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
Agears I hope I did not say mine was better than yours. Even musicians don't agree on sound. But that it is my perspective. I haven't even speculated in this thread as to the reason why, I think I know the simple answer, it is the 'why' in every other situation that causes something to be closest to the original. Anyway I thought my perspective would help someone looking at this thread or LSA for a view. I appreciate others view. We can learn something if we contribute. So George, Pub, Clio09, Atmasphere, Fiddler, Tvad, Grannyring and others thank you for some good information.
Regarding the question on the diode effect. For those that missed it or don't recall it George explains it as follows:

The (diode thingy) "diode effect" is bought around by very fast music transients from the source, CDP or phono, which can be in the order of 100's of volts per micro seconds (volts per uS) these happen as the name implies in micro seconds.

When we view a static (constant) 1k-10k square waves on an ocilloscope all looks fairly fine going through a good pot (Alps Bournes ect).But it's when you pulse the waves at micro seconds (transients) an then store it on a very good super fast digital storage ocilloscope play the micro second pulses back frozen in time, and magnify the corners of the waves it's then you see the ringing/occilations effect of the light wiper contact on the conductive track of the pot, (I have named it for want of a better word, "dynamic contact bounce")It's the wiper being ever so slightly bounced on the track.

When pressure is applied to this wiper (with in my case a wooden skewer) so the wiper presses down hard down on the conductive track, the ringing occilations stop when doing the same test. When a soldered resistor is in place of the pot it's not there either, when a Lightspeed Attenuator is in place of the pot it also is not there either.All pots no matter how good bounce to a certain degree this is why they all sound different, they are all fundamentially flawed.

The diode effect that George references and that the LSA eliminates is clearly something designers of some well known preamps understand and can hear. Here is a quote from one:

Having done some audition in this regard (we 'switched', if you will pardon the pun, to our custom Shallco part about 15 years ago as a result of some of these auditions), the difference in contacts that George is describing above is clearly audible.

Its my opinion that the volume control is what shoots many preamps down (especially preamps with remote control) before they can even get off the runway. One of the consequences is that the majority of line stage technologies are in a deplorable state- I don't fault anyone for thinking that a passive might be better.

FWIW - The custom Shallco switch referenced above is used in his top of the line preamp that uses gold contacts, with a double-spring-loaded wiper. Highly superior and much more costly compared to other switches.

The designer also had this to say about the LSA:

I had the opportunity to compare the Lightspeed against one of our own preamps and I have to say it was the most neutral passive I have heard.

Anybody want to take a guess at who it is? I doubt anyone will question his knowledge on the subject.
you might find this interesting

http://wajonaudio.webs.com/GET%20THE%20PERFORMANCE%20of%20a%20$20k%20PRE-AMP%20for%20$200.html