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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
 
09-17-11: Banquo363I should add: what else should we look at other than impedance matching concerns.

If the impedances are right, nothing, so long as the dac or cdp has volts high enough to clip/overdrive the poweramp which nearly all have, and enough current which nearly all have, except some tube output dac's and cdp's.

Look at any of the user manuals of the higher end dac's and cdp from Wadia going right back now to the late 80's that had digital domain volume controls in them. The manual states going direct into a poweramp with any of these units will yield a superior sound than going through any preamp, so long as the digital volume is in the top third so there will be no bit stripping.
There are no preamps inside these top Wadia's I have personally seen inside a few of them they are just like all other dac's and cdp's on the market, with a current to voltage conversion stages after the dac chips then output buffers to the rca's. The Wadia's magic happens before the dac chips, in their propriety filtering techniques and receiver stage .

Cheers George
pubul57 OP
3,712 posts
 
In the Aleph L manual, NP goes on to say,

"If you need gain, above the 3 o’clock position the volume control provides 2 dB of gain per step, for a maximum of 10 dB. In this region you will be listening to the active circuitry of the Aleph L.

As an interesting experiment, you may want to try listening to the difference between the straight-through position and the next higher one, seeing how well you can discern the character of the active gain system."

The tenor of his comments seem to speak of the effects o gain stage as producing flavors, granting that even straight through might have a signature too. It always brings me back to Ken Stevens design goals for his (CAT) preamps, he said he wants the "flavor" (his word) to be like water - in his mind, no flavor.

As for gain, I an tell no difference between my 2v and 4v settings on my EMM player, other than I turn back the volume control a bit.

So we are left with. Passives are....

1. Always better than actives
2. Never better than actives
3. Sometimes better than actives

No lover of passives in general or the LSA would argue 1. - that would be foolish and clearly not the case.

It seems hard to argue 2, since some folks with a long history of fine active line stages of considerable merit hear things differently and prefer the passive, their judgment not swayed by a lack of resources or inability to have tried the options.

It does seem 3 is the most likely case and it it raises the question -- if so, when? Under what circumstances. I think this thread has provided enough guidance as to when a passive, and possibly the LSA best of all, will provide a quality of sound comparable to the very best available - for a fraction of the cost - as long as it is not made in Switzerland or ensconced in a 2" inch aluminum case.
clio09
3,360 posts
 
This is also very important. An active preamp will be needed if the amp's voltage need is higher then the source's output voltage.

I used to think this too until I tried my LSA with my Atma-Sphere S-30. Source = 2V and S-30 = 2.8V - nearly 6V depending on how it was configured. In either case the source did just fine driving the amp via the LSA.
grannyring's avatar
grannyring
6,525 posts
 
Actives also need to be well matched with the amp. My cuurent tube active was a poor match to the Sunfire Signature amp which has an input impedance of 24k ohms.

The bass was muted and highs were etched. The Sunfire amp does not sound this way at all nor do my speakers or pre. I inserted a modest SS amp with an 100K ohm input impedance and all was much better.My system is magic again. Impedance matching is also important for actives. I think most, if not all, of our opinions of actives vs passives are based on the synergy of the system they are placed in. It's the total system stupid:-)
georgehifi's avatar
georgehifi
10,312 posts
 
09-17-11: Grannyring Actives also need to be well matched with the amp. My cuurent tube active was a poor match to the Sunfire Signature amp which has an input impedance of 24k ohms.Grannyring

Yes Grannyring, tube output active preamps are just as susceptible to poweramp impedances as passives are.
I looked at what Teajay is using. The output stage of his Concert Fidelity CF-080 is a 12AU7 in cascode configuration direct to the SE output rca's, I thought this is a high output impedance. So I checked with our tube gurus, they confirmed to me for this tube to be use in this configuration in it's best linear way, it's output impedance will be around 33K! And at best it will only give 10mA maximum output current.
This is fine if it sees a poweramp with 100k or higher input impedance, but he is using it into a Pass Labs XA100.5 which has 20k SE input impedance??? Bad Match this one!!

Cheers George
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