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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
3,345 posts
 
What I am most curious about is how well The Truth preamp will drive the S-30. The LSA does drive it well, but I'd like to hear if The Truth will improve upon dynamics. The bandwidth measurements are off the charts with the Truth and the output impedance is a constant 2 ohms. Apparently the input impedance is too high to measure.

No risk to try it so we'll see.
pubul57 OP
3,712 posts
 
George, obviously you could have made a buffered version of the Lightspeed, what are the pros and cons to that approach. What are your thoughts on buffering? Go Spain!!
georgehifi's avatar
georgehifi
10,312 posts
 
About buffers, I will always say the best buffer is no buffer if your system meets the following impedance requirements. If your source output impedance is less than 200ohm and your poweramp input impedance is more than 47Kohm then the Lightspeed Attenuator is a shoe in, no buffer will sound better.
But if your source is more than 200ohms output impedance or the power amp is less than 47Kohm input impedance then you may (but not always) need a buffer, the best commercial buffer I've heard is the Burson Buffer. But the best sounding buffer is the (diy) Super Linear Cathode Follower (SLCF) buffer. But still they don't sound as good as NO buffer at all.
P.S. those who want the circuit of the SLCF send me an email
Cheers George
pubul57 OP
3,712 posts
 
Thanks George. That is pretty much what Roger Modjeski (Music Reference / RAM Labs) said and "I'll make you a preamp with a buffer, but you don't need it and it will sound better without it". Now Roger is a guy I pay attention to, he is an electrical engineer, make classic and much admired amps and preamps, and is a tube maven - he also is aghast as audiophile tomfoolery and nonsense. I've been drawing the conclusion that active preamps and even buffered or transformer based passive will sound better than a pure passive when the system needs it, and many do when the impedance and gain issues are not properly addressed, but that in a system metting the requirements for a passive (without buffer - not the Pass, The Truth, etc)something like the Lightspeed will provide the very best possible sound. It will be interesting to hear Anthony's observations of The Truth, since I do think his system is a good setup for a "pure" passive.
clio09
3,345 posts
 
I just started running the Lightspeed off a battery power supply. It is the same batter power supply used by Galibier Designs to power their turntable motors (Sears Diehard Portable Power 750), 12V DC and 12aH. Thom Mackris made me the appropriate adapter cable (mine needed to be center pin negative). I've been listening for a bit now and so far I like what I hear.
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