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

Showing 6 responses by dpac996

Quick question: would the LSA's full potential be realized in this setup: PS Audio DLIII ( 99 ohms Z out ); low capacitance one meter interconnects; aragon 8002 power amp ( 22k Z in). Speakers spendor s3e. Average listening level : low to medium 85 db ish... I use a buffered passive in same system. Volume range is more than adequate. Somewhat concerned about lowish input impedance of amp...thanks.
whoops..stupid droidx autocomplete...Macrodynamic = Microdynamic.

George: regarding the matching, is it a single channel's series/shunt pair that should be macthed, or the left/right series and left/right shunt?
Hi George. Thanks for the suggestion. Somewhere I have the schematic for the 8002. Ill take a look. Have you considered creating potted drop-in attenuators so that folks could upgrade their current preamps if so desired? For instance say I have found excellent synergy with amp/speaker but the amp is not remotely passive friendly...or another scenario: I have more than one source to switch? Im thinking that your volume control would ( if pot resistance compatible) be a marked improvement as a replacement for existing traditional pots. In a similar twist any thougts on designing a tube output buffer with your ldr attenuator?
If I may, one corollary to George's rules:
1) despite an on-paper mismatch ( amp with 22kohm Zin ) a passive might work very well...so be sure to try anyway

I am waiting for parts to build my own lightspeed and in the meantime discovered a 25k Noble log pot controlling the volume of my Sacd player sounds fantastic. Macrodynamic shadings, pure sweet treble, no loss in bass lines...etc. the magic is back! I was quite surprised ! My amp has a 22k ohm input impedance.
When I have tried passives in the past I have had negative results. This is the first time for a very positive one. I suppose I have been too hasty in my previous dismissal of passive as an effective volume control--harumppph!
I have figured out that the buffered output is a better match in my system. I am amazed, however, at my system performance with this new twist on a buffered volume control. The Lightspeed attenuator coupled with Theta's (Mike Moffat design) implementation of the BUF-03 results in an outstanding linestage. There is an ease and naturalness of presentation that makes listening a real pleasure.