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.
For Sony to quote that this unit should see 10kohm or higher as the load, says to me that one, it could be tube output (which it's not), or that it has a 1k series output resitor (which is dumb to do), or that it maybe have a capacitor coupled output to stop any dc offset at switch on, or just when it's on, to stop it from taking out amps and speakers. Trouble is with is, some of todays amps at 2k or even 1k input impedance that capacitor would have to be 200uf odd to get the frequency response down to -3db @ 1hz, and a cheap bi-polar or plastic at those values could have very high ESR (series resistance) whch could be adding to the problem of not being able to take loads of less than 10kohms.
If 10k is the minimum load the Sony is comfortable seeing and the input impedance of the LSA is 10k, then I assume this could work out.
My Sony 900 also had the video outputs removed as well and the battery power supply. I think I had the remote too. When the Sony 900 mod was introduced by TRL about 5 or 6 years ago there were about a half dozen of these players available in SoCal that I snapped up for Paul. They were modding them up and the players were going out the door like hotcakes. I think it may be their best effort with a digital player.
Happy new year to you all, the 10kohm load impedance that Sony and some other are are saying about their output, is the minimum load that this output would be comfortable (mathematically) seeing. Not it's output impedance. The only way to determin what the output impedance of it is, is to load the output to ground with different resistors unlit a 1k sine wave is halved in level, what ever that resistor is is also the output impedance of the unit as you have formed a voltage divider with the resistor to ground with the output impedance(resistance) of the unit. Cheers George
I just looked at the manual and it appears the audio output and 5.1 channel output are both listed at over 10k ohms. Not sure what more I can say at this point. The high output impedance is unusual for a solid state player but my guess is that is due to it being a DVD player as well as CD/SACD.
Do you have the TRL modded Sony 900? If so you might want to check with Paul to see about the impedance. I had one for a bit that was modded by TRL.
This is a solid state player so output impedance should not be that high. However, since it is also SACD/DVD and has a lot of other functions not relevant to 2 channel audio the impedance could be higher. I recall the manual being pretty daunting so it might be hard to pin this down.
Why don't you give it a whirl and see. I don't place as much value on the impedance matching criteria that is talked about around here as much as I used to. I've used the LSA with some pretty interesting combinations and it's worked fine each time. However, the one thing I haven't tried yet is a high output impedance source. That will happen after CES/THE SHOW with a tube phonostage I'm auditioning.
I have a cd player with 2 volts of output, but the only spec I can find on Impedance reads " load impedance over 10 kilohms". Not sure if this is suggesting the output impedance is 10,000 ohms! Does not seem possible!?
The unit is a Sony dvp ns900v sacd player. I purchased the LS for a second system and to just play with.
I have a question regarding the relationship between a cd player's output impedance and the input impedance of the Lightspeed. I have read the cd or dac should have an output impedance of 200 ohms or lower. This seems to be needed even if all the other hurdles are met.
What I did was to stop someone else from trying to patent it a couple of years back, what they wanted was for audiophiles to think it was their idea, but my first one was made back in 1974, using t/t and phono stages as the source, but they were not very reliable with the ldr's back then, lots of channel drift, and no led's I had to use low voltage bulbs. This was when I should have put a patent on it. As for now just the TM of the name Lightspeed Attenuator will suffice. And the small ego boost that the IP was mine all those 37 years ago (yikes!!!!). I believe as the manufacturing technology gets better they will be able to supply the Silonex led/ldr packages as perfect matched quad sets for stereo use and you will see the demise of the potentiometer with it's lightweight internal touch contact of a metal wiper on a carbon track , as they are the weakest link in the audio chain. Cheers George
I think it is patented, in fact I think George has already nixed one such attempt of using his design commercially without permission - but George could speak to that.
You would think the real market for George's attenuator would be in licensing to other manufacturers for use in other preamps and integrateds. Virgin works well for me, but a combo with buffering when needed seems like the next iteration.
I have figured out that the buffered output is a better match in my system. I am amazed, however, at my system performance with this new twist on a buffered volume control. The Lightspeed attenuator coupled with Theta's (Mike Moffat design) implementation of the BUF-03 results in an outstanding linestage. There is an ease and naturalness of presentation that makes listening a real pleasure.
Good to hear Dpac996. In your quest to sample a buffer after it, even though I believe the best buffer is no buffer so long as the impedance boxes are ticked for passive use. If you want to try an simple good stable at unity gain opamp buffer, the most transparent/dynamic one I have come across in my experiments with I/V stages and buffer stages for cdp's is the AD825, the OPA627 is a tad cleaner but it doesn't have the dynamics of the AD825 and dynamics = rhythm and pace. Cheers George
Do let us know how the buffer works for you. It would seem if you don't need a buffer than a buffer will always be worse, and if you do need a buffer a buffer will always sound better - know if you do or not, there lies the rub. Let us know how your experiment goes.
Dpac996 hi, yes a Lightspeed can be used to drive a poweramp that have as little as 22kohm input impedance or even lower and there is no harm to the components doing this. I have many customers that are doing just that, but I like to present the parameter specs that are well over with headroom, so 47kohm which is the industry standard was chosen, even though we use it at 33kohm at our audio society meetings. As for LDR matching, it is a must to have all 4 series and shunt matched as this will give a better logarithmic feel to the volume control, if you only match the series L/R and then match just the shunts L/R this will still work but the volume control will either be very touchy down low or very vague down low.
When I have tried passives in the past I have had negative results. This is the first time for a very positive one. I suppose I have been too hasty in my previous dismissal of passive as an effective volume control--harumppph!
Clio9 has also reported that listening and theory are two different things and he has had excellent results even when the match was less than ideal on paper - so yes, always worth trying.......
If I may, one corollary to George's rules: 1) despite an on-paper mismatch ( amp with 22kohm Zin ) a passive might work very well...so be sure to try anyway
I am waiting for parts to build my own lightspeed and in the meantime discovered a 25k Noble log pot controlling the volume of my Sacd player sounds fantastic. Macrodynamic shadings, pure sweet treble, no loss in bass lines...etc. the magic is back! I was quite surprised ! My amp has a 22k ohm input impedance.
Sounds like you are one of the many who have no need of a active preamp with gain because you already have an abundance of gain from either your source, amp, and or very efficient speakers. Yes the Lightspeed Attenuator could help here, as well as improve the transparency/dynamics of the sound, being truer to the source than active preamps.
Just a couple of parameters that should be met.
1: Your source cdp or dac's output impedance should be 100ohms or lower (which most are).
2: Your amp's input impedance should be 47kohm or higher (which most are)
3: The interconnect from the Lightspeed to the amp/s should be 1.5mts or less and of good quality
Above, Georgelofi mentioned the Rothwell attenuators. I tried these (both XLR & RCA versions) trying to reduce the gain of my preamp and they sounded terrible, blunting things a lot. Am I doing something wrong?
Any thoughts on if the Lightspeed might be more transparent than the Rotwhells in this application.
(Though they did work as advertised, cutting the gain and letting me get a proper volume level with my stepped volume control.)
(I've had other related posts on my gain reduction issue, so forgive me for this. Thanks.)
I think that might very well be the case with passives and SS, aside from impedance, you need tubes:) It might be one of the reasons that some, like Teajay a while back, may find the LSA less appealing than a nice tubed preamp matched with SS amp.
Thanks again Pubul. I actually have 2 amps, an Edge NL12.1 and the Luxman (both solid state), and the tube preamps I tried with these really makes a superb sound, w/o the heat & tube maintenance issues of powered tube amps. Of course, this works better with speakers that aren't ruthlessly revealing or tipped up (but I don't favor these speakers anyway).
But really, the tube preamp makes all the difference with these amps, especially with some good NOS tubes, with life, palpability, gorgeous texture and tonality and lack of fatigue with detail simultaneously. The solid state and passive preamps were just flatter and not as engaging.
With the Luxman amp you might want to try the Dodd Audio tube buffer. It gets quite a bit of praise from those who have tried it. In fact, there are some really nice solid state buffers out there as well, namely the Pass B1 and the Horn Shoppe Truth (which uses a photo optocoupler). Buffers are similar to passives in that they generally will not add gain to the signal path, but they also eliminate impedance mismatches.
You might enjoy your Placetter, and passives in general, much more with a tube amp - or what you are doing with the excellent Luxman amps - use a tube preamp that matches well with the lower impedances of SS amps. I love the sound of tubes, and I need them somewhere, but not in my pre if I have them in the amp. Always interesting discussions on where the tubes make the more important and significant difference = preamps or amps - I suspect the sonic stamp is stronger when the tubes are in an amp -- but that is a debate.
The LSA will sound much more like the Placette than either will sound like a tube preamp. You should stick what you enjoy most. Are you using the Placette with an SS or tube amp? I could not, would not[?] use a passive with an SS amp for a variety of reasons, but that's me.
Does the Lightspeed sound different than the Placette? I tried a Placette, and it did sound very open and really "not there", but then I went back to my tube preamp and there was some sort of magic sound with the tubes that I could not give up. I guess the tubes add something, but what they add sure sounds nice.
But he repeats the myth regarding dynamics, which seem very dependent on system matching across the board, then again, what do you write about when you have found the "best preamp ever"? :)
Stereophile had a booth at RMAF and I picked up a copy of the November issue because my digital source, the Resolution Audio Cantata (disclaimer: I'm a Resolution Audio dealer), made the cover and was being reviewed. Low and behold though, Sam's Corner had a nice piece on active versus passive preamps and some comparisons between a few of them including a new player from Japan). One quote stood out and was even spotlighted: "The best purely passive attenuator I've come across is the George Hi-Fi Lightspeed."
Guess Sam still has a soft spot in his heart for the LSA. Although he is flirting with the new Conrad-Johnson active linestage.
I ask one thing, for a single ended, low capacitance interconnect of 1-1.5mt, what are we trying to control in electronic and mathematical terms, when phrase "controlling the ICs" is used?
Paul, I've always interpreted the phrase "controlling the interconnect cables" to mean simply minimizing or eliminating their effects.
As you know, Ralph has made the point that in the case of a balanced cable driven by a balanced output circuit having very low output impedance, that is capable of driving 600 ohms without issues, and with a 600 ohm termination applied at the destination end, cable effects and cable differences will be completely eliminated.
I see no reason to doubt that, and I too have great respect for Ralph's opinions. But obviously most available equipment is not designed to those standards, which is one reason among a great many why assembling a system inevitably involves compromises and tradeoffs. The bottom line on those compromises and tradeoffs, though, seems to simply be the common sense notion that there are many paths that can lead to excellent results, including both passives and actives.
All technically explainable cable effects that I can envision are either directly proportional to or highly correlated with length, so I would not consider controlling the effects of a 1 meter or shorter cable to be a major factor in those tradeoffs.
George and AL, Ralph Karsten always makes the point of "controlling the ICs" as the reason for needing and active line stage, and I have to believe Ralph is right about many things regarding equipment, though I also recognize he has an interest in selling active line stages...... to what degree do you find his observation true and under what circumstances - valid with 1 meter or less of ICs, true but not to observable in practice?
We did a comprehensive listen test with the Lightspeed Attenuator with 20 odd "golden ears" from our audio society. The amp we had was specially modded on the input that we could changed the input impedance in steps on the run while listening from 200k down to 10k. The source was 10ohm output impedance. What we found that everyone agreed on was there was no change from 200k down to 47k only when we got down to 33k it was felt by some that a slight compression was noticed, then when we went down to 20k all noticed slight compression. This is why I state in the Lightspeed Attenuator info/instruction sheet the poweramp should be 47k or more, to get 100% transparency and dynamic transfer, 33k is still ok and safe to use, but you may notice a slight compression of the dynamics.
In a situation where the LSA is being driven by a component whose output impedance is low to the point of insignificance at all frequencies (which appears to be the case here, with the Metrum Octave DAC being solid state and having a nominal output impedance of 85 ohms), and where the LSA is driving a load impedance that is purely resistive (i.e., the Rothwells), and *IF* the LSA truly acts at any given volume setting like a pair of resistors, I don't see why it shouldn't be able to drive 30K without issues.
IIRC the LSA's output impedance may be as high as about 7K when driven by a low impedance source. Obviously 30K/7K falls far short of meeting the 10x guideline, but if all of the impedances that are involved are essentially resistive, and therefore constant as a function of frequency, why would there be a problem (other than the inability to drive the amplifier to full power, as I had pointed out)?
Yes you are correct Tony. The reason I posted them up 16 posts ago was to say that there is a problem these days with too much gain in systems, and that there is almost no reason for active preamps with even more gain again, they nearly all need only to be unity gain buffers only, if one wants an active pre.
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