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 15 responses by gooddomino

Just picked up one of the preamps today on the 'gon, mkII. I will be using it with 1 meter ic's into a Krell KSA 50S amp. It has 49 kohms input impedance, output impedance .28 ohms, max output voltage 75.8V and source is 2.5V. Do these stats add up to a winning combo with the Lightspeed pre?
Have a level one plus modded Music Hall 25.2. Gain is 2.5V. Just ordered a NAD 565 BEE. Gain is 2.2V. IC's are AU24,Straley Reality and Morrow.
I'll check into the shielded vs. non shielded issue. I know my Morrow's are noisier than my AU24.What shielded ic's do you recommend? Hey Clio I saw you have have the Tel Wire powercords. I have them on my preamp and CDP. They are very,very good. Don't come across too many guys who have Tel Wires. What do you think of the HC powercord. I currently use original Lesslosses on my high current applications.
Thanks guys,I'll check into the Rothwells. I did plug my tuner into the LSA and the "0" setting gave me acceptable low volume. Maybe it's my DAC output? I don't think it would be my transport output?
Just picked up a lightspeed. Here's what I have,how can I get it to work best with the lightspeed.
Krell KSA 50S amp
Music hall CD 25 transport - Black Cat Veloce ic - Rega DAC
AU 24 ic or Straley ic or Morrow ic to preamp same to amp
Clear Day or Straley speaker cable to Tekton Lore

My ears are the ultimate test but am I off to a good start?
Clio - looks like the output impedance is 600 ohms on the Rega DAC. is this too high?
George, I'll have to shoot Rega an emai. None of my IC's are over a meter.Thanks.

Jack
Clio - looks like the output impedance is 600 ohms on the Rega DAC. is this too high?
Hi - With my lightspeed I still get significant volume when my volume knob is set all the way down. Is that because my speakers are 98 db efficient? I need to be able to reduce my volume lower.
I get to 9 easily without it being too loud. 12 gets me pretty good volume and I've been up to 2 on a temporary jam.
My main concern is that when I'm at "0" volume I'd like less signal to be conveyed to my speakers.
Plinko, please see my 3-29 post for component list. I really like the lightspeed.Can't imagine not having it in my system. I'll have to work with George on work arounds for the volume issue.
My Krell amp has an input sensitivity of 1.34 V RMS and gain of 26db. Looks like I need an amp with lower input sensitivity . Not sure how the gain number factors in.
I see Gene Reuben Audio does carry the attenuators. Looks like I'll give them a try.
I see that George recommended lowering my gain of the amp or source. My amp input impedance is 47k ohms and output impedance of my DAC has been confirmed at 600 ohms by Rega. What numbers do I need to look for in an amp or source to match with my 98 DB sensitive speakers so that I achieve lower volume in the "0" volume setting?