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.


128x128ramtubes
ramtubes's avatar
ramtubes OP
460 posts
 
@rollintubes  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?


It is my understanding that 200 watts per channel is a maximum to not blow up the speaker. That is a lot of power for a voice coil to absorb. Almost everyone has too big an amplifier in my opinion. I know this as I have measured power at listening levels in customers homes to be only a few watts. To say 200 watts is "needed to drive a 85 db speaker" means that the speaker will be putting out 105 db SPL. I listen at 85 db, anything higher is for short periods. Do you listen at 105 db?

Your 40 watt tube amp sounds terrific because thats all the power you need. Small amps generally sound better than big amps. In designing big amps, certain sins are committed. Small amps can be more responsive and delicate. 

I am currently designing several 30 watt/channel amps for those who agree with what I have said above.


ramtubes's avatar
ramtubes OP
460 posts
 
http://www.audiosystemsgroup.com/TransLines-LowFreq.pdf

The last paragraph of this 3 page paper dealing with transmission lines admits that we are not in transmission line territory at audio frequencies..    
Electrical Wavelength at Audio Frequencies can be computed from Fig 2. At 1/20 wavelength and below, transmission line effects are negligible, and the circuit can be analyzed using simple lumped circuit parameters. At 1/10 wavelength, transmission line effects are still quite small, and can generally be neglected. Fig 3 shows the characteristics of the RG59 cable of Fig 2. Typical balanced audio cables have similar properties, typically differing from Fig 1, 2, and 3 by no more than a factor of 2 in frequency. Thus, at audio frequencies, a cable less than 2,000 ft long is no Fig 3 Electrical Wavelength at Audio Frequencies more complicated than its series resistance and parallel capacitance. As the cable becomes longer, or as frequency increases, the cable will begin to behave as a transmission line.

michaellent
Why can’t people stay focused? Ramtubes started this discussion about amplifiers and it looks like it fell into the cable whole again!
Start your own thread about cables of any different kind and stay out of the ones that have nothing to do with it!
Thanks Michael. I appreciate your request for a return to amplifier discussions. 
ramtubes's avatar
ramtubes OP
460 posts
 
the velocity of propagation of the signal (versus the velocity of the actual electrons) is determined by the dielectric or insulation material that the electromagnetic wave is predominantly traveling through.


I would like to see some proof of this. 
ramtubes's avatar
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
ramtubes's avatar
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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