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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
agear
1,362 posts
 
Tvad, you logic regarding transparency is confusing. A passive is not a gold standard for transparency due to its circuitry. So, then we have to rely on the mythical Bolero Test. I am frankly amused that it even has a name. Non-audiophiles would howl with laughter if they were to eavesdrop on this thread. The Bolero test is flawed logically IMO. It is not some some empircal plumbline. A CDP is not designed to drive amps directly due to low output voltages, etc and sounds bad for a reason. As I said before, I have done this test on numerous occassions, and it sounds flat and hard and nothing like the real thing in several different systems. Why would you make that your logical frame of reference for judging a pre-amp? That baffles me. Bill very poetically described a good test for any system: live music.

An experiment along the lines of one desribed in this article would be useful for this debate: http://www.stereophile.com/features/203/
grannyring's avatar
grannyring
6,519 posts
 
Transparency means something far different to me. To me it has nothing to do with how the inclusion of a new piece of gear "changes" the resulting sound. That fact needs another word - not transparency IMHO. Transparency refers to how see through or clear the performance sounds without smear, distortion, obstruction of detail by noise etc. Two preamps introduced into a system may result in two different sounding systems both of which can be very transparent.

The Bolero test is simply ANOTHER SYSTEM and not a test for transparency my friends. Tvad's definition and explanation of transparency is completely true and understandable based on how he uses the word.

The preampless system is a STEREO SYSTEM with the purpose of reproducing music that sounds like, well, the "real thing". The real thing is the actual sound of the voice or instrument live or on a very well recorded vehicle.

To the extent a system does this, it is transparent and a clear view into the performance. A system without a preamp is still a system made up of several parts all working together to kick out the resulting sound. By simply removing a preamp one does not necessarily, in effect, get closer to the recording or to the sound of live music.

The two piece system of a source and amp is not necessarily more true to the source or live event. In fact, based on my experience it is missing a piece in the sound reproduction chain of a stereo system that seems to be the heart of a live sounding & natural sound system. What I have termed the "heart" of the system - an active preamp. This has been my experience thus far. I do think it is possible to get the "real thing" with an LSA or no preamp, but that is absolutely system dependent.

A CD player pushing signals out to an LSA or directly to an amp is a system that has a sound and personality that may or may not be transparent or reflective of live music.

Another example - A crossover is part of the sound reproduction system. By removing it one does not automatically get sound that is more transparent or live sounding. Some argue it is, but just like the active preamp question it is still a matter to judge at the end of the system chain - a set of ears in a listening chair. The piano either faithfully reproduces the full sound of that piano (transparent - clear window) or not.

Ok, that is my take on this and why the Bolero test is interesting, but really not much beyond that.
larkston_zinazpic
41 posts
 
I too will be getting an opportunity to hear the LSA and compare it to my TRL Dude. That should be fun. More importantly, I will involve my non-audiophile, musician wife in a blinded listening test between the two and will report on her findings rather than mine. ~Agear

Looking forward to this comparison and your wife's perspective.
pubul57 OP
3,712 posts
 
Non-audiophiles would laugh at 99% of what is said here, there view is not the gold standard for judging the argument here.

I understand that CDPs are not meant to play directly into amps as you would have to add the expense of volume control, but I'm not sure what electrical deficiency there might be in terms of voltage or impedance (my CDP puts out 2v or 3.6v with 200ohm output impedance)issues driving amps - not sure I understand the argument that the Bolero test is not in fact the gold standard for establishing what a source actually sounds like, nor why judging the transaparency of a passive against the direct connection is not fair test of whether or not the passive is transparent to the source, sure it has ciruitry, but 1% of what you would find in any active. This in no way says that folks won't prefer a coloration pf the source signal to a transpatent view - no argument there.

That Atma-combo is the best pre/amp combo for driving my Merlins, but I cannot deal with the heat in the summer. I can compare the Atma pair to my other gear, but I cannot isolate the LSA compared to the Atma pre, I simply think I would prefer the OTL amp to other amps no matter what quality preamp I was using.

That being said, the LSA/Music Reference RM10 is about as good as it gets for $2,400 new as long as 35 watts is enough.
pubul57 OP
3,712 posts
 
"the Lightspeed's simulated output impedance varies from about 37 Ohms to about 14.6 kOhms"... Does the output impedance go down as the volume goes up?
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