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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
chakster's avatar
chakster
2,482 posts
 
@dgarretson 

I expected to hear sonic trade-offs, with the passive winning on treble resolution & overall sonic purity, and the active winning on dynamics and LF control. In actuality the hybrid buffered approach won on every point. As a result I opine that if the impedance match is anything less than perfect(and who really knows for certain what is perfect?), a passive would benefit by being equipped with an active buffer on an A/B switch. There are several simple & inexpensive buffer designs(including one contributed to the Lightspeed DIY thread by Nelson Pass) that will do justice to a top-quality passive. In this scenario the comparison of LSA to other preamps becomes more of a contest between volume controls-- which is a critical and oft-neglected determinant of a preamp's performance.

Hello, have you compared LSA to FW B1 ? 

georgehifi's avatar
georgehifi
4,966 posts
 
chakster

Nelson designed a buffer for the Lightspeed Attenuator over 10 years ago on diyAudio so my Lightspeed customers could drive some of his low impedance (10kohm) amps with it, here it is. Later he called the B1 buffer.

https://www.stereo.net.au/forums/uploads/monthly_07_2013/post-106386-0-51349800-1374036585_thumb.jpg

If you have a high impedance amp (>30kohm) the buffer (B1) is not needed and the Lightspeed will sound better without it.
The best buffer is still no buffer.

Cheers George
chakster's avatar
chakster
2,482 posts
 
Here is a picture of my opened B1, and this is another view on this beauty. Sadly, even 2 inputs is not enough for me as i normally use two turntables with 4 tonearms (different cartridges and phono stages). On my tube amp i got remote control, sadly there is no remote on B1, but dual volume control is a nice option to adjust the balance if needed.

Always a trade offs :( 

Yes, the input impedance of by First Watt F2J power amp is 50k Ohms. 

What i don't like is even more limitation with Lightspeed to have just ONE input. BUT has anyone with the same problem ever tried Luxman Line Input Selector AS-4III which is easy to upgrade ? 

 
georgehifi's avatar
georgehifi
4,966 posts
 
hat i don’t like is even more limitation with Lightspeed to have just ONE input.


It meant to be like that on purpose, because it eliminates the "source selector" switch which is another lightweight potential distortion causing contact taken out of the signal path. The Lightspeeds all about no contacts in the signal path.

As you can see if you follow the green signal path, the music goes from input to output through nothing but a fixed resistor, unlike other preamps which have many contacts (that are very light in contact weight) that the signal has to go through.
http://www.diyaudio.com/forums/attachments/analog-line-level/470539d1425885769-lightspeed-attenuator...

A couple of customers use these external "source selectors switches" if they want to switch multiple sources and couldn’t be bothered changing over interconnects for non serious listening.
That way they have the option of still hearing the best without it when they want or to impress their friends by going back to direct into the Lightspeed. with no source selector.

The Goldpoint one is the better, it also seems it has the option of bypassing the source selector switch (see they know), BUT!! with what? another contact inside, so they take the nasty away but replace it with a not so nasty pin plug jumpers?
http://www.goldpt.com/sw4.html


https://cdn.shopify.com/s/files/1/0933/8332/products/51NDp9qHxUL._AA500_grande.jpeg

Cheers George
dgarretson
2,394 posts
 

@chakster

Wow, your reference to my post is from the deep archives. I recall trying the Lightspeed schematic together with battery-powered monolithic Nat Semi buffers. I ended up (and still employ) the Lightspeed schematic as a volume control in a tweaked-out AtmaSphere MP-1 tube preamp. TX2575 series resistors and Silonex LDR shunts in a differential balanced circuit. It sounds fantastic relative to the stock Shallco series attenuator.

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