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
So the 10db Rothwelll should get you to the similar volume levels of your tuner, more or less.
I don't vouch for the Rothwell's but in this particular case it is the best bet. I'd actually get the resistors built into the interconnects.
I see Gene Reuben Audio does carry the attenuators. Looks like I'll give them a try.
Wow this threads been active since I went on an outback holiday to the deserts of Australia for the last week.

As for some of the questions asked.

When the power is disconnected from the Lightspeed Attenuator both the series and shunt ldr's go high in resistance to around a few megohms they never go open circuit, so even with power disconnected they still allow some small amount of signal to pass through.
As for never being able to go to zero volume, most do not find this a problem as if they want zero they can mute,pause, or stop the source with the remote.

If the source is vinyl the gain of phono stages are quite small compared to a cdp and is never a problem either but a very small signal can be heard through the speaker if next to them.

Saying this if someone has one of the many clones getting around, most use the NSL32SR3 led/ldr combo, these do not go as low in volume as the NSL32SR2S that is used in the Lightspeed Attenuator because the minimum resistance is higher on the NSL32SR3, and cannot be shunted to ground as well as the NSL32SR2S.

Also some clones are using the MkI Lightspeed circuit which I first used 25 years ago, which has one a fixed value resitor for the series component and a ldr for the the shunt component, these are far cheaper and easier to make but are quite high in volume at minimum and also don't sound as good because of wildly differening I/O impedances.

Cheers George