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
Yes, you want the linear regulated PS, not a switching PS. 400mA is plenty. No need to go the super beefy route with the LSA. Of course you need the correct pin adapter with center pin positive too.
George, this may be an odd question to ask a designer, but can you envision any future implementation that might sound even better in a passive friendly environment (no need for gain or buffer)on the LSA? I mean sonics. Sure cosmetics could evolve, perhaps some more I/O flexibility, but given that this is the best sounding "preamplifier" I have heard in my system, and that you have been sorting it out for 30+ years, is the any room for improvement that you can envision?
None really, it's maxed out because of it's simplicity, the siganl travels through one soldered resitor only with no volume pot contacts or other contacts in the signal path.
All that could be done is to 12vdc battery power it, but that is a very very small gain, most cannot hear a difference over the shipped wall wart.
The difference in supply noise between the battery and wall wart at the Lightspeed's output is microscopic using the very best test gear. "It is in effect noiseless"
Cheers George
I can think of one: If a remote were built into the product, the actual volume control system (as a module) could plug directly into the input of the amplifier (with separate left and right hand channels) rather than being in a box that needs an interconnect at its output.

In this way, the interconnect would play a lesser role in the resulting sound as it would only be used at the input and not at the output. IOW you would then be able to get around the traditional problem that affect all passives- the inability to drive a cable. In this system the remote would be mandatory, but it would be easy to build balance and mute functions into the system.