2. amps-preamps
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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
 
@btp24
Roger, why is damping such an outdated term? ;-) I have heard you speak of how even a low output impedance amp doesn't, contrary to common believe, "damp" a woofer. You have quoted Paul Klipsch on the subject, as I recall.


As Paul said, What does it matter if you have some ohm or so of external resistance in series with 6 ohms of voice coil resistance?   

Its how output impedance affects and modifies the frequency response that we need look at. Its so obvious. That happens to be the first thing in every Stereophile test report. JA knows and he tells. Its fun to read the manufacturers response to high output impedance. They have no excuse but to make something up. 

Low damping amplifiers will bump up the bass at the resonant frequency of the speaker by providing extra voltage that is undesirable. One bump for sealed, two for ported. 

So we really aren't damping anything, are we?
ramtubes's avatar
ramtubes OP
460 posts
 
@stfoth... where do these forum name  come from?

Hello, RM! You mentioned the recent measurements of the Cary SLI100. Reminds me a bit of one a few years back on the 300SEI.

https://www.stereophile.com/content/cary-audio-design-cad-300sei-integrated-amplifier-page-3

That's something of a sort of classic amp with quite a few fans.
Compound question.
Your thoughts on Dennis Had and legacy Cary gear?
Your thoughts on the disparity between the measurements and folks who say things like that in the subjective review?


I believe Dennis was a RF engineer that switched to audio. His first amp with the torroid output transformers was a quickly discontinued disaster. He should have know torroids are good for RF but no good for audio ouput. He learned though. I dont know anything about the legacy gear. Got a link?

Anyone who thinks a gapless torroid is good for an audio output transformer is kidding himself. Luckily few exist. 

Not sure i understand the second question. Can u clarify and expand?
roberjerman
4,319 posts
 
I read a report by JA measuring a Prima Luna tube amp (some years ago). He found an output impedance of 8 ohms! This means a DF of 1 ohm or less! Combined with the typical varying impedance of most speakers this is way too high! How can supposedly competent engineers get away with something like this? Because the result is far from neutral, accurate SQ! No matter how pleasing the "golden ear" crowd claims!
ramtubes's avatar
ramtubes OP
460 posts
 
@mapman 

I do not have spl measurements but will give that a shot with my cell phone over the weekend maybe and report back.


 My concern about cell phone SPL meters is how do they know the sensitivity of your microphone. Is there one specific to your phone?

You have some nice equipment, no SPL meter?:( bad bad 

Let me know when you get one. The RadioShack  is known to be quite accurate. Hope its still available. Velleman has one too I have both the digital and analog RS meters and have tested them extensively. I just use my phone to tell when BART exceeds 100 Spl. Dont trust it for more than that even though its an Iphone. 

Whats more important is to get a peak reading meter of scope and get down to business.
roberjerman
4,319 posts
 
Ohm's Law rules the amp/speaker interaction! And I agree with you that DF need not be excessively high to have adequate results!
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