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
From what has been told to me OPC271 (one of the first Lightspeed copies) is like my original Mk 1 Lightspeed Attenuator but with more glitz, which is a series resistor and shunt ldr, while it was still sounding very good and better than all other volume control devices on the market, is not as good as the MKII Lightspeed Attenuator which is series LDR and shunt LDR, which has a lower low volume and more stable input and output impedances, and the main difference it sounds far better, especially in the bass and dynamically.
This is why all the MK1 Lightspeed Attenuators were recalled and converted to MKII status and were well praised by their customers.
I wish I could have continued to make just the MKI as it is far easier to manufacture as the MKII is exponentially harder and expensive to do.

Cheers George
If the OPC271 has a fixed series resistor, how can they claim an adjustment range of -99dB to -0.3dB? Shouldn't the fixed series resistor limit that range?
Their shunt LDR could be paralleled by other shorting components, as there is no way of getting -99db of attenuation any other way, not even with best NSL32SR2S's which have the lowest on resistance of 60ohms at 20mA in quad matched form, sure you can push them to 25-30mA to get 30ohms but then they will fail after time.

Cheers George
Clio09, Tony hi, wonder if you can confirm something for me. As I think you have purchased both stereo and dual mono Lightspeeds from memory, as I have never had the opportunity to do it and it goes against all logical reasoning.
I have had a few report from customers that have the dual mono (left & right volume led brightness controls) Lightspeed Attenuators that they have done comparisons with friends that have the single stereo control Lightspeeds and they believe that the dual mono sounds a little bit better, this goes against all logic for me as the only difference is that the dual stereo pot is split into two mono pots all values and circuits are the same and as all probably know they only control the led brightness and have nothing to do with the ldr signal component.

Cheers George