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
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hopkinstk

That’s an impressive list of gear you have there hopkinstk

1: Two Spectron Musician III MKII in mono blocks
2: Usher BE-20 Diamond
3: VPI Prime turntable with Dynavector xx-2 MKII cartridge
4: Whest PS.30RDT SE Phono Stage

I have a buddy that also has the Usher BE20’s and wow they are very good and full range to boot, I couldn’t see that the Rel sub would be needed with them they go so low.
(maybe from 30hz down? if you listen to a lot of organ recitals)
I’m pleased you think so much so much of the Lightspeed Attenuator passive pre to keep it in that company.

Cheers George

I’d been searching for a preamp, so for a giggle I Googled “best preamp ever audiogon” to see to see who had recommended what.

The top hit was for tube preamps, but I didn’t want to limit my search to tubes. The second-top hit was not it either – just preamps for sale.

But the third and fourth hits were more like it. They came from this very thread. I started reading. My reading extended over two nights. (Thanks guys!) My interest turned to intrigue when I twigged that the preamp – the Lightspeed Attenuator of course – was Australian (which is what I am and where I am).

What really kept me reading was seeing actual users were replacing expensive and much-loved amps – tubes even – with something straightforward and cheap (by comparison).

Now, the OP here (thank you Pubul57) had made it clear that the Lightspeed needs the right environment in which to work.  A source ouputting 2V or more, which is pretty much everything these days I believe, a short interconnect to the power amp (three metres or less), low capacitance interconnects – and a power amp whose input is preferably the industry standard of 47K ohms or more.

I checked the specs on my Halcro DM38. Only 10K ohms on the RCA input. The Lightspeed outputs RCA only. That might be a problem. But I wasn’t going to stop now, was I?

Just to test before shelling out, I plugged my passive Schiit Sys into the Halcro. The Schiit outputs up to 5K ohm (not dissimilar I believe to the most the Lightspeed puts out). So we are a long way from the ideal 1:10 ratio, which would have us up around the 47K standard. But the Schiit provided enough bass and volume to make me push ahead. It worked, at least. But I thought I was probably going to need a buffer, so as to fix the impedance mismatch between the Lightspeed and the Halcro.

And I should detail the rest of the system. Speakers are a massive pair – Be-One, The One. Five drivers per cabinet, about 100 kgs each, sensitivity 89db. Streaming via an Auralic Aries Mini, listening to 320 MPs, CD rips, hi-res files and DSD. Switching between DACs – the Aries, an Emotiva and an R2R Audio-GD 11. Preamps on hand for comparison were the Aries Mini again, a Xindak XB 8250, and a Geiseler preamp (another boutique Australian product) (and the pre-outs of a few integrated, including a Jungson JA-88D, Yamaha AS200, Harmon Kardon 990). There were two tube preamps around, an Audile using Jan Philips 5814a tubes, and a SoundMaster Mk 23 using 2A3, but the tubes were so different, I didn’t make comparisons with the Lightspeed. The room is roughly 30 foot long and 12 foot wide.

So the Lightspeed arrived. One great thing about it – no burn-in. Because there is nothing to burn it. That’s a relief. Just give it one minute to get warm. We’re off.

First impressions: this is good.

It was clear. Like water. There was no shortage of bass. Or volume. Highs were clear. Volume – more than enough. I had it playing around 2 o’clock to play it loud (90db, sitting four to five metres from the speakers.) There is no sweet spot on the volume dial – the sound is the same all the way. There was no channel imbalance.

That’s what it sounded like – which is to say, it had little sound of its own.

It was dead silent – which I suppose is a function of no gain and no mechanical parts to speak of. My room is very quiet, so that silence is impressive – and necessary.

Whenever I get a new component, I make a point of listening to it. By which I mean, not comparing, but listening. (And I only change one thing at a time – so I can be sure where the difference is coming from.)

So only after a few days did I start to compare – with a little bit of fear.

Comparison confirmed my suspicions: what the Lightspeed delivered was good, but insufficient. It was approaching the weaknesses commonly attributed to passive preamps. The attack on notes – be they guitar strings or piano notes or kick drums or electronic bass bombs – wasn’t quite there. That one thing amounted to the music losing life and shine.

But what was there was all good – it just felt the thing was struggling, pushing the music uphill. But it was clearly good enough that I had to know how it would sound given the right conditions. So let’s get a buffer.

I got a Musical Fidelity X10v3 (not XD.) It puts out just 33 ohms. It deploys two military-spec tubes – which Musical Fidelity says are designed to withstand the radiation of a nuclear war. Pity the rest of the system won’t survive.

And, voila. Now we’re talking.

If the taste was water before, it was water out of a plastic cup. Now it’s water out of quality glass. Transparent.

All the life and dynamics were there. Transients had zing. Slam had slam. If the recording has depth and height and placement (ie soundstage), so does its reproduction.

It just sounded like I was hearing the music – be it Billie Holiday, Kraftwerk, Crazy Horse or Chopin. The lack of distortion from both components is quite the treat.

So, there you go. This will be old news to some of you – but I had to share it, and the odd fact that I had to go so far afield to discover something in my own backyard.

This thing really is ingenious.  Theoretically, it seems to me the ideal preamp: adding nothing, subtracting nothing, with no touching moving parts and no noise, simply providing a channel through which the music can flow. Like straight wire with gain – except there’s no wire, only light dependent resistors, and no gain either.
One with a switch for different sources would be nice. I know I can put a switch ahead of it, but that would add another box, more Interconnects...

Alas.
toddverrone
One with a switch for different sources would be nice.

Hi Todd.
Yes it would be, but here’s the problem I have. The Lightspeed is all about not have any light contacts in the signal path, this includes volume controls and yes input or output switching.

My prototype still measures and sounds as good as it did when new, but it has got two inputs with switching (WHAT!!! you say), it has the best switching/wiring possible, because I need to A/B dac I/V stage modifications which I also do on the side as well.

This this prototype Lightspeed is the benchmark test for all production Lightspeeds to be A/B’d against with before they are sent to customers, to make sure they all perform as expected.

From even when it was new everyone that has heard the A/B’s including me production ones vs the prototype, says that the production ones with only one input sounds just a little better
You can’t put your finger on what it is, but the productions ones have just a touch more ease/transparency to the music presentation than the prototype.
It’s a bit like when you hear the battery supply vs the mains supply, you have a feeling the battery is just a touch ahead of the mains.

This is the reason I don’t do input switching, as I want the production Lightspeed Attenuators to be as transparent as possible, without any compromises done in the manufacturing process.

Cheers George