You are right Pubul57, the momment you start to lower a digital based volume control, you start to whats called "bit strip" the name says it all, and this lowers the resoution. Aways leave it full up when using in conjuction whith the Lightspeed.
But also be carefull some dac's and cdp's have analog based volume controls and these are usually sub grade passive motorized or non-motorized on the output of the cdp or dac. Most times you have also fixed ouput rca's as well on these cdp/dac, always better going for it and a Lightspeed than the analog variable output. If there are no fixed ouput rca's, better to open it up and bypass the passive pots by taking them out of the output totaly.
Cheers George |
From what we have learnt and heard for myself, the only way to make all interconnects invisible (sound the same) with no sonic signature, is to have the poweramp input impedance at 1kohm or less, this then becomes a hard load for the pre to drive unless it has an output impedance of close to 1ohm and plenty of current behind it, something like the top Krell pre amps may be that low, then the pre itself has a sonic signature itself, so it's not an easy task.
Cheers George
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That is correct, buffers are there to drive long interconnects, and or low input impedance amps. There is no perfect buffer they all sound different As there is no perfect interconnect they all sound different, unless the amp is so low in input impedance then this puts all interconnects (within reason) on a level playing field
I keep comming back to this, plug the cd player straight into poweramp ( with more than 47kohms input impedance) with good quaity 1-2mt interconnects, this is the perfect transmission of the cd players sound (save for the interconnects signature), then put in the Lightspeed Attenuator without buffer and see how little it influences that sound compared to any other active pre or buffer.
Cheers George |
Hi fellow audiophiles, first off let me thank you Paul for starting up a Lightspeed Attenuator thread as writings about it were so scattered amongst the other non descript threads, it would have looked sus if I had started it.
I have a simple website at www.lightspeedattenuator.com and you can also access it via the Audiogon manufacturers listings.
If any of you would like a PDF sales/pricing/shipping brochure you can pm me via this forum with your email address and I will send it to you.
Cheers George |
For members who wish to know how I started the Lightspeed Attenuator project, a small portion of the history is available on this Audiogon post.
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1275616047
Cheers George |
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 |
I assume you are using the input that is full range not the one with the roll off at 70hz.
The diagram actually shows it's 27k input impedance this together with the 1uf coupling cap (yuck) gives a 5hz -3db roll off, the opamp is a 14watt chip amp that has an input impedance of 5megohm, you could change the 27k for 82k and you will see it will sound better. And go lower theoretically as the 82k resistor now with the 1uf coupling cap (yuck) will now go down to 2hz -3db but you will not hear this as the interstage transformer and output transformer cannot go down this far anyway.
But don't switch on the amp without the Lightspeed attached as that will let the chip amp see only the 82k resistor and chip amp may complain, when the Lightspeed is attached it sees the 7k odd of the Lightspeed and it will think everything is fine still.
Cheers George
by Georgelofi |
I much prefer direct coupling, I can hear coupling caps. But I do not think this circuit can be direct coupled as I think there is a high input offset from the chip amp, I could tell better if they gave a the internal circuit diagram to it, but they don't.
Cheers George |
The Morrison Elad is just a normal active preamp using normal pot and a 50 cent Analog Devices AD797 opamp with no gain.
It has nothing what so ever in similarity to the Lightspeed Attenuator and it has nothing what so ever to do with LDR's or LED's.
Cheers George |
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Faziod Hi you will hear very low level of music at minimum level as this is the characteristic of ldr's in this design is they can never go to complete darkness or infinite brightness as these are the controlling factors for resistance. Think of it as there is no such thing as infinite brightness or infinite darkness.
Cheers George |
Clio09
but the Noble pots, as good as Roger feels they are, will impart a sonic signature.Clio09
This is what I found, all have a sonic signature because of their very soft wiper contact, this has to be a very soft as not to wear out the resistive track it runs on when you raise the volume up and down. This soft contact behaves like a rectifier (diode) trying to convert some of the AC music signal into DC especially the faster transients and higher frequencies. This is why all pots sound different even switched resistor pots, all are a little different in this wiper pressure/material/ & and mechanics, none are perfect as a soldered resistor would be, which is what basically the Lightpseed Attenuator is.
TVC are better here as they do not have wipers, but their problems lay in the 500mts or so of very thin wire the signal has to pass through, this itself is a mine field of current limiting, capacitance & inductance all of which is harmful to the original source (CD DAC or Phono) signal.
The best sound you will get is to put your (CD DAC or Phono) directly into your power amps with a VERY quite CD track first, this is the most perfect "true to the source" sound you will get, and only the Lightspeed Attenuator is closest pre or passive to mimicking that sound.
Cheers George |
I would guess nearly 99% of good quality cdp dacs have an output voltage of 2v (Redbook Standard) or higher and an output impedance of 200ohms or lower.
Amps may have a input impedance of 47K (industry standard) or higher, nearly all tube amps are 100k or higher and an sensitivity of 1v or higher to clip.
So 2v feeding 1v to clip? no preamplfication needed here
200ohm or lower output into 47000ohm? no impedance mismatch here either.
So if a active preamp tube or transistor sounds better in the above "common" situation it is as Paul says giving the owner the tonal quality they want to hear (less bass more bass) you get the picture.
This however a band-aid fix for that system by throwing in a costly preamp to fix a system problem and at the same time missing out on all the transparency dynamics and sweetness that no active pre can give. Would it not be the wise thing to do and fix system imbalance (different interconnects speaker cable and positioning) problem instead of throwing a costly band-aid at it?
Cheers George
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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 |
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 |
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 |
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
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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 |
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 |
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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 |
You are right Paul, in some instances.
But in our case with the parameters I have outlined for the Lightspeed Attenuator, if you have a source that has low output impedance, less than 100ohm and 2v or more output voltage, and the power amp at more than 50kohms input impedance, there is absolutely no need for preamplification, (it's Ohms Law). No amount of extra current in the form of extra active current stages will have the desired effect of giving more drive and control, if fact the opposite could be had and heard, as well as a loss of transparency.
Cheers George |
Darkmoebius
As we all know, it is almost impossible to know which component is "true" and others are additive, or subtractive(except for truly bad components), unless one was present for the actual recording session. As to knowing what is the "true" amount of soundstage width or depth on a myriad of recordings, I think that would be an impossible task.
In reality, any preamplification is probably "truest" if it helps bring the listener a deep emotional connection to their music within the context of that listener's musical preferences and system/room acoustics. Nothing else should matter, in the end. Darkmoebius
Thought I'd chime in on this one being the manufacturer of the "Lightspeed Attenuator".
Hi Darkmoebius, welcome to the discussion, you used the magic word "truest" twice in the above reply. Having not yet heard one for yourself, can I make a suggestion to get the "truest" idea of what pre/amp passive or active is "truthful" to the original recording.
Plug your CD player or dac directly into your poweramp "this will be a perfect impedance match" As you have no volume control, first off play something that is low in level to gauge how loud it will be, doing this you are playing the "truest" form of cd/dac playback you can possibly get. Then slip the Lightspeed or any other pre active or passive back in adjust for the same level, and you will see and hear which one is "truest" to the source.
Cheers George |
09-09-10: Darkmoebius But, it did pose a problem playing vinyl w/ low output cartridges. I needed the extra gain of an active preamp or a phono pre with a lot more gain.
Darkmoebius
Strange? I have lots of Lightspeed Attenuator customers that use vinyl with low output moving coil cartriges, all they have is a good phono-stage like the Tom Evans and then Lightspeed Attenuator directly into their poweramps, and they are at 12o'clock on the Lightspeed for good loud level, with plenty headroom left in reserve, they say it the best they have ever heard their vinyl sound.
Cheers George |
Zendent7 Does anyone how where or how to buy this preamp. I have tried to contact the manufacturer using the email from their website, with the intention to purchase, but there has been no response. Zendent7
Zendent7 you can email me through the Audiogon Industry Directory
http://www.audiogon.com/cgi-bin/manu.pl?lightspeedatten&1&showmanu&Lightspeed+Attenuator+
Or the Lightspeed Attenuator website www.lightspeedattenuator.com
And I will send to you PDF pricing/shipping/sales brochures. And remember as says on the web site remove the spaces before and after @ on my email address
Cheers George
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Also Zendent7 I get about 50 Lighjtspeed inquiries per day, the only one I have had trouble sending to in the last week was this one if you are tag***@earthlink.net I cannot send anything to you, not even an email let alone a PDF as your provider earthlink is hell bent on blocking anyything, I've tried everything, it's so frustrating getting emails bounced back.
Cheers George |
Ooops! 50 per week
Cheers George |
06-19-10: Pubul57
With quality products like Supratek and Lightspeed coming from Australia/Australasia
For the amps list you should add: Halcro, Cymer, ME, Asaka, SGR, Redgum, Electra, Amber, Earl Weston, Aspen, Plinius (NZ), Perreaux (NZ, )
Just to name a couple
Cheers George |
Clipsal
I also would like to know the poweramp used in this shootout and also the CDP or DAC.
Cheers George |
About buffers, I will always say the best buffer is no buffer if your system meets the following impedance requirements. If your source output impedance is less than 200ohm and your poweramp input impedance is more than 47Kohm then the Lightspeed Attenuator is a shoe in, no buffer will sound better.
But if your source is more than 200ohms output impedance or the power amp is less than 47Kohm input impedance then you may (but not always) need a buffer, the best commercial buffer I've heard is the Burson Buffer. But the best sounding buffer is the (diy) Super Linear Cathode Follower (SLCF) buffer. But still they don't sound as good as NO buffer at all.
P.S. those who want the circuit of the SLCF send me an email
Cheers George |
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I also use a Lithium Ion rechargable sometimes, I hear a difference but cannot pinpoint what it is, even on a very hi rez system.
They say the Lithium Ion has the least chemical bubble noise of all batteries. Sometimes I forget which one I have on, the battery or the wall wart it's that close.
You can get these batteries on ebay from Asia for around $20 with international charger, do a search for Lithium Ion 12vdc rechargable usually made for cctv cameras were low noise is a must, just make sure it's center positive for all the production Lightspeed Attenuators I have made as I do not want to have to repair fried componets if I can help it. Yours Clio09 is the only one I think I made center negative I forget the reason why. They have about 12hrs constant use before a recharge of .5hr
Cheers Georgehifi |
The 0.25mV 103D into my phono pre+active stepup's 64dB gain yielded 0.4V, that just didn't cut it into either of my amps, especially the 1.5V monoblocks.
Looking at those measuremnts you should have had 2.65v output more than most cdp's.
You either have a fauty phono stage not giving 64db of gain, or the cartridge is faulty and not giving .25mv
Cheers George |
Agear hi your questions to me are answered here it's a big read, I started doing these some 30 years ago it was new then, I should have patent it, it is refined sonically to the max today, without being overly complex, and pricing kept low as possible.
http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp.html
www.lightspeedattenuator.com
Cheers George
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Agear and guys, let's get the name of the main devices inside the Lightspeed Attenuator correct, they are not solar cells, they are not optocouplers, they are LDR's (Light Dependent Resistors). These LDR's are made from (back in the old days) Cadmium Sulphide, which back in the 70's were almost impossible to match up for me, and were unreliable, I needed about 100 units to get 4 matched. Now the ones I use are made of something else they won't say what they keep it close to their chest, but it has enabled me to match 4 out of about 30 units and the reliability is no longer a factor.
Some of the "tech heads" are saying that it's the Cadmium Sulphide or whatever it is that these LDR's "Light Dependent Resistors" are made out of , is what makes the Lightspeed sound better than metal or carbon film resistors, this could have a slight bearing.
But you know what I believe and have seen if you read my explanation on DIY Forum or read my PDF broucher about "Dynamic Contact Bounce"
Cheers George |
1mt each each side of the Lightspeed Attenuator of Eichman Express Six unshielded.
I have found shielded cable a little constricted compared to unshielded of the same construction, I believe these days with CD high level output 2v there is no RF break-through any more. Shielded cable is just a hang-over from the low output mV phono days.
Cheers George |
For those who follow Stereophile, the Lightspeed Attenuator has made it into "Class B" Recommended Pre-Amps with a $$$ value tag in the October issue.
I received an anonymous email saying if your wondering why it didn't get into "Class A" just have a look, nothing below 10K, it will never happen.
Cheers George |
I could but instead of $450 it would end up costing $1450 and would then be no longer a "Stereophile $$$ value"
Quality remote, reciever, motorized pot, different power supplies and larger chassis.
Cheers George |
Dual L&R controls in every PDF broucher I send out, is the only option I do. It's a $30usd option, but I tell everyone who inquires about it they are not as user friendly as the single stereo pot. As for different cd level volume change, you have to get the balance right again.
Cheers George
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10-09-10: Grannyring
Quote>Perhaps the 2D forwardness speaks more to my system synergy then to anything else. This may well be the case as I have no way of really knowing.
What you should do Grannyring to see if the Dude is artificially giving depth, is what I preach all along, put your CDP straight into your poweramp (Bolero Test) no preamp. Put on a quite cd so you can then ascertain a good level of cd to play, then swap in the Lightspeed then your Dude and see which is closer to no preamp. The one that is, is the one that is truer to the source.
BTW the English and some Aussie speaker manufacturers back in the 70's & 80's use to purposely -3db the level of midrange units to give the illusion of greater 3D depth.
Cheers George |
Let's get this right!!!!
The Ravel's Bolero test is just a level test, that all, as it starts off very quite and builds slowly so you can gauge level when directly connecting CDP to poweramp, so you don't blow up your amp/speakers.
You can use any cd that starts off quietly, not just the Ravel's Bolero cd!!
Cheers George |
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Yes, Nelson Pass very kindly did get involved, and designed a nice direct coupled discrete (no yuk opamps) DIY buffer for the Lightspeed Attenuator, because some of his amps were 12k and 20k input impedance, and this made Lightspeed Attenuator match those low impedance amps correctly.
Cheers George |
Yes the Burson is also discrete but with +6db of gain, but not DIY, and Nelson's is unity gain and I would say more transparent.
As for running a single ended Lightspeed into a balanced amp, you could use something like these on the input of the Atma-Sphere's
www.jaycar.com.au/productResults.asp?keywords=rca+to+xlr&keyform=KEYWORD&SUBMIT.x=29&SUBMIT.y=7
Cheers George |
10-11-10: Agear
CDPs generally suck when driving amps directly due to a lack of current (not merely a function of output voltage as some have suggested above in this thread). Current, from my limited understanding, is needed to reproduce in particular lower frequency information. Agear
CDP's (not tube output ones) have lower output impedances and therefore and higher driving current ability into power amps than 99.9% of tube preamps.
Cheers George |
Well said Pubul57.
If I could just add to that, as I tell many customers, a direct connection between CDP (non tube) and Poweramp is the best/truest transfer of what is recorded on the disc. And the Lightspeed Attenuator comes the closest to that direct CDP (non tube) to poweramp connection.
If an active preamp sounds better than this, then it is the system that has a problem and needs the coulouration of the active preamp to band-aid fix that problem, it would be better to fix the problem than to cover it up.
Cheers George
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Just looked at the Merlin VMS impedance graph (Stereophile), at it shows it only drops (over a very narrow band)to a minimum of 6 ohms at around 170hz at 0 phase angle.
This is an easy to drive speaker and should be driven off the 8ohm tap. Buy driving of the 4ohm tap all you achieve is loss of power from the amp, vitually no gains whatsoever.
Cheers George |
You may find that the OTL's are getting loaded down some by the speakers and dropping their output requiring more push from the Lightspeed/CDP. The sensitivity of the OTL was probably judged/measured with an unloaded outputs.
Cheers George |
Sorry forgot the other part of your question, as for the position of your Lightspeed control, that's fine it's a good place to be, at around 2o'clock it really starts to increase/rampup the gain rapidly, so you have oodles of gain left.
Cheers George |
11-02-10: Pubul57
>But there is no output impedance optimization based on dial position 10-12-2 o'clock - is that right? Some attentuators seem to have optimal positions in that sense.<
Anywhere between minimum and 3-o'clock is good if i/o impedances are met. If it's after three o'clock for normal level listening in a system then (cdp/amp)has a gain shortage, or ridiculously inefficient speakers (80db or so).
I have a friend that has JBL4350's and Array 1400's and his 80watt Transcendent OTL monoblocks just have enough power driving the 4350's full range but the bass is seriously lacking, but they do sound good on just the upper bass, mids and tops. As for the 1400 Array's they can't even drive the mids and tops on those let alone the bass as well.
Cheers George |
Hi guys and Knghifi, glad your enjoying the Lightspeed Attenuator, you've put it up against a very expensive ($14,000) in the Vac Signature pre, I'm over the moon it held it's head up high against to it. One question Knghifi the poweramp TRL Samson you used for the comparison, it's a solid state amp and I have looked everywhere for it's input impedance and nowhere can I find it, as the Lightspeed Attenuator likes to see 47kohms or higher for the poweramp it's feeding. If the TRL is lower than this you have still not heard the Lightspeed at it's best, and heaven forbid it may beatout the VAC Signature if it sees an amp with the input at 47kohms or higher. Does anyone know the input impedance of the TRL Samson?
Cheers George |
It would be good for someone to grab an ohm-meter and measure the input terminals (Amp off naturally).
If it is bipolar transistor input you can bet you life it's going to be less than 47k.
If it's fet transistor input there's a chance it's 47k, maybe higher.
If there is no reading or wavering all over the place it has capacitor coupled input (yuck and double yuck)
Cheers George |
