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
That is overstating the argument, but a good design will have as few parts as necessary, but no less (in the case of pure volume attenuation you don't need many)and the quality of parts matter, too - especially if you are relying on fewer parts (less places to hide). In the case of the LSA, it also not just a matter of the number of parts, though that helps since you don't need a lot of parts to control volume if you are adding no gain, or providing any buffering (those function do require more parts), but also a contact free interface between the volume knob and the resistors. The freedom from the mechanical connection is one of the reason it is felt to be a better mousetrap than any other potentiometer or stepped attentuator. But hey, I studied philosophy , so I rather the tech folks explain that part of it.
Ok, based on the reasoning that less parts and simplicity ALWAYS is truer to the source and more accurate, then this SS preamp certainly must deliver a perverted or somehow “additive” portrayal of the music compared to the LSA….. Also no tubes in this one….

http://www.balabo.com/amps/control/

I suppose one may think it, ague it, but the proof is in the hearing only. This highly reviewed and often touted pinnacle of preamps is full of parts. Looks at all those parts…

To actually get all of the nuances and notes off of that source requires a preamp that can actually extract it and amplify it. It needs to convey the dynamic contrasts and subtleties including those subtle micro and marco details. Perhaps a passive is, well, “too passive” to extract all of that information (on the source CD etc). This requires an “additive” (accurate gain) approach. Our stereo systems must be “additive” to even play a single note through a speaker. A passive may simply leave these higher order musical realities out – they may be subtractive. They may constrain or compress for lack relative drive. That is perhaps why, in my experience, I miss the depth, body and dimension with a passive.
I understand why a moving coil cartridge would need gain (and RIAA equalization) to create a sense of drive and dynamics, but why would a 2 volt signal need any gain to drive an amp that plays at maximum output with 1v of input? Is "drive" something different than simple voltage which is either sufficient or insufficent to drive an amplifer? I suppose a source could have a weak output stage, but I would think that would be as much of problem for driving an active preamp as a more direct connection to the amp. There is something appealing about "horsepower", but does it really serve any purpose where input sensitivity is simply not an issue? Does an active really provide something "in reserve" for hearing micro and macro dynamic inflections?
Sources these days, esspecially CD can drive (have enough output) by themselves (without the need of a preamp) a poweramp into cliping, there is your strait wire with no gain (the interconnects only).
All we need is something so we can attenuate that source so it doesn't blow the amp up, we do not need a preamp that preamplifies again on top of the source that can already by itself blow an amp up with the amount of output it has.

Cheers George