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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
 
Pubul57
The one you have is already MkII. The only way I could improve to a MkIII is the versatility of the unit, that would be to have a discrete unity gain buffer (like Nelson Pass designed for the Lightspeed) on the output to lower the output impedance so it could then drive poweramps of lower than 47Kohm input impedance, and of course longer IC cables. But this would be a compromise as they would never sound as good as the MKII, I have done it, and would cost more, this is not what I'm about.
As for the switching for multiple inputs this is also not the purest way for me. If someone needs multipule inputs I suggest one of these.
http://www.decware.com/newsite/rotary.htm
That way you can still go direct to get the purest best sound when needed to show off your system.
The whole reason is to get the signal from the source to the poweramp with the least amount degradation.
And in case your wondering, all MkI's were converted to MkII years ago.
And if your wondering.
MkI = series resistor and shunt LDR "very good" still better than the best pots.
MkII = series LDR and shunt LDR "even better" more consistent i/o impedances, better bass and dynamics were noted by all previous mkI owners.
Cheers George
atmasphere's avatar
atmasphere
11,970 posts
 
Digital volume controls have always been an irritant. As far as I am concerned, they are a failed concept. Given the brilliance of the Lightspeed system, it would seem a natural in a DAC or CDP.
fas42
58 posts
 
Atmasphere, you are echoing what has been said many times, that digital volume control is "bad", which is always perplexing to me. By contrast, once a system is of sufficient resolution it is actually quite obvious the distortion all conventional volume controls add to the sound, as George states.

Yes, digital attenuation is a no go if you then follow that stage with another variable gain stage which you use at times to boost the signal. But that's a silly thing to do! The digital attenuation must be the one and only gain control in the system and then it works perfectly, because the loss in bits is always well below the audible level, unless you want to jam your ear against the tweeter while doing serious listening.

I have a 25 year old CD player with pure digital volume control on it; I play a test music track that's recorded with an attenuation of 60dB -- that's effectively the dynamic range of a very good quality master tape -- and with my ear pressed against the tweeter, can JUST hear the effect of the digital volume control ramped to maximum gain on this almost super quiet signal.

Frank
clio09
3,360 posts
 
IF we assume that a straight line from source (phonostage) to amp is the best/least colored way to get at the information on the source (vinyl), then can we assume that finding an amp that has a volume control built into it would be a good way to go? Since it would allow for direct connection and also allow for volume control. In such a scenario we would bypass the LSA (or any preamp) and any colorations it may add. And also bypass a set of IC's and whatever potential issues it raises.

I take it that the answer depends upon the nature of the volume pot design/quality on the amp?
Banquo363

I have to say that the idea of a volume pot in the amp is a pretty good idea. Of course, implementation is everything in terms of quality. At THE SHOW we were running a 45 SET amp with built in volume control. THE CDP we were using was the very reputable Resolution Audio Opus 21, that also has a very nice analog volume control. In the best scenario the volume control on the CDP had to be pinned and we had to use the volume control on the amp to attenuate.

Now I have heard Ralph state the best means is to have the volume control at the amps input if you do not wish to use a preamp. He does offer this as an option on his amps, unfortunately though not my S-30, else I'd take him up on the option. However, one of the things about the LSA that I believe is overlooked is that the use of the LDR's takes the switch right out of the equation. No wipers or contacts of any sort to interfere with the signal. You could use the best switch out there (the custom Shallco's in the Atma-Sphere MP-1 are quite impressive BTW) and it's going to impart a sonic signature. With the LSA it wouldn't matter, a Radio Shack switch would work as well as TKD, Alps, Seiden, Shallco, etc.
pubul57 OP
3,712 posts
 
I'm guessing here, but I would imagine the only concern would be the linearity of the LDRs, proper matching, and performance over time (George has had these in the field quite along time). The brilliance of the LSA is that it takes away the need for a very high quality, and usually expensive switches, which no matter how good, can't overcome the laws of physics, the diode thingy George talks about.
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