MFA Lumi - possible to "un-darken" the sound signature?

[kevinkr]

Re building: if you don't like it you change it until you do..

They may be flying off to Asia these days, but there were quite a lot of them in this area at the time I was commercially active, I saw more of them than anything else other than the ARC SP11..

[trombone]

This is one of those questions with two extreme answers, and judging from what you've been saying, I think I know with one applies here.

If you want to dig into rebuilding the LUMI you can make it sound extremely good, clearing up the dark sound, etc. Or you can give up and buy something else. There are a few middle steps worth taking, but only rebuilding will really turn this into a less dark–and cleaner, I think--unit.

Before starting, I'm not sure what design you have. Mine was an older one, with a single HT supply, not the twin supplies that followed it. I suspect that the later ones had better components, though I'd have swapped them out, too.

You already heard from Kevin, a good friend and a wonderful designer in my experience. Much of what I did to the LUMI was at his suggestion. That includes his HT power supply and solid state regulators for the filaments, and a regulator for biasing the 6EM7. Each made a major improvement, especially the filament regulators. Scott Frankland's suggestions eliminated a coupling capacitor in each stage (a change that also reduced feedback and allowed me to exchange the 6DN7 for a 6SN7 type tube) and reduced some circuitry in the RIAA circuit. (The elimination of coupling capacitors may have been part of the designs after mine. If you've been talking to Scott, you probably know about his changes).
Beyond that, I can suggest the following.

Use 5691s instead of 6SL7. Mine came with 5691s; perhaps yours did. Believe it or not, the Electro-Harmonix 6SN7s work as well or better than 5692s. Use Sylvania 6EM7.

A huge component upgrade is required. Coupling caps have to be upgraded. I've gone through MITs and now use the new Teflon Vcaps. The latter was a major–and expensive–improvement. The big coupling caps remain Relcaps. All decoupling caps were replaced with Panasonics.

Resistors include Mills wirewounds, Kawames, metal films. Current requirements play a major role in resistor selection.

I went to stepped volume controls. Big difference.

Wire was a big problem in the unit I had. I ripped it all out and replaced all the power wire, umbilical, power cord, and signal wire with stuff I got from Michael Percy. I also found ways to eliminate a great deal of signal wire by rerouting parts of the circuit, etc. Again, major improvements.

I rebuilt the fusing circuits to run on one fuse rather than 2 or 3. (One fuse is eliminated right out when you built the filament regulators.)

Finally, I rebuilt all the grounds and added RFI blocking caps.

There's probably more, but that's what I recall.

[marknoir]

Wow!

My expertise is far below yours, guys!

My Lumi is an older version too, with single power supply. I also had a very late C version, which used exactly the same schematic for signal path, with exception of some changes to values, so tubes worked in a slightly different regime. That unit sounded much more open, why, I have no idea. Coupling caps were there just like in early version, and, how can you eliminate those without changing the rest of schematic? My knowledge stops here. I also had a different, very moded Lumi, all solid state regulated, and I didn't like the way it sounded - it was not very open sounding but extremely sterile.

The only things I did to my unit are: interstage coupling caps are russian military teflon, output caps are InfiniCaps with MIT bypasses, PS electrolytics were replaced because old ones began to hum. My pots are original and are STEPPED. As to tubes, I tried everything. Original set-up in a Lumi called for RCA red-based 5691s and 5692s, but I found them to be too constricted and DARK sounding. I use Jan Phillips tubes, which are more open, brighter and have a bit more gain for phono. Line stage uses Sovteks, which I find to be the most open sounding in it. In any case, search continues. As far to moding my Lumi - no. They are TOO rare these days, and it will bring far more in original condition.

[marknoir]

BTW, IMHO the Lumi proto that KBK was LUCKYYYYY! to get on e-bay, is not a pre-, but rather a post-Lumi unit. Scott may be mistaken. It is far more advanced than the Lumi and is much closer to later MC Ref. M

PS As to Lumis being rare these days - I will personally buy each and every one that surfaces - everybody I know wants one, and, if I get another one, I can mod the hell out of one! The last one I saw was offered in Canada for a mere $4000 US! I'm lying - one sold last month on Audiogon for about the same. May be it was the same unit?

Cheers

[marknoir]

Got a CAT to try out (again). Cooked it for two days. Couldn't listen to it at all... Up for sale here on trading post and elsewhere... PAC was much more acceptable.

[KBK]

yep. $106. 05? Or thereabouts, give or take a few cents. I did wait by the river for 20 years, as sun-zu said..and the body of my preamp did finally float by....

It has a few issues..that I gotta fix. It's in the process of getting a 'insurance estimate' right now,as I had situation where the power browned out for 5 minutes.., peaked!... and then... turned off and on like a motorboat..for an hour.

Blew my highly modded Belles 450 (300kuf), my Lumi....and my one-of-a-kind prototype speakers..with now defunct (no longer manufuactured) bass drivers. Turned the woofers into crunchy toast. 90VDC rails on a happy little unfused DC amp, at nearly a coupla bhp'o power...tend to do that. oops.

I'm out around $6500. Ouch! My first insurance claim!..and I've not got a 'second opinion' in the entire area within 200 miles, except me and one other guy (who has the items right now) , who is even remotely capable of evaluating the gear. The insurance company wants two evaluations.

That reminds me, I better get back on it! I just hooked up another system and completely forgot about it...now it's been nearly two months. dang.

[marknoir]

Originally posted by KBK
yep. $106. 05? Or thereabouts, give or take a few cents. I did wait by the river for 20 years, as sun-zu said..and the body of my preamp did finally float by....

It has a few issues..that I gotta fix. It's in the process of getting a 'insurance estimate' right now,as I had situation where the power browned out for 5 minutes.., peaked!... and then... turned off and on like a motorboat..for an hour.

Blew my highly modded Belles 450 (300kuf), my Lumi....and my one-of-a-kind prototype speakers..with now defunct (no longer manufuactured) bass drivers. Turned the woofers into crunchy toast. 90VDC rails on a happy little unfused DC amp, at nearly a coupla bhp'o power...tend to do that. oops.

I'm out around $6500. Ouch! My first insurance claim!..and I've not got a 'second opinion' in the entire area within 200 miles, except me and one other guy (who has the items right now) , who is even remotely capable of evaluating the gear. The insurance company wants two evaluations.

That reminds me, I better get back on it! I just hooked up another system and completely forgot about it...now it's been nearly two months. dang.

I can not beleive! Sorry... How come you didn't have some sort of protection??? I have afew power strips thru which my gear runs and each and everyone of them has surge protection. Good luck...