Why am i not surprised about the darkness? This monstrosity has just too many tubes, stages, coupling caps, wire. No idea how good are the regulators either. A simple first step would be to cut down the tube count by a factor of three 
A more realistic approach is to look at the types of coupling and PS decoupling caps and improve on those. This will very possibly bring in some improvement but at a cost.
It's a nice chasis - very tempting to reuse. And yes, i know it's the greatest preamp known to mankind.
A more realistic approach is to look at the types of coupling and PS decoupling caps and improve on those. This will very possibly bring in some improvement but at a cost.
It's a nice chasis - very tempting to reuse. And yes, i know it's the greatest preamp known to mankind.
Lumi
Contrary to most postings I have read here and other places, I do not think it is the best preamp known to mankind. However, I find a lot of things that it does very hard to beat. If I could afford AtmaSphere, I wouldn't be using it!
Thanks for your reply. I have tried coupling and interstage caps upgrades, they improve resolution but sonic signature remains exactly the same. Later Lumi C that I used to have (but sold because was offered ridiculously high amount of money) was much more open and brighter with same tube complement but different power supply. I don't want to mod mine to that extent. If it is what it is, I'd rather sell it.
Rgds, M
Contrary to most postings I have read here and other places, I do not think it is the best preamp known to mankind. However, I find a lot of things that it does very hard to beat. If I could afford AtmaSphere, I wouldn't be using it!
Thanks for your reply. I have tried coupling and interstage caps upgrades, they improve resolution but sonic signature remains exactly the same. Later Lumi C that I used to have (but sold because was offered ridiculously high amount of money) was much more open and brighter with same tube complement but different power supply. I don't want to mod mine to that extent. If it is what it is, I'd rather sell it.
Rgds, M
I'd recommend selling it and applying the funds to something you like better. Lots of people like the Lumi, and you should be able to get something more suited to your taste.
I'm well acquainted with the sound of same and agree it is very dark sounding, and actually not totally my cup of tea either. For the time though it was one of the best pre-amps available that would not put you in the poor house..
Perhaps consider building an Aikido if you don't need the phono stage.
Or build both... There's lots of good designs here.
Lots of people like the Lumi, and you should be able to get something more suited to your taste. I'm well acquainted with the sound of same and agree it is very dark sounding, and actually not totally my cup of tea either. For the time though it was one of the best pre-amps available that would not put you in the poor house..
Perhaps consider building an Aikido if you don't need the phono stage.
Or build both... There's lots of good designs here.
Lumi
Thanks Kevinkr
I do need a phono stage, and an MC at that. I was just wondering why it is so dark. May be there is a do-able solution. I know I can sell it in a bit, however I have a very hard time finding affordable preamp which would be in the same league but open sounding. I tried a lot (CAT, PAC, VTL, Counterpoint) but no sigar. The only pre I liked a lot was a solid state Metaxas Opulense, but that thing nearly burned my speakers down (a famous Metaxas fringe benefit!). I'll check out designs available on site. M
kevinkr said:I'd recommend selling it and applying the funds to something you like better.
I'm well acquainted with the sound of same and agree it is very dark sounding, and actually not totally my cup of tea either. For the time though it was one of the best pre-amps available that would not put you in the poor house..
Perhaps consider building an Aikido if you don't need the phono stage.
Or build both... There's lots of good designs here.
Thanks Kevinkr
I do need a phono stage, and an MC at that. I was just wondering why it is so dark. May be there is a do-able solution. I know I can sell it in a bit, however I have a very hard time finding affordable preamp which would be in the same league but open sounding. I tried a lot (CAT, PAC, VTL, Counterpoint) but no sigar. The only pre I liked a lot was a solid state Metaxas Opulense, but that thing nearly burned my speakers down (a famous Metaxas fringe benefit!). I'll check out designs available on site. M
Re: Lumi
I don't have a schematic in front of me, but as I recall the Lumi used octal tubes. The grid-plate capacitance in octals is typically about two or three times as high as it is in "comparable" 9-pin tubes. If the grid is driven by a fairly high source resistance, such as by a volume pot or a fairly high preceding plate resistance, then bandwidth can suffer due to the Miller effect. In a balanced design there are neutralization tricks that can be played. However, in a single-ended design the only recourse is to drive each octal grid with a fairly low preceding resistance (leaving feedback out of it for now). This isn’t usually possible without changing the entire topology. I don’t know for sure if this explains the dark sound of the Lumi, but it might. I agree with Kevin; it’s probably better to sell any valuable vintage amplifier that you aren’t really happy with rather than to tweak it, ruining its value. Use the funds to build your own. BTW, I think octals are a marvelous choice for new designs, with the above design constraint kept in mind.
marknoir said:
I don't have a schematic in front of me, but as I recall the Lumi used octal tubes. The grid-plate capacitance in octals is typically about two or three times as high as it is in "comparable" 9-pin tubes. If the grid is driven by a fairly high source resistance, such as by a volume pot or a fairly high preceding plate resistance, then bandwidth can suffer due to the Miller effect. In a balanced design there are neutralization tricks that can be played. However, in a single-ended design the only recourse is to drive each octal grid with a fairly low preceding resistance (leaving feedback out of it for now). This isn’t usually possible without changing the entire topology. I don’t know for sure if this explains the dark sound of the Lumi, but it might. I agree with Kevin; it’s probably better to sell any valuable vintage amplifier that you aren’t really happy with rather than to tweak it, ruining its value. Use the funds to build your own. BTW, I think octals are a marvelous choice for new designs, with the above design constraint kept in mind.
It's always a trade off, paralleling sections reduces tube produced noise that is essentially gaussian in nature in this case by as much as 6dB, however this is at the expense of 4X the miller capacitance of a single triode.
Moving coil cartridges generally can drive quite high capacitive loads without much difficulty, but if you are using a step up transformer the reflected capacitance can be a bit of a problem at higher step up ratios.
I am not sure what kind of tubes you are running in the LUMI, however a lot of people running these report better performance in the phono stage with 5691's in place of 6SL7 and 5692 in place of the 6SN7 in the line section. This may help lighten up the sound a tad.
Depending on version carefully selecting 6DN7/6EM7 may help the sound. Note that you do want to avoid the later coin base types if possible, and IIRC the Sylvania label tubes might have sounded slightly better.
Operating currents are high in most stages and source impedances quite low. I have never heard anyone complain about bandwidth in one of these pre-amps.
Try to contact Trombone or I will direct his attention to this thread as I did a whole lot of mods for his pre-amp and Scott Frankland has also passed along a lot of tips that substantially improve the sonics of this design.
I've worked on a number of Lumis, but unfortunately ceased all commercial activity nearly 7 yrs ago, and my memory on the details of these mods is sketchy. I seem to recall redesigning all of the power supply filament regulators, and the HV supply as well.
Both the line stage and phono stage use global feedback, and in the line stage in particular the margin is rather high. IIRC there is a mod to sub a 6SN7 in place of the 6EM7 which results in about a 10dB reduction in feedback. This should open up the sound a bit I would think.
The Lumi is not that rare (relatively speaking) and doesn't command particularly stellar prices on the used market so given your previous comments I would be inclined to reverse my recommendation and suggest you follow the same path Trombone did. (I was going to recommend one of the more recent versions of the CAT SL1, so we won't go there.. )
Moving coil cartridges generally can drive quite high capacitive loads without much difficulty, but if you are using a step up transformer the reflected capacitance can be a bit of a problem at higher step up ratios.
I am not sure what kind of tubes you are running in the LUMI, however a lot of people running these report better performance in the phono stage with 5691's in place of 6SL7 and 5692 in place of the 6SN7 in the line section. This may help lighten up the sound a tad.
Depending on version carefully selecting 6DN7/6EM7 may help the sound. Note that you do want to avoid the later coin base types if possible, and IIRC the Sylvania label tubes might have sounded slightly better.
Operating currents are high in most stages and source impedances quite low. I have never heard anyone complain about bandwidth in one of these pre-amps.
Try to contact Trombone or I will direct his attention to this thread as I did a whole lot of mods for his pre-amp and Scott Frankland has also passed along a lot of tips that substantially improve the sonics of this design.
I've worked on a number of Lumis, but unfortunately ceased all commercial activity nearly 7 yrs ago, and my memory on the details of these mods is sketchy. I seem to recall redesigning all of the power supply filament regulators, and the HV supply as well.
Both the line stage and phono stage use global feedback, and in the line stage in particular the margin is rather high. IIRC there is a mod to sub a 6SN7 in place of the 6EM7 which results in about a 10dB reduction in feedback. This should open up the sound a bit I would think.
The Lumi is not that rare (relatively speaking) and doesn't command particularly stellar prices on the used market so given your previous comments I would be inclined to reverse my recommendation and suggest you follow the same path Trombone did. (I was going to recommend one of the more recent versions of the CAT SL1, so we won't go there..
)MFA
Thanks to all.
I corresponded quite intensively with Scott on this subject and there were no mods specifically to address this problem, except for a complete upgrade to a later "C" schematic with a different power supply and other changes from the early one. I will look for another pre with signature that will be closer to my taste. However, as I said before, there are some things that Lumi does great. As to Lumi not being that rare, beg to differ: every one offered for sale flies out of the window for a ridiculous price (mostly to Asia). So I'll probably stick mine into closet for now. As to building mine from scratch - interesting project, but perhaps over my technical knowledge... And then, what if I don't like it?))
Thanks to all.
I corresponded quite intensively with Scott on this subject and there were no mods specifically to address this problem, except for a complete upgrade to a later "C" schematic with a different power supply and other changes from the early one. I will look for another pre with signature that will be closer to my taste. However, as I said before, there are some things that Lumi does great. As to Lumi not being that rare, beg to differ: every one offered for sale flies out of the window for a ridiculous price (mostly to Asia). So I'll probably stick mine into closet for now. As to building mine from scratch - interesting project, but perhaps over my technical knowledge... And then, what if I don't like it?
))
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.
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.
Rebuilding
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.
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.
Lumi
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
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
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.
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.
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