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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  (System | Threads | Answers | This Thread)

06-12-10
  Responses (1001-1050 of 1334)
Click title to read one, or click date to read all below it.

10-05-11   Thanks clio, i'll look into it.   Banquo363

10-08-11   Ok...when i first received the lsa, it was placed in the sys ...   Devilboy

10-08-11   Not really.hello!!   Ebm

10-08-11   I had close to that issue with my cd player. i used to max o ...   Banquo363

10-09-11   Different amps will have different gains, so will sources, a ...   Georgelofi

10-10-11   Devilboy, with my 97db efficient speakers - similar to your ...   Kevinzoe

10-10-11   89db merlins, .8v sensitivity amp, 2v source - 12 normal 3 a ...   Pubul57

10-10-11   Similar to pubul57 except my speakers are rated 92 db (close ...   Clio09

10-10-11   My amp is 1.3v sensitive. after i get my 2v dac, the only o ...   Devilboy

10-10-11   I never liked those rothwell attenuators. you can accomplish ...   Clio09

10-10-11   The rothwell attenuators work just like the lightspeed atten ...   Georgelofi

10-11-11   Thanks, george. the input impedance of my amp is 470k. i c ...   Devilboy

10-11-11: Georgelofi
10-11-11: Devilboy
Thanks, George. The input impedance of my amp is 470K. I can't imagine that being an issue with the Rothwell's.Devilboy

No that is not a problem, what is the problem if you go passive or tube preamp, is that while the 470k input of your amp is fine for these preamps, when you plug in the Rothwells then this changes that 470k for something much smaller. What I don't know as I have never measured the shunt to ground resistor of the Rothwell, It maybe say "10k?" then this is seen by the passive or tube preamp not the 470k, and then it will not be a good impedance match for them.
As Clio09 found out when he used them, it wasn't the Rothwells them selves that he didn't like it would have been the input impedance change of the poweramp he heard that then was not a good match with whatever pre he was using at the time.
There is no free lunch, you have to do your homework, regarding impedance matching. Like I said before it goes on right through the whole system from source through to speakers, up to about 6 to 10 times, you can't do anything within the components themselves unless you are a good tech, hopefully the designers of individual components have done the right matching inside their units, but you can look at the output and inputs of each component to make sure you have a good match and give everything a fighting chance to sound it's best.

Cheers George

Georgelofi  (Threads | Answers | This Thread)


10-11-11   Devilboy, i have a pair of the 10db rothwell's, and as measu ...   Almarg

10-11-11   Jeez, if 470k isn't enough, what the hell is?   Devilboy

10-11-11   If the rothwell is 9.5k shunt to ground and the amp is 470k ...   Georgelofi

10-11-11   Sorry plus the 21k added to the 9.3k, yes 30.3k. cheers geo ...   Georgelofi

10-11-11   i think you may have misread our posts. :-) the 470k is no ...   Almarg

10-12-11   30.3k doesn't seem like it would be ideal for the lsa either ...   Clio09

10-12-11   Yes you are correct tony. the reason i posted them up 16 pos ...   Georgelofi

10-12-11   I agree clio09.   Devilboy

10-12-11   Gentlemen, in a situation where the lsa is being driven by ...   Almarg

10-12-11   We did a comprehensive listen test with the lightspeed atten ...   Georgelofi

10-13-11   George and al, ralph karsten always makes the point of " ...   Pubul57

10-13-11   George, thanks for providing that background. paul, i've al ...   Almarg

10-13-11   Thank you. i do love my atma. pre/amp combo too, nice to us ...   Pubul57

10-13-11   I ask one thing, for a single ended, low capacitance interco ...   Georgelofi

10-19-11   Stereophile had a booth at rmaf and i picked up a copy of th ...   Clio09

10-19-11   But he repeats the myth regarding dynamics, which seem very ...   Pubul57

10-19-11   He still has to be politically correct i guess.   Clio09

10-19-11   Wait till george takes out a year's worth of cover 4s:)   Pubul57

11-12-11   Does the lightspeed sound different than the placette? i tri ...   Rgs92

11-12-11   The lsa will sound much more like the placette than either w ...   Pubul57

11-13-11   Yes, i have a solid state luxman amp. the combination of my ...   Rgs92

11-13-11   You might enjoy your placetter, and passives in general, muc ...   Pubul57

11-13-11   With the luxman amp you might want to try the dodd audio tub ...   Clio09

11-13-11   Thanks again pubul. i actually have 2 amps, an edge nl12.1 a ...   Rgs92

11-13-11   I think that might very well be the case with passives and s ...   Pubul57

12-11-11   Above, georgelofi mentioned the rothwell attenuators. i trie ...   Rgs92

12-11-11   Sounds like you are one of the many who have no need of a ac ...   Georgelofi

12-12-11   If i may, one corollary to george's rules: 1) despite an on- ...   Dpac996

12-12-11   Whoops..stupid droidx autocomplete...macrodynamic = microdyn ...   Dpac996

12-12-11   Clio9 has also reported that listening and theory are two di ...   Pubul57

12-12-11   When i have tried passives in the past i have had negative r ...   Dpac996

12-12-11   Dpac996 hi, yes a lightspeed can be used to drive a poweramp ...   Georgelofi

12-18-11   George, i experienced first light with the lightspeed the ot ...   Dpac996

12-18-11   Do let us know how the buffer works for you. it would seem i ...   Pubul57

12-18-11   Of course, the lsa ultimate would allow for buffer switchin ...   Pubul57

12-18-11   Good to hear dpac996. in your quest to sample a buffer after ...   Georgelofi

12-22-11   I have figured out that the buffered output is a better matc ...   Dpac996


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