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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
clio09
3,355 posts
 
Banquo363, regarding the RM-10, perhaps some DC on your AC line if you can hear the hum at the amp. It doesn't take much. When I lived in a tri-plex in CA if my neighbor used her hair drier or turned on her window unit AC I would get similar symptoms to what you are describing. Unfortunately dedicated lines were not an option for me.

To really isolate the problems after you begin plugging other components into the amp you should get a set of the Jensen plugs. One of the better investments I have made. Also, I won't advise you to do this, but in my system I float all but one of the grounds. Definitely on all my sources, then either ground the preamp, or ground the amp, but not both. The RM-10 manual discusses this too as I'm sure you know.

The K&K phonostage, along with the Hagerman Trumpet were two of the best phonostages I have owned. The K&K was the quieter of the too. In general it is a very quiet phonostage due to the solid state PS and input. The newer versions are supposed to be better and I'm seriously thinking about revisiting it.
georgehifi's avatar
georgehifi
10,312 posts
 
Hi guys, as I have found out input switching is almost as detrimental to the sound quality as a volume potentiometer, this is why I always recommend a separate good quality input switching unit so you can still go direct when you want to bypass all contacts and get the best out of your system or when you want to show it's transparency off. http://www.decware.com/newsite/rotary.htm

Now the obsessed fiddlers on diy audio have found this out also, and to their credit they have now devised their own way of input switching unit using ldr's
http://www.diyaudio.com/forums/analog-line-level/197894-ldr-based-input-selection.html

I still think the one I posted was simpler and it auto shorted the unused inputs.
http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp-153.html#post1640716

Cheers George
clio09
3,355 posts
 
Very interesting and thanks for posting George.

I've grown pretty accustomed to swapping interconnects so any type of input switcher has lost it's appeal.
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banquo363
371 posts
 
Clio09: what's a jensen plug? I looked up Jensen 'iso-max' products but there is a legion of them. Which one are you referring to? Is it for diagnosis or treatment?

Regarding lifting the ground, the only other item I have with a 3 prong plug is my stage. I use the walwart that George pointed to and it is two pronged. My tt's power supply is also 2 pronged. I tried a cheater plug with the stage and it didn't help. I had entertained the thought that it was the LSA's walwart that might be responsible. But I swapped in a battery supply I have and the same noise persists.

I once considered a switcher but I'm over it as well. I use almost exclusively my tt, and swapping IC's is easy because I have an open rack. I can see the appeal though if one had a cabinet and switched sources constantly.

I'd be interested in hearing the difference a switcher makes though. Anyone use one?
georgehifi's avatar
georgehifi
10,312 posts
 
There should be only one mains earth point in a system, (if you have more than one you will have a loop), all the other components will get their earth via the interconnects from the one that is earthed. Once you have two components earthed then it will become a loop via the house earth line.
Even when I had two monoblock 805 tube SE that I built, I got a virtually no hum when only one was earthed and the other got it's earth via the interconnect to the Lightspeed and back down the other interconnect to the unearth monoblock.
PS wonder if I'll get the magic 1,000 post with this as they moderate my posts for up to 6 hours before approval.

Cheers George
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