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
 
@fleschler   
Funny that the latest ARC amps I've heard sound greyish, muted dynamics, etc. My friend has an ARC 75 which is no match for his Classic 60s or my voltage regulated amps. Worse, his amps, Ref 5 preamp and $10K CD player all have had significant break-downs after only a year or two. Yuk!

That is how I would expect the ARC amps to sound given their measurements. Sometimes there is a correlation. I see we still have reliabiity issues. I feel for ARC and the many people who work there. When Bill was selling the company he had 10 requirements of the buyer. One was to not move the company. Bill did some nice work, however he left a few things undone. He never made a short circit protected power supply. That makes techs and the owners who pay them really unhappy.  He had a thirst for new products which resulted in many mods because the first releases were unfinished designs. When a preamp goes from SP-6 all the way to SP-6E thats a lot of mods.

My question remains, I'd like to know what you opinion is of the VAC IQ (continuous autobias) amplifiers. They sounded great wherever I heard them and they appear to be conventional designs well executed. They must have good impedance outputs to make them adaptable to drive many types of speakers like your own amps.

VAC seems to be doing some good work these days. I have worked on one of their big preamps, it was nice but picked up hum from a power amp 2 feet away. We were surprised. 

Autobias can be done many ways. The problem with many autobias schemes is that they shift bias in the wrong direction when the music gets loud (above the class A region). If Kevin worked it out well Kudos to him. I still prefer a bias pot and meter. My bias is so stable as to be checked only a few times a year. 

However many  are looking at amps that dont need adjustment as my newer RM-10. We have found that many of the new tube generation do not like the though of having to use a meter and adjust something.

I am very happy that I put the LEDs in the RM-9 in 1985.The bias circuit lended itself to them and balancing the DC coupled driver was important. When I did the RM-200 bias LEDs were a complicated option due to the circuit and the driver needed no balancing.

I feel in some ways I'm punished for putting a supermatched pair of transistors at the input and thus entered the "Hybrid" land. As always I choose the parts to do the job best. A tube in the input would have gone back to Driver Balancing pots, CMRR pots, tube selection. Sometimes doing an audiophile a favor does one no good. 

Well, at least "Mikey likes it"
ramtubes's avatar
ramtubes OP
460 posts
 
@bdp24

Roger I happened to make my first visit to a new hi-fi shop just opening in Livermore, CA in 1973, Audio Arts. It was a 1-man shop, that man being Walter Davies, now the maker of the great Last Record Care products. And as luck would have it, that was the same day Bill Johnson was delivering and installing a complete ARC system in his new dealer Walt’s listening room; a Thorens TD-125 MK.2, a Decca Blue mounted on a prototype ARC arm (it never went into production), an ARC SP-3, and Tympani T-I’s (as you said, at the time distributed by ARC) bi-amped with a D75 and D51.

I was just a kid, and spent a couple of hours getting an education in high end hi-fi. A couple of months later I had that exact system (with a Decca arm) in my own room. All set up and connected, I pushed in the power switch on my SP-3, and immediately heard a "poof" and smelled the aroma of something burning, which turned out to be a resistor in the power supply. Welcome to the wonderful world of using under-rated parts!



Thank your for the walk back in time. Anyone who is not old enough to have your experience I encourage to read every word above. Thats exactly how is was back then. My store in Richmond VA was called Audio Art and is still in business. Manufacturers visited us. Nakamichi flew in on their private Mitsubishi plane. We ate, we drank, Bob Fulton told the story how the monkeys behaved when they heard sounds carried by different speaker cables.He said bad cables confused them. No kidding. In his Fulton J system, one of the best things going back then, he used Ford solenoid coils for woofer chokes. He was delightful.


The J was cool because you made it in pieces as your funds allowed. First you bought the bookshelf speaker which was a fine speaker in itself. Did what a good "monitor" should. Then you could either buy the 8 Cu Ft woofer box or the RTR ESL tweeter. When you were done you could please the missus with a dark brown cloth and wood "hat" that covered the whole thing. Stood about 4-5 ft tall. Marvelous. No bullshit, even the monkey story is better than most cable claims today. He made some good wire when this current crowd of cable makers were babies. I think some of them are still babies the way they rant and bend science.

As to your "POOF of smoke" thats is simply an unprotected power supply. Bill didnt seem to get the point that the down side filter capacitor looks like a short every time you turn on the preamp. Rather than take the time to discover how to make a Short Protected power supply he just added band-aids. It was always claimed to be some "sonic improvement" to make it easier to swallow. Most times it was a fixing a failure mode in an unfinished design. Power supply failures were never mentioned. As I recall the SP-6A upgrade was $150 for a little circuit board with two diodes and a resistor. He always kept the price you paid plus the upgrade cost equal to the price of the newer unit. Of course you had to send the preamp back, wait 6 months and some claim they got someone elses preamp back. ARC database has lots of information, though no stories. http://www.arcdb.ws/ It is the work of a group of dedicated ARC fans. Good place for ARC info on prices, modification dates, some schematics. 

Back then the joke was. If you buy an ARC preamp you have to get two because one will always be in the shop and by the time you get that one back its aready one or more behind the latest version. People like Harry Pearson turned that inconvenience into a virtue.

If you dont believe me ask bdp24. He has obviously been around the block. Im sad for the horrible choices newbies have to make. The pressure to buy expensive cables and power cords and fuses and products that do nothing. Those did not exist when I got into this. We had to make real stuff. However we had coloful fellows like Bob Fulton, Jim Whiney, Matt Polk and Co, Arthur Jansen was still alive and I interviewed him as well as Saul Marantz and SId Smith. And last but not lease Harold Beveridge, my mentor.

bdp24's avatar
bdp24
9,874 posts
 

Roger, funny you mention the Fulton J, as that was what I replaced my Tympanis with! After having lived with the T-I’s for a year, in ’74 I heard the Model J at John Garland Audio in San Jose, powered by Fulton’s own mono tube amps (a modified Dynaco Mark III, I believe). I had heard ESL tweeters before (in the ESS Transtatic I---they had used the same RTR tweeters as did Fulton in the J, 3 of them to the 6 in the J), and the Infinity Servo-Statics, and those tweeters made the Tympanis sound SO veiled. I also was hearing and feeling the bottom octave, which was missing in the Tympanis. The J’s midrange (provided by the available-separately Model 80) was great by itself (unusually transparent for a cone speaker), but adding the RTR ESL tweeters and Fulton’s transmissionline-loaded woofer box made it a very full range loudspeaker. I no longer have the Fultons, but I picked up a pair of Transtatics in 1982 for 400 bucks.

Bob Fulton was also a great recording engineer, and his ARK label LP’s are fantastic; very alive (immediacy, like a Decca/London cartridge), transparent, and detailed, with extremely natural vocal and instrumental timbres. He recorded local Minnesota choirs and orchestras, which in their amateurishness are charming.

ramtubes's avatar
ramtubes OP
460 posts
 
@tomic601 
first thanks for the input on Ralphs amp, speakers likely the dead ESL-63 I mentioned in another post. I am away from them but I am assuming with ago all the panels are toast, the limited fault tree look I have done so far indicates EHT power supply issues. I am away from them so do not know on panel color, will check that when home next. Thanks all for inputs on rebuilders.
The fault tree should have the panels at the top and EHT at the bottom.  The EHT power supplies are usually NOT the problem in the 63's. The problem is dried out contact cement. All the panels fail over time and temperature cycling is their worst enemy. My friends died in a hot room one summer day. There are many videos on YouTube that show how the glue lets loose and how to rebuild them. Its not for the faint of heart. It is indeed sad that the 57 panels last forever and the 63 panels have a very limited lifetime due to.... GLUE!

I am away from my toolbox also but I will get DMM peak voltages measured today, SPL at 1 M

fun, real data will set you free was our mantra at work for 30 years..

As I listened to the modified and unmodified OTLs the other day on the 57s (that story is told in an earlier post of 11/26), I had the 57 terminals hooked up to the scope. I was constantly monitoring voltage. Music is fun to watch and anyone can get a good scope on eBay for under $100 and learn to use it if nothing else to look at music, look for oscillations, look for offset drift  Its really not hard, really. I suppose I sould make a video. 

I could see certain things the amps were doing. It takes a lot of experience to see and hear music and correlate, but indeed I could see current clipping and hear the mud is produced. I could see bass peaks due to low damping (that took a oscillator or sweep CD). I could hear that the low damping amp produced a boomy one note bass while the one with 4x the damping produced actual bass tones.

Years ago in the Stereophile "As we see it" column the writer asked several people what they listen for. His daughter said she listens to the "beat". Someone else the tonality, someone else the separation of instruments, someone else the soundstage, yada yada yada. 

I think this is important for listeners to think about what they listen for when they judge a system. If his daughter puts on a recording where she likes the beat it might not reveal any of the other things. But she just wants the system that gives her the "beat" 

I particularly wanted to hear high level high frequencies where the low impedance of the 57 would tax the amplifier. If I had Miles Davis I would have used him, but I dont have Miles. I do have Bach organ works with trumpet enchmade. Thats even toughter. 
      https://en.wikipedia.org/wiki/En_chamade

I could see and hear the current clipping. More hear than see. But I also knew I was in the 3% and over distortion area of the amp and 12 dB of simple feedback made a big difference in the clairty of this organ stop. I had a brief experience of being mentored by an old German organ builder so I knew and was facinated how organs worked. This music was chosen precisely to provide an audible test. It was done with levels matched by pink noise and immediage A/B switching.

BTW the 57 has a dc resistance of 0.5 ohms. If an amp has even 50 mV of offset that is 100 mA of output current which is also similar to the bias of most SS amps so at idle either the top or bottom transistors are turned off. This is not good for the speaker or amp. The 57 was meant to be driven by an amp with an output transformer where there is never any offset.

This is the stuff I think people should know that is never talked about. If you doubt me go measure it for yourself.
krelldreams
128 posts
 
@bdp24 

Thank you for your reply. Roger commented on your reply, but my question remains somewhat unanswered. Your advice, which is common (though not universal), is why I’ve never tried a 25-50 w/ch “quality” tube amp. I’d love to be able to try some amps at home, but the few dealers within reasonable distance don’t have much to choose from. One guy carries Line Magnetic, but I’m not interested in buying one of those, and don’t want to try something I’m not planning to buy, just to see if it has enough power. I’ve had five different pair of Maggies in the past 32 years, among other types of speakers. I always end up going back to them after trying something different. I don’t listen very loudly, and I don’t feel like I’m using anywhere near 200 watts per speaker, so I asked a tube amp designer what he thought would be an appropriate power output for my speakers. I have a Dynaco st 70 in my weight room system, but it isn’t a “high end” amp, so I’ve never used it in the main system, as I don’t think it would represent what a really good amp could do. I had a VAC 100 w/ch amp in the past. It was plenty powerful, but ended up losing out to a Krell KSA 250 (purely on sound quality) when I was able to do a side by side comparison. I also had CJ Premier 5’s, but they’re very powerful, so not what we’re talking about here, and ultimately proved problematic, so I replaced them with the hotrodded CJ Evolution 2000 tube input/mosfet output amp I have now. I do know that in the late 80’s/early 90’s, iirc, Magnepan had a 1960’s tube integrated playing into their speakers in their lobby... I think it was a Scott, @ 20 w/ch. I’m sure it was played at a very low level. Roger’s RM 10 looks interesting to me, as does the Decware Torii Mk IV. From an electrical stand point, would these drive MG 1.7i speakers playing music at 80-85 dB ? That’s what I’d like to know before I buy something without the benefit of hearing it first. 
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