2. amps-preamps
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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
fiddler
581 posts
 
"...George keeps pushing for his own finacial gain."

How do you know what George's motivations are? Maybe you should set up a psychic hotline.

Seems to me if a guy was interested in financial gain, he would price his unit more in line with other passives (read: higher priced) and that same guy wouldn't put his design out there for free on DIYaudio.com.

Doesn't make much sense does it?

Next conspiracy theory...
dgarretson
2,601 posts
 
George's sharing of ideas in 678 posts to DIYaudio forum suggest that he has freely given far more than he has taken.

http://boardreader.com/thread/Lightspeed_Attenuator_a_new_passive_prea_5n7lzX1pvm.html

Dave
teajay
1,702 posts
 
Fiddler,

This has been gone over before on this thread that George's motivation has nothing to do with financial gain,
but is just sharing from the goodness of his heart.

Directly to your two points:

1) What he charges for the LSA is very reasonable, it should be, it's nothing more then a few relatively inexpensive parts and a generic metal box. No remote and we won't talk about ergonomics because their are none. Unlike other passives with features like RCA/XLR inputs, remote, phase switch,etc that add cost to a passive linestage if built to high quality.

2) As I have stated before on this topic someone like Nelson Pass who has given much to the DIY community along wih his relatively low cost First Watt line of amps and preamp to make these pieces available to more people then his higher level Pass Labs gear does not get on a GON thread to self promote what a genius he is, even though he is, and push and push his piece so it becomes one on-going advertisment. He also self proclaims that all other active linestages are inferior to his LSA, by using his version of "scientific" information to try to make this claim seem objective.

So, I wish I had psychic abilities, but I don't, oh well. And as far as conspiracy theory, why don't you offer one regarding my reason for one, just sharing my opinion and two finding it annoying that this thread is one long unpaid ad for George's OK, inexpense passive that he tries to prove makes all other pramps obsolete, if the conditions are meet for a passive, yea right. No conspiracy as I can tell, it seems pretty clear to me what he actually does here, along what his reasons are for doing it.

pubul57 OP
3,712 posts
 
Interesting you mention Nelson Pass, surely one of the greatest designers in the audio world. He seems to really like the LSA design, at least based on his comments on the DIY thread. Would be nice to have a First Watt Lightspeed/B1, with the ability to toggle between straight and buffered (when needed), along with multiple inputs (3?) and possibly XLR - that could be a real winner assuming no need for gain. Though it would likely be $1500 or so for nice casing. I would buy that in a minute. Still, even then, it would not make other preamps obsolete for many different reasons.
clio09
3,360 posts
 
Considering Nelson has freely participated and contributed schematics on the Lightspeed thread over on DIYAudio, I'd have to say he must feel this is a pretty good design and it certainly got his attention (as it has other designers of note). Problem with most Pass/First Watt amps is they are not ideally suited to passive designs due to their low input impedance (this is obviously why Nelson designed the First Watt B1 buffer and Pass Labs markets an active line of preamps).

Here's a good read from Nelson:

http://firstwatt.com/articles.html

Click on the B1 Buffer Preamp link.

Seems Nelson reiterates a few things we've been saying around here about ideal conditions (impedance matching) and offers his method and design to avoid that.

Here's an excerpt:

So here we are in the New Millennium, and thanks to Tom Holman and THX we’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.

Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.

Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control. What could be better? Hardly any noise or distortion added by these
simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.

And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.

I suppose if I had to floor the accelerator to drive 55 mph, maybe I’d think the life was being sucked out of my driving. Then again, maybe I like 55. Nice and safe, good gas mileage…

Is impedance matching an issue? Passive volume controls do have to make a trade-off between input impedance and output impedance. If the input impedance is high, making the input to the volume control easy for the source to drive, then the output impedance is also high, possibly creating difficulty with the input impedance of the power amplifier. And vice versa: If your amplifier prefers low source impedance, then your signal source might have to look at low impedance in the volume control.

I especially like the use of the terms "just musical perfection", "really - I'm being serious here", and "reacting psychologically" in the article to emphasize some very interesting points (and all of this of course coming from a genius).
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