Lew M's system June 18, 2019, 2:16pm
Welcome, Guest. Please login or register.

Forum Login
Login Name: Create a new account
Password:     Forgot password

Archived Sound Lab Owners Forum - Please go to http://www.soundlabowners.com/cgi-bin/yabb2/YaBB.pl    General Boards    DIY, Tweaks & Modifications  ›  Lew M's system

Lew M's system Print
1 Pages 1 Recommend Thread
April 15, 2013, 6:34pm Report to Moderator
Guest User
I'll say it up front. Lew's system may be the best one I have heard.

I was in Lew's area for a high school reunion and arranged to spend Saturday morning listening to his system: non-PX A-1's, with the Australian toroid--resistors removed. Amps: 60-watt Atmas, much modded by Lew. No subwoofers. Absolutely wonderful. Very clean, with lots of texture and impact. Stunning depth and palpability. Great from sweet top to growly, solid bottom. Congratulations, Lew.

My system sounds very good, but I believe it should sound better; but it doesn't (yet!). At least Lew has shown me the potential of what I have but have not yet realized. I have M-1's (new toroid, PX) but, so far, I have had to use subs to beef up dynamics and bass. I have Atma MA-1's, but I am still experiencing a rolloff of the highs.

So here's what I am working on:
1. I sent my input tubes back to Ralph Karsten (Atma-Sphere). He tested them and found one that was shorted. It's possible this was in the circuit of the MA-1 I did my testing on (Murphy's Law). I haven't had a chance to check the amps out again yet. Maybe tomorrow.
2. Ralph suggested that even though I have new output tubes, in his experience some may have been damaged in shipping. Since the loss of a tube in OTL amps raises the output impedance, this might account for the rolloff of high frequencies I have been experiencing. I gave them the eyeball test this afternoon; a friend is coming over with his tube checker tomorrow. The tubes can pass the tube-checker test and still not be very good. Tube checkers normally do not stress tubes as much as amps do.
3. If the tubes check out OK, I (well, my metrologist friend) will run frequency response tests on both MA-1's into a dummy (resistive) load.

That's it for now. If anyone has any more ideas, please pass tham along.

BTW, both Ralph Karsten and Roger West have been absolutely super and a joy to work with. They are very responsive, forthcoming, and willing to listen.  

April 15, 2013, 6:36pm Report to Moderator
Guest User
Sorry, the computer ate my PS.
I meant to add that I am still thinking about removing the resistor bank from the backplate. I have a feeling they are robbing me of power and lowering the impedance seen by the amp, thus helping to roll off the highs.
E-mail Reply: 1 - 5
April 17, 2013, 12:21am Report to Moderator
Guest User
Hello Chuck

Good to know that you have met up with Lew and checked his system out.

From what you are saying, his backplate configuration is pretty hard to beat.

His backplate is similar to mine, and I have tried many things and I am still going with the minimalist approach without the extra resistors and caps that SL current set-up utilises.

Putting resistors and caps in circuit is a backward step in my set-up and to my ears.

What would be interesting is for either Lew or me to compare the performance of the Australian Transformer to the toroid that SL is currently supplying.

So far my correspondences with Lew seem to suggest that the sound we are getting is too good to bother with trying out the toroid. You already have both, perhaps you can try them and tell us what you reckon.

Please note that without caps and resistors in place, SL speakers may not be able to publish commercial specs on their speakers which is necessary for any commercially marketed speakers (as the backplate is not 100% stable for every type of amps).

For people wanting to try-out Lew's backplate configuration, please proceed with caution.


E-mail Reply: 2 - 5
April 17, 2013, 12:25am Report to Moderator
Guest User


I thought Lew upgraded to 845s. Are you sure it was M1 non PX?

E-mail Reply: 3 - 5
April 17, 2013, 5:29pm Report to Moderator
Guest User
First, thanks to Chuck (Throwback) for the compliments. Second, Will is correct; the speakers Chuck heard are 845PXs, not A1s.  Chuck, I can understand how one might not know a PX at face value, but the 845s are gigantic enough to distinguish themselves from A1s. (Kidding.)

Chuck's plan to visit galvanized me to get my own highly modified Atma-sphere amplifiers up and running so as to be able to entertain Chuck.  I had been having a completely vexing problem with one monoblock. It was blowing output tubes, and as I have changed over from 6C33Cs to very costly and unobtainium 7241s, the problem was very expensive indeed. A total of five 7241s (replacement value around $175 each at current eBay prices) were blown before I finally think I identified and fixed the problem. (7241s are a single-section tube, but each contains 3 cathodes that are separately and internally fused. I was blowing one or more of those internal fuse wires, such that the damaged tubes now have only 2 out of 3 functioning cathodes, which proportionately reduces the current-carrying capacity of the tube as a whole.)  Anyway, I "solved" the problem (I think) literally two days before Chuck arrived.  Why these 7241s have more than doubled in value over the past year is beyond me; I cannot figure out who uses them and why, besides me.
E-mail Reply: 4 - 5
April 18, 2013, 7:37pm Report to Moderator
Guest User
The new toroids are a double edged sword. On one hand, there is increased efficiency, on the other hand there is  the kind of brightness that new PX panels displayed before about 200 hrs. breakin. My last correspondence with Dr. West indicated that between the brown  and green wires on the new toroid there is a lot of variety about the crossover and the strength of the high frequencies. I am using the brown wire with the old 36uF, as opposed to the 24uF. What I finally did was put back the brilliance control to before 12 0'clock to cut down on the brightness. As the system breaks in, I am turning up that control.
I would say that you have to have at least 200 hrs. on the new toroids before anything can be judged. Another unfortunate thing is that solid state amps don't really perform as well with the new setup, based on subjective listening. I was completely pleased with my Bryston monsters: now I am not sure. With the new efficiency, the choice of amps is much wider. I wish I had my two-chassis custom Moscode 600's to try on this rig. What we have gotten with the PX technology and the new toroids is a very pleasing midrange and controlled bass. I have not solved the problem of the extreme highs. Perhaps more seasoning will ameliorate the problem.
E-mail Reply: 5 - 5
1 Pages 1 Recommend Thread

Thread Rating
There is currently no rating for this thread

Powered by E-Blah Forum Software 10.3.6 © 2001-2008

Valid XHTML Valid CSS Sourceforge.net Powered by Perl