2. amps-preamps
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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
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banquo363
371 posts
 
I don't know what it is (thanks Almarg for the explanation above), but I've been switching my short (1.5 ft) and long (3ft) interconnects as described above and I always get better sound when the short IC is between LSA and rm-10. Perhaps it's as Almarg noted: that there's an attenuation of bass due to variations in the impedance of my tubed phono stage. At any rate, I now get more dynamic and better bass (articulate and rich). I get 15-20db dynamic swings (as measured by my radio shack meter) on symphonic music, from the average sound level to peaks. Not bad at alI, I think. What counts as a good dynamic swing?

Joe Morello's drum whacks can now sound like a shot in the dark.

I've made a myriad of changes to my system of late and I'm continually impressed by how the LSA allows me to note them all, good and bad. I guess that it's the LSA's neutrality 'at work'.

Thanks, Clio09 for the shorting plugs idea above. I made some and went through the procedure. My rm-10 is not dead quiet, close but not quite. Transformer hum, I believe. But the LSA with shorting plugs adds no additionally noise. My phono stage however...There's a dreaded ground loop I think. I bought a cheater plug but that didn't help. Mercifully it's not too loud. I need to have the LSA at 3 o'clock to be bothered by it at my seat.

On a side note for those using the rm-10: I've been using NOS GE El-84's and they're fantastic. Superior to the stock tubes and to the Genelex reissues.
pubul57 OP
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Brent Jesse?
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banquo363
371 posts
 
Andy at vintage tube services
pubul57 OP
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Two of the best:)
clio09
3,355 posts
 
Banquo363, have you tried the cheater plug on the RM-10? How loud is the hum? If you have to put your ear to the driver it is okay, but if you can hear it standing in front of your speaker or further away then maybe you should talk to Roger about it. In my system I do not get any hum at all from the RM-10 or EM-7 V12. When adding the LSA and shorting the inputs did you check for noise at various volume levels?

The phono stage is more complicated. If a cheater plug did not work try running a ground wire from your phonostage to another ground point, maybe the center screw on the nearest outlet. Any possibility it could also be your phono cable or cartridge wires?
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