Lightspeed Attenuator - Best Preamp Ever?


The question is a bit rhetorical. No preamp is the best ever, and much depends on system context. I am starting this thread beacuase there is a lot of info on this preamp in a Music First Audio Passive...thread, an Slagle AVC Modules...thread and wanted to be sure that information on this amazing product did not get lost in those threads.

I suspect that many folks may give this preamp a try at $450, direct from Australia, so I thought it would be good for current owners and future owners to have a place to describe their experience with this preamp.

It is a passive preamp that uses light LEDs, rather than mechanical contacts, to alter resistance and thereby attenuation of the source signal. It has been extremely hot in the DIY community, since the maker of this preamp provided gernerously provided information on how to make one. The trick is that while there are few parts, getting it done right, the matching of the parts is time consuming and tricky, and to boot, most of use would solder our fingers together if we tried. At $450, don't bother. It is cased in a small chassis that is fully shielded alloy, it gets it's RF sink earth via the interconnects. Vibration doesn't come into it as there is nothing to get vibrated as it's passive, even the active led's are immune as they are gas element, no filaments. The feet I attach are soft silicon/sorbethane compound anyway just in case.

This is not audio jewelry with bling, but solidly made and there is little room (if any) for audionervosa or tweaking.

So is this the best preamp ever? It might be if you have a single source (though you could use a switch box), your source is 2v or higher, your IC from pre-amp to amp is less than 2m to keep capaitance low, your amp is 5kohm input or higher (most any tube amp), and your amp is relatively sensitive (1v input sensitivity or lower v would be just right). In other words, within a passive friendly system (you do have to give this some thought), this is the finest passive preamp I have ever heard, and I have has many ranging form resistor-based to TVCs and AVCs.

In my system, with my equipment, I think it is the best I have heard passive or active, but I lean towards prefering preamp neutrality and transparency, without loosing musicality, dynamics, or the handling of low bass and highs.

If you own one, what are your impressions versus anything you have heard?

Is it the best ever? I suspect for some it may be, and to say that for a $450 product makes it stupidgood.
pubul57
I meant to say not very dimensional as recorded.
Yes, the sound stage and imaging manipulation that active components and even some cables add to the equation is very evident after listening to a passive preamp in the system. I would agree that the LSA does not have the spatial capabilities of some other active preamps, but I'm fine with that as it does reproduce the music in a truer form.

Hanging out with a recording engineer of late, I have learned that most of what we perceive to be the sound stage created by our systems comes straight from the recording. Room acoustics play another part, as does speaker placement. I myself dislike hearing a drummer whose arms appear to be 8 feet long, or a piano that appears to be 12 feet wide, or a vocalist whose mouth appears to be a 3 foot round oval. Too much for me. I'm not sure who it was that said this, it was a reviewer I think, but the point was that the sound stage should not extend beyond the speakers. I think I might agree with this thinking. Depth and height, as well as space between the performers are another matter though.

I have a couple of compilation discs from Ridge Street Audio that offer excellent recordings where the sound stage is well reproduced. I made some copies for a friend and he commented on the improved depth of the sound stage he heard with these recordings. He seldom hears the same level of depth with other recordings. Goes to show what can happen when the recording engineer is paying attention.

The Truth awaits us...
09-05-10: Clio09
Yes, the sound stage and imaging manipulation that active components and even some cables add to the equation is very evident after listening to a passive preamp in the system. I would agree that the LSA does not have the spatial capabilities of some other active preamps, but I'm fine with that as it does reproduce the music in a truer form.
This is not meant to be to be an attack on the Lightspeed or any other optocoupler, but more a statement about overall component dedication.

Almost all devotees of a particular type of component swear theirs presents a "truer" form of reproduction. I can remember the long, long, threads dedicated to Placette's passive(resistive) units and how they were the ultimate of transparency and everything else was simply distorted. Then came the Transformer Volume Control(TVC) adherents, of which I am one, swearing theirs bested all others and were the truest form of reproduction, soon to be challenged by the Autoformer crowd for that title.

And all of these camps heaping scorn on solid state, tube, and hybrid active preamplification for being "colored", "distorted", etc, etc.

As we all know, it is almost impossible to know which component is "true" and others are additive, or subtractive(except for truly bad components), unless one was present for the actual recording session. As to knowing what is the "true" amount of soundstage width or depth on a myriad of recordings, I think that would be an impossible task.

In reality, any preamplification is probably "truest" if it helps bring the listener a deep emotional connection to their music within the context of that listener's musical preferences and system/room acoustics. Nothing else should matter, in the end.
I'm not sure who it was that said this, it was a reviewer I think, but the point was that the sound stage should not extend beyond the speakers. I think I might agree with this thinking. Depth and height, as well as space between the performers are another matter though.
I would think this would be an oddly distorted "view" of a recorded performance. Most live, and even studio, venues are wider than the average 8 ft that speakers are apart. Recreating a symphony into an 8 foot space would itself seem to be a artifice equal to one that extends beyond the speakers. Neither is being "realistic", but closer to scaled down versions of reality. Much like the difference between watching movies on a 40" or 65" screen.

Having said that, Lightspeed attenuators have fascinated me ever since the first threads started appearing on DIY Audio years ago. I would love to hear one in the near future, but my next system will be (hopefully) all balanced/differential with sources and preamp across the room next to my listening position and the amps/speakers on the other end. This could end up being quite a long distance.
I enjoyed reading that, well said, and certainly the issue of what gear will connect the listener to the music is as varied as there are people. As far as soundstaging is concerned, what I do notice with the LSA is that the apparent soundstage seems to change quite a bit from recording to recording, which I suspect is a good sign that the LSA is making and effort to "get out of the way" between source and amp. I also notice, as Clio9 suggested, that instruments do not seem to be oversized or stretched as often occurred with Patricia Barber's piano with some other very fine preamps I have owned. I don't know if you took 10 audiophiles and had them compare the LSA to, let's say, the ARC Ref5, how many would choose one over the other in blind listening, and both can certainly make for an excellent sounding system. But the fact that you could make the comparison tells you just how good the LSA (and other passives - I too have followed a similar path, Placette, K&K, Bent AVC, etc)are in the right system. Will prefer them to fine active preamps? Only listening will tell and I'm sure there will be those that walk out of the room with that Ref5 in tow.
Darkmoebius
As we all know, it is almost impossible to know which component is "true" and others are additive, or subtractive(except for truly bad components), unless one was present for the actual recording session. As to knowing what is the "true" amount of soundstage width or depth on a myriad of recordings, I think that would be an impossible task.
In reality, any preamplification is probably "truest" if it helps bring the listener a deep emotional connection to their music within the context of that listener's musical preferences and system/room acoustics. Nothing else should matter, in the end. Darkmoebius



Thought I'd chime in on this one being the manufacturer of the "Lightspeed Attenuator".
Hi Darkmoebius, welcome to the discussion, you used the magic word "truest" twice in the above reply. Having not yet heard one for yourself, can I make a suggestion to get the "truest" idea of what pre/amp passive or active is "truthful" to the original recording.
Plug your CD player or dac directly into your poweramp "this will be a perfect impedance match" As you have no volume control, first off play something that is low in level to gauge how loud it will be, doing this you are playing the "truest" form of cd/dac playback you can possibly get. Then slip the Lightspeed or any other pre active or passive back in adjust for the same level, and you will see and hear which one is "truest" to the source.
Cheers George
Sounds like the Bolero Test by Arthur Salvatore, which also concludes that if ANY active linestage sounds better than a passive there is an impedance mismatch and the system NEEDS a an active stage. In his view, there is no better connection between a source and amp than the direct connection, and then a passive preamp. Hard to think that all those beautiful tubes in an active tube preamp does not bring beauty and flesh, etc - but it does not seem that any of that is actually in the recording (as the direct connection makes perfectly clear).
09-06-10: Georgelofi
Plug your CD player or dac directly into your poweramp "this will be a perfect impedance match" As you have no volume control, first off play something that is low in level to gauge how loud it will be, doing this you are playing the "truest" form of cd/dac playback you can possibly get. Then slip the Lightspeed or any other pre active or passive back in adjust for the same level, and you will see and hear which one is "truest" to the source.
Great point, George!

I actually did this years back with a borrowed Museatex Bidat when comparing my TVC to some active pre's I was considering. The Bidat(300ohms/3.5V RMS max) went directly to an Art Audio PX-25(180k/700mV/6wpc) SET amp driving Cain & Cain IM-Bens(~95dB/8ohm). Obviously, I preferred the passive route.

But, it did pose a problem playing vinyl w/ low output cartridges. I needed the extra gain of an active preamp or a phono pre with a lot more gain.
09-09-10: Darkmoebius But, it did pose a problem playing vinyl w/ low output cartridges. I needed the extra gain of an active preamp or a phono pre with a lot more gain.
Darkmoebius

Strange? I have lots of Lightspeed Attenuator customers that use vinyl with low output moving coil cartriges, all they have is a good phono-stage like the Tom Evans and then Lightspeed Attenuator directly into their poweramps, and they are at 12o'clock on the Lightspeed for good loud level, with plenty headroom left in reserve, they say it the best they have ever heard their vinyl sound.
Cheers George
So it seems that true to the source (or at least to the output from the CD/DAC with no impedance mismatch)has to be the standard and that any alteration caused by even the most expensive and sophisticated active preamps is an alteration having nothing to do with what is actually on the recording, not part of the music as recorded, and yet there is an enormous contingent of folks who swear that the passive approach is missing something (staging, PRAT, warmth, etc)that the actives, especially tube actives, provide. But logic seems to dictate that whatever is being heard through the actives simply is no part of the recording, it is coming from somewhere else, a distortion of the signal seems to be the only thing to call it. Any yet, many seem to prefer it, but true to the source it cannot be, or so it seems. Now maybe it is a matter of not being able to take the truth, and pleasant alterations are what people prefer. Ken Stevens of CAT once said he wanted his preamp to have the sound of water, no coloration, clear, transparent. The Lightspeed seems to meet that goal, as long as gain and impedances are what they need to be, if they are not, than an active is needed or the "direct connection" won't work. I do know it is hard to accept that a "simple" attenuator can possibly be better than a 50lb, $10,000 preamp full of stuff, and there is nothing in the LSA nearly as endearing as a NOS Amperex tube.
09-09-10: Georgelofi
Strange? I have lots of Lightspeed Attenuator customers that use vinyl with low output moving coil cartriges, all they have is a good phono-stage like the Tom Evans and then Lightspeed Attenuator directly into their poweramps, and they are at 12o'clock on the Lightspeed for good loud level, with plenty headroom left in reserve, they say it the best they have ever heard their vinyl sound.
It just so happened that my active stepup(+22dB) amp and phono preamp(+42dB) were just a little short when it came to overall gain using my Denon 103-D(0.25mV) and Grado "The Statement" (0.5mV). It was possible to use the Grado with my PX-25, but but not with my 300B monoblock amps(1.5v) and other amps.

Obviously, there are other phono preamps with more gain, but I really liked the performance of mine(+TVC) with higher output carts, at the price I paid for them.
I have used the Lightspeed with both MC and MM cartridges. No issues whatsoever. With MC I use 68db gain on my phono stage and the Lightspeed is at about 2 o'clock or so on the dial. With MM I use 42db gain and the Lightspeed is at 11 o'clock or so on the dial.

I have even used the Ligtspeed with an amp whose input sensitivity is nearly 3V. I even doubled the sensitivity to nearly 6V and in both cases the Lightspeed worked fine. at 6V I was pretty far around the dial, but that is what the amp manufacturer recommended having tested a Lightspeed on his own.
Great sound does not have to cost a lot. Great looks are nice to have, but it doesn't necessarily equate to great sound. Convenience seems to be something many audiophiles want, but a remote or multiple inputs can do more harm than good. Tubes are fun to play with, but can inject noise or colorations.

We get to make our choices and we get to live with the results, for better or worse.
Anthony, I agree. There are many reasons to own a full-featured, robust active preamp and yes, even the "audio jewelry" aspect is as legitimate as any other reason for prefering a piece of gear.

What I am missing is the "active" argument solely on the basis of sound in a system with appropriate gain and impedance matches. There was some conversation earlier on about "true to the source", and by that I don't mean true to the live event being recorded, but true to everything in the signal coming out of the source (e.g. CD player output) - at least once removed from the live event - but anyway all the rest of the system has to play with. It seems to me that if anything is different, in any way, from the direct connection, it is an artifact and not true to the source. I won't argue that some, many may prefer the sound of those artifacts, and they are perfectly right to choose according to their ears and preferences, what I don't think can be argue logically is that any active preamp, no matter how expensive, can be as "true to the source" as the Lightspeed Attenuator (assuming proper gain and impedance matches). There may a difference in preferance based on accurate versus pleasant, and we are all free to choose the camp that makes most sense to us, and that choice can't really be argued with. I would though argue that a neutral preamp can be mixed with the widest range of sources and amps, which are then left to present their own sonic signatures.
09-09-10: Clio09
I have used the Lightspeed with both MC and MM cartridges. No issues whatsoever. With MC I use 68db gain on my phono stage and the Lightspeed is at about 2 o'clock or so on the dial. With MM I use 42db gain and the Lightspeed is at 11 o'clock or so on the dial.
What was the output of your low MC's? (maybe I screwed something up, I'm a vinyl newbie)

The 0.25mV 103D into my phono pre+active stepup's 64dB gain yielded 0.4V, that just didn't cut it into either of my amps, especially the 1.5V monoblocks.

I suppose other important factors would be size of room, sensitivity of speakers, listening distance from speakers, musical complexity, and desired listening volume.
The 0.25mV 103D into my phono pre+active stepup's 64dB gain yielded 0.4V, that just didn't cut it into either of my amps, especially the 1.5V monoblocks.

Looking at those measuremnts you should have had 2.65v output more than most cdp's.
You either have a fauty phono stage not giving 64db of gain, or the cartridge is faulty and not giving .25mv
Cheers George
What was the output of your low MC's? (maybe I screwed something up, I'm a vinyl newbie)

Dynavector 20XL low output version rated 0.25mV. However, mine was going into amps whose sensitivity was rated 1V and 0.7V respectively.

As for being a vinyl newbie, maybe I'm mistaking you for someone else, or maybe the vinyl set-up listed in your system is a mirage. However, I've been to that pictured location in San Pedro listed on your system page (I think you've moved since then) and bought one of your two Scheu turntables at the time. Having two of those tables, me thinks you're probably not a vinyl newbie, but hey, when it comes to vinyl set-up we all make mistakes.

Try again and see.
I would though argue that a neutral preamp can be mixed with the widest range of sources and amps, which are then left to present their own sonic signatures.

That's exactly why I'll only have tubes in the amp and nowhere else in the chain. Too many tubes, too much coloration/artifact (granted other non-tube components such as transistors and op amps can add coloration/artifact, but IMO tubes can be the worst culprits). Not to mention we haven't even discussed cables and as Ralph Karsten so often states, the coloration/artifact added by cables also has to be taken into account. Too bad the Lightspeed couldn't be developed as a balanced version that supported the 600 ohm pro audio standard. Then we could eliminate the cable from the equation as well.
09-09-10: Clio09
Dynavector 20XL low output version rated 0.25mV. However, mine was going into amps whose sensitivity was rated 1V and 0.7V respectively.
The extra +4dB gain that you have over my phono leads to ~37% more output. That could be the difference between barely acceptable and good performance. But, now you've got me thinking that I may have jumped to a flawed conclusion and I should have played around with more IC's. Sadly, I sold the Graham Slee Era phono & EXP stepup, it's possible I didn't need to.

The upside of this may be that I have no reason not to try the Lightspeed in the near future. Especially at it's price.

maybe I'm mistaking you for someone else...I've been to that pictured location in San Pedro listed on your system page (I think you've moved since then) and bought one of your two Scheu turntables at the time. Having two of those tables, me thinks you're probably not a vinyl newbie, but hey, when it comes to vinyl set-up we all make mistakes.
Ha! Good memory, that's me. I moved out of that house 3 years ago, and have slowly been selling off the system for "the next big thing"(which still hasn't happened). I still have the Cain & Cain speakers and the Scheu w/ 80mm platter, though. I'm in a much, much, smaller apt right now, but want to get a vinyl and really good headphone system going in the next few months to hold me over until I move again.

I guess I should be saying "Full Lightspeed ahead!"
Pub- Thank you for referencing some jazz. Yes, good-ol' Cannonball. Years ago, the guys in my band (the instrumentalists, I was the singer) got to sit-in with 'Weather Report' (Jaco was a friend of my bass player), and possibly coolest of all, Benny Goodman, Bobby Rosengarden(drums), and Bucky Pizzarelli(guitar), on what might have been Benny's last performance tour. You should hear some clarinet on vinyl thru a Lightspeed. When I use the Lightspeed for records, all I'm running is a "budget" Cambridge Audio 640P into it, behind a N.O.S Grace F9F mm on a Thorens TD160, and it's incredible. Re: "The Shootout" ... Whatever they were hearing was not the Lightspeed, unless there was a black hole nearby, with it's singularity pulling on, and distorting the light between the LED and the LDR. That might have given the Lightspeed the colorations and artifacts some needed ... in case the rest of the system was perfect, and soundless.
Anthony, if I read Ralph right, "Not to mention we haven't even discussed cables and as Ralph Karsten so often states, the coloration/artifact added by cables also has to be taken into account." what he has been saying, and given the fact that he makes and sells activ e tube linestages, I seem to hear him say that the reason for an active is to control the ICs, and that is the basic reason for an active, it's buffering of source-pre-cable-amp. Suggesting a preamp makes for a more universal tool in more systems, but that when the total capacitance is dealt with a passive is about as good as it gets, absent the need or desire for colorations of tone or "space".
There are a number of DACs on the market with 1V or greater output and digital volume control. Setting aside potential loss in resolution from the DVC, would the LSA provide better sound than direct-to-amp?
Is it the case that one a digital volume control is fully open, no attenuation, there is no loss in resolution? That was my understanding, but I am not technically proficient.
Yes, if the control is wide-open, or at least above a certain level, there is no loss in resolution. Assuming you were able to use/keep the DVC at a level above which there was no loss in resolution, would there be a benefit in using the LSA?
I would think so, as in essence a fully open ouput with a variable output CD player would be the same (I think)as a regular CD player with a fixed output and you would be controlling volume with a superior attenuator than what is built into the CD/DAC. That is what I think, but I would rather have someone more technical pipe in.
You are right Pubul57, the momment you start to lower a digital based volume control, you start to whats called "bit strip" the name says it all, and this lowers the resoution. Aways leave it full up when using in conjuction whith the Lightspeed.
But also be carefull some dac's and cdp's have analog based volume controls and these are usually sub grade passive motorized or non-motorized on the output of the cdp or dac. Most times you have also fixed ouput rca's as well on these cdp/dac, always better going for it and a Lightspeed than the analog variable output. If there are no fixed ouput rca's, better to open it up and bypass the passive pots by taking them out of the output totaly.
Cheers George
Yes the idea of an active preamp, or in the case of The Truth preamp, a buffered passive, the idea is to control the ICs. However, in unbalanced designs its my understanding that while this might provide some benefit to using longer runs (ex. you can use 30 ft. ICs with the Truth with no sonic degradation), it doesn't mean that the coloration/artifacts of the cable itself can't be heard.

I've convinced my tech here to design a passive balanced preamp that supports the 600 ohm standard. If I use this with my Atma-Sphere S-30 I should be able to eliminate the cable coloration/artifact from the equation.
From what we have learnt and heard for myself, the only way to make all interconnects invisible (sound the same) with no sonic signature, is to have the poweramp input impedance at 1kohm or less, this then becomes a hard load for the pre to drive unless it has an output impedance of close to 1ohm and plenty of current behind it, something like the top Krell pre amps may be that low, then the pre itself has a sonic signature itself, so it's not an easy task.
Cheers George
George, is it your view that the Buffering used in preamps, and passives like the BENT, The Truth, or the First Watt B1 is there for handling worst case scenarios - long or high capacitance interconnects, or amps with low input impedances, but where the ICs are low capacitance (Cardas GR 12p/ft) or high input impedances (100kohm)that a bufferless approach will always be superior? That is how I read it, and that something like the LSA is about as good as you can get in not altering the source signal to the amp.
That is correct, buffers are there to drive long interconnects, and or low input impedance amps. There is no perfect buffer they all sound different As there is no perfect interconnect they all sound different, unless the amp is so low in input impedance then this puts all interconnects (within reason) on a level playing field

I keep comming back to this, plug the cd player straight into poweramp ( with more than 47kohms input impedance) with good quaity 1-2mt interconnects, this is the perfect transmission of the cd players sound (save for the interconnects signature), then put in the Lightspeed Attenuator without buffer and see how little it influences that sound compared to any other active pre or buffer.
Cheers George
George, maybe you can help me figure something out. I was using the Lightspeed with a pair of monoblocks that supposedly had a 10k input. Theoretically this would not be an ideal match for the Lightspeed, but I heard nothing out of the ordinary. Any explanation for this? The link shows a schematic for the circuit.

http://electra-print.com/singleended_a2.php
I assume you are using the input that is full range not the one with the roll off at 70hz.
The diagram actually shows it's 27k input impedance this together with the 1uf coupling cap (yuck) gives a 5hz -3db roll off, the opamp is a 14watt chip amp that has an input impedance of 5megohm, you could change the 27k for 82k and you will see it will sound better. And go lower theoretically as the 82k resistor now with the 1uf coupling cap (yuck) will now go down to 2hz -3db but you will not hear this as the interstage transformer and output transformer cannot go down this far anyway.
But don't switch on the amp without the Lightspeed attached as that will let the chip amp see only the 82k resistor and chip amp may complain, when the Lightspeed is attached it sees the 7k odd of the Lightspeed and it will think everything is fine still.
Cheers George
by Georgelofi
George, what don't you like about that 1uf coupling cap? Any suggestions for modifying the circuit?

I will try the 82k ohm resistor. Thanks for the suggestion.

BTW - the amps I have in house are full range only.
I much prefer direct coupling, I can hear coupling caps. But I do not think this circuit can be direct coupled as I think there is a high input offset from the chip amp, I could tell better if they gave a the internal circuit diagram to it, but they don't.
Cheers George
George, the "passive" "active" debate seems to me more problematic the the tube versus SS debate, for in the latter, there remains room for both to coexist. The passive argument, if right, threatens manufacturers of active preamps, reviewers and magazines supported by advertising from makers of active preamps, and also threatens owners of active preamps that have invested in them and might feel compelled to justify the expense of the gear and protect it from dimishment of the value of their asset. Not to say that there are not systems that need an active to perform well, and I think that is covered here pretty well.

In a review of the Wytech Opal in Positive Feedback, the reviwer said:
Something very interesting goes on when a preamp handles a low-level signal (or not so low in the case of CD). In theory, a preamp should be unnecessary when the source is capable of 2 volts (standard maximum output for a CD player), but experience has shown me that doing without an active preamp does not lead to improved sound. One possible explanation for this is that most CD players have relatively weak output stages. In most cases, they consist of a few op amps and/or some discrete transistors, driven by a power supply that can barely be deemed adequate by high-end audio standards. For the purpose of driving an amp, most are inadequate, and the result is often a bit harsh and/or harmonically "bleached." There is resolution but not refinement, suggesting a system under stress at musical peaks. Also, the sound often lacks dynamics. Many internet contributors claim that this is the sound that was actually recorded, and that if you don't like an aggressive, flat soundstage and lifeless dynamics, you simply can't handle the truth. Some even conclude that an active preamp, which can provide effortless dynamics, a deep, wide soundstage, and palpable, 3-D imaging, is in fact generating artifacts or "enhancements" that are not on the recording. I don't believe that these effects are artifacts, but information that is lost when those recordings are played on lesser systems. Making classical recordings in a real space has led me to believe that these spacial characteristics are real, and can be either captured or added in the mix.

Another argument for eliminating an active line stage is it does not in fact amplify anything, but acts "merely" as an attenuator 90 percent of the time. While it is true that the input is often of a higher voltage than the output, an active preamp also gives the signal a deep reservoir of current drive and voltage stability from its own power supply. Think for a moment about how a preamp works. First, the signal from the source arrives and is attenuated, then the signal is amplified again—replicated, if you will—by a circuit that has a larger and more stable power reserve than the original source. Since the gain of most preamps is fixed, the active part of the line stage is always amplifying the signal, not attenuating it. Since it is only the amount of signal to be amplified from the volume attenuator that changes, the concept that an active line stage is only attenuating the signal is false. In fact, the preamp first reduces the incoming signal, then beefs it back up with (ideally) the same amount of information, but greater drive and control."

What do you think of that? I think my EMM Labs must have a pretty good power supply....

"
Maybe you have even better amp/speaker synergy. That's where the real magic in sound reproduction lies.
You are right Paul, in some instances.
But in our case with the parameters I have outlined for the Lightspeed Attenuator, if you have a source that has low output impedance, less than 100ohm and 2v or more output voltage, and the power amp at more than 50kohms input impedance, there is absolutely no need for preamplification, (it's Ohms Law). No amount of extra current in the form of extra active current stages will have the desired effect of giving more drive and control, if fact the opposite could be had and heard, as well as a loss of transparency.
Cheers George
I think this is beyond the reach of logic, it is simply a matter of trying it within the system context as you proscribe and listening for yourself. With all the preamps I have tried (most $5,000+ tube preamps)I've concluded that most negative comment about passives (and resistor versus TVC/AVC for that matter) must come from those with a financial interest (as makers or owners of active preamps), or simply not evaluated in the right system context, or one simply likes euphonic colorations - and they have every right to prefer that. In the wrong system context, it would be like proclaiming the weakness of low watt SETs by evaluating them with a pair of Thiel or B&W speakers, a meaningless assessment of what SETs can do.
Publus57, the active vs. passive debate is indeed an interesting (and old) one. Many of the guys making active pre-amps today have toyed with passive designs in the past.

My crude understanding of the Lightspeed and devices like it is that its a variable resistor triggered by light. This idea is not new. Georgelofi, what is proprietary or unique about your particular design?

For end users, I wonder if the sonic signature of the Lightspeed (an oxymoron) is easily distinguishable from other passives? If you were to undergo actual blinded listening sessions, could you even pick it out in a lineup? That is a question I ask myself about my own equipment.

A friend of mine (who owns a big name active) demoed the Lightspeed and said it did a lot of things well, but it did not displace his active pre-amp. He did have some long ICs which may have sullied the demo in his mind.

For the sake of clarity and unbiased reporting, I would be more than willing to do some blinded listening sessions of active vs. passive pre-amps (in the Charlotte NC area). I will make sure to involve more people than simply devotees of the individual devices involved.
I like the idea of blind listening sessions, why are so many audiophiles and reviewers agaisnt it, or at least to believe in it as a effective method for assessment? That always seemed odd to me. Yes, it would be a good idea to do such a test absent the knowledge of when one is listening to a particular piece, epsecially when they have invested themselves in a piece financially and/or emotionally. I don't know if the LSA is the best preamp, which doesn't exist, but I pretty happy knowing that for $450 I was able to sell my active preamp that was $7,000 more without any obvious sense that is not as good (enjoyable). That can make anyone a devotee on the basis of value alone.
One thing that would be nice in the LSA, and most modern preamps, though it might "ruinous" or a least "deleterious", is a scheme for balance control to account for recodring mixes, room geometry, and human frailty as we age - not sure how many ears are balanced L/R- perhaps than we would like. I think HP once said not having a balance control was a fatal design flaw - yet one that is very, very common in purist designs.
Agear hi your questions to me are answered here it's a big read, I started doing these some 30 years ago it was new then, I should have patent it, it is refined sonically to the max today, without being overly complex, and pricing kept low as possible.

http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp.html

www.lightspeedattenuator.com

Cheers George



Pubul57, I like the concept of blinded sessions to remove bias. It is quasi-scientific. I think a lot of manufacturers are sensitive to the whole shootout model (blinded or not) since a poorly executed setup can talk the results and hurt their business. I am aware that most hi end audio companies in the US are mom & pop outfits, and the last thing I want to do is damage their livelihood. That being said, my pre-amp maker (TRL Dude) was stoked about the idea.

I think a second issue is pride. A lot of philes are wedded to their gear and get tribal on you fast (myself included) when challenged. At this point, I don't care about looking like a rube. If something is better, its better. The truth sets you free at the end of the day.

Prior to owning a Dude, I experimented at the level of the pre-amp quite a bit. My Wifi front end has enough juice to easily drive amps directly. I liked the sense of clarity, but the soundstage was always too flat for me. It did not sound right. In my previous rig, I used a Granite Audio 657 tubed CDP without a pre-amp. It had an enormous amount of gain in the output stage, and my system always sounded more dynamic and alive without a pre-amp. This was an experience shared by a majority of 657 owners. Conceptually, it harkened back to the 80s/90s when a straight wire with gain was thought to be optimal (by some).

Bringing things into the present tense, I discovered the TRL Dude (thanks Bill/Grannyring). It had the dynamics and sense of control of the 657 with with so much more. That being said, I am always open to hearing "more." TVAD mentioned his new VRE-1 as being a passive "with balls" and how much he is in love with that device. I did not realize that the Concert Fidelity pre was a "passive with balls" also. Dale Pitcher from Intuitive Design is using that pre at RMAF this year. I own some of his equipment and respect his ears. That being said, a buddy of mine who owns a highly modded but vintage TRL GT3 pre-amp (15 years + I believe) recently demoed both the Concert Fidelity and Lightspeed and still preferred the TRL pre. In particular, he said the LS lacked "dynamics and control."

Pubul57, out of curiosity, what pre-amps have you compared this device to? Atma-sphere per chance? Have you ever hear it with solid state amps? What is your source? It does seem as if you need fairly specific conditions for the LS to thrive.

As an FYI, I used to be a Merlin owner. Loved those speakers. Was about to purchase the ARS Filharmonia and got sucked down another rabbit hole audiophile style....
Owned the Ars Sonum (twice:)) Most recently I have owned CAT SL1 Ultimate, Lamm LL2, ARC LS25, Dodd Battery, Joule LA 150MKII Signature Edition, Placette Active Linestage and RVC, K&K TVC, and the BENT TAP AVC. Of that batch, the Joule was my favourite, but sold it after a month or so with the LSA, just did not make sense to me to keep it, in my system with an EMM Labs front end (switchable 2v and 3.6v output), the LSA played on par or better to those, though I only had the Joule at the same time. I never compared it with the Atma preamp I own becuase I use it exclusively with the Atma-amps. The LSA is used with my single ended Music Reference amps. If I were to make a sane recommendation for Merlin owners, it would be to get the Ars Sonum, and "stop worrying about it":) Not that is was the best, but it is good enough to get off the equipment merry-go-round.
I like the idea of blind listening sessions, why are so many audiophiles and reviewers against it, or at least to believe in it as a effective method for assessment? That always seemed odd to me. Yes, it would be a good idea to do such a test absent the knowledge of when one is listening to a particular piece, especially when they have invested themselves in a piece financially and/or emotionally.

Most of these tests as conducted today are flawed to some extent. Unfortunately you can't create an accurate enough control environment. That being said I think they are fun and a method by which opinions can be shared and discussed. Not that we're going to get any definitive answers, more likely the usual subjective opinions.

One thing that would be nice in the LSA, and most modern preamps, though it might "ruinous" or a least "deleterious", is a scheme for balance control to account for recording mixes, room geometry, and human frailty as we age - not sure how many ears are balanced L/R- perhaps than we would like.

Mine technically has a balance control by virtue of it's dual volume controls. I like this feature for all the reasons mentioned above.
I should have thought about that, take that over remote cotrol any day.
I did not realize that the Concert Fidelity pre was a "passive with balls" also.

Not sure what you mean. The CF-080 preamp has a gain stage so technically it can't be a passive. The Si2 preamp which I own and uses the same volume control as the CF-080 is a zero gain device using an active buffer. That could be classified as a passive with balls IMO. IIRC I believe the VRE-1 engages a gain stage when the volume control reaches a certain level. So it too has passive attributes. Quite a nice preamp to boot.

For some light reading on the Si2 lineup look here:

http://db.audioasylum.com/cgi/m.mpl?forum=hug&n=150154&highlight=Silicon+Arts+Design+clio09&r=

I was pleasantly surprised to receive an email from my friend Hajime Sato regarding RMAF and the use of Concert Fidelity gear by Dale Pitcher. It will be interesting to hear with his speakers.
George, for the sake of those who don't want to sift through all the technical particulars and for this thread, what are the salient features of your design? George, as a resister, how does the optocoupler compare to a fixed 1% metal film Roederstein or Vishay in terms of noise?

The actual history behind this device is interesting (and George, correct me if I a wrong). Solar cells that changed resistance with light were developed in the 50s. Audio Amateur articles mentioned the use of these cells in a compressor circuit. Audio Directions ran an article in about '75 about a dynamic range expander based on the optocoupler. This so-called optocoupler was apparently adapted from radio station and recording opto compressors.

Pubul57, so you owned the ARS twice? I was looking at pics of it recently, and it looks like the level of fit and finish is high. I was also looking at the JE Monoblocks and pre further down the road if I had stuck with the Merlins.

Tony, I agree that blinded sessions can be a mixed bag if not set up correctly. In light of the LSAs requirements, it would be easy to tilt things towards an active in a shootout. That being said, it would be fun and informative.

In terms of the VRE-1 and Concert Fidelity, I was simply quoting TVAD from your review/thread of the LSA. I was not aware of these technical specifics. I would be helpful for him to chime in.

Dale is indeed using the CF piece. I believe Hajime Sato has admired Dale's Essence pre-amp designs and speakers. I did not know there was a relationship there. Dale is supposed to have some crazy new speaker at RMAF. TBD....I wish I was going.
I should know today, but I hope to be going to RMAF. If I attend I will be doing so as an assistant to Hajime Sato in the Concert Fidelity/Silicon Arts Design room. So I will definitely have time to stop by Dale's room as well. Last time I was at RMAF Dale canceled his visit at the last minute, so I never had a chance to meet him. It's something I hope to check off my to do list.

I agree the thread over at the DIY site is a bit winded, but there is a lot of great information about the history and uses of the opto coupler. Nelson Pass even partakes for a bit. In comparison, The Truth preamp I have uses photo cells, but not opto couplers. The idea is basically the same though as attenuation is controlled by an LED that shines light on the resistors. Looks pretty cool in action.
Tony, that will be kool. Dale had talked about showing with Silcon Arts 2-3 years ago. In addition to the CF pre, he will be using those frankenstein tube amps, the Amber Waves. Crazy. He will also be demoing his new conditioning technology. Let me know what you think. Dale drives me to drink in terms of timeliness, but his gear is superb.

When I have more energy and time, I will attempt to slog through the DIY thread.
Agear and guys, let's get the name of the main devices inside the Lightspeed Attenuator correct, they are not solar cells, they are not optocouplers, they are LDR's (Light Dependent Resistors). These LDR's are made from (back in the old days) Cadmium Sulphide, which back in the 70's were almost impossible to match up for me, and were unreliable, I needed about 100 units to get 4 matched. Now the ones I use are made of something else they won't say what they keep it close to their chest, but it has enabled me to match 4 out of about 30 units and the reliability is no longer a factor.
Some of the "tech heads" are saying that it's the Cadmium Sulphide or whatever it is that these LDR's "Light Dependent Resistors" are made out of , is what makes the Lightspeed sound better than metal or carbon film resistors, this could have a slight bearing.
But you know what I believe and have seen if you read my explanation on DIY Forum or read my PDF broucher about "Dynamic Contact Bounce"
Cheers George