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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
grannyring's avatar
grannyring
6,519 posts
 
Clio09

"Passives don't extract anything. They just pass an attenuated signal. Your source is extracting the music off the medium."

Passives behave more as you say above. I am suggesting an active or any other part of a stereo system certainly extracts or gets at more of the music. Certainly amps and speakers and wire can extract more of the recording. By extract I mean "get at it and pass it along". This is the point where we are not in agreement.

The best and often times most expensive gear (not always) does just this.
The best "systems" do this. The source is not the only place a stereo system can extract or lose fidelity.

I had a good impedance match with the Atmasphere MA1 amps (100K ohms) but the resulting sound was relatively flat as I have already said. So impedance matching was not all the issue.
pubul57 OP
3,712 posts
 
Grannyring, I think you are right, there is not an impedance mismatch with the Atma-sphere. And as Teajay cautioned, it would not be fair, or simply too easy to say that something else "must" be wrong or you would necessarily, you must like the LSA better than anything else - of course that is not true, and nobody should try to tell you otherwise. Yet, there might be another "compatibly" issue (electronic, not psychoacoustic)beyond impedance caused by cable capacitance - if too long, or a high capacitance cable, or the input sensitivity of the amps might be too low, I think Atma amps, or at least mine, have a 2.8v input sensitivity which is not ideal driven just by the output voltage of a CD player. Or there may be absolutely no electronic issues and you simply prefer the sound of your TRLpreamp in your system, and that is that, and a perfectly legitimate conclusion and preference.
fiddler
581 posts
 
Grannyring,

You keep arguing with conventional and accepted audio design that the ultimate attenuator would be a straight wire. You can argue all you want about extracting this and that, but your argument flies in the face of generally accepted wisdom.

You may prefer the sound of your preamp. Fine. But it is not extracting more of anything. It is simply adding a particular color and artifacts to the original source that you find appealing. Nothing wrong with that, I like tubes too, but that's simply the fact of the matter.

And I don't understand why you continue to argue when in your own words in another thread you make the case, "In general tubes will get you more midrange warmth and bloom. But this is not always the case. I am sure the TRL will give you this while also improving a host of other things we all want in our sound systems."

Once again, in your own words you are "sure" the TRL Dude, "will give you" ... "more midrange warmth and bloom." That is additive - end of story! And don't even try to say it does that by extracting more of the signal. That's simple nonsense. And it's easy enough to prove. Just roll some tubes and listen to the subtle or not so subtle changes.

You can't have it both ways. Either you were wrong in the thread I quoted or you are wrong here. Which is it? Conventional design wisdom says you are wrong here.

You are beating a dead horse.
clio09
3,360 posts
 
I had a good impedance match with the Atmasphere MA1 amps (100K ohms) but the resulting sound was relatively flat as I have already said. So impedance matching was not all the issue.
Grannyring

Yes I agree looking to 100k ohms the LSA would be a good match impedance wise. That wasn't what I was referencing in my last sentence of my previous post.

I can't see how a preamp, active or passive extracts anything. Someone is going to have to educate me on this one. The information is already extracted from the medium prior to getting to the preamp. I don't think it gets extracted any further at that point. Depending on the type of preamp other things could happen to the signal, but as Fiddler said it would be additive, or as you said, it could be subtractive.
pubul57 OP
3,712 posts
 
Like I said, the maximum and complete set of signal information is at the output of the DAC/CD Player, there is nothing more to be extracted, whatever happens after that is some deviation from the closest thing we have to the "source". In a well matched system, I don't think any active preamp can cause less deviation from that output signal than the LSA. If there is not the right impedance and gain requirements, the LSA will cause deviation indeed, perhaps more so than a well designed active and in those cases an active would be preferred, it is causing less "damage" to the source signal. As Arthur Salvatore put it, if an active line stage, any active line stage sounds better than a passive, then you need an active line stage. I think that is true, but not sure it fully accounts for the fact that some people simply prefer the color of the preamp to a less colored version of the source - and you cannot argue with that preference (indeed, why bother); but less subjective is what the systems does to the signal originating at the source output and philosophically, some people seem choose to prefer the idea that the "chain" is preserving that source signal as it, warts and all. There is no right or wrong as far as preference goes, but there is an objective truth as to which approach best leaves the source signal intact with minimal alteration. Other than a straight wire, I think the LSA does that in a way no other attenuation device can do, where impedance and sensitivity issues are taken out of the equation. But, even if we accept that, it does not mean that any given person will prefer it to their active line stage, that is a different issue, and not readily resolved through discussion.
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