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
 
I said I was done in this thread and once again, I lied. I swear this question is in good faith and not meant to challenge or make a point. While looking over at Tungsol's website I saw this;

Engineers and musicians have long debated the question of tube sound versus transistor sound. Conventional methods of frequency response, distortion, and noise measurement have always assumed linear (clean) operation of the test amplifier and have shown that no significant difference exists. In actual operation most amplifiers are often severely overloaded with signal transients. Under this condition there is a major difference in the harmonic distortion of tube and transistor circuits.
http://www.tungsol.com/html/faqs14.html

Please be aware that this paper was not written by any Tungsol engineers who are long gone as well as their factory and any tribal knowledge. 

This is the work of New Sensor who has taken over the name, probably with no resistance, and making the tubes in Russia. Im not saying these are bad tubes but they are not Tung Sol of America.  The KT series apperars to be good and I have tested the 120s and 150s. The data sheet for the 150 is in Tungsol style but not of Tung Sol quality. No plate curves, Gm seem too high. Not informative as in the good old days. I have offered to help them.

Also keep in mind that New Sensor sells to the guitar amp market by 100 to 1. Nothing wrong with that. Thanks to the guitar guys for keeping the demand for tubes going. We audio users are a drop in the bucket. 


ramtubes's avatar
ramtubes OP
460 posts
 
@andrew 

This has been a great and informative thread. Thank you for sharing your time, knowledge, and insight. I've learned a lot.

A question for you: any further thoughts on ARC's M300 monoblocks? They're a fairly...unique design and perhaps the best evidence of your view that WZJ's ARC designs were often over-complicated. That said, I enjoy them, and they've only blown up a couple times over the years. Any further comment?

(As to your point about the reliability of ARC products, I also have a pair of Ref 600s and pray every time I switch them on that they don't go up in flames.)

One other question: for those of us with super-inefficient speakers like Magnepans, what should we be looking for in an amplifier?


Look at this from Stereophile 

Peak Current (via 1 ohm, 2ms pulse)
8 ohm tap: +13.7A -13.5A
4 ohm tap: +16A
2 ohm tap: +18A
1 ohm tap: +24A
Read more at https://www.stereophile.com/content/audio-research-m300-monoblock-power-amplifier-measurements#8yHmL...
That is an impressive amount of current. The damping factor of 30 and 0.05 THD are impressive also. The full review is good reading. 

A continuing wonder of Audio Research's designs is how they can sound so good with such a complex signal path.
Read more at https://www.stereophile.com/tubepoweramps/585/index.html#REEwDyeIIFoMddwp.99

We can see that current ARC amps are no where close to what Bill achieved. One problem with complexity is fixing it. How bad did yours "blow up" 2 times?

If you can handle the the praying for no smoke and afford the rather short tube life then carry on. For those who cant I would go SS. 

There comes a point when tube amps just get too big. The alternative is get a high power tube amp with transmitting tubes. One pair of moderate sized transmitting tubes, like 833s,  can produce 300-1000 watts. Having a lot of smaller tubes in parallel is not so practical. One pair of 833s is about the same cost as one pair of KT 150s. or other KTs. And they look really cool. Id make you a pair if you wanted. Thats the big tube WAVAC Uses SE but I would go push pull. 

What is the re-tube cost on the 600?

ramtubes's avatar
ramtubes OP
460 posts
 
@prof  So my question is: What exactly is happening to cause the type of sonic changes on hears when changing impedance settings for a cartridge?

My know-nothing layman’s hunch is that it’s similar to how speaker impedance interacts with certain tube amps, where some combinations contour the frequency response...and (sorry for the word) damping factor? (The changes in the bass in lower impedances do give me that "lower damping factor in the bass" vibe).


Good question. Cartridges are very different in how they respond to loading. My Denon 103 is a 14 ohm cartridge (as I recall) and likes 100 -200ohms load. More load drops signal level, dont ever go that far, and makes the sound rather dead. No load is rather bright. 

On the other hand the Lyra cartridges are so low in impedance that they dont respond to loading so we, in the SF audio society did some tests and found the Lyra best unloaded. 

There is not any relation to speakers and amps that I would care to make. A cartridge is a source, the load is a resistor. Not much else going on. 
ramtubes's avatar
ramtubes OP
460 posts
 
@bifwynne  Btw, I owe you two quads of KT-150s for matching. The 3rd party vendor from whom I purchase the tubes didn't match the tubes to ARC spec.

Btw, I owe you two quads of KT-150s for matching. The 3rd party vendor from whom I purchase the tubes didn't match the tubes to ARC spec.


We have been awaiting your tubes. Time has passed and we have to get back on the same page as to the specs for current and G2 volts. Better not to wait on these things. Strike while the iron is hot as they say.

The difference between Bill Johnson amps and the current products is night and day. I appreciate the simplicity but not so much the performance specs. However specs arent everything. We are finding out some very interesting things on some listening tests. Very hard to get a really good handle on an amp without an A/B and a reference. 


ramtubes's avatar
ramtubes OP
460 posts
 
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 


Nice circuit, simple. The 16 ohm tap is a bit silly and taking the feedback off it can have both good and bad effects. Otherwise, classic Marantz, Heath, Eico, etc.
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