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.
.
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.


Fe8c8cab 4117 4c51 b1aa 6b134ad0dca6ramtubes
@mapman 
I figured it out by listening and trial and error over time and based essentially on those parameters as a guide. However specifications alone seldom tell the whole story. The devil is always in the details much of which is never specified. Detailed measurements like those in Stereophile help a lot but I have found there may still be surprises playing real music even with very comprehensive test measurements at ones finger tips, though if done correctly, measurements certainly help with the decision making process of what to try next or not.

Today I compared two identical amplifiers, level matched, A/B switch in hand. I played Willy Nelson (raspy male voices are very telling), I played Bach Organ works, piano, lots of things. Sometimes listeners bring in music to these tests that they like, but will not expose differences. 

All I had done is add 12 dB of feedback to one amp and left the other stock. i didnt change any caps, didnt replace resistors with naked ones, didnt put in premium wire or fuses.

Both had been measured and were in proper operating condition. 12 dB of feedback will reduce distortion by a factor of 4 and increase damping by a factor of 4. It was not hard to hear the clairty, dynamics, and defined (rather than one note) bass. 

This is the story that the specs told and the listening confirmed. Come on over and have a listen. Lets not worry about comprehensive measurements when even the basic ones arent even good. The stock amp has a damping factor of less than 1 and 4% distortion at full power and I played it at full power. 

These tests are not easy to do even for me. It can take a whole day to set it up, and ive only been doing it for 40 years. Very few people set up these tests.

Why do audiophiles try so hard to ignore, object to, claim that measurements are irrelevent? Why is one reviewers impression more important? Many readers of Stereophile dislike measurements so much they say its a waste of space?

I don't design by measurement but I know what minimum performance is required to make a good amplifier. Of course some designers loose sight of balance in design and drive one spec to the limit. That often results in a bad sounding amplifier. 

What are you going to say to the poor lad who buys the Cary SLI-100 hooks it up to a pair of Maggies, turns it up loud and smiles. If you have a good sense of clean sound you will not enjoy 10% distortion, compression, muddy bass. Without JA's measurements there would be no warning. His reviewer did not use more than a few watts of a 100 watt amplifier, what happens when someone does?
@unreceivedogma

 By “more power” I’m just going by where I set the volume control before and after. It was a surprise, as I thought there would be less, and I was pleased because in my layman’s view it meant less stress on the tubes and circuitry.


This is a popular thought, however where you set the volume control has nothing to do with power or stress on the tubes and circuitry. A volume control controls gain, not power. You an be at full power anywhere on the control setting depending on the gain of other parts of the system. 

Also, I’m not sure what you mean by better technology than cone speakers. First off, the Altec is a horn/cone hybrid. That aside, while electrostatics have their virtues, they don’t move air the way a cone does, as someone here also observed. That’s what I mean by the dynamic punch of the Altecs. I’ve heard some great horn speakers, with prices in the stratosphere.


The Altecs were designed to get a lot of SPL with not a lot of power. When they were designed 20 watts was a lot of power, now its not. I have not heard any good horn speakers, though one of my students has the Avantgarde 3 way. We are having a demo this coming week. Horn speakers tend to have peaks in the response. They are very efficient, however I am not running a movie theater.

Actually ESls couple better to the are and are virtually massless. A cone speaker is a "mass loaded driver" whose motion is totally controlled by the mass. The problem with mass, as we well know is how to start and stop it. 

Rather than defend cone speakers, lets open our thoughts to why they are so popular and do they belong in the home? Fine for cars and portable radios, but that is not HiFi.

There was a time when the best and most expensive speakers were ESLs. But then came along Wilson and the world changed. We made a $4,000 ESL with DD amplifier at Beveridge when wilson was still working in his garage. He won, we lost. What happened?
Speaking of Maggies... I would like use a quality, lower powered tube amplifier to drive mine. What is your idea of an appropriate amount of “tube” power for them? I sit about 9 1/2 feet from the speakers in a 14’ x 21’ x 8’ room, and typically listen at 80-85 dB (measured with a RS meter; C weighting/slow response). They’re rated for 86 dB/ 2.83v/ 500 hz. My preamp volume control is almost always around to 9:00. I really appreciate the idea of simple circuit design for both the amplifier and the preamp. I just feel like I’m not using the power in my amp (200w/ch), and also that I’m not using the gain in my preamp (12 dB). Power is expensive, and I’d rather put the money into the quality of the amp if I don’t “need” the hundreds of watts. 
@fsonicsmith

you can’t possibly mean that preamps are easier in general and I am unaware of any accolades for your preamps (whereas you are lauded for your amps). Obviously you mean that for your tastes and purposes, preamps are easier than amps.


I mean precisely that. You might want to do a little more reading on the RM-1 and RM-5. Perhaps you are new to this hobby.

This has nothing to do with my tastes and purposes. The RM-1 (1976) was lauded for its RIAA EQ accuracy, was the first popular preamp to use the 6DJ8/6922, has the lowest noise possible for that tube. Has 5 fully regulated, short circuit proof power supplies. Built in two chassis and weighs 55 pounds ! It is the only tube preamp to my knowledge that id DC coupled throughout with servos, relay protection and no output coupling capacitor.

That was a lot of work, But once you make a good preamp what is there left to do?

Power amps, on the other hand are a world of variety. Circuit topoligies, output transformers, protection, tube life. These are really difficult things to do.

Granted most people who dont design preamps will agree with you, but they dont design preamps, now do they?

A great preamp does more than attenuate a signal. It breathes life into music. A great preamp is quietly powerful, while a great amp simply provides grunt.
A preamp does not attenuate a signal, it amplifiers a signal, provides selection of sources and control of volume, accurate phono EQ. But these are easy to obtain. There are only about 3 ways to make a preamp gain stage. There are an unlimited distinct ways of making a power amp and a good one is a challenge.

I will say that many preamps fail because of poor power supplies. My power supplies are among the finest and they dont break like ARC power supplies. You can short my power supply, go to lunch, come back, remove the short and all is well, doesn’t even get hot. One millisecond short on an ARC power supply and you wont have time for lunch or dinner. Ask any tech.

A power amp is the finess in a system, certainly not the grunt.

May I remind you this is a thread to ask a technical question.

using a few of your own words, perhaps you did veer into “ tall poppy “ turf a bit...

in my inteactions w very talented engineers over the years - and there have been many , many outside of audio, ego is also an essential design ingredient... there are some speaker people doing a bit more than just buying off the shelf cones...some of them make amplifiers..

” I was about to write that the M7-HPA measures well for an amplifier with zero loop-negative feedback. Actually it measures well period. John Atkinson.....

I think he liked how it sounded also with cone speakers ;-) I think there are several paths the enlightenment....