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.


128x128ramtubes
ramtubes's avatar
ramtubes OP
460 posts
 
@terry9
Thank you for your interest, Roger. I take your comments in the helpful spirit in which they were given.

You have motivated me to look again at the stock Quads, and think about driving them with my current amps. These amps have proven themselves to be very stable over the years, and don’t really need protection circuits in the speakers. I think. So I just may continue to do without. To be clear, I am not using the Quads’ protection circuits.

I would be interested in a DD amplifier, but I am somewhat frightened of the high potentials. The one thing I know about super-KV work is that it’s qualitatively different from sub-KV work. Perhaps you could point me to your website?


They are not on my website, not really a Music Reference product. More of something I make when someone interesting who is doing something interesting contacts me. We made 4 for a guy in Australia and his friends. I also sold them 8 Acoustat panels and advised them how to set them up. He had been playing with Acoustats for many years and appeard very comfortable with high voltage. Acoustat panels are very useful and flexible and not expensive.

The high potentials bother me not at all. Perhaps because I was a TV tech from age 16 through college. 25,000 volts DC in a color tv is just not a big deal. One should be attentive no matter what the voltage. Ive blown up more things with current than voltage.



ramtubes's avatar
ramtubes OP
460 posts
 
@georgehifi

I think that one comes later for free on line, as I’m such a tight arse, I only read the ones Stereophile drip feeds online for free.

But it must be bad to beat the Leben CS300, check out the HF boost because either the output transformers are ringing or the circuit is oscillating. And it’s shown in the 1khz square waves as well.
To me another one, that should not be passed on final inspection to be sold.

https://www.stereophile.com/images/1111Lebfig01.jpg

https://www.stereophile.com/images/1111Lebfig02.jpg


Yea thats all pretty bad and if they were smart that is a good one not a failure on inspection. That kind of response is simply a result of poorly applied feedback. Strangely, given that the damping factor is horrible there isnt much feedback and they didnt manage to pull off even a little. Certainly the work of someone who doesnt care or couldn’t do any better.

Notice that the top rings longer than the bottom in the SQ wave. That is because the two halves of the primary do not have the same coupling to the secondary.

What a mess, their standards of performance are rather low. Might sound ok at low levels on easy speakers but the low damping will certainly modify the response of the speaker. The bass rolloff is bad too Probably everything is bad. I’ll go read what JA said.

Hey, do you have a link to the complete review? I got 29 hits for Leben. A lot of mention for a poorly performing amplifier.

Heres another poor performer from Jadis..https://www.stereophile.com/content/jadis-orchestra-reference-mkii-integrated-amplifier-measurements

He was kind to measure the distortion vs frequency at just 2 watts on a 50 watt amplifier.  Imagine how bad it would be at 10,20,30 watts.
georgehifi's avatar
georgehifi
10,312 posts
 
Hey, do you have a link to the complete review? I got 29 hits for Leben. A lot of mention for a poorly performing amplifier.
https://www.stereophile.com/content/leben-cs300-integrated-amplifier-measurements

JA does make mention of the ultrasonic resonance, but "maybe" because they're an advertiser, didn't make too big a deal of it.

Cheers George
bdp24's avatar
bdp24
9,874 posts
 

John Lennon: "All I want is the truth, just give me some truth".

Amen, brother! "High End" reviewers like Harry Pearson convinced lots of audiophiles that the measured performance of an amplifier and that amp’s sound are unrelated. That making a "good" sounding amp was more art than science. Yes, the race for as-low-as-possible static-measured distortion did lead to bad audio engineering, but good designers understand that, and perform bench tests that reveal the dynamic behavior of their designs.

I can’t count the number of times I have heard an audiophile (or even hi-fi retailer), when presented with evidence of the poor engineering of a component the audiophile likes (or the retailer sells), or worse owns, defend that component by saying something like "Well, it’s the sound that matters". If a poor design, showing obvious performance weaknesses, sounds "good", something is very wrong somewhere.

In the mid-80's I was in a hi-fi shop, and the owner was playing a system for a potential customer. I knew the following about that system's components: the tube pre-amp have a pretty high output impedance, and the interconnect cables very high capacitance, especially at the 30' length of the pair in use (from the pre at one end of the room to the mono power amps at the other). I couldn't stop myself from commenting that the combination of those two factors was obviously creating roll off starting at an audible frequency. The retailer responded by saying, you guessed it, "Well, it sounds good". It didn't to me, sounding, predictably, soft and dark. Cymbals were missing their brassiness and sheen, strings lacking life. I slowly learned some consumers, even "High End" ones, believe whatever they're told. The pre-amp was considered Class A, as was the interconnect. How could they not sound good together?
geek101
284 posts
 
If an amplifier is class A/B implementation does it not matter to mention the Class A bias i.e how many first watts are class A. Does crossover distortion matter?. If not why and if yes what do Class A/B designers do to make it go away or mitigate it. 

Generally reading around good Class A/B amps that have high bias seem to be well reviewed. Again interested to learn more about this.
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