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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
 
You are right Paul, in some instances.
But in our case with the parameters I have outlined for the Lightspeed Attenuator, if you have a source that has low output impedance, less than 100ohm and 2v or more output voltage, and the power amp at more than 50kohms input impedance, there is absolutely no need for preamplification, (it's Ohms Law). No amount of extra current in the form of extra active current stages will have the desired effect of giving more drive and control, if fact the opposite could be had and heard, as well as a loss of transparency.
Cheers George
pubul57 OP
3,712 posts
 
I think this is beyond the reach of logic, it is simply a matter of trying it within the system context as you proscribe and listening for yourself. With all the preamps I have tried (most $5,000+ tube preamps)I've concluded that most negative comment about passives (and resistor versus TVC/AVC for that matter) must come from those with a financial interest (as makers or owners of active preamps), or simply not evaluated in the right system context, or one simply likes euphonic colorations - and they have every right to prefer that. In the wrong system context, it would be like proclaiming the weakness of low watt SETs by evaluating them with a pair of Thiel or B&W speakers, a meaningless assessment of what SETs can do.
agear
1,362 posts
 
Publus57, the active vs. passive debate is indeed an interesting (and old) one. Many of the guys making active pre-amps today have toyed with passive designs in the past.

My crude understanding of the Lightspeed and devices like it is that its a variable resistor triggered by light. This idea is not new. Georgelofi, what is proprietary or unique about your particular design?

For end users, I wonder if the sonic signature of the Lightspeed (an oxymoron) is easily distinguishable from other passives? If you were to undergo actual blinded listening sessions, could you even pick it out in a lineup? That is a question I ask myself about my own equipment.

A friend of mine (who owns a big name active) demoed the Lightspeed and said it did a lot of things well, but it did not displace his active pre-amp. He did have some long ICs which may have sullied the demo in his mind.

For the sake of clarity and unbiased reporting, I would be more than willing to do some blinded listening sessions of active vs. passive pre-amps (in the Charlotte NC area). I will make sure to involve more people than simply devotees of the individual devices involved.
pubul57 OP
3,712 posts
 
I like the idea of blind listening sessions, why are so many audiophiles and reviewers agaisnt it, or at least to believe in it as a effective method for assessment? That always seemed odd to me. Yes, it would be a good idea to do such a test absent the knowledge of when one is listening to a particular piece, epsecially when they have invested themselves in a piece financially and/or emotionally. I don't know if the LSA is the best preamp, which doesn't exist, but I pretty happy knowing that for $450 I was able to sell my active preamp that was $7,000 more without any obvious sense that is not as good (enjoyable). That can make anyone a devotee on the basis of value alone.
pubul57 OP
3,712 posts
 
One thing that would be nice in the LSA, and most modern preamps, though it might "ruinous" or a least "deleterious", is a scheme for balance control to account for recodring mixes, room geometry, and human frailty as we age - not sure how many ears are balanced L/R- perhaps than we would like. I think HP once said not having a balance control was a fatal design flaw - yet one that is very, very common in purist designs.
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