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Lightspeed Attenuator


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I’ve been searching for a preamp, so for a Google giggle I searched for “best preamp ever audiogon” to see what would happen. I thought the Americans would have tackled the subject that way, and I wasn’t wrong.

The top hit was for tube preamps, but I didn’t want to limit my search to tubes. The second-top hit was not it either – just preamps for sale. 

But the third and fourth hits were more like it. They came from the same thread, which began in in 2010 and – 36 pages later – is still going (just). I started reading. My reading extended over two nights. My interest had turned to intrigue when I twigged that the preamp they were talking about was Australian.

Users were claiming that the Lightspeed Attenuator,  a US$450 passive preamp was the best they had heard. They were saying this little preamp had bested the likes of Cary, a bunch of Audio Research (SP22, SP10, LS3, LS8, LS2), Mark Levison 380S, NuForce P8, Gryphon MKII. The names went on. 

Now besting another amp in a get-together is one thing – but actually getting rid of a very expensive/very good/very respected preamp and replacing it with something cheap (by comparison) and (at the time) unknown is an altogether different thing. 

And that’s what some of them were claiming to have done. Like ditching a Supratek hand-made triode tube amp. (Which also happens to be Australian.)

The Lightspeed Attenuator, which will be well familiar to some people here on stereonet. My intrigue turned to astonishment when it became apparent that the creator/manufacturer is someone active in this forum – @georgehifi.

So what is this thing?

The Lightspeed Attenuator is, as the name suggests, an attenuator. A passive preamp. All it does is transfer the signal – and give you the capacity to turn the volume down (attenuate).

Also as the name suggests, attenuation is done by the use of light. Turning the volume control up or down decreases or increases the resistance of the internal light-dependent resistor (LDR).

All I had ever heard about passive preamps was that they ultimately lack bass punch, transient attack and big soundstage – three vital elements of music IMHO. I’d always thought no, I don’t want a passive.

But I kept reading this thread. Users kept saying the same thing – that this thing was as close to the proverbial straight wire with gain as you can get.

Except there is no gain – and no wire either.

And they kept saying that the common complaints about passive amplifiers (see above) did not apply.

What made this especially intriguing was that some of these users were big fans of tube preamps. Now I like tubes too, but tubes are as far as you can get from the ‘straight wire with gain’ aesthetic.

All of that was impressive, but the clincher for me was that the thread had gone on for years – and some of the users were still using the Lightspeed. Now we all know how people who are interested in this stuff will turn over components, either out of curiosity, the desire for a change, FOMO, because the grass is always greener, or just for the hell of it. So the fact that they had stuck with the same preamp for years…

So I had to try, didn’t I?

Now, the OP in that thread had made it clear that the Lightspeed needs the right environment in which to work.  A source ouputting 2V or more, which is pretty much everything these days I believe, a short interconnect to the power amp (three metres or less), low capacitance interconnects – and a power amp whose input is preferably the industry standard of 47K ohms or more.

Hmmm. I checked the specs on my Halcro DM38. Only 10K ohms on the RCA input. The Lightspeed outputs RCA only. That might be a problem. Theroetically, it really should be problem. But I wasn’t going to stop now, was I?

Just to test before shelling out, I plugged my passive Schiit Sys into the Halcro. The Schiit ouputs up to 5K ohm. So we are a long way from the ideal 1:10 ratio, which would have us up around the 47K standard on the power amp. But the Schiit provided enough bass and volume to make me push ahead. It worked, at least. But I thought I was probably going to need a buffer, so as to fix the impedance mismatch between the Lightspeed and the Halcro.

While I think of it, it’s worth adding that as well as having only one output, the Lightspeed also has only one input – and no remote control. It runs from a supplied wall wart.

And I should detail contextualise the rest of the system. Speakers are a massive pair – Be-One, The One. Five drivers per cabinet, about 100 kgs each, sensitivity 89db. Streaming via an Auralic Aries Mini, listening to 320 MPs, CR rips, hi-res files and DSD. Switching between DACs – the Aries, an Emotiva and an R2R Audio-GD 11. Preamps on hand for comparison were the Aries Mini again, a Xindak XB 8250, and the Geiseler preamp, also made by someone active here. (There were two tube preamps, an Audile using Jan Philips 5814a tubes tubes, and a SoundMaster Mk 23 using 2A3, but the tubes were so different, I didn’t make comparisons.) And I listen to most genres of music (except opera).

So the Lightspeed arrived. One great thing about it – no burn-in. Because there really is nothing to burn it. That’s a relief. Just give it one minute to get warm. We’re off.

First impressions: this is good.

It was clear. Like water. There was no shortage of bass. Or slam. Highs were clear. Volume – more than enough. I had it playing around 2 o’clock to play it loud (90db, sitting four to five metres from the speakers.) There is no sweet spot on the volume dial – the sound is the same all the way. 

That’s what it sounded like – which is to say, it had little sound of its own.

It was dead silent – which I suppose is a function of no gain and no mechanical parts to speak of. I really like a silent preamp.

Whenever I get a new component, I make a point of listening to it. By which I mean, not comparing, but just listening to it. (And I only change one thing at a time – so I can be sure where the difference is coming from.)

But it sounded not quite right. Hard to pinpoint, but it just felt like it was struggling. There was nothing i disliked, and what was there was good – but it just felt a bit lifleless. So after a few days I compared.

Yep, the Lightspeed was approaching the weaknesses commonly attributed to passive preamps. The attack on notes wasn’t quite there. That one thing meantthe music losing life and shine.

But what was there was all good – it just felt it was pushing the music uphill. But it was good enough that it deserved a proper chance – so let’s get a buffer.

I got a Musical Fidelity X10v3. (not XD.) It puts out just 33 ohms. It deploys two military-spec tubes – which Musical Fidelity says are designed to withstand the radiation of a nuclear war. Pity the rest of the system won’t.

And, voila. Now we’re talking.

If the taste was water before, it was water that wasn't quite flowing freely from the cup. Now it’s water out of a perfect glass. Transparent. Delicious and pure, as water can be.

Absolutely none of the usual criticisms generally aimed at passives apply. All the life and dynamics were there. Transients had zing. Slam had slam.

It just sounded like I was hearing the music.

So, there you go. This will be old news to some – George apparently made his first version as far back as the 70s. And that Audiogon thread where this journey began started back in 2010.

But I wanted to share it – this thing really is ingenious.

I like the fact that theoretically, it’s the ideal preamp. As far as I can see, adding nothing, subtracting nothing. (Used in an appropriate context, as explained.)

 

 

 

862303-lightspeed-attenuator-most-transparent-volume-control.jpg

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Wow Mick, what a rap, you made me blush, very hard thing to do.

 

Yes your power amp having only 10kohm input impedance was a slight limiting factor from getting the very best out of the Lightspeed, if it were >33kohm or higher you would have not needed nor wanted the X10-V3 buffer, the sound would have been (the opposite) better without it, one day you may change your poweramp or borrow one that is >33kohm and find out, keep in touch if you ever get around to doing that.

 

And you may want to try pure rechargeable Li-Ion battery (linked) on the Lightspeed some say it's even blacker and more transparent. 

I must admit I use one and there is something you just can't put your finger on that makes you keep using it, it's not a hassle either as the Lightspeed only consumes around 50mA and these Li-Ion batteries will give you around a week of listening before a recharge is needed. just make sure with the seller it has a 2.1mm plug and centre is positive.

 

https://www.ebay.com.au/sch/i.html?_odkw=12v+li-ion+rechargeable+battery&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.XDC12v+li-ion+rechargeable+battery.TRS0&_nkw=DC12v+li-ion+rechargeable+battery&_sacat=0  

 

Cheers George 

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Have to join the chorus.....my Lightspeed is a piece of gear I love to use. It truly is transparent, even while only in a temporary set up (renovating) I had to put the LS into service....it just works.....no fuss, just music. I love it. And such an inexpensive “try it” piece, like Zaph’s coax cables.....ya just have to try it. And at the price it is not a buyer substantiation piece, just buy one and wonder how it does what it does :thumb:

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It's funny this thread just popped up as I had the opportunity yesterday to compare my lightspeed to a more expensive Passive transformer attenuator. I found the transformer to give a relaxed type of sound with maybe highs that were slightly less pronounced. 

  The lightspeed gave a more dynamic presentation with larger sound stage and great details. Not bad for a much cheaper product, especially if going the diy route. 

The session just showed how components need to synergise in a system. The transformer is still a great product, but I would use it in a system with speakers that are on the brighter side, a room with no treatment or components that tended to favour highs etc.

   Thanks for sharing this to the diy community @georgehifi 

 

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Yes @niss–man, it gets even cheaper when you get into DIY territory. Pity I have no skills...

So as not to mislead, I should make it clear that a price I mentioned in the original post was the price in the US at the time. It's cheaper here now.

And as it happens @georgehifi, I have one of those lithium ion batteries to try. Also George, I'll give the Attenuator a go on some other power amps I have lying around, which are a better impedance match. But they are no match for the Halcro...

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7 minutes ago, campo007 said:

@georgehifi, do you make a version with more than one input? 

 

Hi Campo, the whole idea behind the Lightspeed is not to have any "touch" contact components in the signal path whatsoever, like "volume control pots", "source input selector switching" or even "relays" ect.

 

Saying that a few Lightspeed users have used external stereo source selector boxes, like the one linked or even far cheaper ones on eBay, this way they can remove it from the system and go direct with their source when they want to seriously listen and get the best from their system.

http://www.decware.com/newsite/ZSB.html

 

Cheers George

 

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Another long term Lightspeed convert here as well. Many, many, many Preamplifiers have passed through my system(s) over the years. Yet the Lightspeed consistently and stubbornly remains my "go to" component for volume control. It really is the elusive "straight wire with gain". The only thing I've found better is no Lightspeed at all! To explain - if you have a source with remote volume control built in. And "if" it has sufficient output to drive your power amp. "If" it does so in a linear and seamless fashion without bit-stripping, well then you'll be hearing everything your source can offer without coloration or interference from anything other than your connections. Lots of "if's" in that equation and it's rare to find a combination that fulfils all ones requirements. The Lightspeed is now a mature and refined product that has stood the test of time. It's been attacked online from almost every angle possible, but remains standing proud as one of the few components I'll never do without.

Those that know of the "rapidly revolving door" that is my system, will realise just how unusual that is for me !

The Stereophile "recommend components" rating for the Lightspeed is well earned.

 

Cheers

 

'Nutz

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I've now posted in the DIY forum, all the info needed so the DIY'er here with the knowledge can build their own purist version of the Stereo and Dual Mono Lightspeed Attenuator.

https://www.stereo.net.au/forums/topic/235189-lightspeed-attenuator-diy/?tab=comments#comment-3782806

 

Cheers George

Edited by georgehifi
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7 hours ago, PicoWattson said:

An LPS feeds mine as an indispensable tool for all interconnect and cable comparisons.

From what I can find on the Geek LPS powersupply you feed your Lightspeed with Pico, it looks like a very good OTT powersupply for it, even better than the Teradak one I recommend as an alternative to rechargeable 12vdc  Li_Ion batteries.

 

Cheers George 

Edited by georgehifi
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Found the Geeks to be right up there for the spend and also use them to energise my stats. Just wish that the effort Benchmark, Jeff Rowland and BMC have put into creating superb switching power supplies would trickle down to become stand alone consumer products.

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  • 1 year later...
On 21/10/2017 at 7:21 AM, georgehifi said:

 

 

And you may want to try pure rechargeable Li-Ion battery (linked) on the Lightspeed some say it's even blacker and more transparent. 

I must admit I use one and there is something you just can't put your finger on that makes you keep using it, it's not a hassle either as the Lightspeed only consumes around 50mA and these Li-Ion batteries will give you around a week of listening before a recharge is needed. just make sure with the seller it has a 2.1mm plug and centre is positive.

 

https://www.ebay.com.au/sch/i.html?_odkw=12v+li-ion+rechargeable+battery&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.XDC12v+li-ion+rechargeable+battery.TRS0&_nkw=DC12v+li-ion+rechargeable+battery&_sacat=0  

 

 

Would the negative to positive converter plug you supplied with the wall wart not suffice? 

 

Cheers

Ben

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8 hours ago, LuzArt said:

Would the negative to positive converter plug you supplied with the wall wart not suffice? 

 

Cheers

Ben

No Ben, sorry that wasn't a polarity swapping 2.1mm plug adapter.

It was a 2.5mm to 2.1mm size changer. Because those lovely wall warts were actually toroidal transformers inside (very rare in a wall wart) the trouble was they came with 2.5mm plug and the Lightspeed needs 2.1mm (almost impossible to tell the difference by eye) so I supplied the 2.5 to 2.1 adapter with it.

 

Cheers George

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No Ben, sorry that wasn't a polarity swapping 2.1mm plug adapter.
It was a 2.5mm to 2.1mm size changer. Because those lovely wall warts were actually toroidal transformers inside (very rare in a wall wart) the trouble was they came with 2.5mm plug and the Lightspeed needs 2.1mm (almost impossible to tell the difference by eye) so I supplied the 2.5 to 2.1 adapter with it.
 
Cheers George
Thanks George, good to know!
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  • 1 month later...

First try today of a battery on my Lightspeed Attenuator. Can certainly hear a difference. Extended top end and more detail somehow. Increased definition of separation. Very interesting!

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On 13/07/2019 at 5:27 PM, LuzArt said:

First try today of a battery on my Lightspeed Attenuator. Can certainly hear a difference. Extended top end and more detail somehow. Increased definition of separation. Very interesting!

It's very subtle, when we've done the comparison many times battery to the Linear wall wart, we all said we heard something different but can't put our finger on it, maybe it's the noise floor changing, Sam Tellig also said the same when he did subjective testing years ago.

 

With the Linear wall wart the measured noise is down to the base line of my Tektronix scope, just a few uV's impossible to hear, but it's there, with battery it's not. And using smp wall warts, no matter how good they raise the noise floor the most, but still only a couple of mV's and should still be undetectable.

 

We tried all forms of good power supplies to power the led's all were virtually the same, but the battery did make us aware something was there.

 

What you need to know is the LDR part is so slow to react (re data sheet) to any LED light fluctuations (even flickers) that they remain unaffected, in a way they are self regulating. 

This reaction time can be sensed by you if you flick the volume control (led control) up or down quickly, you sense it takes a few milliseconds to react, this is what I mean by "they are self regulating" So in a way are unaffected by power supplies.

   

 

Cheers George    

Edited by georgehifi
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