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

Showing 30 responses by devilboy

Thanks Clio09. It's nice to know that you've had success with such a wide window of input sensitivity....makes my decision easier. There are a number of passives that I'm interested in but given the price of the Lightspeed and its overwhelming popularity, I think I might try it.
George,

I'm sure that the information I need is listed somewhere in the vast number of posts but could you please tell me what the ideal specs that the Lightspeed would work best in? What output voltage and output impedance of source would the Lightspeed like to receive and what input voltage sensitivity and input impedance of amp would the Lightspeed like to "see"?

Again, sorry if I'm asking something that's been discussed previously.

Best,

Luka
This preamp simply, "isn't there". I just shake me head at all of the ridiculously overpriced preamps out there after hearing this thing.
Ok...When I first received the LSA, it was placed in the system downstream of a Burson HA-160 DAC/pre. When the Burson's volume pot was fully open, I had a wide range of volume control on the LSA, with moderate volume achieved at around 10-11 o'clock on the LSA. The Burson is gone and I am awaiting arrival of the Metrum Octave DAC. Now....I took out an old, cheap-o dac I had in a closet (I have no idea what the specs are), and connected it to my Mac Mini via toslink. Doing this results in HIGH volume levels at 9 o'clock. I put a cd player into the LSA. I don't know the cdp's output impedance but at 2V it has the same output voltage as my incoming DAC, the Metrum. Same thing! 9 o'clock on the LSA is too loud.

Anyone else have an issue with the LSA achieving very high volume levels at a low position on the volume pot?
Thanks, George. The input impedance of my amp is 470K. I can't imagine that being an issue with the Rothwell's.
My amp is 1.3V sensitive. After I get my 2V DAC, the only other change I will make will be to use 1/2 meter pair of solid core interconnects leaving the LSA to go to the amp (I'm in the process of cutting a one meter pair to half them). So, as George said, I can use RCA attenuators to cut the gain down a bit but I really don't want to add anything else in the path. I'm more of a "less is more" mindset. Anyone have experience with these devices degrading sound quality? I've come so far, I don't want to start going backwards...
George, are you joking? Some actually complain about the cost of the current unit? To those that do, I say go out and build a better one at a lower cost. Until you can, buy George's and feel content knowing you have a world class preamp in your system.
Sorry to go slightly off topic here. Don't want to derail the direction this thread is currently going but....I just have to say something. Something that you all already know. After spending a few months listening, nothing, and I mean N-O-T-H-I-N-G I've heard in audio has made me shake my head in utter disbelief more than listening to music through the Lightspeed. Put simply, after listening with the Lightspeed, EVERYTHING is overpriced. Just had to get that out to anyone unfamiliar with this preamp. You may continue with the thread...
Jult52: As Clio09 said, I no longer have the Bent. It was in a completely different system at the time and I believe every single component has changed since then. Boy, would I love to throw it in right now to compare with the LSA though. In the meantime I would take Clio09's word for it. I'm sure he knows his stuff.
So sad to hear of this. My deepest sympathy goes out to Paul's friends and family. His comments have always been a pleasure to read. Each time this thread exposes new people to George and the Lightspeed, Paul played a part in filling their lives with beautiful music.
Hey, thanks to George, Minh, and Whart for helping out here!!

George, I have a system on this site but I never made it private. So I guess you've read my email regarding the Lightspeed. If you don't wish to discuss it here, I can send Minh an email from another computer. It's a crappy way to communicate, but if it's all we can do privately, I guess it will have to do. Of course if you wish to discuss it on this thread that's ok with me. Just let me know in this thread what you want to do.

It's a shame about all the comcast.net emails that you are having a problem with. Must be something with the security.
George: Ok. I will contact you from a computer that does not have comcast as its provider.
George: Forgive me but what I'm about to ask has been mentioned 100 times in this thread but I guess I just want some reassurance. I'm about to purchase a solid state amp with a 51,000 ohm input impedance and a .75V input sensitivity. My dac outputs 82 ohms and 2V. I'm also thinking about buying a TVC preamp while used, is still considerably more than your preamp. I listen to classical and jazz at moderate volume levels at most. Is the 51k of my next amp adequate, or borderline for my listening habits?

By the way, I'm a former LSA owner who was THRILLED during entire time of ownership. However, that was with an amplifier with almost a 400,000 ohm input impedance!
Oops, sorry George. It appears I got you confused with Clio09. Thanks to all for responding.
I received my LSA last week. It's working WONDERFULLY with my Job 225 amp's 51K Zinput. The 51K concerned me so I put off buying the LSA for a couple months. My only regret is not doing it sooner.
By the way, this is the second time I purchased an LSA from George and the second time I wondered why I even considered anything else.
@ Wisnon: I had the LSA on my Job 225 for a little while. I thought the input Z of the Job might be borderline but it wasn't the case at all. The LSA sounded lovely with the Job. Complex orchestral passages played at high volumes didn't sound too congested. Moving up to the Bent TAP-X autoformer freed it up even more. If you want to eliminate input/output Z issues all together, consider an AVC or TVC. I will say this, at no time with the LSA did I feel the need to change to another preamp. I happened to come across a Bent TAP-X (again), and loved the first one so much I bought it. In the end, I preferred the TAP-X just on musical tastes alone. Throw in the remote volume/balance control and it was a no-brainer for me.
George, I purchased that amp I was thinking about. I tried going amp-direct and controlling volume via PureMusic. The new amp's input impedance is 51K. Due to the amp's .75V sensitivity and 35db gain, most of my listening was 40% or less on PureMusic's volume bar. This resulted in a "swooshing" hiss coming from the speakers which is clearly audible from my listening seat 9 feet away and obviously unacceptable. My previous amp was an integrated so now I need a preamp which brings me back to you. As I said before, I'm a former LSA owner and sold it when I went to the integrated.

I've been looking around for low capacitance rca's on the cheap (for now), to run from the LSA to my amp. I've narrowed it down to Mogami, Blue Jeans, and something else which escapes me now. You said you use Mogami. May I ask which? Studio Reference (or something like that). Also, do you know the capacitance of your Mogamis?
Thank you both for responding.

Clio09: I know you said the sound was fine, but did you have ANY issues with limited dynamics, or felt at any time that you were "borderline" regarding dynamics? As I said, my listening volume is on average fairly low, but I still want the low level detail and weight that I get at lower volumes.

George: Since I'm kinda close on specs for the LSA not losing any of its magic, I want to squeeze as much out of it as possible. I want to find the lowest capacitance interconnects I can. May I ask what you recommend?

Again, thank you both. No offense to anyone else on this wonderfully informative thread, but you were specifically the two gentlemen I wanted to here from!