2. amps-preamps
  3. 1276356977

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
 
Dpac996 hi, yes a Lightspeed can be used to drive a poweramp that have as little as 22kohm input impedance or even lower and there is no harm to the components doing this. I have many customers that are doing just that, but I like to present the parameter specs that are well over with headroom, so 47kohm which is the industry standard was chosen, even though we use it at 33kohm at our audio society meetings.
As for LDR matching, it is a must to have all 4 series and shunt matched as this will give a better logarithmic feel to the volume control, if you only match the series L/R and then match just the shunts L/R this will still work but the volume control will either be very touchy down low or very vague down low.

Cheers George
Post removed 
pubul57 OP
3,712 posts
 
Do let us know how the buffer works for you. It would seem if you don't need a buffer than a buffer will always be worse, and if you do need a buffer a buffer will always sound better - know if you do or not, there lies the rub. Let us know how your experiment goes.

Cheers.
pubul57 OP
3,712 posts
 
Of course, the LSA Ultimate would allow for buffer switching :)
georgehifi's avatar
georgehifi
10,312 posts
 
Good to hear Dpac996.
In your quest to sample a buffer after it, even though I believe the best buffer is no buffer so long as the impedance boxes are ticked for passive use.
If you want to try an simple good stable at unity gain opamp buffer, the most transparent/dynamic one I have come across in my experiments with I/V stages and buffer stages for cdp's is the AD825, the OPA627 is a tad cleaner but it doesn't have the dynamics of the AD825 and dynamics = rhythm and pace.
Cheers George
More to discover