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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
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banquo363
371 posts
 
I've been playing around with interconnects and note that the LSA really responds to changes. I was having the LSA drive a 12 foot run of blue jeans cable into my rm10 amp. Sounded good to me...until I moved some stuff around which allowed me to put in a 3 foot cable I had. Much, much better--I'm pretty satisfied with them in fact. However, I can't leave my equipment as it is, so decided to buy a 6 foot (the shortest I can use if I leave my rack where it is) Mogami 2534 cables. Not good. The mogamis are supposed to have low capacitance, so I'm wondering what the issue is.

What cables are people using with the LSA? I'm cheap, so nothing over $350. Also, have people noted the differences in sound depending on length? I can't imagine the 3 foot cable I used is better constructed than the mogamis (although they do have nice locking terminations) so I infer it must be the length that's the culprit.

I'm thinking about trying the Tempo Electric silver cables. Any comments on those?

Another point to note is the following. I bought a 2 foot Soundsilver cable (gold and silver) to connect my source to the LSA. I noted that it sounds much better using itthat way than using it to connect LSA to amp. I would have thought my cd player could easily drive a longer cable and the that the LSA would benefit from driving the shortest length, but that turns out not to be the case for me. Why?
pubul57 OP
3,712 posts
 
I must admit that difference between cables simply don't jump out at me - though I did buy Cardas GR just because it is often recommnded with my speakers (Merlin VSMs) - I do know they are about the lowest capacitance cable on the market (12pf/ft) so I suspect that helps with the LSA. I tried a 1m and 2m connection between pre and amp and it was simply much too difficult to indentify any difference - so I stopped trying. The only IC rule of thumb that seems to matter is short/low capacitance and you should be alright with most cables with good connectors. Can you hear a difference between 6ft - 3ft - 2ft - I don't think so - at least I can't.
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banquo363
371 posts
 
I'm not at all a 'cable guy'. It would please me no end if I couldn't hear significant and pleasure undermining differences between cables. FWIW, I'm just listening for musicality, whether my reference recordings draw me in more with one set of cables over another. I was very surprised to find that I could detect a difference.

I don't know if it's the differences in length of the cables that I'm hearing or differences in the variances in construction. I don't have the same cables in varying lengths to test that. Incidentally, the blues jeans have low capacitance of 12.2pF/feet--that's why I bought them in the first place. I auditioned a 5 foot pair of magnet wire interconnects last weekend. Too lean; the harmonic richness in my Johnny Cash cd's were almost entirely missing.
clio09
3,360 posts
 
Banquo363, sent you an email.

Not sure why the Mogami didn't work out for you. It is one of two types of interconnects I use with the LSA, and as you know I also have the RM-10 MkII.

In reality, the Blue Jeans cable should have been the problematic one. Anything over 2m is definitely pushing it with the LSA.

One other note, use shielded or cables that use good noise rejection designs (ex. Litz). Seems to work better than unshielded by my own personal tests and I think George has recommended shielded cables as well.
georgehifi's avatar
georgehifi
10,312 posts
 
Hi guys, interconnect cables can be a mine field, not just with the Lightspeed Attenuator but with all forms of audio gear.
Cables can form a hi frequency filters with their capacitance (pf picofarad)) when combined with the input impedance or output resistances of sources and loads, as can output/input coupling capacitors of some sources and amps, they can create a low frequency filters with the load of the next stage/s. Then there's the inductances and resistances of cables which can also form filters (hf, lf, even band pass) of some description.
A good general rule I find is to have direct coupled outputs (no Caps) on sources you own, and direct coupled inputs on the poweramps you own, and to keep interconnects as short as possible (even if it means reconfiguring the system) and to get ones that have low capacitance less than 100pf per foot.

Cheers George
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