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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
clio09
2,978 posts
 
The LSA plays the instruments more up front and forward - and I mean all of them! The instruments play on the same plane at the front of the speaker. Some may like this. However, to others it is a lack of 3D perspective or depth.

Bill, was this true of every recording or was it recording dependent? I do find with the LSA in my system it exposes the recordings for what they are. Meaning some have a more 3-D sound stage than others. Some are also more immediate in their presentation than others. However, I can't recall one where all instruments are in a flat plane at the front of the speaker. What specific recordings were you listening to?

If the recording offers only a forward perspective for all the players, then the Dude reveals that. If the recording is more layered, then the Dude gives that deeper layered presentation.

Exactly how it should be with any preamp, active or passive.
tvad
9,467 posts
 
Grannyring, your further explanation further reinforces the idea of the LSA preamp being less colored than the TRL preamp.

If one accepts the definition of a passive preamp as a device that passes the source’s signal unaltered, except for attenuation of gain, to the amplifier; and assuming a proper impedance and gain match between source, LSA preamp, amplifier, speakers and cabling, then one also accepts that the recording is being reproduced as if the passive preamp were not in the system at all.

Therefore, if there is a difference in the reproduced sound with a different preamp (in this case an active design) in the system; and assuming again a proper match between the active preamp and the source, amplifier, cabling and speakers, then one must conclude that the active preamp is responsible for any difference one hears, and that the difference is a result of an alteration of the source signal beyond volume. This alteration is coloration, or lack of transparency.

If one doesn’t accept the basic premise above, then the discussion regresses back to the beginning.

There's no right or wrong choice of preamp here. However, based on the descriptions being posted of the two preamps, I can only conclude that the LSA preamp least alters the source material.

Now, if a listener prefers The Dude because it appears to reproduce a recording more like what one recalls hearing in a concert hall, then the discussion becomes one of preference, and there's little point to debating preference.
clio09
2,978 posts
 
That was Paul's prototype of a battery-powered, solid state pre right? Not a Dude. Out of curiosity, did you ever hear the LSA side to side with that entity? Are you speaking from sonic memory?

It was the Pre-1.5 battery powered preamp and no, I never compared it with the LSA. My comment was a blanket comment on all the active preamps that I have heard since I have been exposed to what well designed passive preamps can do in ones system. To me they are all additive (some more so than others), not necessarily in a bad way, as I do enjoy listening to some active preamps. Again, it's my opinion and anyone can feel free to agree or disagree. Perhaps the Dude is different and maybe some day I'll get to hear it for myself and come to my own conclusion. After all I lent my LSA to Bill so he could do exactly that.
dgarretson
2,394 posts
 
I have not heard LSA but have used the same LDR resistors to provide variable cartridge loading in a modified phono stage. LDRs are about as clean sounding as the best nude Vishay, Caddock, and tant resistors, so I imagine they would make a first class passive.

Regarding the allegation of "forwardness," assuming that we are not talking about strident aggressiveness, the quality of forwardness in a top component is often a good thing in the sense that the piece sounds more alive, faster, dynamic and resolving. The listener is literally closer to the music, in fact the stage may extend both forward of and to the rear of the speakers. In this scenario depth-of-field cues are delivered through high resolution. Instruments appear layered in depth more by virtue of low-level cues than by soundstaging per se. The more astonishing hat trick may be when a system throws instruments outside the L & R speaker boundaries, or does a perfect job of imaging intentionally-recorded phase anomalies to the side of or behind the listener. Some of this is contingent upon room characteristics, but with great electronics it can be surprising how much of it can be pulled off independent of room.
pubul57 OP
3,712 posts
 
Interesting article by Robert Harley in the 2011 Buyer's Guide (TAS) on audio vocabulary - including "fowardness" and "laid back".

What I find with the LSA is that soundstage and imaging changes with the recordings - that to me is a good sign.

One thing for sure, there is simply no arguing preferences, unless you really want to start a winless argument.

What is not arguable in my view is that the LSA provides a very high level of sound quality at a very low price point (for the hobby).

Glad to see that some folks are giving the LSA a try.
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