I just got through reading Sam's Space in the October issue of Stereophile and have to give the old boy for nailing why this thread really says the same thing over and over again and gets no were really at all.
Tellig has really changed his position that the best preamp in no preamp at all. Remember, he gave great praise to the LSA, yet comes to the conclusion that it ultimately leaves something out of the music that only an active preamp can provide in most systems.
Now, Paul would call this either a pleasant added distortion or it just is some euphonic change that gets in the way of the "pure signal", yet when I asked him way he uses some of the most "colored" IC's and speaker wires to muck up this "pure signal" coming from the LSA in his system he never did answer that question. This total thread, besides being a free advertisement/promotion of George's product, is techno-babble going over and over why the purity of the LSA or passives in general is objectively the only way to reach the truth of the music, and any active preamp just an out dated expensive waste of years gone by.
I totally accept that many passives including the LSA offer great performance for the price, but to say that they are on the same sonic level as world class reference active linestages for some factual/objective scientific reasons is just a realization regarding what is personal taste and system synergy in different systems for different people.
So, Sam just flipped from no preamp is the best preamp to why many music listeners would still invest their money in an excellent active linestage really shows why this thread is really a discussion that is a closed circle of logic developed by true believers regarding the LSA and passives in general. Take a look at Tellig's piece and tell me what you think. |
Oh, and Miguel, beautiful system! |
"I can hear the input/output wire flavor of its internal wiring." Now that is pure, imagine the effect of all the wiring, capacitors, resistors, and solder points in a complex, two-box, mega-weight preamp -- might obscure the sound of the internal wire. I find some Jamesons also changes the LSA's voicing - a ver yrevelaing device. |
The LSA has its own sonic signature in my system. I can hear the input/output wire flavor of its internal wiring. Grounding the unit also changes its voicing. |
As a photographer, I always preferred working with black and white film. Simpler, easier to develop, and the end results always seemed to stand out better than equivalent color shots. |
And to put it in $$$ perspective, we are talking about a $450 product up against cost no object active which can run into 5 figures..... given that, I know where the frugal audiophile has to head; a passive, and none better than the LSA in my experience. |
What puzzles me, is what it is that causes very seasoned experienced listeners to find active line stages give them something, that I don't quite feel comfortable saying is simply pleasant distortion, though that might be what it is, that leads them to prefer an active line stage no matter how expensive, when it seems so clear that a straight connection between source and amp has to be about as pure and clean as the chain can be, assuming no problems with impedance, gain, or "controlling" the interconnects. I don't know what to make of it, other than they have problems with one of those 3 elements, or they simply like what an added coloration does for them - but I don't question their preference, it is what it is. |
It actually only becomes a gain reducer when the input impedance of the poweramp is lower than the output impedance of the preamp.
Cheers George |
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Paul, think of it this way, you have 4 lanes of peak hour traffic coming into two different cities, one of the cities has a bridge that can take all 4 lanes into that city without any speed reduction to the cars,. the other one has less lanes on the bridge therefore the cars have to file over the bridge at slower speed than they approached it at.
Same thing happens to electrons,the bridge/input impedance compresses the music to get it through. This happens every where in the audio chain, from cartridge to phono stage, from phono stage to preamp, from preamp to poweramp, and the big one from poweramp to speakers.
Cheers George |
I am a little confused - the compression is an impedance issue, not a gain issue? |
The long answer is yes, you can get a slight compression with the Lightspeed Attenuator if the input impedance of the poweramp is below the industry standard of 47k ie: 5k to 30k, because it will be being slightly loaded down.
If it is at or above 47k, the standard Lightspeed Attenuator WILL actually give 100% of the dynamics the source is producing, because there are no active components in the signal path, and it is not being loaded down.
All active components have a limit to be able to try to pass 100% of the dynamic input through their circuitry, this is why they all have specs that will never show "dynamic range"=unlimited. Or signal to noise = unlimited
Except if it is a purpose built dynamic range expander like the old DBX 118, but you would not want one of these in a high end audio setup, they sound disgusting.
Cheers George |
The short answer to your question is yes. |
Does lack of "gain" have anything to do with the claim some make that passive are not as dynamic as actives (lifeless, dull)? That us not my experience, but I assume it is true for some in their systems; so, is that attributable to gain or something that would account for this fairly frequent criticism of passives? |
Perhaps Dave's approach using an existing balanced active circuit and substituting the LDR attenuator into it is the closest we can get. Combining the LDR technology with active balanced circuits offers relief from the usual SE vs. balanced, passive vs. active debate. Some proponents of Lightspeed tend to dismiss balanced circuits altogether. Personally I am a balanced guy from phono coil all through system to amplifier output, and am not ready to give this up. I like what I'm hearing :-) / reading! -Sam |
I can see the point regarding complications of adding an input buffer to the circuit of an active preamp. It certainly moves away from my simpler is better philosophy. However, I was more curious about adding this type of volume control, or more accurately, attenuator, to the Burson AB160 XLR buffer itself.
I run an Atma-Sphere S-30 in one of my systems and currently am using a Resolution Audio Cantata CD/USB source and running it direct into the S-30 via it's own buffered balanced outputs and using its analog volume control. I also run my Otari MX 5050 with volume control direct into the S-30, just swapping cables when I want to swap sources. I can certainly hear the benefit of a balanced set-up in this case.
I do feel though that I would like to extend this system to add something in the middle that might provide the opportunity to take advantage of a balanced phono stage. One option I'm considering is the Atma-Sphere MP-3, which can be configured as a buffer. However, I'm open to other suggestions as well, including a modification to the MP-3 taking advantage of an LDR volume control. |
"A respected designer of $15K active preamps recently opined to me that approaching SOTA, the quality of the volume control accounts for 85% of the performance of an active preamp."
Very telling.
Does "gain" have anything to do with the claim some make that passive are not as dynamic? or, if true to the experience in some systems, is that attributable to something other than gain? |
Indeed adding a buffer stage to an active preamp at input to the volume control allows the LDR to operate within its more linear range below 10K impedance. However in a balanced mode there is no escaping imperfect common-mode noise rejection if using LDRs in the Mk II switched ladder arrangement. However carefully the LDRs are matched, they always deviate from each other by at least 5%-- not close enough for optimal balanced operation. On the other hand, the simpler Mk I configuration ensures perfect CMRR-- provided that the shunt LDR is located between phase and anti-phase and not between each signal phase and ground.
Any active tube preamp has at least several fixed resistors in signal path in addition to the volume control. Provided that the preamp can tolerate a shunt volume control, I can't imagine that one LDR more or less in place of one of many fixed resistors in signal path will matter much. Moreover, adding an input buffer just adds more components in the signal path and may thus introduce as many problems as it solves.
I think this is an interesting development in the discussion. Combining the LDR technology with active balanced circuits offers relief from the usual SE vs. balanced, passive vs. active debate. Some proponents of Lightspeed tend to dismiss balanced circuits altogether. Personally I am a balanced guy from phono coil all through system to amplifier output, and am not ready to give this up. Moveover, adapting the Lightspeed to a high impedance phono stage source, presents further challenges a passive. IMO it's preferable to be able to combine these all these design constructs with minimal compromise, rather than to insist upon a purist approach that mandates exclusion of a particular construct.
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Well it might be a great suggestion but in the MkII version it appears to be somewhat impractical according to George. IIRC the single ended version of the LSA uses 4 matched LDR modules. In balanced mode it would be 8. It's difficult enough to find a lot of 4 tightly matched, to find 8 would be much more difficult. In addition George feels the reliability suffers. I have the schematic George provided for the balanced version. Just don't think it would be worth building. Perhaps Dave's approach using an existing balanced active circuit and substituting the LDR attenuator into it is the closest we can get.
I'm curious though, Burson makes a balanced active buffer, but sans a volume control (unlike their single ended version). Wondering what possibilities exist to take Dave's approach and apply it to the Burson. Could be interesting if it can be done. |
George, given the non-linearity of LDRs at high impedances, I don't think that it is practical to adapt your Mk II approach to a high-impedance volume control for an active preamp, whether balanced or single-ended. The Mk I approach with fixed series resistor and variable shunt LDR, may be the best that can be done in this regard. If the system is sensitive enough that in normal use the volume control is operated in the region between say -25db and full attenuation, then the Mk I approach will present a stable & benign input impedance similar to a traditional switched ladder.
A respected designer of $15K active preamps recently opined to me that approaching SOTA, the quality of the volume control accounts for 85% of the performance of an active preamp. If one is committed to an active preamp, it's nice that a few hundred dollars and some relatively simple DIY gets the job done with LDRs.
Clio09, my delay was due to the nagging fear that the failure of an LDR shunt LED will take the preamp to full volume, with disasterous conseqences downstream. A simple insurance bet is to parallel the LDR shunt with a fixed resistor, whose value is chosen to put a brake on max volume.
To control the LDR LED segments, I use a 500K dual log pot as a master volume control for coarse adjustment, and a 50K log pot on each channel to trim balance. The LEDs are powered 5V by a Twisted Pear Placid current-shunt regulator kit. This set to pass 10ma to each LED. |
Dave,
MKII LSA in a true differential balance circuit topology...
Balanced LDR preamp -- great suggestion, Clio09 :-)
Vbr,
Sam
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Dave is using it the way the first Mk1 Lightspeed Attenuator was designed. This is a series resistor with an ldr for the variable shunt to ground. This is still better than any potentiometer, but when I compared it to the MkII Lightspeed Attenuator which is series LDR and shunt LDR exponentially harder and costlier to make, it was clearly another step up in sound quality and usability, so much so that I recalled all the Mk1's and they were all converted over to MkII status, and all the owners were amazed at the difference. It was more dynamic, punchier in the bottom end and a more transparent sound stage, also the min volume went down closer to zero, and it had more stable i/o impedances at different settings. Dave you should try to make a MKII you will be very pleased with the difference again.
Cheers George |
Dgarretson - So you finally were able to get it done. I had recalled earlier you were attempting this. I take it the Shallco is the one used in the MP-1 and that is now replaced by the LDR? If you can provide some more details on how you did this I would appreciate it. I've always been interested in building a balanced LDR preamp, but George has always recommended to proceed with caution on that front and I understand his reasons why. |
Thinking about those DartTZeel and Constellation preamps with LDR volume controls, I just replaced a four-deck Shallco series resistive attenuator in a differentially balanced tube preamp, with a 100K impedance LDR volume control. This is a relatively simple series/shunt arrangement, with fixed series resistors and a single LDR per channel as a variable shunt between phase and anti-phase of the balanced signal. One nice thing is that if limited to use as a shunt, the LDR only needs to operate through a range of 35R-10K ohms or thereabouts(similar to the range used in a passive) to provide a wide range of attenuation down to -70db in a 100K attenuator. It's still breaking in, but so far it's clear that an LDR volume control is superb. Thanks to George for popularizing their use! |
Clio09: What exactly is an array of 48 optically controlled resistors and why can't my LSA have this feature? ;)Clio09
Not too sure Tony, could be 48 1% trimming resistors to go with the quad unmatched ldr's, which in my opinion would detract from just a quad matched set, as the i/o impedances for both channels would not remain constant, and there would be another component in the signal path.
Or it could be 48 x ldr's in some paralleled setup for series and shunt ldr's, again this would detract from a simple matched quad set. Or it could be a 48 position switched volume control instead of continuous rotary pot with a quad matched set, this would then sound the same as my production Lightspeed Attenuator.
Cheers George |
Optically controlled resistors for volume control.
Instead of using a potentiometer to perform volume control within the circuit, we use an array of 48 optically controlled resistors. These resistors are controlled through a temperature-compensated tracking circuit that maintains ideal signal balance in all conditions. Because they are completely electrically isolated from the control circuits, the optically controlled resistors are as sonically benign as an ordinary resistor. See George, if you use fancy language like this you can get a lot more money for your Lightspeed. What exactly is an array of 48 optically controlled resistors and why can't my LSA have this feature? ;) |
An interesting little snippet for those of you who own or have built a Lightspeed Attenuator, this will give you maybe some bragging rights.
Not only does the $28k DarTZeel NHB 18-NS preamp have a form of Lightspeed Attenuator controlling the volume (which they tried to patent).
But now there is a new player on the block Constellation Audio with their $60k fet line stage preamp the Altair which also uses a Lightspeed Attenuator form of volume control. (at least they didn't try to patent it)
http://www.constellationaudio.com/ca/reference-series/altair/altair-features
Cheers George |
If you wish to see the measurments at CD playing levels, even better than what I said in the last post, I have posted the Silonex graph and an Audio Precision distortion measurement graph, by the measurers calculations is said to be .0025% only at cd levels.
http://www.diyaudio.com/forums/attachments/analog-line-level/232027d1311212462-lightspeed-attenuator-new-passive-preamp-silonex-ns32sr2s-distortion-measurments.jpg
Cheers George
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At line level, at 2vrms which a cdp hardly ever hits, even with peaks, you get .2% of 2nd harmonic which is pleasing to the ear, and as we know with tube amps this can be 10 x this figure.
All tech info/graphs and circuits can be found at this site http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp.html which is more for the diy'er in which I give all info on how to make one yourself, sounds as though you maybe capable, you should try it, and maybe be converted.
Even Nelson Pass has designed a buffer in this diy thread for the Lightspeed so it can drive his low input impedance amps which some are 20k and 10k.
It is a massive thread 100x more than this one with over 4,000 posts with some pretty knowledgeable tech guys giving their input for the diy'ers.
Cheers George |
George:
Interesting concept, but what about the distortion of these devices as shown in the Silonex data? .1% THD is not low these days, particularly if you listen to folks like Nelson Pass. I know you will say there are a lot of tube equipment that produces distortion higher than this that still sound great, but I still have a problem with a so called "passive" device having a non-linear distortion characteristic. A pot or switched attenuator will have nearly zero distortion.
Also have a bit of a problem with folks calling this a passive attenuator as it need a power supply to operate.
And the rectification process you describe may be occuring, but I have to ask if microsecond type transients are really audible. You will get the same artifacts by testing many types of solid state amps if you use the same storage scopes and look for micro-second transients on the leading/falling edges of square waves. Does not prove that these artifacts are audible, even if they are present. Still I applaud you for trying to find some explanation for the effect. I also wonder why you might think this is universal to switched resistor types, as these vary widely due to the relay contacts and rotary switches used in the designs. A switch or relay can have a much higher contact pressure than a pot.
Sorry if I have repeated subject matter previously covered, this was a mongo thread. |
07-09-11: Devilboy
George,I'm sure that the information I need is listed somewhere in the vast number of posts but could you please tell me what the ideal specs that the Lightspeed would work best in? What output voltage and output impedance of source would the Lightspeed like to receive and what input voltage sensitivity and input impedance of amp would the Lightspeed like to "see"? Again, sorry if I'm asking something that's been discussed previously. Best,Luka
Hi Luka, the Lightspeed will happily slot right into most systems, the only thing that is needed for it to give it's 100% performance is that:
1: The output impedance from your source (cdp, dac, phono stage, etc) should be 200ohms or less output impedance and 1v or more output, which most are.
2: The input impedance of your poweramp should be 47k or more, which most are, 47k being the industry standard.
3: The interconnects from the Lightspeed to the poweramp should be 1.5mts or less and of low capacitance (100pf per foot or less) which most good quality IC's are, this measurement is in the cables specs, if not the supplier/manufacturer should know this.
Cheers George |
How do you get music for the Otari? PM me, sounds interesting! |
My speakers are probably close to 95 dB sensitive even though they are listed at 92 dB. I think Duke is pretty conservative with the rating. Normally with amps that are closer to 1V I get to about 2 o'clock for normal listening. Less if the CD is hot, more if I'm playing vinyl. On the S-30 I get pretty close to 4 o'clock and with vinyl it's wide open, which according to Ralph is an ideal situation. Right now I use the LSA with the Music Reference EM-7 amps and I have a second set up using an Otari MX-5050 direct into the S-30. |
Anthony, you have pretty sensitive speakers, no? Might be a factor in the "gain factor". WIth the 89db Merlins, 2:00 is about as loud as I want to hear them with my 1v RM10 - 35 watts. |
Assuming all your ducks are in a row impedance wise and you use short low capacitance and shielded cables between the LSA and amp you should be quite pleased. |
Thanks Clio09. It's nice to know that you've had success with such a wide window of input sensitivity....makes my decision easier. There are a number of passives that I'm interested in but given the price of the Lightspeed and its overwhelming popularity, I think I might try it. |
The source should put out 2V or there about and less than 200 ohms output impedance. The amp should have an input impedance greater than 50k ohms.
As for sensitivity, I'm of the opinion that this is less of a factor. I've used the LSA with amps whose sensitivity ranged from .8V to 3V. Never had a problem. |
George,
I'm sure that the information I need is listed somewhere in the vast number of posts but could you please tell me what the ideal specs that the Lightspeed would work best in? What output voltage and output impedance of source would the Lightspeed like to receive and what input voltage sensitivity and input impedance of amp would the Lightspeed like to "see"?
Again, sorry if I'm asking something that's been discussed previously.
Best,
Luka |
Well at least MF is comparing it to something a bit closer in price. Then again MF liked the LSA too, just wasn't high enough in cost to get Class A rating. I'm sure he'd look pretty stupid to the industry if he said a $500 component was comparable to one that cost $26k, but wouldn't it be interesting if that is what he privately felt;)
From the information I saw on the Ypsilon PST-100TA preamp it has two operational modes, each with a 150 ohm output impedance. One operates in unity gain and the other 20 dB of gain due to a tube output stage IIRC. Leads me to believe this is an active preamp all around, but I could be wrong, just not that much information to go on. |
Tony, I only have a hard copy Stereophile sub and is in the current July issue. I've only skimped through MF review ... basically it best his reference, his darTZeel. |
Knghifi, you do have to wonder how much better it can possibly be (if it is) - you really have to wonder about this market place; who really buys this stuff? 10 people in the world? |
King, can you post a link to the review? |
Just read the review on the Ypsilon active and passive preamp. Anyone compared the passive one to a LSA? Only a $25,500 price difference :-):-) |
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Sorry, I should have made it more clear, it's not for more $'s. As it is I'm finding it increasingly harder to keep up supply. At it's current shipped pricing of $490usd it is only viable if the overheads are kept low as I have done, family based, with no outside employees or premises.
This would be more of a licensee/distributor to manufacture the Lightspeed Attenuator in the US for US customers only.
Cheers George |
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George, up to now you have distributed your product direct to consumer. What is the reasoning behind using a distributor? How does that affect the consumer? I understand that this is only a potential relationship, but since you mentioned it I feel you should disclose your intentions. |
Hi guys, I have a potential future CA distributor, who asked me about the comparison between the Lightspeed Attenuator and the Music First TVC, I remember someone did the comparison and it was very favourable for Lightspeed can anyone give the link to it for him?
Cheers George |
With the Lightspeeds output at worst 7k, this together with a 1mt cable with a max of 100pf per foot gives a -3db point at 75khz, which is plenty high enough and still higher than any cdp noise filtering.
Cheers George |
