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
Assuming all your ducks are in a row impedance wise and you use short low capacitance and shielded cables between the LSA and amp you should be quite pleased.
Anthony, you have pretty sensitive speakers, no? Might be a factor in the "gain factor". WIth the 89db Merlins, 2:00 is about as loud as I want to hear them with my 1v RM10 - 35 watts.
My speakers are probably close to 95 dB sensitive even though they are listed at 92 dB. I think Duke is pretty conservative with the rating. Normally with amps that are closer to 1V I get to about 2 o'clock for normal listening. Less if the CD is hot, more if I'm playing vinyl. On the S-30 I get pretty close to 4 o'clock and with vinyl it's wide open, which according to Ralph is an ideal situation. Right now I use the LSA with the Music Reference EM-7 amps and I have a second set up using an Otari MX-5050 direct into the S-30.
07-09-11: Devilboy
George,I'm sure that the information I need is listed somewhere in the vast number of posts but could you please tell me what the ideal specs that the Lightspeed would work best in? What output voltage and output impedance of source would the Lightspeed like to receive and what input voltage sensitivity and input impedance of amp would the Lightspeed like to "see"? Again, sorry if I'm asking something that's been discussed previously. Best,Luka

Hi Luka, the Lightspeed will happily slot right into most systems, the only thing that is needed for it to give it's 100% performance is that:
1: The output impedance from your source (cdp, dac, phono stage, etc) should be 200ohms or less output impedance and 1v or more output, which most are.
2: The input impedance of your poweramp should be 47k or more, which most are, 47k being the industry standard.
3: The interconnects from the Lightspeed to the poweramp should be 1.5mts or less and of low capacitance (100pf per foot or less) which most good quality IC's are, this measurement is in the cables specs, if not the supplier/manufacturer should know this.

Cheers George