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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
grannyring's avatar
grannyring
6,479 posts
 
Well, I am taken back. The Atlas amp I own is high gain(26 db) if memory serves. It is also a zero feedback design. It has a measured input impedance of 570k ohms. It has a rated input sensitivity of: 60mV for 1W output, 2.3V for full power.

If this amp is a poor match, then the LS is not suitable for most all amps ever made and not a real world product - period. Several vocal and seasoned Aphiles own the Atmasphere/LS combo,and the Atma amps have a rated sensitivilty of 3.1v to full power. They say the Atma amps are good matches and this whole input sensitivity thing is overblown. I happen to think your product is real world, and the Atlas amp was a wonderful match. Please understand the consequence of your statement is a clear message that only in the rarest of circumstances will any stereo owner ever hear the true possibilities of this unit. I must say this seems near impossible George.

No, my amp and set-up were most accommodating to the LS. If not, good luck to you owners who think you have begun to hear your LS system's possibilities. You have not. It is even better then you imagine. LOL
pubul57 OP
3,712 posts
 
Grannyring, I know you amp is a hybrid, but not sure how much it works like and SS amp versus a tube amp, but there does seem to be some consistency in folks with SS amps being less enamored of the LSA than those with tube amps, and I suspect it has less to do with impedances and sensitivities, than tube versus SS sonics. Not commenting on your amp in particular since I am not familiar with its sound or operation, but more as a general comment - I think most folks that fall in love with the LSA own tube amps (no?).
grannyring's avatar
grannyring
6,479 posts
 
Well the thing is this Paul. The LS sounded glorious in my system. Really downright glorious. The Atlas is a tube amp at heart in the way it sounds. It is a beautiful sounding amp. Quite special.

The LS sounded amazing and let the Atlas and my speakers shine. No doubt, in my small mind, that my system was a supurb match for the LS. I guess I simply cannot say my active was better. When I say that it seems something must not have been perfect for the LS. Oh well. I will let that frustration go and know George truly believes, with passion, that the LS is the gold standard. Good to have that passion!

As awesome as the LS is in my well suited system, the tube active I own was just awesomerrrrrrr....
pubul57 OP
3,712 posts
 
Yes Jult52, it would be interesting to hear your comments on the BENT versus LSA, I have owned the TVC and AVC versions, and I think Clio9 has heard a Slagle AVC, as well as an S&B -based TVC. UNfortunately, I did not have them at the same time as the LSA to a careful comparison over time.
clio09
3,355 posts
 
The Atlas monoblock is 3.1V to full power so I'm assuming Bill has the stereo version which is 2.3V. That should pose no issues for the LSA IMO.

The gain stage in the amp is tube driven. Output stage would appear to be solid state. The amp does double its power output from 8 to 4 ohms and it has an output impedance that is incredibly low and somewhat of a norm for solid state. I am curious how Jim White gets such a low output impedance from a zero feedback design.

While the LSA does match up well with the Atmas-Sphere S-30 in my system, I do feel it matches up better with the Music Reference amps I have. Driving the S-30 direct from my Resolution Audio Cantata (5.5V buffered output) seems to offer some benefits as well, but it is not as pure a signal transfer. In fact nothing has been as pure as the LSA in my system.

If you go to Devilboy's system page he comments on the fact that he did not do a head to head comparison between the Tap-X and LSA. In my direct comparisons with my Slagle DIY unit and the LSA they are pretty close, but I give a slight edge to the LSA, again it is more pure where there is some coloration from the autoformers.
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