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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
3,353 posts
 
I agree with the assessment, although some tube rolling could change that. Pubul57 might be able to share more on that as I believe he has done some tube swapping with the amp. I use the stock tubes as supplied by Roger and the way Srajan describes it is how I hear it. FWIW and if IIRC, Roger designed the RM-10 using Quad 57 speakers with it for his listening tests. There are some other interesting design characteristics about the amp that fly in the face of typical amp designs and how we audiophiles associate various sound qualities with them.

Tvad, if you're interested in hearing the RM-10 let me know. I'm not using mine at the moment. If possible I'd like to compare the RM-10/LSA combo versus RM-10/VRE-1 combo.
pubul57 OP
3,712 posts
 
I would say the RM10 is quite neutral and fast with the LSA, as described in the 6moons review. But, use it with a 6sn7 based active preamp, and use RCA 6sn7s and you might have a "tubier" flavor, but the amp itself seems neutral, with tube bloom and soundstaging that only tubes seems to do compared with even the best SS. The RM9 with EL34s is a slightly darker flavor, but I think Roger has always designed with neutrality in ,ind and nothing overtly tubey in the CJ/Cary vain. I am always amazed by the RM10. I wonder what the mono setup wpould sound like - I suspect Roger would say the stereo version is better if you don't need the extra power (35 versus 70 watts).
wilsynet's avatar
wilsynet
264 posts
 
I do agree with the review. It's a well balanced amplifier, does everything well, some things very well and nothing at all poorly. It is very, very good with the LSA.

Regarding speed, it's fast but not fast like the Atma-sphere S-30. On the other hand, to these ears, it has more density than the S-30.

The 6moons review notes that the amp is not as good with complex music at scale, I have no such observation, although my speaker load is particularly benign and efficient.
pubul57 OP
3,712 posts
 
Wilsynet, I agree with everything you just said, and the Merlins, like the Zus are very benign loads, and efficient enough for 35 watts. I think, not always sure, that my preferred system is the all Atma-sphere rig, but the LSA with my RM10s and RM9 SEs, are might fine, can't really get myself to sell any of them. In my system, I preferred the Atma M60s and MR RM9 Special Editions to my CAT JL2s which I thought were just about as good as amps could be, certainly the CATs can handle a wider array of speaker loads than the Atma-sphere, but those RM9 SEs put out 162 watts into 8 Ohm and 200 into 4ohms, that is alot of tube power - if I could only own one amp for all seasons it would proabably be the RM9 (with my LSA).
clio09
3,353 posts
 
Off to the closet to unpack the RM-10.

I light load my RM-10 since my speakers are 12 ohm nominal and don't dip below 8. Anyone else light load their RM-10?
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