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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
almarg's avatar
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almarg
9,670 posts
 
So, yes there is a slight loss in max power, but do you think it would be relevant?
My guess is that it would not be a problem, especially considering this statement by Jult52 in the other thread:
My power amp has a continuous rated output of over 500w which I never fully max out being a law-abiding middle-aged person :) I like the power for the instantaneous peaks, especially at the onset of sounds and for the feeling of headroom.
BTW, my rough estimate of 3db as the amount of the amp's power capability that would become unusable was based on the following:
1)1.3db due to the disparity between dac output voltage and amp input sensitivity.
2)0.5 to 1.0db due to tolerances or possible inaccuracies in those specs.
3)0.5 to 1.0db estimated margin in the recording, between the highest musical peaks and digital full scale. That's what I've actually seen on a number of commercial cd's, that I've analyzed with an audio editing program called Sound Forge.

Best regards,
-- Al
georgehifi's avatar
georgehifi
10,312 posts
 
All this is not an issue, most amps/speakers are fine.
If you have an amp that is .5 or 1v input for full output sensitivity and 110db speakers, then you my have a problem with having to use the Lightspeed way down on the volume and never being able to go past 8 o'clock on the volume. And an active pre would be even worse in this situation. But this is very rare as most amps are 1.5 to 2v sensitive and most speakers are 93db below.

Cheers George
clio09
3,360 posts
 
I think you'll be fine. Your CD has a good amount of output voltage and your amp isn't too insensitive. You should definitely be able to swing the volume knob past 12 o'clock which is ideal.

I do use my LSA with the S-30 single ended inputs. I've also removed two of the driver tubes and shorted the tube sockets, effectively lowering the gain of the amp 12db. In each case the LSA worked fine. My speakers are rated 92db, but that is conservative. 94 or 95db is probably more accurate. Had they been under 90db I doubt the LSA would have worked well with the S-30.
almarg's avatar
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almarg
9,670 posts
 
George, note that the issue is not whether or not the volume control will have to be used too close to the bottom of its range. The issue is that even with the volume control set to its maximum position, a substantial fraction of the power capability of the amp (perhaps half) will not be able to be utilized. And keep in mind that the gentleman's speakers are relatively insensitive, at 83db/1W/1m.

I doubt it will be a problem, as I indicated, but that is the issue.

Best regards,
-- Al
atmasphere's avatar
atmasphere
11,874 posts
 
Jult52, you have no worries, in fact this is more of an ideal situation (so long as you can get the amp to make satisfying power)- you *want* the amp to have less sensitivity than the maximum level of your source, as this allows you to run the passive volume control at higher levels. The math works more in your favor in this case- you are less likely to loose bass and impact since you will not be running the volume control at a lower level.

When the amp has higher sensitivity, so that your source makes more voltage than you need, then the math works against you; with any passive as you turn the control down more, the more bass and impact is reduced.
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