Does anyone care to ask an amplifier designer a technical question? My door is open.

Preamps are much easier and to me not so interesting

Roger, IME this statement is false. Many good amplifier designers think that a good preamp is no big deal and then go right ahead and design a poor preamp as a result. This is totally because they really in fact for real don't know what a preamp does! - which is to say, a lot more than just the gain and bandwidth, that sort of thing. If a preamp isn't right, it makes no difference how good the amp or speakers are, the missing information can't be recovered downstream.

I wanted the RM-200 to have good CMRR (hum rejection in simple terms). One cannot do that with a tube at the input.

We get pretty high figures and we do it with a tube.... As a hint, look into 2-stage CCS circuits. You aren't going to get good numbers without a decent CCS, a resistor or a single-stage CCS won't hack it.

It also has something few amps do not have which is the abilty to drive a dipping load with increased power rather than decreased power. Neither CJ, Rogue, ARC or anyone else I can think of has done that.

A good number of 300b SETs can do that. The Wolcott did as well.

Horn speakers tend to have peaks in the response.

Some but not all. CAD has done a lot to improve horn response- if there are problems in the throat where it couples to the horn, all is lost. But I've heard several horn setups where this common problem is overcome, and the result is that they sound very much like ESLs.

I have 6,000 LPs. A lot of them have a good bottom, some have an excellent bottom.

I love the Theodorakis performance, but alas it’s like listening through cotton.

Let’s see what it sounds like in my new room. I’ll let you know.

I have a similar number of titles. The bass really is there. There were only 1000 pressed, so its not likely to be a worn stamper. 

I still find that OTLs at low impedance are current limited. As to 10 amps without damage. When I put a 6AS7 on the curver tracer and go just a bit above the peak rated cathode current I see flakes of cathode coating coming off like sparks from a sparkler at much less that one amp. WIth the grid being so close they can easily fall into the grid wire and POOF. Horizontal output tubes that Futterman and I use are specified for high peak current about 1 amp.

I guess this really depends on what is meant by 'current' (since the word has become a charged term in audio)! And a lot depends on the 6AS7 in question too- the GAs don't hold up; most American tubes have problems in our circuit as well since they really aren't intended for fixed bias operation. We prefer the Russian variant; they hold up the best of any we've seen.

BTW, I like your approach to the whole 'damping' thing and I also appreciate your use the the phrase 'output regulation' (which I see as opposed to 'output impedance') which I see as a more accurate term. You are spot on that far too much attention has been placed on damping factor- have you seen this article by the former head engineer of EV? http://www.dissident-audio.com/Loudspeakers/CriticalLSDamping.pdfIn is we see that no speaker made needs a 'damping factor' of over 20:1 and some need quite a bit less! FWIW the original AR-1 was designed for a 1:1 damping factor.
Also kudos for the comments about too much power. Many amplifiers make excess distortion at lower power levels and when too much power is available in the amp, 90% of the listening will be in this higher distortion region- so not really taking advantage of the amp's capabilities.

BTW I first met Bill Johnson and Robert Fulton at Bob Fredere's house in Minneapolis where the two would meet for listening sessions (at the time the D-150 was ARC's SOTA amp). I wound up running a set of Fulton J's and then Premiers for several years.

RM love your idea about a utility grade ( birch plywood ? ) base for an RM-10 w exchange IF client buys amp. I would be interested in that. I have to say 14# tube amp is attractive as all heck.....

STOP recommending stuff...got the B&K tube tester yesterday, Analog circuit book is due today - you scored yours  for less €
and now a scope? Remember the Mac MPI indicator ? I recall Marantz also has a scope on some gear, as you say fascinating....

so assuming my needs are kit amp building, ESL repair and this and that, which used scope to get ?????

and yes the ESL-63 panels are toast....

Roger, lots of good information as well as memories here.  So much in fact it is hard to keep up!

As one of the older audio hobbyists here I too remember these names from the past.  I recall a visit from William Z Johnson at a local dealer to set up his Tympani/ARC system.  Interestingly that same dealer later took on the Fulton line.  Regarding Bob, "Fulton made good sounding stuff. I don't know how but I always assumed him to be a competent engineer with great listening skills.", did you know his involvement with instrument design?  For example I'd read that he designed trumpet mouthpieces.  That was confirmed by an alumni club buddy who played trumpet with a Fulton mouthpiece.  He was so sensitive to colorations in musical reproduction that he assigned a characteristic color (his interpretation) to the unique tonality of each orchestral instrument. 

atmasphere6,745 posts11-27-2018 1:15pm

Preamps are much easier and to me not so interesting

Roger, IME this statement is false. Many good amplifier designers think that a good preamp is no big deal and then go right ahead and design a poor preamp as a result. This is totally because they really in fact for real don't know what a preamp does! - which is to say, a lot more than just the gain and bandwidth, that sort of thing. If a preamp isn't right, it makes no difference how good the amp or speakers are, the missing information can't be recovered downstream.

I love being vindicated. I have personally never encountered a manufacturer who seems as neutral and knowledgeable as Ralph.
Roger, you may not think that this is a technical question, but why don't you believe that preamps do more than regulate gain and provide ample bandwidth and select sources? What is your scientific engineering basis for making such a claim? Do you feel that volume controls are a simple design choice? Are off the shelf rotary pots good enough for you? You tried to put me down that I must be "new to audio" (I am not, been at it for 43 years since age 16) and yet I bet 99% of us who have similar time in this hobby are not familiar with your preamps. Heck, your amps are miles under the radar as well. Frankly, and here is a technical question for you too, your designs, particularly your RM100 appears awfully similar to those of Don Sachs. His amps are less money. What sets yours apart from his (other than is being far more widely known by word of mouth).I can't help but note that you keep insisting that this thread is for technical questions and yet on multiple occasions you have pitched your products. You in fact asked me why I did not consider your RM200 rather than my ARC Ref 150SE. The answer is one I think I answered previously; I believe as does Ralph evidently that it does no good to have a great preamp and a mediocre preamp. Shite flows downstream. I picked my ARC Ref 6 first and then picked the ARC Ref 150SE because I could count on it mating well with my pre. In addition to my question above, I have another one. And this is not meant to be a challenge despite your likely impression that it is. What is your scientific engineering basis for concluding that damping factor, adequate power, and low distortion are the most important performance criteria for an amp (reliability and serviceability not falling within performance criteria)? You keep beating the dead horse of a single Cary amp as if it that one amp represents all that is wrong with most every competitor's design! It is my impression that damping factor being a non-issue with the great majority of competently designed amps, your design philosophy boils down to your preference for the better dynamic range afforded by the high voltage of tubes combined with low distortion. I accept the former premise-greater dynamic range from higher voltage afforded by tubes-but I reject your fixation on low distortion. Note that I used the word "fixation". Sure low distortion is critical but low distortion can be obtained and yet the amp can sound terrible. An amp can sound great and provide accurate renditions of the recording and yet be on the higher side of accepted distortion levels. My point being that there is a hell of a lot more that goes into a great amp than low distortion. You admit that you eschew premium parts because they allegedly don't afford better sound and because the price increase magnifies 5 fold to the consumer (and I agree on the effect of higher priced parts). Where is your scientific engineering proof that premium parts and wire don't make a beneficial difference? You imply (no, you outright state) that my ARC amp is overpriced compared to your RM200 "at half the price" and yet you disregard that both my preamp and amp are chock-full of expensive parts. 
There were warnings that this thread could go south if it did not remain Q and A. I appreciate that. I promise not to respond in any way in this thread again. But let me leave with these words; I believe that most who read through this thread with an open and unbiased mind will see a lot of very useful and candid information combined with some highly biased viewpoints by Mr. Modjeski and a  fair amount of self-promotion and shilling mixed in. 

Im not going to go too far with the preamp vs power amp ease of design controversy. Everyone is parroting back the party line, which I disagree with. 

I did a shootout for phono stages for our local audio society. It was a strict A/B. We had several name preamps all the way up to $20,000. I will never do this again for a club. They were sad that only one of 8 preamps sounded really different and that one is also well respected. However that one was +3 dB at 10 KHZ and it was obvious. They left shaking their heads because when they compare the same preamps one at a time they "think" they hear big differences. 

I pride myself in preamp power supplies, RIAA accuracy, lowest noise. The RM-5 is the lowest noise 6922 preamp new or old. I know this because the noise is at the limit of the tube itself, not the circuit. 

I think a lot of designers have problems with the power supplies, noise (tube rush) and hum. .These problems are not easy to solve. Perhaps that is the source of the comment. 

Ralph, I measured your preamp's RIAA and it was +4 db in the bass. That is not accurate EQ. My RIAA accuracy is +/- 0.2 dB.
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What interests me is how it came to be thought that preamps are harder. What designer is going around saying that? Im not.