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
Wow isn't this fun. Nothing I'd rather be doing New Years Day after a night of no sleep and a couple Bloody Caesar's in me to take the edge off last night (or actually this morning).

Seriously though, I love it when this thread gets revised because it seems the debate just gets better each time. More people trying the LSA and of course more opinions added to the mix.

I am certain my preamp is not adding distortion or fuzz or any additional "stuff" unless my hearing is not as good as I think :-)
Grannyring

First off I'm not questioning your hearing. It took a while to understand your preferences and clearly they cannot be met through the use of a passive preamp in your system. However, since you like the debate I'm going to nitpick a bit here:).

Active preamps (and tube circuits in particular - we'll get to that in a few) in general will always be additive just for the fact they add gain to the system. Gain results in additional noise and distortion. The designer has control over limiting the effect of noise, but gain is gain no matter how you slice it. It's additive period.

Tubes by nature are microphonic (distortion), it's how they operate. I have a good friend here who designs tube circuits and he admits this. One of his favorite phrases is, "It's in the book, look it up." Microphonics equals distortion. Some tubes are more microphonic by nature than others. Take the 6SN7 for example (and the tube your preamp was originally designed around), one of my favorite tubes but one of the worst for microphonics. Some tubes are so microphonic you can clearly hear the ringing in your system. In some instances tubes (and transformers - but that is another subject) can also pick up RFI more easily. Now do tube (and their inherent) microphonics result in a pleasing sound to some. Absolutely, that's why there are so many threads on tube rolling, etc. The opposite is also true as well, you see enough threads from folks with gear whose noisy tubes are driving them nuts. The designer can again minimize the effects of microphonics in a number of ways, but there cannot be a debate on whether or not microphonics are additive, they are.

My point is one component (preamp) cannot, by itself, always give a more accurate TOTAL SYSTEM SOUND.
Grannyring

True enough, but I subscribe to the theory that less is more and specifically, less complexity in the signal path will result in more accuracy. Now system matching under those conditions is another matter. However, I think I've done a great job of it and like you think my hearing is pretty good.

For masters of their craft, you often see a less is more approach to design.
Pubul57

Just got done saying that from a system perspective, but I'm glad that someone mentioned it from a design perspective as well. The designer of a certain tube preamp under discussion takes a similar approach. In fact in a conversation I once had with him he eschewed balanced designs because inherently they are more complex and add more components into the signal path. You also often read about how some designers create circuits that minimize the wire utilized in a signal path to a matter of inches or the number of parts to a bare minimum.

However, there can be no debate that the LSA adds less to the signal than your VAC preamp if you are hearing more artifacts from the VAC. It is clearly not debatable.
Fiddler

I'm only commenting on this one because I also have VAC components and they clearly have a house sound. It's very distinguishable. IMO VAC gear creates wonderful music, but it does add artifacts and coloration and even the designer will admit it. It's also very pleasing sound and I will admit it. I have just come to prefer less artifacts and coloration from my system.

Did someone say Bloody Caesar, by golly my glass is half-empty, or is that half-full. Don't think I can take another debate today but it's getting crowded in here and I think I better get the bar tenders attention before my cup runneth out. Sorry I went on for so long. Guess I was just having too much fun.

Now back to the real fun. Roll tide...chi-ching.
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The irony about "simple" designs, with fewer parts, etc, is that it really requires some design chops to execute a great, simple circuit and I suspect it requires a master like Nelson Pass to design some great First Watt and XA.5 amps with such apparent simplicity in lack of complexity.
Or as my fellow Nutmegger Samuel Clemens once wrote:
"I'm sorry that this letter is so long, but I didn't have time to write a shorter one".

Translating this to the post I quoted, it's usually easier to fix a problem by adding a bandaid than it is to go back and rework the design to eliminate the problem.
Clio09, nice job indeed and I have a question for you and all. Seems then all the high end preamps, tube or SS, costing up to $100,000 that are not passive, just can't get it right? Or should I say as right as a passive?

Wonder why all of these manufacturers even bother? Wonder why they are considered by the "experts" as the very best.

Perhaps a passive conspiracy..just kidding.

Let's assume my active preamp is more noisy then the LSA. If it outperforms the passive in many other areas, then it may still be a preamp truer to the recording. Benefits outweigh the short comings kind of thing.

I so want a $450 passive to sound as good, or closer, to my active. I tried several passives with no luck yet. Perhaps I need a tube amp like the RM10 and some high efficiency speakers. While the Atmasphere Ma1 amps had a 100K ohm input impedance perhaps my Soundlab's just did not like the signal from that combo. It was 2D and quite thin. Very clean, quiet and detailed, but kind of white - washed. It reminded me of some Nuforce amps I once owned.

I will say the LSA had great promise when I first put it in my system. I did take notice of how much quieter it was for sure. I also noticed it was smooth and extended in the highs. I also found the bass to be pleasing. Over time the white-washed nature seemed to reveal itself on every CD I played. If I played the LSA and had to make a decision after 30 minutes it would hard to pass it up. After longer listening I became fatigued.

Something tells me my Soundlab speaker/Atmasphere amp combo just preferred an active unit. It would have been very interesting to hear the LSA on my previous Silverline Bolero speakers with the same amps.
If I can take this tube microphonics a step further for those who have tube preamps.
Try this little experiment.
Take the top off the tube preamp and turn on your system and set the volume control at your normal listening position. Then with your finger nail flick down the tops of each tube and have someone listen at the speaker for any sound comming through the drivers. This will show which tubes are microphonic. And in the case of really bad ones it will be heard out in the kitchen. And really really bad ones will feed back to the said tube and cause a runaway effect that can't be stoped.

Cheers George