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

Regarding the A/B testing, while we began last weekend Roger spent the better part of the week optimizing the set up, no easy task said he. He has now been inviting folks over to listen and I took another stab at it today. This time I brought some go to CDs that I like to use, simple music for the most part, trios and duos, but there are certain things I’ll be listening for. In some cases it’s not even the music, Edgar Meyer’s and Yo Yo Ma’s breathing, Keith Jarrett’s chirping and Gary Peacock’s fretting, The footsteps in Todd Garfinkle’s Jun, the resin on the bow, stuff like that. In other cases it’s the bass, piano, strings, cymbals and high hats.

My session lasted an hour or so and in addition to some unique experiences there were some consistencies across all the music. I originally commented in my notes that the bass produced by the un-modded amp sounded fat but pleasing. However, after more listening, and especially as the bass notes went lower, it was clearly bloated. Not to mention that while the individual bass notes during the solo on Keith Jarret’s version of When I Fall in Love on the modded amp were clearly defined, they were at times smeared on the un-modded amp. In addition, the cymbals and the high hats were slightly muted on the un-modded amp and I could hear a bit of hash as well.

A couple lessons I received in the process. If I didn’t get it before, and I thought I did, I now know for certain the effects a low output impedance amplifier has on a speaker and the resulting sound. In addition, while I can easily hear the effects of an amplifier that clips or has higher amounts of distortion, I think for the first time I could clearly hear the effects of low amounts of IMD as I A/B'ed the amps. Now Roger has invited a few folks from the SFAS to be part of the next group who will participate in the listening test. It will be interesting to hear others impressions and compare notes.

Damn, now I REALLY wish I still lived in San Jose!

@ramtubes

Roger, you wrote:

"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."

Not sure what you feel is deficient with the ARC Ref 150SE specs.  If you care to elaborate, please do.

Also, have you ever bench tested the Ref 150 SE or Ref 6 linestage?  Further, have you ever A/B'd any current ARC models against other brands that you think highly about?

My speakers are pretty sensitive.  Rated at 92db.  I can play music (rock or classical) at ear-splitting levels without any apparent sonic congestion. Of course, I can't speak to distortion because I don't have the means or ability to measure those specs.

That said, maybe it really does not matter what I think.  There are a million threads where folks tout the attributes of their gear and so I guess everyone has their own favorites.  

In any case, I would like to know your reactions if you bench tested or critically listened to any *current" ARC gear.

Keep an eye peeled for my KT-150s.  I am also sending some old ARC winged C 6550s that I used on some older ARC amps (roughly 2000 hours on the tubes).  I would like to know if they have juice left in them.  Also, the 6550s might give you a clue about the tubes specs ARC used to match their tubes for purposes of matching my KT-150s.  The KT-150s are da*n expensive tubes.

Regards

BIF

Jim B did Dynaco 400, SAE, GAS and SUMO products. Brilliant guy.

@bdp24 - Eric this has truly been an eye opener. Roger can now do A/Bing on any number of amps. Fritz Heilor lives in the area recently donated a pair of speakers to us to use in a biamping experiment (Roger is impressed with his designs), so besides the Quads we have some box speakers available to us as well. The more the merrier I say. However, this listening stuff is really hard. After an hour or so I really needed a break. While some of the  differences were not subtle, in may cases you really had to focus to hear the differences, and at least to my ears, there were cases where there was no difference at all.