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

Is there a particular Direct Drive Amp you can recommend to drive the panels? (Again I’m in a 240V 50Hz country).

I dont know of anyone making DD amps but myself. It a rather special thing.

@rost 

 I´m using a balanced configured Pass SS XP20 pre with output impedence stated at 1K/leg, balanced and 200 ohm, single ended (according to manuel) driving tube monoblocks with rated input resistance at 47K.
     Amps have both RCA & XLR (only + phase) inputs. So my question is what input is preferable and why ?
     Your response will be greatly valued and appreciated.

If I understand your correctly the XLR is unbalanced + only. If that is the case there is no difference which input you use.

@unreceivedogma

What you are doing sounds fine to me. Shows are shows and rarely a good place to judge a system. I'm lucky to fiind one system I like. 

@prof 

If my amps are being run at levels that do not bring on distortion, why do they still have that classic "tube-amp" character even at those low listening levels? If it’s not the clipping characteristics that are coming in to play...what is it that produces that classic tube sound as I described it? 

I don't know what "classic tube-amp sound" is. I mean I don't design for it. I just make a good amp and I like to use tubes rather than transistors. 

Though I see some amps intentionally colored like this Cary SLI-100 Most of us designers dont do that.Good performance is not a mystery. I am tempted to call Cary and ask them what are they thinking. I read the review and the manufacturers comment. This is a sad turn for a company that was making some good stuff. 

I will be sad if anyone buys that amplifier, however someone will like it. There always someone.

With low damping the response modification will simply follow the impedance curve.  I set up an A/B this past week and we did some listening today. We could easily hear the differences, levels matched, carefully set up for instant comparison. If I were simply swapping amps not by a relay, I doubt the difference would be as apparent. 

I did one other thing that astounded me when we went from the QUAD 57 to a competent Alan Jones monitor I said... Why do people listen to little monitors when they can have a nice, room filling ESL?

@fsonicsmith 

\\ Roger, I have two questions though the second is a doozy.

1) What do you think of the Tungsol KT150?

2) What are your top 5 criticisms of the ARC Ref series components (i.e. the Ref 75SE or Ref 150SE amp and the Ref 6 preamp)?

I ask because I own and am proud to own the Ref 150SE and Ref 6 and more importantly, they deliver untempered joy and because while you said some negative things about Bill Johnson, you passed over the fact that Ward Fiebiger was the mind behind the latest designs.

Hears what JA had to say in Stereophile..  The Audio Research Reference 75 measures well for a classic tube amplifier design with a single pair of output tubes for each channel and a modest degree of loop negative feedback. Its output transformers are also of good quality, the only proviso being that the amplifier should not be used with loudspeakers whose impedance drops significantly below the nominal value of the output transformer tap
Read more at https://www.stereophile.com/content/audio-research-reference-75-power-amplifier-measurements#jbpCd1H...

He wasnt too happy about the output impedance.

I have tested the KT-150 but as yet not interested in using it as it has a single source. It is expensive, It is cool looking in some ways, the data sheet is way off and there are no curves. 

#2 What do I think of ARC.

No tech likes to work on their equipment. I won't any longer.

I did a repair on the M200 that had been back to the factory for expensive repairs that did not fix the problem. The problem was a regulator transistor installed backwards. So much for QC. Since the same mistake was made in two mono amps, how many other amps off that run had the same problem. It was intermittant, very hard to find. 

Bill Johnson got way over the top with complicated circuits, never learned how to make a proper power supply that was short circuit protected. The first SP-6 took the regulator transistor out of safe area every time you turned it on. So the 6A had a little zener board to bypass the turn on. I mean really, this is the solution of a child. Since the power supply problem never got fixed he finally put a tube in place of the transistor... and called it a sonic improvement, of course.

They made too many versions of everthing collecting $$ everytime you passed go. Most of the mods were called "sonic improvements" but all the mods on the SP-6 (which went to E) were reliability mods not sonic. 

Their build quality is lovely sadly their circuits are not. I have not met Ward. I see that things are departing from Bill's complexity back to something reasonable. Yet why send an amp to JA that is not going to test well?  The IM on that amp is pretty high. It doesn't meet its own spec. 

The new power amps have the power tubes on the PCB which is a horrible thing to do. 

If not for Harry Pearson they might have died on the vine. Harry, the self claimed "Audio Pusher" got in bed with them and profited from a lot of loans never returned. When I visited Harry at Sea Cliff there was a ARC preamp standing on its side in the bar sink. 

The meters are cool looking, the price is high, I can see why people buy it but I cannot recommend it. 

Im sorry, but you asked. I'm sorry to be so negative about ARC, but  I was a dealer for them from 1975 to 1980. If you have not heard about the "pink papers" thats a story in itself. ARC treats dealers with a heavy hammer, large opening order and threats if you do not follow the party line. Bill called us up one day because he heard we were doing A/B comparisons for our customers. He said "stop immediately or I will pull the line"