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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
pubul57 OP
3,712 posts
 
Yes, it would be good to hear from someone who has actually owned both, or auditioned both at length? Anyone on Audiogon? You?

As far as I know, the LDRs themselves are identical, but Alan appears to have tried to address some ergonomic issues, a more complicated device it seems. Sometimes a tradeoff, especially with an approach principled on simplicity and minimum of parts, contacts, etc. Would not mind trying a WS to see, but not many available, and I certainly could never make one for myself from a kit.
georgehifi's avatar
georgehifi
10,312 posts
 
It's all good to add fancy ways of not having to quad match the LDR's but the end result is there's more junk in the signal path and it results in differing sound qualities (not levels) at different listening levels for each channel. This below is what I posted at DIY about the same subject.

"You need to look and measure that the I/O impedances of both channels at differing levels remain the same to each other, if not and they have different values of Z in and out (i/o), this will effect the sound quality of each channel hence may/will effect the stereo imaging. It will simulate the same effect as having large different lengths of interconnects for each L and R channel.
That is why quad matched sets have a consistency between channels, they remain equal for both at all levels of listening, unlike some of the pseudo Lightspeed Attenuators that are comming thick and fast. There is no free lunch."

Cheers George
pubul57 OP
3,712 posts
 
As you noted earlier in my question about an improved version, it seems that after 30 years of tinkering, the LSA is well sorted out, and at some point there is little to improve, without as you say paying a sonic cost in the service of some other goal. To me, the only issues are stability over time, and balance control - which unfortunately requires dual volume controls for best sonic results.
georgehifi's avatar
georgehifi
10,312 posts
 
Dual L&R volume controls are the only option I provide for the Lightspeed Attenuator.
It is the only one that does not effect the sound quality, though as you can imagine it is slightly more difficult to use, but a boon to those who have unsymetrical systems or room acoustics.

Cheers George
pubul57 OP
3,712 posts
 
Or ears:)
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