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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
augwest's avatar
augwest
43 posts
 
Excellent question. I've got the Master BAM upstream of the LSA per Merlin's recommendation when using a preamp, but you have to be cognizant not to overload the LSA. My Audio Aero SE DAC puts out 5.5 Volts (!) so if you boost that by 5dB using the BAM you can end up with pretty huge signal (~12V?). The LSA can't handle that.

Fortunately the AA DAC has vairiable output (actually a complete built-in preamp) so I set it at ~ -20dB and forget it. Of course you need to take into consideration the input sensitivity of your amp(s), i.e. how many Volts Input results in Full Output. But if your source puts out a more conventional voltage of a volt or two you might have no issue whatsoever.

RELEVANT ASIDE: I sometimes wonder if part of the reason that the LSA does works well in my system is because of the robust tube output section of the Audio Aero DAC (100 Ohm output impedance). It may not be perfect but I'm impressed with its resolution and musicality, and it will drive just about anything! I will probably be holding on to it until I decide to ditch my CD's in favor of a server.
clio09
3,360 posts
 
Thanks for the comparison. I have used my LSA with an Atma-Sphere S-30 amp for vinyl playback with great results. Right now though until I get my vinyl rig hooked up again I am running my Resolution Audio Cantata direct into the amp via the balanced outputs and using the internal volume control. It works quite well for my digital needs. Have you tried running the AA direct to the amps?
georgehifi's avatar
georgehifi
10,312 posts
 
Hi Paul (Augwest) I had no idea that was you that gave the glowing review on the Lightspeed Attenuator I sent to California.
As said with a source that could give out 5.5v this the Lightspeed will take but if it goes through the BAMM as well before getting to the Lightspeed this can add a further 5db boost to the bass which takes the 5.5v up to something like 10v before hitting the Lightspeed.
That is why I would try the BAMM after the Lightspeed, or my second choice if the BAMM must go as you have done is to turn down the 5.5v of the source to a volt or two as you have also done.
Good to hear that it still sounds better than all those preamps you put it up against, as I always claim the Lightspeed Attenuator will give the most transparent and dynamic way from lows to highs of controlling the volume from a source to a poweramp, and at the same time being totally honest to the source not adding or subtracting anything. The closest thing one can get to a straight piece of wire with control over the volume.

Cheers George
augwest's avatar
augwest
43 posts
 
Once again a very insightful question. The hitch for me is the need for the Merlin inline bass EQ module (BAM) that constitutes an integral part of my speaker system. In short, Merlin doesn't recommend hooking the BAM directly up to the amp so I stick the Lightspeed in between. A full answer is well beyond the scope of this thread ;-)

I owe thanks to Paul Rosenberg for recommending the LSA and the Atma-Spheres, though I don't think he ever used them in combination. He is dearly missed.
dgarretson
2,603 posts
 
Augwest, IIRC the BBAM is a capacitive load with 40K input impedance. This could present a difficult load to an LSA passive. In my instance the challenge is compounded: I split the preamp's output between the downstream BBAM and a sub with 47K input impedance, yielding a combined load of 22K. With the AtmaSphere MP-1 preamp I can't hear any difference between the BBAM placed upstream or downstream of the preamp. However I bet that in your case placing the BBAM downstream of LSA will degrade performance.

I replaced the stock volume control in the Atma preamp with a balanced shunt LSA Mk I type volume control that employs a TX2575 Z-foil resistor in the series position and a Lightspeed/Silonex shunt resitor. This was a major upgrade. Some preamp builders will argue that most of the performance gains to be had in a top-quality active preamp are made at the volume control. Based on this experiment I tend to agree. For a true apples-to-apples comparison it would be interesting to compare your LSA passive to an active preamp with an LSA-type volume control. The only current commercial product I'm aware of that employs an optical volume control is darTZeel.
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