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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
georgehifi's avatar
georgehifi
10,312 posts
 
Hi soundwise (Michael) you asked in a pm,
What about he CAT output impedance any way to adjust that?
MS

Your Verity’s are an easy load for your Cat most of the time, but at 5khz there is a hard load of 4ohms in conjuction with around 50 degrees of negative phase angle. http://www.sonicflare.com/IMG_1966.jpg
http://www.stereophile.com/content/verity-audio-sarastro-ii-loudspeaker-measurements#Xb47wFP2V0w59G7...
But your Cat should be fine still at this frequency as well. As the Cat has only one speaker tap (no way to adjust the output impedance), but having a bit of negative feedback brings the output impedance low enough to handle this, and also there’s not much power needed at this frequency either.

Quote: Cat JL2
http://www.soundbysinger.com/UserFiles/image/JL2%20Sig%20resize.jpg
Circuitry
*Ultra-wide open loop in-circuit bandwidth of the output transformers enables operation of the amps closed loop response entirely within the open loop response, eliminating any requirement for the output stage to perform beyond its natural capability.
***Unprecedented stability into complex speaker loads.
I can see why your liking the sound of the Lightspeed in this very nice system you’ve put together.

Remember the mil spec GE6550’s with the green label I mentioned a few posts back, they are a "cracker" of a tube.


Cheers George
soundwise
39 posts
 
George,

wondering if you have tried to upgrade the parts, if it is possible, and if so, can the sound get even better than it already is!? Noticed that the stage is wider, and that you can hear outer edges if that makes any sense. Also, does dual volume control do anything? I have tried your preamp with same type of audio note dac with Vac music block 160s…also with def tech bp 7002 speakers…not as good as the other setup , but not bad..I will use 1 ohm resisters to tame the tweeter output , but these speakers are 800 used and they sound holographic like the MBL radialstraters which cost as much as a large benz….   imho, bipolar is a far superior design compared to regular speakers..
best,

I am looking forward to your next project!

Soundwise
georgehifi's avatar
georgehifi
10,312 posts
 
Hi Soundwise, once again thanks for the praise you’ve given on the Lightspeed.
As it stands with me there’s not much that can make it sound better. Others here may give things they’ve tried.
1:Some say battery power, the best power you can give to the Lightspeed, then some (including me) say it’s virtually undetectable. you can try this using one of these rechargeable ones.
http://www.ebay.com/sch/i.html?_odkw=12v+rechargable+Li-Ion&_osacat=0&_from=R40&_trksid=...
2: Some owners have replaced the gold rca’s with more expensive ones??
3: As for the dual mono Lightspeed, 90% of owners that have both Lightspeeds (stereo and dual mono version), prefer the dual mono. I think maybe it’s because they can get perfect centre image due to system/room imbalances.

As for the Vac vs the Cat JL2 maybe the Cat is just a better amp, the Vat being a tube should also be a great match but I can’t find anything (specs wise) on the VAC Musicblock 160’s

Can you link us to anything (spec wise) on them, or can anyone else?

Cheers George
ozmium
2 posts
 
Hi George,

I thought I'd share my quest for audio nirvana and how the Lightspeed was the final piece of the puzzle.

Most of my setup is fairly standard gear - a Logitech Touch playing flac files over Cat6 cable from a Debian file server.  Its optically connected to a MiniDSP 2x4 HD, which provides a flat freq response and acts as a DAC.  Then a Cambridge Audio 651W power amp.  

The (less conventional) speakers are omnidirectional (from OmniAudio) with single Lowther DX4 drivers in each.  My wife and I love the ominidirectional sound but we've never been fully satisfied with the sound in our house. The MiniDSP was a big help to fix room issues and the CA amp added the power and control but something was still missing.  Or was something in the way?

When we added the Lightspeed attenuator the difference was obvious to us both.  Digital volume control (from either the Touch or MiniDSP) was actually getting in the way and also raised the noise floor (as you would expect).  Adding the Lightspeed gave us deeper bass, much wider soundstage, and transparency that finally took full advantage of the Lowther's speed.  Noise floor dropped into the black.  

We've been listening to the new setup over Xmas and we're both very impressed.  My wife keeps telling me she is hearing new things in the music.  I'm amazed it made such a difference to the soundstage and bass.

So nirvana has been achieved. The Romp by My Friend The Chocolate Cake, as one of our standard test tracks, was a special treat for our ears.

I'd also like to thank you George for your fabulous support and emails prior to getting the Lightspeed plugged in.  I really appreciated it.

Cheers Scott..
georgehifi's avatar
georgehifi
10,312 posts
 

Thanks very much for the great rap osmium, much appreciated.

So nirvana has been achieved. The Romp by My Friend The Chocolate Cake, as one of our standard test tracks, was a special treat for our ears.
Great Aussie talent, so much of it here, undiscovered.
https://www.youtube.com/watch?v=We3HrsuqYJk


When we added the Lightspeed attenuator the difference was obvious to us both. Digital volume control (from either the Touch or MiniDSP) was actually getting in the way and also raised the noise floor (as you would expect). Adding the Lightspeed gave us deeper bass, much wider soundstage, and transparency that finally took full advantage of the Lowther’s speed. Noise floor dropped into the black.
Yes digital domain volume controls can be very good if near full up, they have to be used at or over 75%, this can be too loud for most systems. If under 75% they can actually reduce the digital resolution "Bit Stripping" to 14bit, 12bit, 10bit ect, and the lower you go, the less resolution you get.
This is why the Lightspeed Attenuator being so transparent/dynamic is great, set the digital volume at full, adjust the Lightspeed Attenuator to the loudest you want to ever hear, and then use the digital volume remote to lower the level as needed, that way your never under 75% with it, this way you'll never "Bit Strip"

Cheers George
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