Lightspeed Attenuator

Brumjam

Well, the Lightspeed is here and it sounds rather....transparent :-)  This evening I've done some comparisons between it and my Croft Micro 25 preamp.  I also tried connecting the Young directly to my new active speakers (I'll save those for another post), to hear what influence the Lightspeed might be having on my system's sound.

The Lightspeed sounds marginally better than the Croft in my system.  It sounds like it is letting more of the music through, like I'm hearing more of the Young's output.  The overall sound is slightly less veiled, with a touch more clarity in all areas.  By way of comparison I tried connecting the Young directly to my speakers and controlling the volume using the Sonos variable output option.  I couldn't hear any difference between this configuration and when the Lightspeed was in the path.  Using the Sonos as a volume control isn't a realistic option due to the way it goes from silence to ear splittingly loud in about a centimetre of travel. Therefore the Lightspeed will be staying and my Croft will be sold.

I did have concerns about whether the Lightspeed would be effective connected to active speakers, given that one of the speakers is a couple of metres from the unit.  George (the man behind the Lightspeed) suggested I should keep the cable runs as short as possible for optimum performance.  To my ears I don't hear any difference between the output of each speaker.  In fact, I've had to reduce the input sensitivity on my speakers to allow more travel in the Lightspeed's volume control to prevent it getting too loud too quickly.  

Sound quality aside, I really like the simplicity of the Lightspeed.  Single input, no fancy lights, unnecessary gizmos etc.  It also fits nicely next to the Young on my shelving.

James

Alan

That looks great James. Or it might with pictures! I am very impressed you hear no artifice at all with the lightspeed in your system as opposed to software volume control. I only hope my EVA with it's hot-rodded power supply can nearly match the lightspeed for quality. The whole LDR attenuation principle is so elegantly simple, and I wouldn't be surprised if George's original design is the best implementation of the idea.

Software attenuation is by far the simplest approach, but if one requires more than one source then a pre is needed, so your findings are most encouraging.

Brumjam

Ha.....my other hobby is photography and I provide no pics  #-o

I would be interested to hear if there is any audible difference between the Eva and the Lightspeed.  There was only a slight improvement over my Croft which is about as far removed from LDR implementation as is possible.....do you think there can be much of a difference Alan given the design similarities?  

Brumjam

PS pics to follow.

Alan

I can't see that there would be tbh, but then I can't see why the power supply makes any difference to LDRs, or the fancy DC cable either! There are clear gains to both though.

Perhaps the Croft's performance is testament to Glenn Croft's abilities, which I would be happy to explore someday.

bhobba

Yes I have heard a Lightspeed and other similar passives.  Transparent - yes - but I feel that impedance matching is an issue.  I think active devices are better eg the truth:

http://www.thehornshoppe.com/the_truth_pre_amp.html

People I know rave about it and have ordered one myself.  They say it betters a Lightspeed and Burson Buffer. Can report further when it arrives.

Thanks

Bill

uglymusic

That's a difficult one to call, Bill.

It depends what you're using it with. For example, a number of us here use NVA power amps, which are designed to work with passives mainly because the idea behind these amps is to minimise component count. For these, active devices aren't an option.

In other words, there aren't any such generalities as passives or actives being 'better'.

Alan

NVA amps have an input impedance of 47kohm, I was told. The only amps I know that are lower are Pass labs amps.

uglymusic

But it's also the worry of overloading the NVAs' input stages because of the higher output from active pres, of course.

Alan

I have wondered what the effect of a buffer would be on NVA, like a pass B1 for instance.

bhobba

NVA amps have an input impedance of 47kohm, I was told. The only amps I know that are lower are Pass labs amps.

There are others lower such as ME's at about 10k.  A special pre amp was designed for it with an output impedance of 10 ohms.  And yes one can not make generalities about how well a lightspeed will work - sometimes it will work flawlessly - other times like with an ME amp it will have problems.  Devices like theTtruth however give you much greater freedom.  As always it is about system synergy.

Thanks

Bill

Brumjam

My speakers have an input impedance of 10kohm. George states that the Lightspeed should be partnered with amplifiers where the impedance is 47kohm or higher for optimal performance. So, I've invested in a Burson Audio buffer to sit in between the Lightspeed and my speakers.

Using the buffer in between the Lightspeed and my Arcam power amp (when I was using passive speakers) didn't work. The Arcam kept going into safe mode after about 30 seconds of use for some reason. Anyway, after a couple of hours use I've not experienced the same problem with my Genelecs. I've not had chance to do any A/B'ing with the buffer in place, but it will be interesting to see if the impedance mismatch is audible.

uglymusic

My speakers have an input impedance of 10kohm. George states that the Lightspeed should be partnered with amplifiers where the impedance is 47kohm or higher for optimal performance. So, I've invested in a Burson Audio buffer to sit in between the Lightspeed and my speakers.

Using the buffer in between the Lightspeed and my Arcam power amp (when I was using passive speakers) didn't work. The Arcam kept going into safe mode after about 30 seconds of use for some reason. Anyway, after a couple of hours use I've not experienced the same problem with my Genelecs. I've not had chance to do any A/B'ing with the buffer in place, but it will be interesting to see if the impedance mismatch is audible.

I must say I'm very interested in your system and the Genelecs, in particular. It seems to have a kind of 'start from scratch in the 21st century' logic to it, with no roots in analogue or retro valvism. (Can I apologise to everyone whose nose I've just put out of joint. I'm not trying to be inflammatory, honest)

Alan

ATC have been doing this well for years...

Word on the street is that the newer ADAM Audio actives are world class.

uglymusic

But I don't like ATCs ;-) Or at least never liked them in the past when I've heard them.

Have you heard Genelecs Alan?

I suspect you may not have fully caught on to what I'm saying. @Brumjam's system looks like the kind of thing I might build if I was starting from scratch, not that the individual component types are brand-new.

Alan

I haven't I'm afraid, though I'd like to. I do take your point about it being a very elegant way to construct a top flight system.

Brumjam

Thanks both.  I've taken a couple of wrong turns with my system recently but it is starting to sound really rather good.  The Burson buffer has made a positive difference.  Without it the system sounds slightly shut-in.  Soundstaging is also improved, with Diana Krall now clearly in front of the band, rather than before where it sounded like she just part of a 2D picture. 

Next step is to change the power supply to the Lightspeed - not because of any potential performance improvements, but because it's so flimsy!  It also uses an Australian spec plug which requires a travel adaptor.  There's a pin adaptor on the other end as well.  Why the cable can't be supplied with a wired connector which goes straight into the Lightspeed is beyond me.

What are you Eva users using for power?  Is there an elegant aftermarket solution ala Teddy Pardo?  Or should I just get an identical spec adaptor albeit with a UK plug?

Cheers,

James  

uglymusic

Thanks both.  I've taken a couple of wrong turns with my system recently but it is starting to sound really rather good.  The Burson buffer has made a positive difference.  Without it the system sounds slightly shut-in.  Soundstaging is also improved, with Diana Krall now clearly in front of the band, rather than before where it sounded like she just part of a 2D picture. 

Next step is to change the power supply to the Lightspeed - not because of any potential performance improvements, but because it's so flimsy!  It also uses an Australian spec plug which requires a travel adaptor.  There's a pin adaptor on the other end as well.  Why the cable can't be supplied with a wired connector which goes straight into the Lightspeed is beyond me.

What are you Eva users using for power?  Is there an elegant aftermarket solution ala Teddy Pardo?  Or should I just get an identical spec adaptor albeit with a UK plug?

Cheers,

James  

Alan and I use a KingRex PSU available from Item Audio of this parish.

Brumjam

Thanks Dave. I'll see if the spec matches what the Lightspeed requires.  Even slightly bending the cable on the standard adaptor causes a loss of power.  

Brain_Dead

Hi chaps, the LDR volume control is a great idea and I have tried it, but check the spectrum response on the LDR I found the Ultra Bright Green Led (VAOL-10GGE4 FEC 1858574 575nm) were best for the NORPS-12 (Peak at 560nm) also I found many year ago green led produce less noise than the other colours when used as a crude voltage reference. Also use 2 LDR in series driven by inverted LED,s and then you can pre bias them to to make a fix value pot. I will draw a rough circuit if anybody is interested. 

Brain_Dead

NVA amps have an input impedance of 47kohm, I was told. The only amps I know that are lower are Pass labs amps.

Mine are all 10K, try a simple emitter follower circuit, cheap and with the right transistor can really work well.

Brain_Dead

Brain_Dead

Another idea

Alan

Col, that all looks fantastic but I don't have a clue what any of it means!!! I would be interested in pursuing a 'pimped' LDR passive, as the EVA is plainly superb for it's price.....but I wonder if it can be improved upon?

The twin cermet pot NVA passive I replaced with EVA is only slightly behind in most areas, the EVA trumps it on the more subjective areas like emotional involvement. I think...   But there is a (substantially) more expensive twin stepped attenuator NVA that could conceivably have the measure of EVA.

One thing though, how could a green LED produce less noise (I presume in the electronic sense) than a red one? I thought the signal didn't interact with the LED directly, that the LED basically enabled a variable resistor in the signal path?

Brain_Dead

It is odd the LED is powered by DC, but the LED has a much larger noise level with RED and note the Green has the closest spectrum for most LDRs. When I use a LED as a voltage ref in the Magnum range, Green was at least 6dB less in random noise, I asked if it was thermal noise but the manufacture had no idea.

So I stuck with Green.

Unless the capacitance on the Stepped attenuator is low at min setting you may lose some top end detail .

Due to the filtering of the Rs+C time constant.

Pimped is possible I will dig out prototype and check it still function, next week when not rushing around like headless chicken.

Best cluck cluck col

Alan

Most excellent Col, thanks for sharing your  experience.

Brain_Dead

Right Alan I have found nearly all the bit for the attenuator, I will try and find the circuit boards.

Then I will send them on to you, do you have a soldering iron?

Best Col

Alan

I have one Col, I even swapped the components on a crossover once. I just wonder how competent you think I am, because I really, really am not! Ask Dave....
|)

uglymusic

Sizzle!  :-D

Brain_Dead

And bangers I hope