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
 
Im not going to go too far with the preamp vs power amp ease of design controversy. Everyone is parroting back the party line, which I disagree with. 

I did a shootout for phono stages for our local audio society. It was a strict A/B. We had several name preamps all the way up to $20,000. I will never do this again for a club. They were sad that only one of 8 preamps sounded really different and that one is also well respected. However that one was +3 dB at 10 KHZ and it was obvious. They left shaking their heads because when they compare the same preamps one at a time they "think" they hear big differences. 

I pride myself in preamp power supplies, RIAA accuracy, lowest noise. The RM-5 is the lowest noise 6922 preamp new or old. I know this because the noise is at the limit of the tube itself, not the circuit. 

I think a lot of designers have problems with the power supplies, noise (tube rush) and hum. .These problems are not easy to solve. Perhaps that is the source of the comment. 

Ralph, I measured your preamp's RIAA and it was +4 db in the bass. That is not accurate EQ. My RIAA accuracy is +/- 0.2 dB.
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What interests me is how it came to be thought that preamps are harder. What designer is going around saying that? Im not.
ramtubes's avatar
ramtubes OP
460 posts
 
@fsonicsmith 

I believe as does Ralph evidently that it does no good to have a great preamp and a mediocre preamp.
would you like to fix this sentence? did you mean one of those to me power amp, not preamp? Look i know ive stirred you up, but you did ask about ARC.I really dont care if you are familiar with my preamps or not. You have a lot to say about something you have neither heard or know anything about.

Frankly, and here is a technical question for you too, your designs, particularly your RM100 appears awfully similar to those of Don Sachs.
I dont make an RM-100. You think this is anyting like I make? http://www.dsachsconsulting.com/CitationRestoration_html_files/7564.jpg

 You tried to put me down that I must be "new to audio" (I am not, been at it for 43 years since age 16) and yet I bet 99% of us who have similar time in this hobby are not familiar with your preamps
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If you were reading Stereophile and other print magazines pre internet you would have read reviews of the RM-5, 9, 10, and 200. I have not had a large internet presence by choice. 

I have another one. And this is not meant to be a challenge despite your likely impression that it is. What is your scientific engineering basis for concluding that damping factor, adequate power, and low distortion are the most important performance criteria for an amp
I have already stated my basis for all those many times here. JA agrees with me, Peter Walker, Bill Jonhson and many others feel these are very important. Since you admit you only have 1% (100-99=1%)  of my engineering knowlege how can I explain it to you. You seem to think I have some magic fairy dust I can sprinkle and make you understand. I really can't and this is making me tired.

If you cant understand regulation (damping) then you cannot appreciate its value. Why do people without technical knowledge want to engage in a technical debate? All they can do is parrott back something they have heard.

There were warnings that this thread could go south if it did not remain Q and A. I appreciate that. I promise not to respond in any way in this thread again.

Thank you for leavning us be. I think you are the only one carrying us south.
ieales's avatar
ieales
1,201 posts
 
The solder joints just fall apart from vibration.
Interesting. My Force is still going strong after 15 years. Pre ROHS.

Two good questions for sub makers :)
Another is "Why provide such useless controls?" Many subs are clearly not designed to be integrated in any meaningful way.

Anyone interested in the effort expended, visit http://ielogical.com/Audio/SubTerrBlues.php

Most 'non-ap' listeners comment on bass definition rather than quantity.
bdp24's avatar
bdp24
9,557 posts
 

Yow, things are warming up around here ;-) . I like opinionated people, it requires and reveals passion. That’s true even if I see things differently; no two people agree on everything, and everyone develops their own priorities and tastes in music and it’s reproduction. I, not being an engineer, love reading about hi-fi design by those who are, and find discussions of design philosophy and styles very intellectually stimulating.

Like many Americans, on Thanksgiving day my assembled family expressed, member by member, what they are thankful for. I’m thankful for having Ralph, Roger, and all the passionate Audiogon music and hi-fi enthusiasts contributing to this forum!

ramtubes's avatar
ramtubes OP
460 posts
 
@atmasphere  We get pretty high figures and we do it with a tube.... As a hint, look into 2-stage CCS circuits. You aren't going to get good numbers without a decent CCS, a resistor or a single-stage CCS won't hack it.


Of course i use good CCS, what concerns me is the variations in the gain of the two sections of the 6SN7. Since I have the M-60 on the bench I will measure that. What kind of numbers should I expect and at what frequency do you measure it?

I guess this really depends on what is meant by 'current' (since the word has become a charged term in audio)! 

Current is well defined by science. I didnt know there was a special audio definition.???

And a lot depends on the 6AS7 in question too- the GAs don't hold up; most American tubes have problems in our circuit as well since they really aren't intended for fixed bias operation. We prefer the Russian variant; they hold up the best of any we've seen.


The 6AS7 is a pass tube in a DC power supply. Heres a link, one has to scroll down a bit and read the application paragraph at the beginning. I dont think brand is going to make a lot of difference as they are all made for the same application as stated clearly here. . 
https://frank.pocnet.net/sheets/191/6/6AR11.pdf

Speaking of bias I note the M-60 offset, which is entirely based in bias stability or lack of. The offset wanders  +/- 100 mV at 0.5 to 5 second rate. Perhaps its all power line related, but nevertheless its quite easy to see on a scope. The DCR of a quad 57 is 0.5 ohms so there is considerable current if the offset gets large.

Having my hands on an M-60 for several weeks now has given me a better opinion of it than I had before. My customer does not want to be adjusting the offset all the time or at all. He has requested I design a servo. I now have the offset down to about 1/10 of the original.
 
Although we disagree on many things I do appreciate your Gentlemanly approach, unlike that other fellow who left us.

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