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
That's cool, Detredwings. Can you provide a link to your battery pack.

I bought a battery for my LSA years ago and the differences were subtle at best. But the battery was suspect and died within a month. I'd like to try batteries again even though I'm very happy with the Teradak.
These are the Ebay 12vdc rechargeable Li-Ion batteries (and similar) that I have been recommending, they have (usually) 2.1mm plugs and centre positive. which is right for the Lightspeed Attenuator, just check to make sure.

All users say they prefer the battery to the linear wall wart but can't pinpoint why. Even Sam Tellig (of Stereophile) says "it's that's close that sometimes he forgets which he has on", but they're cheap enough and give a couple of weeks use before a recharge is needed.

http://www.ebay.com/itm/12V-DC-Rechargeable-Li-ion-Battery-CCTV-Cam-6800mAh-F47-/221117937029?pt=US_Surveillance_Accessories&hash=item337ba7f585

Cheers George
I compared the LSA with a switch-mode ps and the linear TeraDak 9v supply discussed earlier in this thread. I am going to report a null result: I could not reliably differentiate between the sound of the two. The TeraDak carried no benefits in my system.
Hi George,

I've been enjoying your Lightspeed Attenuator for three days now, and it prompts the following remarks.

As a lifetime analog fan, I only lately invested in a truly great CD player, an oppo 95 with Ric Schultz's all-out mods, only to discover that the digital volume control noticeably degrades information at lower -and what I would consider reasonable- levels. Additionally, the increments are less than subtle, and the lowest audible setting is still too loud for my taste. A friend told me that digital volume controls deserve to be banned. I concur.

In my experience a system's ability to resolve lower levels is essential. Not being the diy type, I started looking at stepped attenuators that plug directly into the amp output, and therefore would require one less interconnect. The only two I found, Ric Schultz and Scott Endler's, were unfortunately no longer made, and TVC's have their own issues. After discovering your LightsSpeed Attenuator on diyaudio.com, I ordered one a couple of weeks ago, which arrived safely ten days later.

I think the best way for me to describe the LightSpeed is that with the CD volume control set to maximum, I can now listen to my interconnects, not to the unit itself, because in every respect -style, size, sound, and setup- , it simply stands out of the way. I power it with an older car battery. It's always difficult to describe a product which has no characteristics of its own, whose presence is in its seeming absence, which adds or subtracts nothing, but the end result is that I now listen far more often to far more music which is far more enjoyable. For $450 I'm finally experiencing the full potential of what I consider to be an exceptional CD player, which now comes very, very close to my $15,000 analog source. I have yet to try the LightSpeed on the REC OUT of my phono preamp, probably because I am enjoying it so much on digital.

The only limitations I can think of, have nothing to do with the sound: leaving the volume control half-way to extend the life of the optoisolators took some getting used to, and indeed the lowest setting lets will let some minimal signal through, which compared to my previous setup, however, is well within my tolerance, and greatly superior to my earlier direct CD to amp connection. The overall experience is far beyond my expectation. This is a product that I will not be parting with, period.

You asked about the volume setting for normal loud listening with the Oppo at full. It's at ten of twelve maximum. If I want to increase that setting, I can then use the remote on the oppo while retaining excellent definition.
05-19-14: Erwann
The only limitations I can think of, have nothing to do with the sound: leaving the volume control half-way to extend the life of the optoisolators took some getting used to, and indeed the lowest setting lets will let some minimal signal through, which compared to my previous setup, however, is well within my tolerance, and greatly superior to my earlier direct CD to amp connection. The overall experience is far beyond my expectation. This is a product that I will not be parting with, period.
Erwann (Answers | This Thread)

Glad you like it so much Erwann, as for leaving it at 12o'clock when not listening, this is not set in stone, as the leds should last 10-20 years at full power, which I never run them at, and by leaving it at half volume should double or tripple this life.
PS don't forget to let us know how your $15K!!!! analogue source sounds through it when you get the chance, as analogue lovers have told me it's the best they have ever had their records sound.

Cheers George