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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
clio09
3,343 posts
 
In the Lightspeed design taking the switch out of the equation further simplifies an already simple design. The Pot in the Box is also a very simple design, but the Noble pots, as good as Roger feels they are, will impart a sonic signature. Transformers and autoformers are wound with lots of wire. I've been watching the transformer winding process and will be learning to do it myself. All that wire has to have some effect on the sound rendering the TVC or AVC less transparent and neutral (silver or copper windings would also have some effect). I can think of two reasons why TVCs and AVCs are popular. One they are more forgiving of impedance mismatches and two, in the case of transformers, they offer some isolation.

I'm considering building a PITB for the fun of it and to compare against the Lightspeed. Also, many people like the Luminous Axiom passive devices. I'd be curious as to any opinions on these from owners. Come to think of it I've got a pair of EVS attenuators lying around I should throw in the system for the fun of it.
georgehifi's avatar
georgehifi
10,312 posts
 
Clio09
but the Noble pots, as good as Roger feels they are, will impart a sonic signature.Clio09

This is what I found, all have a sonic signature because of their very soft wiper contact, this has to be a very soft as not to wear out the resistive track it runs on when you raise the volume up and down. This soft contact behaves like a rectifier (diode) trying to convert some of the AC music signal into DC especially the faster transients and higher frequencies. This is why all pots sound different even switched resistor pots, all are a little different in this wiper pressure/material/ & and mechanics, none are perfect as a soldered resistor would be, which is what basically the Lightpseed Attenuator is.
TVC are better here as they do not have wipers, but their problems lay in the 500mts or so of very thin wire the signal has to pass through, this itself is a mine field of current limiting, capacitance & inductance all of which is harmful to the original source (CD DAC or Phono) signal.
The best sound you will get is to put your (CD DAC or Phono) directly into your power amps with a VERY quite CD track first, this is the most perfect "true to the source" sound you will get, and only the Lightspeed Attenuator is closest pre or passive to mimicking that sound.

Cheers George
clio09
3,343 posts
 
The best sound you will get is to put your (CD DAC or Phono) directly into your power amps with a VERY quite CD track first, this is the most perfect "true to the source" sound you will get...

This is the actual test recommended by Arthur Salvatore to determine if your system is passive friendly and if so whether or not you will like the sound. He recommends Ravel's Bolero as the test track since it starts off with very low volume passages. You need to be careful when conducting a test like this because if you use a track that has a loud volume passage, or even an unexpected loud drum kick, you could blow out your speakers.
pubul57 OP
3,712 posts
 
Arthur Salvatore also says, in an interesting way, that if your systems sounds better, in any way, than a direct connection or passive, then your system needs and active preamp (he says most systems do) - because in some way your just not matched right. AS' views is that passive is the best, unless you need active. I'm pretty sure my system does not need an active for gain or impedance matching and therefore it is unlikely that any active preamp or volume control/gain device will improve over what essentialy (as George points out) is as close as you can get to a direct connection between my source and amp.

If amplyfying that signal through additional wire, capacitors, transisitors or tubes etc, only to attenuate that additional gain can some how improve on the original source signal, I just don't see how it can do that unless that signal needs all sorts of conditioning to drive the ICs and amp. My 2v or 3.9v outputs from the EMM Labs CD player don't need such help to drive the amps, and if there is dimensionality and warmth in a recording it is there at the output of the CD Player, not fabricated in an active tube or SS linestage - and if it is the byproduct of the linestage, I don't want to hear that as it will be an overlay on everything you listen to.
grannyring's avatar
grannyring
6,436 posts
 
Actives can sound better to some because they like the change those tubes, caps etc give the sound. Yes, a good active tube preamp may in fact change the sound and that can be a great thing for some people.

Larger stage size, more romance, or even a greater sense of ease to the music can be (ADDED) by a tube preamp. Some like that.
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