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'm sure I asked this earlier, but can't find my question or the answer - can the LSA be built as a balanced output, if so, any serious advantage to that with let's say an Atma-sphere amp?
Yes you did ask. I've gone down this road with George. Bottom line he gave me the schematic, but warned that overall this is an inferior design due to the difficulty in matching the additional LDRs (versus single ended operation). In addition, if you can get one built there could be a higher probability of reliability issues, again due the higher number of LDRs to achieve balanced operation.

That being said I recall Audiogon member Dave Garrettson trying to match LDRs for balanced operation to use as a volume control internal to his Atma-Sphere MP-3. He gave up on the effort IIRC. There have been a few people on DIYAudio who have tried to build a balanced unit. I didn't sound like it was a lot of fun.

You really should try it single ended into the M-60 amps. You're going to be really surprised. I get the balanced thing, especially with Atma-Sphere components due to their supporting the 600 ohm standard, but the LSA is quite optimal with these amps too.
Al, as you might know, I am very non-technical, so I had to read what you wrote a few times. Is it correct to say that

A transformer replaces resistors as the means of attenuating the signal and provides some impedance matching help.

Buffers attenuate nothing, but creat ideal impedance matching.