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
"What you should do Grannyring to see if the Dude is artificially giving depth, is what I preach all along, put your CDP straight into your poweramp (Bolero Test) no preamp. Put on a quite cd so you can then ascertain a good level of cd to play, then swap in the Lightspeed then your Dude and see which is closer to no preamp. The one that is, is the one that is truer to the source." George...

As I stated on the 9th, using the Bolero test to argue for a pre-amps' relative transparency or "trueness" is circular and flawed logic IMO. After rereading George's statement, the real burning question is not whether the Dude is adding an artifical depth but rather whether the LSA is simply not able to convey information that is inherent to the recording. CDPs generally suck when driving amps directly due to a lack of current (not merely a function of output voltage as some have suggested above in this thread). Current, from my limited understanding, is needed to reproduce in particular lower frequency information. When that is missing, soundstaging is effected among other things. Driving higher frequencies (tweeter) generally requires less current, and when done without proper representation of the lower frequency info, people often misinterpret this thin sound as "transparency." I myself have experienced that transitory illusion when playing direct. Ergo, a device which more closely mimics this phenomenon is not desirable IMO.

I am signing off. I will report back with results from the "Heather test." Some particulars you need to know about this particular test: I usually have to ply her with at least one glass of red wine in advance. A vintage Vera Neuman scarf (of her choosing) as a blindfold. 5-10 familiar tracks played at between 80-90 dB. Each single track will be played on each device and will be verbally labelled A + B. Just now, Heather giggled with glee when I informed her that a test has been named after her.
The "Heather Test" has entered the lexicon, and I suspect well all do it:) Now, where did I put the Chianti....?
The "Heather Test" has officially entered the Audiogon lexicon, and I suspect we all do it and rely on it from time to time:) Now, where did I put the Chianti....?
10-11-10: Agear
CDPs generally suck when driving amps directly due to a lack of current (not merely a function of output voltage as some have suggested above in this thread). Current, from my limited understanding, is needed to reproduce in particular lower frequency information. Agear

CDP's (not tube output ones) have lower output impedances and therefore and higher driving current ability into power amps than 99.9% of tube preamps.

Cheers George
George, that is what I thought but being an E.E. ingnoramus I did not feel comfortable making that claim, or the my EMM Labs CDP seems to have a pretty well built power supply. I think that whatever it is that some prefer with active linestages (even when impedance matching, current, and gain is not a problem), and they have every right to feel that way, it is not something actually in the recording, but a distortion that might "feel" truer to some, but cannot be truer to the source in fact.

The argument of passive versus active may be as unwinnable (and it does not have to be "won") as the old SS/tubes argument, what I feel pretty comfortable saying however, is that in a well matched source, cable, amp environment, the LSA is the best passive volume control I have had in my system after trying all the major alternatives. In a different system setup than what I have, I might prefer a unity gain with buffer, or an active tube linestage.