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
jdjohn's avatar
jdjohn
39 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!
atmasphere's avatar
atmasphere
11,901 posts
 
I'm still in the Polypropylene camp. Best thing for the money. Remember any part I buy is 5 x cost to the final buyer. So I cant buy too many $50 caps expensive resistors.
For a long time polystyrene was an alternative that performed better and was no more expensive. Things fell apart though after the German company that supplied polystyrene got out of the business. It was easy to hear how the polystyrene was better- and this seemed to verify the specs on paper.
The whole argument about 2nd harmonic distortion being "benign" totally ignores Intermodulation distortion which is far worse and always higher.
While I agree with your point here (and that of the rest of the post from which this is taken) this particular statement is false. It is possible to have low IM while THD is considerably higher, although clearly that isn't the case with the example you cited.
"Well, it’s the sound that matters". If a poor design, showing obvious performance weaknesses, sounds "good", something is very wrong somewhere.
The problem here is that the bench specifications used by the industry do not reflect the physiology behind how the ear/brain system perceives sound. The most egregious example is how we perceive sound pressure, which is done via the higher ordered harmonics- 5th and above. The reason this is a problem is that to obtain really 'good' specs on paper, a fair amount of loop negative feedback has to be employed to suppress distortion. As Norman Crowhurst pointed out 60 years ago, feedback introduces distortion of its own and its entirely higher ordered harmonics. Because our ears convert all distortions into a tonality, this causes circuits employing feedback to be brighter and harsher than the original signal.

None of the above is controversial- we've know this stuff for decades. But the industry continues to do nothing about it, which means that there has been little progress. IMO/IME the harmonics produced by a given circuit should be weighted so that higher orders are given a greater weighting than lower orders (for example small amounts of a 7th are considerably more audible than a 2nd at the twice the level). IMD of course should be kept low.
Question: Tube Phono preamp. Would replacing the 1N4007 diodes (in bridge config) in power supply with HEXFREDs or Schottkys improve it? The bridge feeds a CRC filter which then feeds a tube regulator. Thanks.

If the power transformer is not properly snubbed, then you will get less noise. But if its snubbed properly there won't be any difference.
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!
Because the ear converts distortion into tonality, just because you have flat frequency response does not mean it will sound flat. A small amount of higher ordered harmonic distortion can introduce brightness. This is an additional reason of why two amps can have the same frequency response yet sound different. IOW, its not just the output impedance, its also the distortion signature.

jfuquay
112 posts
 
A good friend has your RM-200, which I’ve heard often. Wonderful sound. Thanks for sharing your experience. Here’s my question: What determines an amp’s “brightness?”
I broke my “hear it before buying” rule when I bought a Musical Fidelity M2si integrated amp (Class A front end/AB power per the maker) because I wanted more power (137 watts at 4 ohms) to drive a pair of Magnepan MMGWs in a living room setup. But while it has great energy and dynamics, the new amp is brighter than the compact Teac HA-01 ICE-powered Class D amp (43 watts at 4 ohms) I had planned to replace. The Teac has a Burr-Brown DAC chip, and I tried a Music Hall 23.5 DAC with a tube buffer and a Musical Fidelity V-90 DAC with the new amp. All too bright for me. And I’m really surprised because I built the Nelson Pass-designed amp camp power amp (Class A) and think it is so natural sounding. I just assumed anything Class A/AB would be warmer than Class D. Apparently not.
twoleftears's avatar
twoleftears
5,318 posts
 

@gnaudio I’ve had several amps over the years plugged in the same room in the same AC receptable. A 300B stereo power amp didn’t hum. My current solid-state monoblocks don’t hum. But a popular US-based, US-manufactured, relatively inexpensive, tube integrated did hum, not a lot, from *both* the transformers and through the speakers, enough that when combined the hum could be heard from listening chair when music fell silent.

I lifted the ground. I ran an extension cord from the other floor of the house. I turned off every breaker in the whole house save for the one receptable being used. I tried ground loop eliminators, like the Hum X. I tried DC blockers, like the HumDinger from AVA. I followed the "how to eliminate hum" instructions from the PS Audio webpage. I tried isolation transformers (Furman pro). I tried a PS Audio unit. I tried a variety of other power conditioners. The company blamed it on the sensitivity of my speakers. I tried different speakers, with same result. Eventually I gave up.

It’s not any kind of discovery that the quality of manufacture of transformers used in different amps varies a good deal (designing to a price point + variable QC), but this demonstrates clearly that what works in location A will not necessarily work in location B, and that makes/models that achieve considerable popularity will not work for everybody, always. Live and learn.

Because mild to moderate hum is not fun or glamorous or sexy or exciting, I suspect it's a problem that occurs more often than is reported or discussed.


unreceivedogma's avatar
unreceivedogma
999 posts
 
Why would triode sound better than pentode?

Why woukd my Altec Lansing 604Cs be better for my Julius Futterman OTL3s At 16 ohms rather than 8 ohms?

And, with regard to the great interconnect debate: do you know of any testing done that approaches that of scientific blind testing that shows that any given wire, if made out of a certain material, and wound in a certain way, and shielded in a certain way, will cause electrons to move in one manner as opposed to another that can be explained as doing so and that because of that movement can be explained as yielding sonic performance that is measurably and quantifiably superior, or even just different?
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