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
I would think so, as in essence a fully open ouput with a variable output CD player would be the same (I think)as a regular CD player with a fixed output and you would be controlling volume with a superior attenuator than what is built into the CD/DAC. That is what I think, but I would rather have someone more technical pipe in.
You are right Pubul57, the momment you start to lower a digital based volume control, you start to whats called "bit strip" the name says it all, and this lowers the resoution. Aways leave it full up when using in conjuction whith the Lightspeed.
But also be carefull some dac's and cdp's have analog based volume controls and these are usually sub grade passive motorized or non-motorized on the output of the cdp or dac. Most times you have also fixed ouput rca's as well on these cdp/dac, always better going for it and a Lightspeed than the analog variable output. If there are no fixed ouput rca's, better to open it up and bypass the passive pots by taking them out of the output totaly.
Cheers George
Yes the idea of an active preamp, or in the case of The Truth preamp, a buffered passive, the idea is to control the ICs. However, in unbalanced designs its my understanding that while this might provide some benefit to using longer runs (ex. you can use 30 ft. ICs with the Truth with no sonic degradation), it doesn't mean that the coloration/artifacts of the cable itself can't be heard.

I've convinced my tech here to design a passive balanced preamp that supports the 600 ohm standard. If I use this with my Atma-Sphere S-30 I should be able to eliminate the cable coloration/artifact from the equation.
From what we have learnt and heard for myself, the only way to make all interconnects invisible (sound the same) with no sonic signature, is to have the poweramp input impedance at 1kohm or less, this then becomes a hard load for the pre to drive unless it has an output impedance of close to 1ohm and plenty of current behind it, something like the top Krell pre amps may be that low, then the pre itself has a sonic signature itself, so it's not an easy task.
Cheers George
George, is it your view that the Buffering used in preamps, and passives like the BENT, The Truth, or the First Watt B1 is there for handling worst case scenarios - long or high capacitance interconnects, or amps with low input impedances, but where the ICs are low capacitance (Cardas GR 12p/ft) or high input impedances (100kohm)that a bufferless approach will always be superior? That is how I read it, and that something like the LSA is about as good as you can get in not altering the source signal to the amp.