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.
.
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
 
@roberjerman
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!

You are correct, 8 ohns is a very high output impedance, way too high. Why do you assume the engineers are competent? Look at the lineage of the people who designed and have promoted this amplifier.

From About us at the primaLuna web site.

The driving force behind PrimaLuna is one of high-end audio’s most astute and colorful figures, Herman van den Dungen.

WHO?

"For U.S. distribution and sales advice, he once again turned to “tube guru” and friend, Kevin Deal".

I have read several places that Kevin is the self proclaimed King Of Tubes. Ive met Kevin at CES, no crown, actually a humous guy, I wasnt expecting that. Unfortunately I understand he’s not too chatty unless you are buying.

Here, see how much of this you can take. https://www.primaluna-usa.com/about

I learned long ago that someone can make a horrible amplifier and someone will love it. This amp is not horrible, however it is not good. Given it is made in China someone is making a lot of money and its not the Chinese. We have no idea how long these amps will last. We have no idea the quality of the components. Its a big box of unknown. We do however know the mearurements which are not good at all.

Kevin has done a wonderful job of salesmanship. Note that he is the importer so he likey gets 10% for every amp coming in the country and 40% more for the ones sells directly. Go Kevin.



georgehifi's avatar
georgehifi
10,312 posts
 
ramtubes
Thats horrible indeed. For some reason people buy these things.

And when I say "easy simulated speaker load" (linked) it’s made for Sterophile and modeled on the easy to drive Kantor speaker by I believe the man himself Kenneth L. Kantor It’s a pretty poor amp design that can’t stay reasonbly flat in frequency (+ - 2db) into this easy load.

Fig.4 Modified Kantor speaker simulator, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).
https://www.stereophile.com/images/archivesart/scan58.jpg

Fig.1 Circuit of Ken Kantor loudspeaker simulator, intended to represent a two-way, sealed-box minimonitor with a nominal impedance of 8 ohms.
https://www.stereophile.com/images/archivesart/scan55.jpg

Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 
ramtubes
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.

I always post this one up by Nelson Pass, and some here "hate it" when I do, so just for them, here it is again.

Quote from Nelson Pass

"We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.

Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.

Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.

What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.

And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp."


I must state, before all the haters start.

The above is correct ( should have been included by Nelson Pass). If a 1:10 or more impedance ratio is met by the source and by passive to the the power amp, and in nearly all cases it is.

Save for some a small scattering of high output impedance (>1kohm) tube output sources and low input impedance (<33kohm) poweramps.


Cheers George


amb3cog
21 posts
 
Sorry. I don't know how to use quotes and all that on this forum. No offense to anyone, but it's beyond outdated, and I've been into computers since the mid 90's.

Anyway. Thank you @ramtubes. I agree that Facebook, and Z, both suck. But you can still effectively use their ads I feel. That being said. Google Ad-sense is a great alternative.

And thank you 10 times over about the OP-amps! I've been told a million times, that it's not OP-amps, it's how they're implemented. When I say I won't buy anything with them. BS! I've got very sensitive ears. It's definitely the OP-amps. They suck arse, period! And I'll have nothing to do with them.

Hope your Thanksgiving was half as good as mine was. God bless! 
Andy B. 
danvignau's avatar
danvignau
935 posts
 
Youe are really great for doing this.  I have read that James Parker (Is that the right name) of Audio Research seems to design in a bit of added second harmonics to his designs. When I consider that some bands, most notably The Grateful Dead with their Wall of Sound array of MacIntosh amps, use tube amps for voices to add harmonics, this seems plausible.  Your thoughts?
More to discover