I think Uriah, just sells kits, no? |
One type of passive I have not tried are the EVS and Endler types. While I get the idea behind why the LSA without contacts would be beneficial, it also seems that EVS/Endler approach might have some theoretical advantage, no worries about IC capacitance, no IC, two less IC RCA connections and I think EVS uses a single Vishay nude in the signal path. Any experience with these? Head-to-head with LSA? |
At one time I had the EVS and Endler attenuators. I preferred the EVS and still have them. They still use an Elma switch and I think it's a shunt to ground design. I might be wrong about that though. It does eliminate the extra set of interconnects but it doesn't sound better than the LSA. |
Pubul57 - Uriah selll kits and finished products as per his website.
anyone tried his Lightspeed product and how it dffers from George's? |
Unless I am missing something, it seems he builds the kit, but you are still required to do the install into a chassis - no? Can you tell me what changes, if any, he has done to the LSA recipe? It does look interesting, other then I am a klutz with any element of DIY. |
Hi Paul, I can answer a few points for you.
1: Nobody as far as I know uses the NSL32SR2S "S" donates selected versions of the NSL32SR2 which are far more uniform and far more expensive.
2: As far as I know nobody does matched quad sets, as this is exponentially harder to do than matched pairs, matched quads gives far better min volume level, a better logarithmic feel when in use, and more stable i/o impedances.
3: All the NSL's need to be potted together for balance stability, this is not mentioned at all with the others.
4: Some of the others, especially the ones from Asia are using a fixed series resistor (instead of a NSL) with only one NSL shunted to ground, this was my first MkI version and though still better than any volume potentiomer (pot) was clearly bettered with the MkII version which was a quad matched sets, all my MkI's were recalled 5 years ago and converted to MkII's because they clearly sounded better.
Cheers George |
Thank you George, it did not seem Uriah was doing doing the same thing, and set himself up to try to provide the DIY community with parts to build their own Lightspeed-inspired derivatives - which I imagine can sound quite good in the right setting. While appreciate the buffer, remote, and switching approaches that others have tried to add, I suspect you only really get the uncompromised LSA (sorry, we do that here) sounds used as you have designed it in a system with the right source and amp requirements - the rest come at a sonic cost I'm not willing to pay. But if I found a remote controlled, buffered preamp with multiple inputs, preferably RCA and Balanced that sounded as good as the LSA, I would buy it, but I have not found it yet. |
...though teak would be nice:) |
Teak does not shield against rf, it maybe a step forward in glitz, but a step backward in sound quality.
One day I may do a remote and have a retrofit scheme for present Lightspeed Attenuators, but it would have to be a quality one, not those chintzy Chinese made ones that people are using that would come back and bite me in warranty claims.
Cheers George |
I've been playing around with interconnects and note that the LSA really responds to changes. I was having the LSA drive a 12 foot run of blue jeans cable into my rm10 amp. Sounded good to me...until I moved some stuff around which allowed me to put in a 3 foot cable I had. Much, much better--I'm pretty satisfied with them in fact. However, I can't leave my equipment as it is, so decided to buy a 6 foot (the shortest I can use if I leave my rack where it is) Mogami 2534 cables. Not good. The mogamis are supposed to have low capacitance, so I'm wondering what the issue is.
What cables are people using with the LSA? I'm cheap, so nothing over $350. Also, have people noted the differences in sound depending on length? I can't imagine the 3 foot cable I used is better constructed than the mogamis (although they do have nice locking terminations) so I infer it must be the length that's the culprit.
I'm thinking about trying the Tempo Electric silver cables. Any comments on those?
Another point to note is the following. I bought a 2 foot Soundsilver cable (gold and silver) to connect my source to the LSA. I noted that it sounds much better using itthat way than using it to connect LSA to amp. I would have thought my cd player could easily drive a longer cable and the that the LSA would benefit from driving the shortest length, but that turns out not to be the case for me. Why? |
I must admit that difference between cables simply don't jump out at me - though I did buy Cardas GR just because it is often recommnded with my speakers (Merlin VSMs) - I do know they are about the lowest capacitance cable on the market (12pf/ft) so I suspect that helps with the LSA. I tried a 1m and 2m connection between pre and amp and it was simply much too difficult to indentify any difference - so I stopped trying. The only IC rule of thumb that seems to matter is short/low capacitance and you should be alright with most cables with good connectors. Can you hear a difference between 6ft - 3ft - 2ft - I don't think so - at least I can't. |
I'm not at all a 'cable guy'. It would please me no end if I couldn't hear significant and pleasure undermining differences between cables. FWIW, I'm just listening for musicality, whether my reference recordings draw me in more with one set of cables over another. I was very surprised to find that I could detect a difference.
I don't know if it's the differences in length of the cables that I'm hearing or differences in the variances in construction. I don't have the same cables in varying lengths to test that. Incidentally, the blues jeans have low capacitance of 12.2pF/feet--that's why I bought them in the first place. I auditioned a 5 foot pair of magnet wire interconnects last weekend. Too lean; the harmonic richness in my Johnny Cash cd's were almost entirely missing. |
Hi guys, interconnect cables can be a mine field, not just with the Lightspeed Attenuator but with all forms of audio gear.
Cables can form a hi frequency filters with their capacitance (pf picofarad)) when combined with the input impedance or output resistances of sources and loads, as can output/input coupling capacitors of some sources and amps, they can create a low frequency filters with the load of the next stage/s. Then there's the inductances and resistances of cables which can also form filters (hf, lf, even band pass) of some description.
A good general rule I find is to have direct coupled outputs (no Caps) on sources you own, and direct coupled inputs on the poweramps you own, and to keep interconnects as short as possible (even if it means reconfiguring the system) and to get ones that have low capacitance less than 100pf per foot.
Cheers George |
Banquo363, sent you an email.
Not sure why the Mogami didn't work out for you. It is one of two types of interconnects I use with the LSA, and as you know I also have the RM-10 MkII.
In reality, the Blue Jeans cable should have been the problematic one. Anything over 2m is definitely pushing it with the LSA.
One other note, use shielded or cables that use good noise rejection designs (ex. Litz). Seems to work better than unshielded by my own personal tests and I think George has recommended shielded cables as well. |
05-31-11: Georgelofi
... Keep interconnects as short as possible (even if it means reconfiguring the system) and to get ones that have low capacitance less than 100pf per foot. George, is that what you really meant to say? I would not consider interconnect cable capacitance that approached 100pf/ft to be anywhere near being "low." For instance, just 6 feet of 100pf/ft cable would have a capacitive reactance at 20kHz of about 13.3K, certainly low enough to be significant in relation to the output impedance of your LSA, which is around 7K iirc. Best regards, -- Al |
Yup, and well above the 12pf/ft of the Cardas, which is why I probably heard no difference between the 3ft and 6ft versions, and as Clio9 mentions, they are of course superduperlitz:) |
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 |
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 |
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. |
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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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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 :-):-) |
King, can you post a link to the review? |
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? |
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. |
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. |
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 |
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. |
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. |
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. |
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. |
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. |
How do you get music for the Otari? PM me, sounds interesting! |
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 |
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. |
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 |
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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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 |
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? ;) |
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 |
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! |
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. |
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 |
Dave,
MKII LSA in a true differential balance circuit topology...
Balanced LDR preamp -- great suggestion, Clio09 :-)
Vbr,
Sam
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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. |
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. |
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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"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? |
