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
Given George's comment, it would seem the burden of proof is on explaining a difference, not the other way around. I find Clio9's comment interesting, as he does hear a difference, but even there hard to put your finger on it, also hard to measure the influence of expectation on something so subtle. However it may be, going to battery supply just doesn't seem like a path with pursuing, at least not to me.
If you know LED lights, you would know they are an extremly stable (even thermally) form of light being powered by battery or regualted mains. This is maybe why battery cannot be picked from regulated mains in an A/B comparisions, like I have conducted many times with fellow audiophiles, a few said they can detect something but cannot put their finger on what it is.

Cheers George
Perhaps the reason some of you are reporting sonic differences between using battery power and the wall wart is simply that volume levels haven't been precisely equalized for the comparison?

I realize that the LSA has an internal regulator, but no regulator is perfect, and so perhaps voltage differences between the outputs of the battery and the wall wart result in slight (fraction of a db) changes in attenuation, that need to be compensated for with the volume control.

To totally rule out the possibility that the sonic differences are attributable to volume changes, I believe that the levels should ideally be equalized to within around 0.1 db, which is probably impossible to do without instruments.

Best regards,
-- Al
Al, that really makes sense. And it seems to explain Clio9s experience, something different but hard to put your finger on it.