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
So taking any power differences to the LED's out of the equation all we have left is noise difference of battery v mains. But if anyone can hear the difference between 6uV and 4uV they must be superman. I have measured this my Tektronix scope which has very good low resolution.
When the shorted input Lightspeed was powered by the battery I measured a noise floor of close to 4uV (that's microvolts not millivolts) When it was powered by the mains it was then 6uV. These are exceptional figures as most things in audio are measured in mV (millivolts) which is 1000 x higher than microvolts. And so it should be this quiet as it is passive and has no noise of it's own.
But if this is perceived difference some hear (as I also hear) between battery v mains comes down to those miniscule noise differences then the book has to be re-written.

Cheers George
Given George's good answer about noise level, and his answer implying that the "line regulation" performance of the internal 5V regulator is good enough to reduce expectable variations in the 12V input to the point that they would not result in a perceptible volume change (which is certainly do-able in a quality design), I'm out of ideas as to what could account for sonic differences between battery and wall wart power (assuming that the wall wart being used is a linear supply, not a switching supply).

Best regards,
-- Al
It is linear. I, we?, sometimes hear what I expect to hear, at least in the short term.
In the February issue of TAS, Neil Gader interviews John McDonald of Audience, and he said something that somehow seems related to this thread:

"At Audience,the Golden Rule is 'first, do no harm,' defining harm as any deviation to the original recording. So high-end to me and to the Audience team is about staying true to the music. Sound-sculpting should be left to the recording artists and engineers"

He could have very well had said, "true to the source" - which I suppose is one reason that those that do like the LSA, like it - true to the source is the raison-d'etre [?] of the hair shirt minimalist approach to do no harm.
You find can many synonyms for the golden rule of audio used by manufacturers and end users alike. It makes for good ad copy. The problem is how you define "source". If by source you mean the recording, then unfortunately 9/10, the harm has already been done. One of the primary "sound sculpting" tools used by recording engineers seems to be compression. The rectification of that and other sins committed in the recording studio makes this hobby a lot more arduous than it should be.

For the sake of clarification, I am referring primarily to digital source material as I am a child of digital revolution.