rewind these transformers making the amplifiers operational again? I have had 4 amps where this is an issue (in both Beveridge 2 and 2sw amps.) My original pair model 2’s had this issue upon purchase (long story.)

This power transformer issue and panel issues seem to be what keep these speakers from being more highly coveted today. Thanks again for your generous participation on this thread. 
Re: Beveridge
Hi, Roger,
You'd worked on the Bev DD amps for my Model II's when you were situated in Santa Barbara.  Unfortunately, Rick was unable to complete the restoration process and my panels require attention.  Can you assist?
Thanks for the attention.
Vbr,
Sam
Roger, thanks for your time.
Some of the technical talk on this thread is way over my head so I’ll have to bone up on my tube electronics, which I learned over 50 years ago in college, then became a computer jock so I forgot about them until recently.
I am sold on tubes for analogue audio but am confused by all of the information on power. I see from many posts that tube power need not be very high or as high as the speaker manufacturer claims as a requirement, i.e. a 200 WPC SS amp is needed to drive a speaker with 85db sensitivity (the manufacturer requires a minimum of 75 WPC, but likes at least 100 WPC), yet I have used a tube power amp with 40 WPC on the speakers and it sounds terrific. I have read that it is in the output transformers and SS amps are generally direct coupled.
Will you please explain this phenomenon?

Thanks. Rollin