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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
clio09
3,355 posts
 
Banquo363, sent you an email.

Not sure why the Mogami didn't work out for you. It is one of two types of interconnects I use with the LSA, and as you know I also have the RM-10 MkII.

In reality, the Blue Jeans cable should have been the problematic one. Anything over 2m is definitely pushing it with the LSA.

One other note, use shielded or cables that use good noise rejection designs (ex. Litz). Seems to work better than unshielded by my own personal tests and I think George has recommended shielded cables as well.
georgehifi's avatar
georgehifi
10,312 posts
 
Hi guys, interconnect cables can be a mine field, not just with the Lightspeed Attenuator but with all forms of audio gear.
Cables can form a hi frequency filters with their capacitance (pf picofarad)) when combined with the input impedance or output resistances of sources and loads, as can output/input coupling capacitors of some sources and amps, they can create a low frequency filters with the load of the next stage/s. Then there's the inductances and resistances of cables which can also form filters (hf, lf, even band pass) of some description.
A good general rule I find is to have direct coupled outputs (no Caps) on sources you own, and direct coupled inputs on the poweramps you own, and to keep interconnects as short as possible (even if it means reconfiguring the system) and to get ones that have low capacitance less than 100pf per foot.

Cheers George
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almarg
9,670 posts
 
05-31-11: Georgelofi
... Keep interconnects as short as possible (even if it means reconfiguring the system) and to get ones that have low capacitance less than 100pf per foot.
George, is that what you really meant to say? I would not consider interconnect cable capacitance that approached 100pf/ft to be anywhere near being "low."

For instance, just 6 feet of 100pf/ft cable would have a capacitive reactance at 20kHz of about 13.3K, certainly low enough to be significant in relation to the output impedance of your LSA, which is around 7K iirc.

Best regards,
-- Al
pubul57 OP
3,712 posts
 
Yup, and well above the 12pf/ft of the Cardas, which is why I probably heard no difference between the 3ft and 6ft versions, and as Clio9 mentions, they are of course superduperlitz:)
georgehifi's avatar
georgehifi
10,312 posts
 
With the Lightspeeds output at worst 7k, this together with a 1mt cable with a max of 100pf per foot gives a -3db point at 75khz, which is plenty high enough and still higher than any cdp noise filtering.

Cheers George
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