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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
georgehifi's avatar
georgehifi
10,312 posts
 
Audiolabyrinth:
Thanks for the invite, but cables and how they sound are such a subjective thing, and very system dependant.

All I say that for all passives and high output impedance tube preamps, one should make sure that the capacitance of the cable is low, as not to form a HF (high frequency) filter if the capacitance of the cable is too high.

Luckily good quality cables are nearly always low capacitance, and just to be certain you should ask the manufacturer.

A good worst measurement case is 100pf (pico-farad) per foot or lower good ones are much lower, for a 1mt interconnect this worst case capacitance would be 300pf, this equates to with a passive and many tube preamps to have a HF (high frequency roll off at around -3db at 76khz.

But if you pick an quality interconnect that is 50pf per foot, then the HF roll off is -3db at 152khz.

Cheers George
audiolabyrinth's avatar
audiolabyrinth
4,555 posts
 
@ Georgelofi, Wow!, My interconnect, The Taralabs Zero Gold's capacitance is 4 pf per-foot!, then the new Taralabs Evolution Grand master interconnect is 2pf capacitance per-foot, I'm good with the capacitance specs then!, thankyou for your reply Georgelofi.
georgehifi's avatar
georgehifi
10,312 posts
 
Yes this what good interconnects should be, as little as possible capacitance.

Otherwise if over 300pf total for a 1mt length, they will start to create 1st order (gradual) HF (high frequency) roll-off's into the audio band when combined with nearly all passive preamps and many of the tube preamps as well.

Giving the impression of sometimes sweeter highs less sibilance (if the system has some).
And because the top end has been curtailed a little less detail, it can also give the impression of more bottom end or richer lower midrange.

Cheers George
dhcod
710 posts
 
I didn't measure capacitance or anything but after trying quite a few interconnects, I found the Purist Audio Museaus to work fantastically with my Lightspeed. Cleaner, clearer, more true.....
georgehifi's avatar
georgehifi
10,312 posts
 
Dhcod hi,
I had a bit of a search and yes your Purest Audio cables are very good low capacitance ones.

They are fine to use with many tube and most passive preamps, and will not cause early (into the audio band) high frequency roll off.
I would keep these to a max length of 1.5mts from pre to poweramp.

I looked at most of the ones they give specs on, and they give the 1mt length pF (pico-farad) capacitance and all that I saw are under the 100pf per ft measurement I gave earlier.

This is good to know that some cable manufacturers are responsible and doing this specification for their customers, who know how to use it, for their systems compatibility with them.

http://www.puristaudiodesign.com/products/interconnects.php

Cheers George
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