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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
 
06-16-10: Pubul57
No, thinking more in terms of power delivery and power supply fluctuations, the ability of the output stage of the CD player to drive the ICs and the amp

There should never ever be powersupply fluctuations in the output of a cd player, if there was it needs to go to the recycling tip.
As for the power delivery, (which means current delivery) If your source (cdp) has a low enough output impedance (say less than 200ohms) and it sees an input impedance (load) higher than this there is no current delivery problem, it's only if it sees a input impedance (load) lower than 200ohm then you can start to have current limiting.
Output impedance of the source has to be lower than the input impedance of the next stage, this goes from cdp to pre, then from pre to amps, and then from amps to speakers. And don't forget all interconnects and speaker cabling have some resistance this should be added to the input impedance of the load, this is why one should not use hair thin cabling as it has more resistance and adds the load resistance.
There endth the "Ohms Law" lesson for today need to build some more Lightspeed Attenuators, will back later.
Cheers George
clio09
3,360 posts
 
And don't forget all interconnects and speaker cabling have some resistance this should be added to the input impedance of the load, this is why one should not use hair thin cabling as it has more resistance and adds the load resistance.
Georgelofi

What type of cabling should one use (or do you use) in terms of gauge? Is there a preference over stranded versus solid core. Would cabling like Mogami or Belden suffice? These typically have low LCR specs.
pubul57 OP
3,712 posts
 
The Cardas GR have really low capacitance, but the Blue Jean ICs, which are Belden made, also have very low capacitance - if that is an issue, which shouldn't be with most cables under 2m (I would think).
tradeontheweb
43 posts
 
"06-16-10: Grannyring
Scott, that would only be in a small room with highly efficient speakers. I assume that combo won't play at 95db in a larger room with speakers under 90 db efficient?

I also assume that combo would never have the dynamic impact of a more formidable set-up. Say 300-500 watt monoblock amps and an active tube preamp with killer drive and scale"

Sorry Grannyring, but nothing could be further from the truth, in my experience. In fact I recall using the LS with a Gryphon DM100 and Gryphon Encore (500 w) into Usher AC 20 speakers of about 92db. This was in a large, well damped room. Dynamic impact was there in spades and no loss of detail or presence either.

At that time, I recall I had an Audio Research SP11 on hand for comparison. It lasted about 2 days before the LS went back in. All this and there were no mods to either of the Gryphons to match impedances for the use of the LS !

My JBL 4350's will approach 125db according to the literature. The LS normally sits at about 10-11 o'clock. Past 2 becomes painfull, literally.

Cheers

Scott
georgehifi's avatar
georgehifi
10,312 posts
 
I use Express 6 MkII interconnect by Eichmann but I don't wire it like they do, I put all reds together and all backs together I found this sounded better and was more electrically logical, the way they had it was strange and sounded that way.
I also like it because it is substantial have 6 solid core individual conductors of about .5mm each 3 red 3 black individually insulated the encased in a blue gel type outer sleeve with no shielding at all, as I have found shielding can increase capacitance/inductance.
Also I like that is pure 99.99%ofc copper, I have never liked silver or silver coated, I find it artificially accentuates the highs, giving a false impression of detail while robbing body from the lower-mids and leaning out the bass.
Then for speaker cable the same Express 6 MkII speaker but its twice as thick probably 1mm conductors
Back to work
Cheers George
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