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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
 
This is the output description "The 12AU7 tubes are on the back panel virtually bonded to the output connectors."

This is where the solid state part is used "It uses a solid-state analogue switch for input switching and an analogue solid-state volume control selected for its sonic quality and tracking accuracy."

All this can be read here, half way down.
http://www.positive-feedback.com/Issue41/concert_fidelity.htm

Cheers George
clio09
3,355 posts
 
George, yes I saw that review and was aware of the other information. As I stated in my previous post, amps input impedance is 47k ohms. What I am having a difficult time with is why the designer would build a preamp circuit with 33k ohm output impedance (assuming this is accurate) to mate with amps that have not much more relative to input impedance. It makes little sense given I have spent approximately 150 hours or so listening to this system and it in no way sounds like a bad match to me.
georgehifi's avatar
georgehifi
10,312 posts
 
Like I have always said Tony, it will work and sound ok with no damaging side effects.
But the source should be at least 3 x or more lower output impedance than the the load. I imagine then it could have sounded even better.
Now can you imagine what Teajay heard when he listened to the Lightspeed into a 15k load and drew his conclusions?

Cheers George
pubul57 OP
3,712 posts
 
George, I'm not sure that Teajay's "LSA test" was with his own system, it might have be a group of audiophiles getting together, comparing notes - obviously testing the LSA with Pass gear would be far from optimal, like testing a 3 watt SET with a pair of Maggies - no way to fairly assess either the amp or speakers in that situation.

Anthony, it will be interested to hear what Tsuda has to say, something does not seem right.
clio09
3,355 posts
 
Just ran into this thread. Seems another LDR attenuator has been making the rounds as a DIY kit. There is a balanced version available as well. Not sure technology wise what the differences are with the LSA, but thought some of you here might be curious to read about it anyway:

http://www.diyaudio.com/forums/vendors-bazaar/176847-warpspeed-optocoupler-volume-control.html
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