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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
 
You could for comparison against the wall wart use one of those small square Duracell 9v Alkaline batteries, or even a rechargable one, it will probably last for 24hrs.
Just wire up a 2.1mm dc plug to it (but please make sure + positive goes to the centre of the plug)
Anywhere between 9v-18v dc is fine, as inside the Lightspeed Attenuator there is a second regulated supply that regulates everything that comes into the dc socket down to 5vdc.

Cheers George
glory's avatar
glory
1,614 posts
 
Think it can power my Placette also. Where do you by the adaptor cable?
clio09
3,360 posts
 
Here:

http://www.minute-man.com/acatalog/Online_Catalog_Cigarette_Ligher_Plugs_and_Sockets_272.html#a90_2d618
lacee
811 posts
 
If anyone is a little put off because George says the LSA is sensitive to the length of interconnect I can state that my 20 ft interconnect doesn't present a problem.

There is no lack of clarity, no loss of treble or bass and no loss of volume.

It sounds like the 1 mtr Nordost I had been using.

So if you think you need to invest in a special interconnect to get the most out of the LSA,give it a try with what you have.

I don't know what George will have to say about this, but a long interconnect going out of the LSA to the amps is not a problem for me.
georgehifi's avatar
georgehifi
10,312 posts
 
I'm very conservative with that statement just in case the interconnect is poor quality high capacitance. I call it like it is and don't try give best possible scenarios only. Here is a simple semi technical explanation.

In your case with 20ft, lets say that the cable is good quality and low capacitance, a nice low capacitance figure would be 10pf per ft, with your 20ft that is total 200pf.

200pf connected to the output of the Lightspeed Attenuator makes a high frequency filter of
-3db at 114khz. No problem as you can see way higher than our best human limit of 20khz

Double that 20ft of cable capacitance to 20pf per ft and the -3db is then at half the above at 57khz still no problem even 20ft of interconnects.

Halve the length to 10ft and then your back to -3db at 114khz way out of the audio band. Halve the capacitance to 10pf and your at -3db at 228khz!!! bat territory

Cheers George
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