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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
miller65
3 posts
 
Thanks George the temperature variation in the power supply makes sense as it is more stable in line with a stable room temperature I also intend trying with a battery in the next few weeks.
As a next stage I am considering using my CD player as a transport and introducing a DAC into my system this will also enable me to include a network player at a later date. However having checked the output spec of the DAC Beresford Caiman mk11 I have a couple of questions in terms of how output impedance can effect the sound quality . The output voltage of the DAC is 2v which is in line with LSA recommendation but the output impedance is 1k ? appreciate it should be 200 ohms or less ideally . Iwill use with a very low capitance Stager silver solid i/c 0.5 metre length .
Does anyone have experience of using the LSA with output impedance this high and if so what if any effect can it have on the sound / volume control . I love the transparent dynamic sound the LSA currently gives me and wonder if this potential impedance mismatch would have any adverse effect on the sound quality or use of the volume control which 
currently operates at 12 o clock , which is generally plenty loud enough

dgarretson
2,588 posts
 

Hi George,  I'm thinking of an DIY LDR attenuator to replace the stock 10K Alps dual pot in a Sennheiser HEV70 energizer for HE60 electrostatic headphones.  I need to step down from 25Vdc to 5V for this application. The chassis is cramped and there is little room inside for a heat sink on the down regulator.  An LM2596 looks like an easy fit in terms of low heat dissipation and compactness.  Do you think this would compromise sonic performance relative to a LM7805 linear regulator?  My concern about the LM7805 is overheating from the 20V step down.

Thanks,

Dave  

georgehifi's avatar
georgehifi
10,312 posts
 
miller65Thanks George the temperature variation in the power supply makes sense as it is more stable in line with a stable room temperature I also intend trying with a battery in the next few weeks.
As a next stage I am considering using my CD player as a transport and introducing a DAC into my system this will also enable me to include a network player at a later date. However having checked the output spec of the DAC Beresford Caiman mk11 I have a couple of questions in terms of how output impedance can effect the sound quality . The output voltage of the DAC is 2v which is in line with LSA recommendation but the output impedance is 1k ? appreciate it should be 200 ohms or less ideally . Iwill use with a very low capitance Stager silver solid i/c 0.5 metre length .
Does anyone have experience of using the LSA with output impedance this high and if so what if any effect can it have on the sound / volume control . I love the transparent dynamic sound the LSA currently gives me and wonder if this potential impedance mismatch would have any adverse effect on the sound quality or use of the volume control which
currently operates at 12 o clock , which is generally plenty loud enough

Hi, yes please post up what you think of the battery once you've listened to it.

Your Dac at 1kohm is fine still into the Lightspeed's 10kohm, but then your poweramp comes into play and series up with the 10kohm of the Lightspeed, I would say amps with over 47kohm all will still be fine.

As for interconnect cable capacitance, stay below 100pf (capacitance) per foot and 2mts max, good cables are usually below 100pf per foot.

Cheers George

dgarretson

Hi George, I'm thinking of an DIY LDR attenuator to replace the stock 10K Alps dual pot in a Sennheiser HEV70 energizer for HE60 electrostatic headphones. I need to step down from 25Vdc to 5V for this application. The chassis is cramped and there is little room inside for a heat sink on the down regulator. An LM2596 looks like an easy fit in terms of low heat dissipation and compactness.  Do you think this would compromise sonic performance relative to a LM7805 linear regulator? My concern about the LM7805 is overheating from the 20V step down.

Thanks,

Dave  

 

Hi Dave, as for sinking 20v on a 1amp 7805 this is too much and will get very hot, best of getting a 12vdc supply for it.

Cheers George  

georgehifi's avatar
georgehifi
10,312 posts
 

Hi all, owners that like to try different ways of powering their Lightspeed Attenuator’s. May like to try something new that Stereophile gave some push for.

It’s the new iFi iPower supply dc wall wart, now before any of you say it, yes I didn’t like recommending smp (switch mode) wall warts. This was only because the ones I tested had a bit of noise, that couldn’t be heard, yet was measurable when compared to a linear wall wart.

This new iFi iPower supply wall wart is smp, yet it’s noise is very low.

http://www.stereophile.com/content/music-round-77#61wYlEfbAywkfiS2.97

http://ifi-audio.com/portfolio-view/accessory-ipower/

If you order one be sure to get the 12vdc one with 2.1mm X 5.5mm plug with centre positive.

Lets please hear a review from anyone that gets one, as I may change to these as supplied wall wart with the Lightspeed Attenuator, as they are multi world wide voltage usable.


Cheers George



georgehifi's avatar
georgehifi
10,312 posts
 

This is what Kalman Rubinson of Stereophile heard when he used this new iFi iPower wall wart on a low powered dac when he compared it to a linear wall wart, it should/could do the same for the Lightspeed Attenuators sound.


"When I switched over from the stock supply, the DAC didn't seem quieter when there was no audio signal, but that's not the real test. Recordings with open, ambient soundstages sounded cleaner, and both instrumental and vocal music was more distinct. This was no major change that struck me every time I listened, but it did make all of my listening much more relaxing—perhaps because, subliminally, it required less effort to attend to individual sounds, particularly those far back on the soundstage."


It has some pretty impressive measured noise figures, of 1uV of noise, (that's microvolt not millivolt)!!!!!

This could be a deal breaker, and the end of linear wall warts for the Lightspeed Attenuator.

I tried to find advertised pricing of them, but couldn't get an exact figure, but it seems to be around $50-$100 which should be a great upgrade for that kind of low noise supply.


Cheers George  

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