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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Showing 3 responses by jdjohn

jdjohn's avatar
jdjohn
5 posts
 
Hi Roger, and thanks for offering to answer some questions for us.

In an earlier post, you offered to comment on specific brands, and I have a few in my stable.
-PS Audio
-McCormack (you already gave a nod to Steve)
-Symphonic Line (German)

As a follow-up on class D amps (and PS Audio), I recently got the PSA new Stellar S300 power amp, and would be interested in your input based on some of this information from their website.  The input stage is handled by their "Analog Cell", described as "a proprietary, fully differential, zero feedback, discrete, Class A MOSFET circuit."  The output stage is a "dual mono design.  [E]ach channel has its own, separate power supply. Each of the two channels is a complete and independent power supply and power amplification stage, based on a modern Class D ICE module, designed in Denmark."  Darren Myers is PSA's designer for this.

And here are the technical specs https://www.psaudio.com/products/stellar-s300-power-amplifier/#tab-specs

I like the sound of it, although interesting with no discernible harmonics.  I had never noticed harmonics in SS class A or A/B until I compared to this class D amp.

Thanks again for taking the time here!
jdjohn's avatar
jdjohn
5 posts
 
Any thoughts on kits like this modeled after the Dynaco ST-70?  http://www.tubes4hifi.com/bob.htm#ST70  This isn't a mod or upgrade for stock ST70s, but a kit for building a brand-new amp.  Some of the design changes are listed under 'ST70 amplifier features' if you scroll down the page a bit.
jdjohn's avatar
jdjohn
5 posts
 
@jdjohn   Any thoughts on kits like this modeled after the Dynaco ST-70?  http://www.tubes4hifi.com/bob.htm#ST70  This isn't a mod or upgrade for stock ST70s, but a kit for building a brand-new amp. Some of the design changes are listed under 'ST70 amplifier features' if you scroll down the page a bit.


Looks good. I like to see the 3 tube driver board. Do they have a schematic?

The original single 7199 tube driver was flawed by tube to tube variations. Some good 7199 would bias up in a region that actually produced a lot of distortion and reduced power. There are many 3 tube drivers. I would like to know more about theirs.

The kit looks good and priced well.
Here's a schematic of the ST-120 version (sans values for resistors and capacitors), which is apparently the same schematic as the ST-70 except for resistor sets.
https://drive.google.com/open?id=1IMaAaaWRuIU8v-_OZ3jfrcQCI5a0gpP8 
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