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
Like your input George. I would love to try your preamp in my system and compare to my tube preamp. I can't believe I even said this as I am usually 100% against passives based on my experience with these in the past. It's just that several highly respected Agoners seem to think your $450 unit is the real deal giant killer. I have a gaint in my opinion :-)

I have found that my active tube preamp is not a tone control at all. Rather, compared to some nice passives I have tried, like Placette, my music has increased texture, body, stage size, layered holographic presentation and much improved sense of control and utter ease at any volume. All of this while being every bit as transparent.

These attributes have nothing to do with the simple attenuation of bass or treble as a tone control.

I may indeed compare soon. I just can't image a passive unit would match the attributes listed above. If so, your preamp is a wonderful value.
I stand corrected in my Morrison ELAD comments. Thanks for the clarification Georgelofi.

I agree with Pubul57 that for many the straight wire with gain approach is as much a philosophical stand as anything else. I was once one of those folks. Then I became heavily involved with tube amps and preamps and my approach softened. I am aware that a SET tube amp most likely "colors" the sound of most recordings I hear. However,I've made peace with that because I greatly prefer that sound. The issue I have with some "straight wire" proponents is that they can take their stance to the extreme by believing they are recreating live like music conditions via their stereo systems. A quick trip to the symphony is a more than subtle reminder that even the best stereo systems I've heard (Shindo,Audio Note etc..) are nothing more than crude approximations of the real thing.
I have never heard a stereo system that sounds like live music, but I have heard stereos that probably sound more the recording - the loss goes from live to recording and it only gets worse from their in terms of sounding live. If you don't go to live acoustic events you might get fooled from time to time, but then I go to a jazz concert and after a few minutes my audiophile mind goes ugghhhhh, and accept that stereo systems are just very enoyable ways to a enjoy music, some better than others, and none close to live.
Grannyring
I have a gaint in my opinion :-)

Good on you Grannyring you've given me my laugh for the day, I'm just a tech with limited English skills I had to look up "gaint" this is what I found in the Urban Dictionary

gaint: loss of blood to the brain due to overly large erection.

Cheers George
I had to google it, hmmmm.
Goodness that is funny stuff.............
Maybe we can have a giant gaint ?
Thought well enough of the Lightspeed Attenuator, that I just sold my beloved Joule LA150 Signature Edition line stage($6,500,)as having two "real" preamps and a single-source volume attentuator seemed like too much gear, but I'm keeping my Atma-sphere pre for use with the Atma-sphere amps:)
With Ralph's assistance I'm tweaking the S-30 so that it will be even further optimized with the Lightspeed for single ended use and my Otari reel-to-reel running direct for balanced use.

Pubul57, sorry to see you sold the Joule, I know how much you liked it. If the Lightspeed is that good that you could let the Joule go, then that is saying something.
Sorry to hear that Paul, (please no hate mail) your in good company though, a customer a while ago just sold his $18000aud Matisse Reference pre because of the Lightspeed Attenuator, he invited me around for a listen, it looked ridiculous, here was the diminutive Lightspeed wired up to these 4 x box (coffee table sized) Jadis Reference monoblocks. Boy did it sound good though into the top Avalon speakers.

Cheers George
Proabably getting quite a bit of warmth, dimensionality, palpability, and bloom from the Jadis. The Lightspeed Attenuator doesn't look too puny driving the Music Reference RM10s which are about the size of hardcover book:) - now if I still had my CAT amp....
Clio9, could you share what those Atma sphere tweaks are?
Also, is anyone aware of a mechanical switching box that would allow one to have, say, 3 rca inputs and one output. That would allow one to have multiple source inputs, and still use the Lightspeed attenuator. The alternative is simply unplugging one source, and plugging in another...how barbarian... but worth it to avoid a line preamp.
Tompoodie
Also, is anyone aware of a mechanical switching box that would allow one to have, say, 3 rca inputs and one output.

There are many out there here is one. This is the best way as it will still allow you go direct when you want the best out of the Lightspeed.
My prototype has two inputs with the best switch you can get and it is still bettered by every single input production Lightspeed I listen to before shipping out.

http://www.mcmelectronics.com/product/DISTRIBUTED-BY-MCM-INP-3-/50-6170

Cheers George
George,

Are you, or could you, consider making a fully balanced version with some sort of remote volume function?
Clio9, could you share what those Atma sphere tweaks are?
Tompoodie

No. Please contact Ralph directly. The tweaks may not be applicable to you and your system. Only Ralph can tell you that.

As for a switch box, Decware makes a nice one. I just unplug my cables. Guess I'm a barbarian. The price you pay for the best (IMO) sound.

Are you, or could you, consider making a fully balanced version with some sort of remote volume function?
Koestner

LOL. Been down that road with George, except the remote part. It's hard enough matching LDRs for the single ended version let alone what it would take to match them for a balanced version. Not too mention according to George it might not sound as good or be as reliable as the single ended version.

Let's bear in mind that the reason the Lightspeed is so good is its simplicity. Adding inputs, remote, balanced design, etc. just complicates things. George addresses all this in detail on the DIY.com site where he has been gracious enough to share loads of information. If anyone wants a balanced version I mentioned in a previous post on this thread that George (or I if you email me) will send you a schematic. You could build one or have one built. There is a site (forgot the name but I think its mentioned in this thread) where you can get matched LDRs, and possibly a completed board, leaving you with just the hardware to sort out.
Since the resistor changes with the amount of light, could I open the case and use a light bulb with a remote dimmer to change the volume?
Many thanks George and Clio09. I'm going to give the Lightspeed attenuator a go. This is fantastic thread. I agree with the above that is is quite noteworthy that Both Arthur Salvatore and Roger Modjeski are in agreement that with the appropriate system an active line stage would be inferior to a passive volume control. I intend to store my Adcom 5802 amp (horrors...transistors,Feh!)and get a Music Reference RM 10 MkII also. I anticipate it and the Lightspeed will be a great upgrade. Cheers all.
Tompoodie,

Music Reference RM-10 + Lightspeed Attenutor = Depends

Don't forget to get a box of those as well before listening to this combination. This is one of the most enjoyable amp/preamp combos I have ever experienced.

BTW - Roger has a few RM-10 MkII amps left at the $1450 price. A great deal only bettered by being able to find one used in near new condition.
I agree Anthony, as enjoyable as several $10-$20,000 combos I had here over the past 5-7 years. With the right speakers, the LS-A/RM10 combo($2,400 list)is incredibly good and competitive with just about any pre/amp combo out there, at any price.
06-16-10:
Koestner:George, Are you, or could you, consider making a fully balanced version with some sort of remote volume function?:Koestner

I'll put it up again, Paul got it almost all.
To do a balanced version takes exponentially more matching time and is exponentially more critical, then if that was achieved, to calibrate it would be exponentially more critical and then it will only stay in calibration a few days.
I have customers that have balanced systems they just use 4 x balanced to rca adaptors on the back of the Lightspeed Attenuator.

http://www.jaycar.com.au/productResults.asp?keywords=rca+to+XLR&keyform=KEYWORD&SUBMIT.x=18&SUBMIT.y=5

After all balanced is only needed if you run extra long interconnects, single ended actually sounds better because of the lack of opamps in the signal path to achieve the balanced signal, and in the end lets face it, the speaker is also only single ended as it run only a + and a - back to the amp and that negative on the back of the amp is at ground potential.

Cheers George
"I agree Anthony, as enjoyable as several $10-$20,000 combos I had here over the past 5-7 years. With the right speakers, the LS-A/RM10 combo($2,400 list)is incredibly good and competitive with just about any pre/amp combo out there, at any price"

Just my 2 cents worth in agreement with the above. Having recently listened to the LS inserted into an expensive system with Halcro Monoblocks (approx AUD $60K)and both Wilson 7's and 8's, I can vouch for the LS's ability to play in any company and far exceed it's modest price/appearance.

Cheers

Scott
Well we may never get to the point that we can say of any preamplifier (or volume control, if you will) that it is the best ever (a silly thought), but I feel pretty comfortable saying that this is by far and away the best such thing for the money, and not a poor man's option, but a true SOTA approach to volume control, in the right system.

Anthony, if you do give the Axiom a listen in your system, your thoughts would be welcome, not sure it would be better than a Goldpoint with the right value attenuator, or the Placette RVC for that matter, but I'm not sure what they are doing that might make a difference compared with those, even with the Caddock option (better than Vishay?).
Scott, that would only be in a small room with highly efficient speakers. I assume that combo won't play at 95db in a larger room with speakers under 90 db efficient?

I also assume that combo would never have the dynamic impact of a more formidable set-up. Say 300-500 watt monoblock amps and an active tube preamp with killer drive and scale.

I must say this thread is interesting as I read about folks letting go of $18,000 preamps and the like. I have heard the RM10 and passives with 90db efficient speakers and while it sounded musical and very good the system was certainly dynamically limited in a medium sized room. I would certainly say it did not come close to approaching the impact and scale of live music or systems costing $20,000 with different gear.

My $8000 amp and pre combo does in my large room.

I have a question for you owners of this exciting volume pot. Will it work well on speakers that are 87 db efficient like Soundlab speakers and other ESL's? I say this assuming the amps are very powerful and the spec criteria mentioned by the poster are meet by the source unit and amps.

Last, this LS volume pot has no sound of it's own so I assume you hear the amp speaker combo and it's particular sonic signature and synergy? If so, an active preamp may well act like the hub or heart of a system bringing everything together the way the owner likes. Perhaps the speaker/amp synergy is just a little shy of perfect to the owners ears, thus the active pre is the crowning jewel or the cherry on top.

Ok, be kind to me as I am only trying open this up to all views and experiences. You guys have my attention on this thread.
I would think a room much larger than 12x18 would be too large for the RM10 with my Merlins which are 89db, the RM9s do have more scale (and 162 watts)so you would expect that, but they are closer than you expect, at 20% of the price of the RM9 Special Edition (not the standard RM9).

I'm not sure why the 87db would be an issue in terms of the LS, if the amp 60 watts or more tube, or 100+ SS, and if their input sensitivity is 1v for full output, the limit would seem to be the amp, not the LS in this situation, but perhaps George will chime in as I have not actually tried it:)
Also, on the RM10, I'm driving Merlins with its 35 watts (actually 27 watts since I use the 4 ohm tap) so it's not really trying to move large bass drivers which might show up the RM10s limitations, don't know. I do know that Roger designs his amps with electorstatics in mind, so....
Will it work well on speakers that are 87 db efficient like Soundlab speakers and other ESL's? I say this assuming the amps are very powerful and the spec criteria mentioned by the poster are meet by the source unit and amps.
Grannyring

I don't see why not, but I'll let George address this. I thought I recalled a conversation where the Lightspeed was being used in a system with Maggies.

However, my own personal opinion would be that the amp driving the speakers and the synergy between the two would be the more appropriate matching criteria when determining this since the spec criteria (source output voltage and output impedance/amp input impedance and sensitivity) is met.

Last, this LS volume pot has no sound of it's own so I assume you hear the amp speaker combo and it's particular sonic signature and synergy? If so, an active preamp may well act like the hub or heart of a system bringing everything together the way the owner likes. Perhaps the speaker/amp synergy is just a little shy of perfect to the owners ears, thus the active pre is the crowning jewel or the cherry on top.
Grannyring

As I said previously, an active preamp is a tone control, or in some systems a band aid.
06-16-10:
Grannyring:I have a question for you owners of this exciting volume pot. Will it work well on speakers that are 87 db efficient like Soundlab speakers and other ESL's? I say this assuming the amps are very powerful and the spec criteria mentioned by the poster are meet by the source unit and amps.Grannyring:

My Martin Logan Monoliths ESL's are around 86db, I am never more than 11 o'clock for very very loud listening. I make it a point of asking customers with low efficiency speaker where the position of the volume control is for good loud level listening, and the worst was 82db speakers and he was still only at 1 to 2 o'clock for loud listening sessions.
You can gauge this for your self by putting your source directly into your poweramps to see if is loud enough for you, I bet not one person says they need more level even with 82db speakers and this is what the Lightspeed Attenuator will let through no more only less if you turn down the volume control.
:This next part is important to read:
There is no need with todays high output sources (cdp,dacs,phono stages) the need to preamplify, they have enough output to clip nearly all poweramps into any speaker on the market. So why would you want to amplify again (with a preamp)only to knock it back down again to below the original source output???.
Cheers George
George, do you think the quality of the power supply of the CD player would make a difference? Might not a poorly designed PS in the source benefit from the "conditioning" of an active preamp?
I also feel the need to share this story, because it offers a bit of a different use case for the Lightspeed.

My speakers are Audiokinesis Jazz Modules. They are a 92db efficient 12 ohm design with a smooth impedance curve. Very easy speakers to drive. I've used a 225 rated TRL D-225 amp (tests out closer to 300 watts as you know Bill) with it, as well as some lower powered amps. The designer, Duke LeJeune, voiced the speakers to an extent with the Atma-Sphere S-30 amp. While the amps input impedance is 100k (single ended) or 200k (balanced) ohms, the input sensitivity is only 2.83V. This figure is not usually what one, including myself, would consider passive friendly. Since I wanted to hear this combo for its synergy I asked Ralph Karsten, the amps designer (who has heard the Lightspeed), if the single ended Lightspeed and another balanced passive unit I'm going to test out would work well with the amp.

Ralph responded that I was making too much out of the volume control issue. My CD players output was more than enough on its own to drive the amp, basically validating a comment George just made (I was able to run my Otari MX-5050 BII reel-to-reel into the S-30 amps using the decks volume control and there was plenty of drive). In fact Ralph feels the further around the volume control you can get on a passive (closest to wide open) and achieve your optimal listening SPL, the better. With my very sensitive amps I get anywhere from 10 o'clock to 12 o'clock. With the S-30, I can push it a bit further, 1 o'clock or so. I can say it sounded wonderful.

Ralph recommends using an active preamp with his amps but it is important to note that his designs support the 600 ohm balanced standard (pro audio). Not all balanced active preamps support this standard. Of course Atma-Sphere preamps do. The benefit of the 600 ohm standard is that it takes the balanced cable out of the equation. Otherwise, based on my experience, when using appropriate cable lengths, there should be no reason why a passive preamp wouldn't work with less sensitive amps, assuming the other spec criteria are met.
Pubul57, what is the active preamp "conditioning"? Are you referring to the preamp being some type of noise filter?
No, thinking more in terms of power delivery and power supply fluctuations, the ability of the output stage of the CD player to drive the ICs and the amp.
06-16-10: Pubul57
No, thinking more in terms of power delivery and power supply fluctuations, the ability of the output stage of the CD player to drive the ICs and the amp

There should never ever be powersupply fluctuations in the output of a cd player, if there was it needs to go to the recycling tip.
As for the power delivery, (which means current delivery) If your source (cdp) has a low enough output impedance (say less than 200ohms) and it sees an input impedance (load) higher than this there is no current delivery problem, it's only if it sees a input impedance (load) lower than 200ohm then you can start to have current limiting.
Output impedance of the source has to be lower than the input impedance of the next stage, this goes from cdp to pre, then from pre to amps, and then from amps to speakers. And don't forget all interconnects and speaker cabling have some resistance this should be added to the input impedance of the load, this is why one should not use hair thin cabling as it has more resistance and adds the load resistance.
There endth the "Ohms Law" lesson for today need to build some more Lightspeed Attenuators, will back later.
Cheers George
And don't forget all interconnects and speaker cabling have some resistance this should be added to the input impedance of the load, this is why one should not use hair thin cabling as it has more resistance and adds the load resistance.
Georgelofi

What type of cabling should one use (or do you use) in terms of gauge? Is there a preference over stranded versus solid core. Would cabling like Mogami or Belden suffice? These typically have low LCR specs.
The Cardas GR have really low capacitance, but the Blue Jean ICs, which are Belden made, also have very low capacitance - if that is an issue, which shouldn't be with most cables under 2m (I would think).
"06-16-10: Grannyring
Scott, that would only be in a small room with highly efficient speakers. I assume that combo won't play at 95db in a larger room with speakers under 90 db efficient?

I also assume that combo would never have the dynamic impact of a more formidable set-up. Say 300-500 watt monoblock amps and an active tube preamp with killer drive and scale"

Sorry Grannyring, but nothing could be further from the truth, in my experience. In fact I recall using the LS with a Gryphon DM100 and Gryphon Encore (500 w) into Usher AC 20 speakers of about 92db. This was in a large, well damped room. Dynamic impact was there in spades and no loss of detail or presence either.

At that time, I recall I had an Audio Research SP11 on hand for comparison. It lasted about 2 days before the LS went back in. All this and there were no mods to either of the Gryphons to match impedances for the use of the LS !

My JBL 4350's will approach 125db according to the literature. The LS normally sits at about 10-11 o'clock. Past 2 becomes painfull, literally.

Cheers

Scott
I use Express 6 MkII interconnect by Eichmann but I don't wire it like they do, I put all reds together and all backs together I found this sounded better and was more electrically logical, the way they had it was strange and sounded that way.
I also like it because it is substantial have 6 solid core individual conductors of about .5mm each 3 red 3 black individually insulated the encased in a blue gel type outer sleeve with no shielding at all, as I have found shielding can increase capacitance/inductance.
Also I like that is pure 99.99%ofc copper, I have never liked silver or silver coated, I find it artificially accentuates the highs, giving a false impression of detail while robbing body from the lower-mids and leaning out the bass.
Then for speaker cable the same Express 6 MkII speaker but its twice as thick probably 1mm conductors
Back to work
Cheers George
Scott, you agreed with me actually as I was talking about about the LS and RM10 combo of only 35 watts. The amps you mentioned are more powerful.
Grannyring, thanks for that - I wondered if that was what you meant !

Cheers

Scott
Ok, one last question. If I run my CD player right into my amps, won't that damage the amps or speakers? When this is done will my system play at full volume? Half volume? I can't image playing at full volume as I never go past 1/3 or so right now - to loud!

I don't see how this "test" is possible with no volume control on my CD player. I have never tried anything like this so I may not understand.
Bill -

Go to the Arthur Salvatore site and read the instructions for the test (see link). There are test instructions for LP and CDP. Ravel's Bolero is a good track to use because it has low passages at the start that will not cause damage.

You're right though, loud passages or even an unexpected loud passage might cause damage. With no volume control on the CDP you wouldn't be able to mitigate damage unless you were to hit the pause or stop button very quickly.

If you are still using the TRL Samsom amps IIRC they have an input impedance of around 67k ohm. The sensitivity is just under 1V. Any CDP with 2V or greater output should be able to drive it. The question is will there be enough volume and will you like the sound. Also, perhaps not with the test but if using any passive preamp the output impedance of the CDP will come into play. Typically this should be under 200 ohms, but under 100 ohms is even better.

http://www.high-endaudio.com/RC-Linestages.html
Thanks Tony,

My CD player is a Cary 306. It puts out 3V - higher then the 2V suggested in this thread.

I am checking on the output impedance from Cary. But my amps are the Samson's as you say and the 67k ohm figure seems low? George says the amp's input impedance should be higher then the preamp's output impedance. Even if the Cary is 100 ohms I may have a problem? I think I just figured it out - the "k"ohms on my amp are much higher then the ohms (not K) out of my CD player?

Sorry, but I am not a big spec guy :-)
Bill,

While the 3V output of the CDP is quite sufficient, the output impedance is 220 ohms single ended. George may need to weigh in here on how that might affect the matching between CDP and Lightspeed. It should work as typically you want a ratio greater thant 10:1 between the input impedance of the passive preamp and the output impedance of the source. The greater the ratio the better. Same is true for the ratio between the input impedance of the amp to the output impedance of the passive preamp. What complicates matters is that the output impedance of passive preamps vary by volume setting.

The 67k ohm input impedance of the Samson amps is lowish (maybe best to check with Paul on that spec, I'm going by memory here) but workable (under 50k ohm would definitely pose some issues). I prefer at least 100k ohm. However, I did use a passive preamp with my D-225 for quite some time with no problem whatsoever.
Anthony, I'm not sure if you would know this, but if a CD player can be switched for output level (The EMM Labs can be switched between 2v and 3.9v)is there any theoretical reason why one should sound better or different, assuming 2v plays loud enough? I imagine based on Ralph K's comments to you on "opening" up an attenuator, you would be better off with the lower voltage - though I'm not sure if Ralph's comments apply to the LS as I think it has the same input and output impedances at all volume levels (I think).
Paul,

To me, if 2V plays loud enough then go with the lower of the two voltages. Why use a jackhammer to drive a nail. 2V was plenty for the RM-10, Auricle Music Blocs, and S-30, and the S-30 had nearly 3 times the sensitivity rating as the other two amps.

I was under the impression the output impedance did vary on the Lightspeed. If it doesn't, that is another significant benefit versus other passive designs.

George?
Correct me if I am wrong. I understand that in applying attenuation to the input signal, the Lightspeed or any passive converts the extra voltage to current and lowers the output impedance, both of which help to drive the amplifier effectively. That may be the reason why 3.9V is preferred over 2V - to achieve the extra headroom?
Interesting point, I'd be interested in someone confirming that.
Maybe it is the input impedance of the LS that is constant? I've confused myself (again).
Wow busy while I was asleep.
Pubul57
Anthony, I'm not sure if you would know this, but if a CD player can be switched for output level (The EMM Labs can be switched between 2v and 3.9v)is there any theoretical reason why one should sound better or different, assuming 2v plays loud enough?Pubul57

You have to watch this one, if it changes the gain via the feedback network of the output stage opamp/amplifier then all will remain the same output impedance wise.
But if the highest output of 3'9v may have say have an output impedance of 100ohms then when you push the switch for 2v this could just introduce a simple voltage divider into the output circuit, which is a series & a shunt resistor this then will change the output impedance of the of the unit from the original 100ohms to whatever the series resisitor is of that voltage divider, it may 1000ohms.
Cheers George
Grannyring
Ok, one last question. If I run my CD player right into my amps, won't that damage the amps or speakers? When this is done will my system play at full volume? Half volume? I can't image playing at full volume as I never go past 1/3 or so right now - to loud!Grannyring

This is why you MUST pick a known quite starting CD like the lead in for an orchestral piece so you can gauge the level. This is a test to show you what the source (CDP) without preamp colourations/distortions sounds like.
You don't hope into a Ferrari for the first time and put the peddle to the floor, you would do it gently at first, then kill yourself when the testosterone takes over.
Cheers George
Hey Milpai'

you stated: "any passive converts the extra voltage to current"

This is true for inductive based units. Resistive based passives turn the extra voltage into heat.

dave