2. amps-preamps
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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
3,374 posts
 
@georgehifi, on a pot the middle tab is the wiper or output if I understand correctly and if I understand you correctly this is positive. Based on the physical layout the positives of each switch are connected with a red wire and then there is a red wire from one of the switches to the board.

Well I installed the stepped attenuators using the same method. I believe I hooked up the other wires correctly as well, but here is my issue. With the original pots the Lightspeed never fully attenuated the sound, the pots in full counter clockwise positions still resulted in some low level sound coming from the speaker. I get the same result with the stepped attenuators, only the sound is much louder, in fact I could just listen to the music without moving the switch clockwise. If I do move the switch clockwise the volume does increase, but not very dramatically. In full clockwise position the sound level is still reasonable.

Something is amiss. Any ideas?
georgehifi's avatar
georgehifi
10,312 posts
 



First off clio, are you 100% sure the new ones you bought are 100kohm logarithmic and not 100ohm logarithmic or even linear???

@georgehifi, on a pot the middle tab is the wiper
Yes on the dual mono it is, and where the + of the power supply goes. But not on the stereo if you look at the circuit.

With the original pots the Lightspeed never fully attenuated the sound, the pots in full counter clockwise positions still resulted in some low level sound coming from the speaker. I get the same result with the stepped attenuators, only the sound is much louder
This is correct, all Lightspeeds Attenuators can never attenuate to absolute zero, as the LDR’s can never go to 0ohms, or complete open circuit

I get the same result with the stepped attenuators, only the sound is much louder
If all was wired up as the original/s were, the problem must be that the pots you bought are either not 100kohm, or not logarithmic but linear.
If they are 100kohm and logarithmic, then the first step up in volume must be way to high.

If I do move the switch clockwise the volume does increase, but not very dramatically. In full clockwise position the sound level is still reasonable.
If 100kohm value and log curve are correct ,this says to me you’ve wired it up wrong.

The only thing I can suggest then to do is put back the original pots and see if it all goes back to normal, if not you’ve wired it up incorrectly

Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 



To all the "Lightspeeders" here at Audiogon and any new ones


OK, time to let all here know that Lightspeed Attenuator has been acquired by a most avid audiophile, and who will do it proud.
His name is Scott Campbell who also resides in Australia in the Sydney country side town of Green Point.
He’s been very committed hi-end audiophile for as long as I can remember. As for his component history I’ll let him tell you.

It was time to let it go after all these years, because it was starting to feel too much like “ground hog day” to me producing them.

He also won’t be doing any orders for the time being, because of the Covid outbreak here, and he will also need to setup his production premises.

His present email is Audio@tradeontheweb.net but no doubt will have another soon, more akin to Lightspeed Attenuator name in the future.
I will still be around for tech assistance, till he finds his feet.

Cheers, and a very big thanks for all your support George

tradeontheweb
43 posts
 
Thanks George & thanks for the kind words.

I’m a passionate audio guy of 60. I’m very proud to have this opportunity with a product I’ve used personally for over 10 years.

George has kindly agreed to remain on in a support role & I'm fortunate to have his knowledge to call upon when needed.

I have some future plans for the Lightspeed, but for now the focus is on supporting existing owners & getting production up & running, once Covid allows.

Cheers

Scott
clio09
3,374 posts
 
@georgehifi, after fudging around with it some more the wiring was not the issue, the amp was. I pulled one off the shelf that I thought was good but is actually in need of repair. Pulled another one out and all is well.

Great news about the Lightspeed. Looking forward to Scott keeping this legendary attenuator alive.
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