2. amps-preamps
  3. 140029-80294

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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ramtubes OP
460 posts
 
@michaellent

 I want to learn about amplifiers


Hi. What would you like about amplifiers? They are my favorite subject and life's work. Did you check out the YouTube videos and Burning Amp?

Realizing early on that the applications in the RCA and other manuals are just one of many possibilities I like to create new applications that are within the capabilities of the tube yet not in the book. Most USA manufacturers copy the same "typical" application from each other. European makers often have many more applications. I noted this in my BAmp talk.

The RM-10 is unique in that it gets over 40 watts (at the plates) with one pair of EL-84s. In the standard application EL-84s achieve 18 watts per pair. However that application is based on a low B+ which is desirable if one wants to make highly cost effective amplifiers. So most manufacturers use that application though many other applications could be created. Mine is at a very high B+ which I have found to be very reliable and gives longer tube life than some of the low B+ apps. 

Emission Labs, makers of large triodes like the 300B, lists many applications (operating points, load impedances, etc) for each of their tubes. I did some for Jac Music on the new 45B and confirmed them on the bench, not by simulation. See note below applications.

http://emissionlabs.com/datasheets/EML45B.htm
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ramtubes OP
460 posts
 
@radiointerference 

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.


We stretched the mylar a bit beyond its elastic limit, so tight as you can get it. A silk screen stretcher works well or look on YouTube for other clever ideas. Weights will not do the job. We have the mylar in stock. It has to be coated both sides and heavy and well attached to the brass strip. There is significant current on the mylar. Nothing like the high resistance film of a Quad.

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.


I dont have any ECOs. I gave Counterpoint the design and Michael Elliott would be the one who changed things. Dont get his individial bias mod. Try to make the amps as original as possible. We have tubes for them. 

You need a schematic and some good diagnostic skills to get them going. 
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ramtubes OP
460 posts
 
@c1ferrari    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.


We havent done any panels for a long time. Chat with the other fellow on here who wants to stretch some mylar. We have the right Mylar as mentioned in my reply.
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ramtubes OP
460 posts
 
@jyprez 

yes, I would be happy to pay for coursework on the subject. What do you offer?

Currrently basic amplifier design. Are you local to Richmond. CA 94806?
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ramtubes OP
460 posts
 
ON TONE CONTROLS

The typical bass control has a hinge point at 1,000 cycles, much too high. In my system I use the Subwoofer level control (100 Hz and below) to set the bass to the right level without making vocals muddy like most tone controls do. Typical bass controls have lift the male vocal 3 dB to get 6 dB in the low bass. We dont want to hear that. 

My woofer level control is right next to my volume control on my crossover and I note I move it several dB depending on the recording, listening level and bass quality.

For treble, usually I want a cut for bright recordings, rarely would I want a boost. A cut control is much easier to make than a boost. Typical cut/boost controls have a hinge at 1,000 also which is too low.

Whoever chose 1 KHZ as the hinge point made a big mistake, and once  made was copied over and over. I would choose around 200 Hz for the bass and 4 Khz for the treble and leave 200-4,000 unmodified.
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