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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
georgehifi's avatar
georgehifi
10,312 posts
 
Just looked at the Merlin VMS impedance graph (Stereophile), at it shows it only drops (over a very narrow band)to a minimum of 6 ohms at around 170hz at 0 phase angle.
This is an easy to drive speaker and should be driven off the 8ohm tap. Buy driving of the 4ohm tap all you achieve is loss of power from the amp, vitually no gains whatsoever.

Cheers George
pubul57 OP
3,712 posts
 
That's what it sounded like to me. It seems that light loading is effective at dealing with speakers that have hard loads for tube amp and it improves the situation - with the Merlins and Audiokinesis Jazz I suspect the extra power of the 8 ohm tap is the better option.

To get back to the subject, I would strongly recommend that all Music Reference RM9 and 10 owners try the LSA if they have a single source setup (actually any tube amp owner with sensitive 1v amps and 100 kohm input impedance). Is it just a coincidence that 3 of the LSA users also have a Music Reference RM10? Or is it just a match made in heaven for $2,500 MSRP?
clio09
3,353 posts
 
The extra power is certainly a consideration in easy to drive speakers. However, the other benefits of light loading should be considered as well, namely lower distortion and increased linearity and head room. If your speakers can handle the loss in power, roughly 7 or 8 watts, in exchange for the increased head room why not try it.

FWIW, I was listening late last night with the speaker cables connected to the 4 ohm tap. I didn't notice any loss of slam or dynamics and I was listening at considerably lower volume. Maybe I'm mistaken but wouldn't that be an effect of increased head room?

This combo is certainly very special. I wouldn't let the single input/output stop you from running it with multiple sources either. I have no problem swapping cables between digital and my three analog sources.

Question for George: In comparison to my Atma-Sphere amp which is less sensitive and has less gain the RM-10 doesn't require me to use as much of the volume control. I seldom get past 12 o'clock and most CDs come in around 10 - 11 o'clock for normal listening. Any potential sonic issues one should be aware of. I would think not base on what I'm hearing but thought I'd ask anyway.
georgehifi's avatar
georgehifi
10,312 posts
 
You may find that the OTL's are getting loaded down some by the speakers and dropping their output requiring more push from the Lightspeed/CDP. The sensitivity of the OTL was probably judged/measured with an unloaded outputs.

Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 
Sorry forgot the other part of your question, as for the position of your Lightspeed control, that's fine it's a good place to be, at around 2o'clock it really starts to increase/rampup the gain rapidly, so you have oodles of gain left.

Cheers George
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