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.
Ok...When I first received the LSA, it was placed in the system downstream of a Burson HA-160 DAC/pre. When the Burson's volume pot was fully open, I had a wide range of volume control on the LSA, with moderate volume achieved at around 10-11 o'clock on the LSA. The Burson is gone and I am awaiting arrival of the Metrum Octave DAC. Now....I took out an old, cheap-o dac I had in a closet (I have no idea what the specs are), and connected it to my Mac Mini via toslink. Doing this results in HIGH volume levels at 9 o'clock. I put a cd player into the LSA. I don't know the cdp's output impedance but at 2V it has the same output voltage as my incoming DAC, the Metrum. Same thing! 9 o'clock on the LSA is too loud.
Anyone else have an issue with the LSA achieving very high volume levels at a low position on the volume pot?
I had close to that issue with my CD player. I used to max out at around 10, which gave me very loud, but not ear splitting levels. Now I'm at 12 with loud (so my wife says) but comfortable levels. I don't know why or when the change. I have changed amps sometime inbetween so that might be it.
With vinyl, I'm now at 3 for pleasing but not head banging levels. I don't think I can get head banging levels with my amp which I'm now light loading.
Different amps will have different gains, so will sources, and speakers also have different efficiencies. This will all govern where the volume control (on any passive preamp or any active preamp tube or transistor), position will be for normal listing. Now with the sources giving higher outputs than they ever have, and the recordings being higher in level also, too much gain is really becoming an issue with most systems. This is why they are starting to make rca attenuators like the Rothwell Attenuators in -10dB and -20dB to take care of this problem. http://www.decibelhifi.com.au/category42_1.htm Another reason why there is no need for active preamps with gain, we have too much gain coming out of nearly every component in a system.
Devilboy, With my 97db efficient speakers - similar to your 96db speakers - I rarely get above 9 o'clock before being too loud. Often depends on the recording's level. Can make for some dynamic music . . .
My amp is 1.3V sensitive. After I get my 2V DAC, the only other change I will make will be to use 1/2 meter pair of solid core interconnects leaving the LSA to go to the amp (I'm in the process of cutting a one meter pair to half them). So, as George said, I can use RCA attenuators to cut the gain down a bit but I really don't want to add anything else in the path. I'm more of a "less is more" mindset. Anyone have experience with these devices degrading sound quality? I've come so far, I don't want to start going backwards...
I never liked those Rothwell attenuators. You can accomplish the same thing by adding a resistor in series with your interconnects (there might be a little more to it, but this is the basic idea). I believe Luminous Audio makes cables like this upon request. Since you are cutting up some cables now might be a good time to consider doing it.
The Rothwell attenuators work just like the Lightspeed Attenuator. That is, they have a soldered fixed series resistor with another shunt fixed resistor to ground, this forms a voltage divider just like the Lightspeed Attenuator. Except the in the Lightspeed Attenuator these series and shunt resistors have variable resistance with the amount of light that shines on them. So what you have is a variable voltage divider in the Lightspeed Attenuator. The only problem with the Rothwell's is that they change the input impedance of the device they are attached to, so this needs to be taken into consideration when using them, with passives and tube preamps.
10-11-11: Devilboy Thanks, George. The input impedance of my amp is 470K. I can't imagine that being an issue with the Rothwell's.Devilboy
No that is not a problem, what is the problem if you go passive or tube preamp, is that while the 470k input of your amp is fine for these preamps, when you plug in the Rothwells then this changes that 470k for something much smaller. What I don't know as I have never measured the shunt to ground resistor of the Rothwell, It maybe say "10k?" then this is seen by the passive or tube preamp not the 470k, and then it will not be a good impedance match for them. As Clio09 found out when he used them, it wasn't the Rothwells them selves that he didn't like it would have been the input impedance change of the poweramp he heard that then was not a good match with whatever pre he was using at the time. There is no free lunch, you have to do your homework, regarding impedance matching. Like I said before it goes on right through the whole system from source through to speakers, up to about 6 to 10 times, you can't do anything within the components themselves unless you are a good tech, hopefully the designers of individual components have done the right matching inside their units, but you can look at the output and inputs of each component to make sure you have a good match and give everything a fighting chance to sound it's best.
Devilboy, I have a pair of the 10db Rothwell's, and as measured with my not particularly accurate analog multimeter the series resistor has a value of about 21K, and the shunt resistor has a value of about 9.5K. As you realize and as George has confirmed, the 470K input impedance of your amplifier certainly presents no issues. (As you no doubt realize, the attenuators should be placed directly at the input connectors of the amp, so that there will be no interaction between their output impedance and cable capacitance).
With the attenuators so located, and driven by the LSA via a short cable, the LSA would see a load impedance of about 30K. I suspect that is not an issue either, based on the assumption that the impedance "looking back" into the LSA is essentially resistive and does not vary significantly as a function of frequency, given that you will be driving it with a solid state DAC having low output impedance. Hopefully George will confirm that assumption.
You will not be able to drive your amp to full power, though, even with the LSA turned up all the way, as 10db attenuation will reduce the DAC's 2V maximum output to about 0.63V.
For most volume control settings of the LSA, btw, the attenuation resulting from insertion of the "10db" Rothwell's will be more like 11 or 12db, because the impedance "looking back" into the LSA will sum together with the Rothwell's series resistor.
Concerning the sonic effects the Rothwell's may have under properly impedance matched conditions, I'm not using them with the VAC Renaissance 70/70 MkIII amplifier I currently have, but I noticed no adverse effects when I previously used them with a lesser quality EL34-based Paxthon amplifier.
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.
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)?
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.
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?
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.
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?
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.
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"? :)
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.
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.
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.
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.
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.
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.
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.)
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
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.
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.......
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!
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.
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.
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
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.
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.
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