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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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!
ramtubes's avatar
ramtubes OP
460 posts
 
@gnaudio   

I spent close to $20k on a pair of brand name monoblocks, plugged them into my dedicated 20 amp outlets and they had a loud line level hum, hired electricians, changed out grounding rods etc to the tune of $3k in costs. Took all my other equipment and cables to my dealer to make sure they weren’t the issue and they weren’t. Finally I paid $10k and bought a used amplifier and bingo the problem went away. My system is silent and absolutely glorious sounding again. The monoblocks worked at my dealer without issue but had an issue in my house. How can a designer build a product like this and what could the problem be. I am out 000’s of dollars and lots of my own time researching the issues. I borrowed isolation transformers etc as the manufacturer said it was my house that was the problem and not their amps... they were a joke to deal with and basically blew me off. The only thing they offered was to pass a name along to me if they heard of anyone wanting to buy a pair. FYI, this company has a 20 year warranty... your thoughts are appreciated. Thank you for listening to my rant...

Hey I like a good rant. I feel you man. Did you ever float the grounds on the amps? If the isolation transformers had 3 wire plugs in and out they likely carried the ground through. Sounds like you had a simple ground loop which is so common with mono amps. Two power cords, two grounds plus the preamp etc= lots of potential for hum. 

Did anyone technical ever look at your situation? Did the amps have balanced inputs available?

I take it your 10K amplifier is stereo, thus no ground loop. 
ramtubes's avatar
ramtubes OP
460 posts
 
@georgehifi 

And the same, even more so, goes for preamps, if it's loud enough that's all you need, there is no advantage to have it "able to be louder" if it's loud enough already


Yes, lots of people assume that they will continue to get more power as they continue to advance the volume control. 

One can be at full undistorted volume at any position of the volume control. That is just a setting of gain not power. In Asia an amplifier must play very loud at 9 o'clock or it will not sell. 

I hope most of you know that volume control position has nothing to do with power or headroom. Might as well close your eyes. 

To those who want a little guidance. A well balanced gain struture will play your usual listening level at noon and a bit above. If you are down at the bottom of your volume control most of the time you have too much gain and little ability to adjust it easily. Also at low settings volume controls tend to have their worst tracking between channels so the image may shift side to side at various volume settings. 

Most systems I encounter have too much gain which often results in a lot of noise. I have made attenuators for several. 

I have found that most volume controls have 20 db attenuation at noon. This means you have 20 db more SPL available...if your speaker, amplifier and ears can handle it. I find 20 dB enough to bring up even the most quiet CDs. Im not interested in 100 db SPL
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