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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
 
I take what you've found out onboard Tony. I can safely say a cap on the output will not change the output impedance of the tube in the audio band for the better (lower). And a resistor would also not change it for a lower impedance, only for higher impedance.
So there is something else we don't know, if what you were told is "5.2k ohms and 900 ohms" As I find it very disconcerting that the output impedance has not been included in the specs or design on the website.
As just one of a few of the tube gurus I queried about cascode output said. And they all say basically the same thing.
Quote" If you want 6 or 12dB gain, you don't use a cascode.
If you want lowish output impedance, you don't use a cascode. (NB. in a preamp you will want low output impedance, unless you are incompetent).
If you are serious about valves, you don't hang them out horizontally at the back of the chassis, even with fancy roll-bars. This is asking for poor contact as the valve slowly drops out of the socket.Quote"

Cheers George
teajay
1,691 posts
 
Well Tony,

You just got a taste of what I keep referring to as George's arrogant know it all attitude, this time towards a gentlemen we both respect, Mr. Masa Tsuda. The quote's from George's "tube gurus" particlarly the crack about, " you don't hang them horizontally at the back of the chassis" shows how ignorant he is about why Mr. Tsuda has them in that position to begin with.

And this is the guy you would want to hang out with and enjoy his company? Well, let's see what your going to do now. Come up with another excuse or rationalization for George's put down of someone you know is a brilliant designer, builder and your friend or finally stand up to this know it all who's full of himself.
fiddler
581 posts
 
All we need now is some cheese...
georgehifi's avatar
georgehifi
10,312 posts
 
You have no constructive critisism Teajay, all you try to do is to get this thread shut down with your personal attack.
Not once have I attacked you personally just questioned the Ohms Law compatibility of components in your system that have not been properly addressed in the specs they have presented, and the voodoo that surrounds them.
agear
1,362 posts
 
George, is the diode effect measureable? What does it do of rather what does it distort?

Paul asked the million dollar question above: what are the effects of gain? Does it produce distortion?

I did try the LSA with a SS amp (TRL Samsons) with 68K input impedance and the sound staging flattened. I have experienced the same thing when running the amps directly with my source. What is this about George?
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