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
 
@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.
ramtubes's avatar
ramtubes OP
460 posts
 
@cardiff  Here is one nobody seems to have asked yet...

What is the role and importance of significantly upgraded power cords in component design? It seems to me that the PC is a fundamental part of the electronic device and that the manufacturer should optimize the cord for the device in building it. What are your thoughts on the matter as someone who actually builds electronics?


I put the proper cord on my RM-9 but now people want me to put an IEC on there so they can use theirs. I did opimize but thats not good enough for the PC and fuse people.  May I also offer that a captive cord has one less pair of connections. When you pull current on a IEC it gets hot, is that good?

Before audiophiles got into power cords most manufacturers went to IEC connectors for no other reason that it makes the amp easier to handle and pack up, not so people could go fooling around with wire. 
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