I find the sonic personality of different microphones to be stunning. Not sure if it was HP or Atkinson, but it was a demo of the same music/location played through a series of mircophones - the soundscape sounded completely differrent and completely out of our control.
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.
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.
1,866 responses Add your response
I have just received some information regarding the output impedance of the Concert Fidelity CF-080 that should put the discussion to rest. According to the designer, the 33k ohm output impedance is an incorrect assumption. In addition to the tubes, the circuit design uses a capacitor and a resistor at the output to prevent harmful DC signal to be transmitted to the power amp. So the actual measured output impedance, which depends on the frequency of the CF-080, is between 5.2k ohms and 900 ohms as measured between various points within a frequency range of 20Hz to 20kHz. From this I would say that the CF-080 will match up just fine with most power amps out there. This includes the Concert Fidelity amps with 47k ohms input impedance. Not that this was ever in doubt from my perspective having heard the system multiple times and regarding it as one of the best I have heard. I fully trust this information as it came from the designer himself. As such I don't feel there should be further debate on the subject. |
And I assume Terry is using the XLR connection which is 30kohms on his amps input so it so match ok, assuming not too much time is spent at 5,2kohms. But this is theory and Terry is a pretty experienced listener, I have to assume the CF works very well in his system. Well, I guess that is enough on the CF sojourn.... |
I take what you've found out onboard Tony. I can safely say a cap on the output will not change the output impedance of the tube in the audio band for the better (lower). And a resistor would also not change it for a lower impedance, only for higher impedance. So there is something else we don't know, if what you were told is "5.2k ohms and 900 ohms" As I find it very disconcerting that the output impedance has not been included in the specs or design on the website. As just one of a few of the tube gurus I queried about cascode output said. And they all say basically the same thing. Quote" If you want 6 or 12dB gain, you don't use a cascode. If you want lowish output impedance, you don't use a cascode. (NB. in a preamp you will want low output impedance, unless you are incompetent). If you are serious about valves, you don't hang them out horizontally at the back of the chassis, even with fancy roll-bars. This is asking for poor contact as the valve slowly drops out of the socket.Quote" Cheers George |
Well Tony, You just got a taste of what I keep referring to as George's arrogant know it all attitude, this time towards a gentlemen we both respect, Mr. Masa Tsuda. The quote's from George's "tube gurus" particlarly the crack about, " you don't hang them horizontally at the back of the chassis" shows how ignorant he is about why Mr. Tsuda has them in that position to begin with. And this is the guy you would want to hang out with and enjoy his company? Well, let's see what your going to do now. Come up with another excuse or rationalization for George's put down of someone you know is a brilliant designer, builder and your friend or finally stand up to this know it all who's full of himself. |
You have no constructive critisism Teajay, all you try to do is to get this thread shut down with your personal attack. Not once have I attacked you personally just questioned the Ohms Law compatibility of components in your system that have not been properly addressed in the specs they have presented, and the voodoo that surrounds them. |
George, is the diode effect measureable? What does it do of rather what does it distort? Paul asked the million dollar question above: what are the effects of gain? Does it produce distortion? I did try the LSA with a SS amp (TRL Samsons) with 68K input impedance and the sound staging flattened. I have experienced the same thing when running the amps directly with my source. What is this about George? |
09-21-11: Agear: 1:George, is the diode effect measurable? What does it do of rather what does it distort? 2: Paul asked the million dollar question above: what are the effects of gain? Does it produce distortion? 3: I did try the LSA with a SS amp (TRL Samsons) with 68K input impedance and the sound staging flattened. I have experienced the same thing when running the amps directly with my source. What is this about George?:Agear 1: Diode effect is the very lightweight pin point touch contact of the metal wiper in a volume control on the resistive track in any volume control, and also on some switches, this creates the diode effect, which has a rectifying (change ac to dc)effect on the ac music signal trying to pass through it. Even Hervé Delétraz of the Dartzeel NHB-18ns also acknowledges it half way down the page here and he also uses the Lightspeed volume control in this preamp to eliminate it. http://www.stereophile.com/content/dartzeel-nhb-18ns-preamplifier-page-2 2: All active circuits produce distortion/colouration whether they have no gain or unity gain. 3:By going directly from your source to your poweramps you are not adding or subtracting anything to that source. The perfect "mythical" active preamp is "a straight wire with or without gain", it doesn't exist. If you insert a preamp that sounds different/better to your ears to this, you are introducing either a coloration or distortion that you prefer, which is a band aid fix, you should have a source that does not have to have this expensive band aid fix. Cheers George |
Hi Charles1dad, Thanks for your comment. Really like the "pompous windbag" description about good old George! Mr. Tsuda is not only one of the highest regarded designers and builders of Japan, but is a total gentlemen on a personal level. I'm still waiting for what Tony's response is going to be to George's condescending remarks about Mr. Tsuda and the CF-080 preamp. I know that you have a friendship with him and great regard for this preamp, so what's your position now? Let us know. |
Hi Unsound, On a post by Grannyring a few days ago on this thread he paraphrased the esscence of George's position. Anyone not in agreement with either his theoretical prespective or did not think his LSA sounded better then any passive or active linestage, if certain impedance conditions were meet, were the following: 1) Have a tin ear 2) like distortion. 3) in it for the money only 4)LSA is the absolutely the standard. If these don't come across as putting anyone down who disagrees with him, I would like your assumption regarding the nature of his remarks. Specifically, his remarks towards Mr. Tsuda that he gathered from his anonymous "tube gurus" that, "if you are serious about valves" you would never use them like Mr. Tsuda does in his CF-080 preamp implies that this world renowned designer is an idiot for not agreeing with good old George's " tube gurus". One of the oldest forms of knavery in a debate is to share very nasty implied information by saying that it was proposed by someone else, not the speaker, to get the dig in and than avoid the heat from the audience. I doubt if good old George would even discuss this with anyone, why should he, he already knows everything about any design flaw in any preamp in the world, which means if its not his LSA its inferior and a waste of money and time. |
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Unsound, I don`t believe Mr.Tsuda, Nelson Pass, Kevin Hayes(VAC) Israel Blume(coincident) just to name a few very accomplished designers of active linestages would come on a public forum and mock/dismiss someone else`s work. There`s such a thing as decorum, class and restraint that would prevent them from such smug and arrogant behavior. I`m sure these men believe in their ideas and products as much as george. I don`t believe they would put down those who after auditioning their components and then decidimg to choose another brand,they would`nt blame the listener`s system or attribute it to an inability to hear(the epitome of patronizing attitude). Following this thread for a while, my take is that for some the Lightspeed will be ideal and make them very content. Those who have taken the time and effort to audition this component and then selected something more to their liking don`t need to be subjected to, well you just prefer distortion and colorations. Utter nonsense. |
Why is a preference for distortion and/or coloration utter nonsense? What is wrong with prefering it. Distortion is measureable, not a subjective gremlin, what if you also happen to like the the piece with more distortion? How many folks have loved CJ equipment over the years knowing full well it was colored, but in a very satisfying way. What I do suspect is that the signal from the source output is closer to the signal coming from the LSA output than if the signal must go through an active linestage. One might differ on whether this is what we should want, or what we should prefer, but I think (not 100% sure) that this would be measurably the fact of the matter, measurably truer to the source (meaning the CD player output, not the live performance). If the active linestage alters the relationship between the two (source ouput/preamp output) it is inarguably a distortion (and not true or part of what is exist in the signal at the source output connection) -- which you might very well prefer. Carver's Hologram generator sure did unflatten a soundstage, but it was no part the recording, it was an effect, an artifact created by altering the source signal and delivering something different to the amp. And it may be lovely, enjoyable, pleasant, wondeful, magical, mysterious, etc. - but whatever it is, I just don't see how it can be said to true to the source, true in a measureable and meaningful way - assuming what we measure is relevant. |
George, You, I, and your tube gurus will just have to agree to disagree on this one. I think there could be more to this than we know and if so it may give you and some of the tube gurus the information needed to fully understand the circuit design. However, I'm not going to waste Masa Tsuda's time on this any longer given that he is not prone to be part of a public debate. Suffice it to say as I have stated before I believe Masa Tsuda's specifications for output impedance and can verify that from my own personal use of the CF-080 the tube sockets hold the tube pins tightly and there is no reason for concern that they would fall out. The purpose of the roll bars is to protect the tubes from being banged up against something. I consider both you and Masa very competent designers who have different approaches to achieving specified goals for your respective products. Each of you also have very different personalities. Like I said in a previous thread, what we probably have is a failure to communicate. It's obvious your personality rubs some people the wrong way. For me, that is not an issue, I can handle that. Others, well we know how they react. I agree that one in particular would like to see this thread go away and their behavior shows it. Enough said on that subject. You have been very generous with sharing your ideas and helping people like me learn about a new product that has enhanced my system. Masa Tsuda has done that as well, and in the process become a friend. Like I also said before, if I ever get down under I would certainly enjoy quaffing a few beers with you. Let's get this thread back on course and continue the discussion on the LSA. Also I'd like to discuss this Warpspeed if you are inclined. Seems like another interesting approach. |
Agears I hope I did not say mine was better than yours. Even musicians don't agree on sound. But that it is my perspective. I haven't even speculated in this thread as to the reason why, I think I know the simple answer, it is the 'why' in every other situation that causes something to be closest to the original. Anyway I thought my perspective would help someone looking at this thread or LSA for a view. I appreciate others view. We can learn something if we contribute. So George, Pub, Clio09, Atmasphere, Fiddler, Tvad, Grannyring and others thank you for some good information. |
For those interested in the Warpspeed: http://www.diyaudio.com/forums/vendors-bazaar/176847-warpspeed-optocoupler-volume-control.html http://www.diyaudio.com/forums/swap-meet/178839-warpspeed-optocoupler-volume-control-kit.html Would love to get George's take on this as it seems to be a different approach. |
Regarding the question on the diode effect. For those that missed it or don't recall it George explains it as follows: The (diode thingy) "diode effect" is bought around by very fast music transients from the source, CDP or phono, which can be in the order of 100's of volts per micro seconds (volts per uS) these happen as the name implies in micro seconds. The diode effect that George references and that the LSA eliminates is clearly something designers of some well known preamps understand and can hear. Here is a quote from one: Having done some audition in this regard (we 'switched', if you will pardon the pun, to our custom Shallco part about 15 years ago as a result of some of these auditions), the difference in contacts that George is describing above is clearly audible. FWIW - The custom Shallco switch referenced above is used in his top of the line preamp that uses gold contacts, with a double-spring-loaded wiper. Highly superior and much more costly compared to other switches. The designer also had this to say about the LSA: I had the opportunity to compare the Lightspeed against one of our own preamps and I have to say it was the most neutral passive I have heard. Anybody want to take a guess at who it is? I doubt anyone will question his knowledge on the subject. |
I for one would love to see this thread die already. I've followed it on and off from the sidelines for the last 15 months and for the most part it's little more than a three way conversation among like minded audiophiles... At one point I even suggested to George that he start his own forum, but as he said it would distract him from surfing. cool. Here's my take, if anyone cares. Even if the LSA is the best, I'll never buy it. It's just to restricting in the real word. I need the flexibility offered by full function preamps, both tube and passives. I've lived for years with a John Chapman, Bent Audio NOH. It's a passive similar to the Music First and based on the same S&B transformers. (Mine are copper.). It has 4 sets of RCA inputs and 2 xlr inputs, it outputs 2 sets of either single ended or balanced feeds, sports 6db of gain, has flooring grounds, etc.... I run 20 foot interconnects to mono blocks and a sub. Short interconnects and one input - no way. I've also lived with a great dual mono tube preamp that offers similar flexibility. I guess since this tread won't go away I will. |
That is precisely what I do when I am not interested in a thread, ignore it. BENT was good, LSA was better in my system. But it is true, the BENT offers much more flexibility, but that was not a priority for me with a single source and short IC to amp, if it were the BENT would be at the top of my list for a passive, especially the version with Slagle auto former, even better than the S&B, at least to my ears. At this point, while I love the LSA, what is interesting is the new approaches taken, especially as the DIY tinkering community pursues new forms of passive forms of attenuation. Though for ergonomics, ease of use, and input/output flexibility, the BENT was heck of an excellent passive preamp. |
Ok some normal hifi speak for a change, I never been a big fan of balanced as 90% of the time to make them balanced a lot of the equipment manufacturers just bundle in more opamps into the single path to make it balanced input or output, very few are true balanced and discrete all the way through, you need to see the circuit diagram to find this out. Even the advantage of it does nothing for me, it's just so I'd be able to run 20mt interconnects with good noise figures. In the end most hi end poweramps speaker outputs are + and ground, single ended again. I have tried doing balanced Lightspeeds quite a few times and even when double quad ldr's are matched perfectly they go out of calibration after just a few hours sometimes days because they are exponentially more critical to temp drift. And it is exponentially harder to match double mathed quads for balanced as it is single matched quads for single ended. It can be done with sensors that would measure a test tone before each listening session and then do an auto calibrate circuit, but that then takes them away from being a matched set with the same i/o impedances for each channel, they would get wildly different readings and therefore each channel will sound slightly different to the other at different levels. Or you could do a feedback type arrangement then your asking for more crap in the signal path and making them active and creating distortions /colourations. After one and a half year of developing Wapo seams to have hit a brick wall with his on diy, http://www.diyaudio.com/forums/analog-line-level/170381-precision-led-ldr-based-attenuator-15.html#post2687081 what I presented to them is the way it is, with development going back to 1974 in all sorts of formats, but they love to tinker, and good on them, this is how man reached the moon, but it's sad to see them as he said "This project has hit what appears to be an insurmountable brick wall." Cheers George |
Love the DIY community, unfortuantely, I can only be an observer:) What I found interesting at the start of the Warpspeed thread was the identification of a few "problems" with the LSA and attempt to improve upon the LSA: -the inability to adjust to complete silence -on low/high volume level settings, power levels on the LEDs endanger/shorten/toast the life out of the optocouplers -the need to improve the power delivery to the optocouplers -the need to improve on quality of the volume adjustment pot -the Lightspeed, simple as it is, still has a number of variables/design factors that affect performance How many of these are valid but not too relevant or important, valid and relevant but insurmontable due to a brick wall and sonic price to pay for addressing the issue, invalid (are the LEDs really in danger)? |
The (diode thingy) "diode effect" is bought around by very fast music transients from the source, CDP or phono, which can be in the order of 100's of volts per micro seconds (volts per uS) these happen as the name implies in micro seconds.While I have no reason to doubt the audibility of diode effects that may occur with many volume controls, I would respectfully point out that this explanation strikes me as fundamentally flawed. For line-level amplitudes, swings occurring at rates of 100's of volts per microsecond would represent spectral components (frequencies) at several tens of MHz. No source material and no source component will provide signal frequencies remotely approaching those rates. Not to mention that the amplifier, the speakers, and our ears would not respond to them even if they were somehow present. Regards, -- Al |
Thanks Al. Your elucidation of the "diode effect" was helpful and confirmed some of my suspicions. "All active circuits produce distortion/colouration whether they have no gain or unity gain." Can you be more specific? And what about amps? Do I need to revert back to the straight wire with gain? I have talked to two other designers of pre-amps who disagree with the fundamental premise behind the superiority of light-based volume controls. That does not make them right, but the gospel according to George is just that. Gospel to some and apocrypha to others. We need more detailed feedback from actual engineers who make this stuff. Things are much more complex than we want to admit. I know that is not going to happen for reasons stated above. If you were to rank system components in terms of importance, where would the volume control be? If this is a paradigm shift, it appears to be away from tubed pre + SS amps to passive pre + tube amps. The "distortion" remains. The villain has just changed clothes.... |
Not sure if diode effect theory drove George's design or the design was in search of a theory to explain its performance. It does seem he is doing something right, as others like Dartzeel deploy this approach in their active linestages where it serves as an attenuator in place of an ALPs, DACT, TKD, etc. |
09-21-11: Teajay Hi Unsound, One of the oldest forms of knavery in a debate is to share very nasty implied information by saying that it was proposed by someone else, not the speaker, to get the dig in and than avoid the heat from the audience. If a desinger is not using LDR, I would be surprised that they would argue for the superiority of LDR. Which does not mean the an LDR is better, but they would have little incentive to suggest that it is, even if it were. I'm glad Al joined in, I always learn something from him. |
I have talked to two other designers of pre-amps who disagree with the fundamental premise behind the superiority of light-based volume controls. That does not make them right, but the gospel according to George is just that. Gospel to some and apocrypha to others. I've talked to some notable designers as well, including Roger Modjeski, whose word I will take as Gospel on many topics, but not this one. Not that he was not correct on a generic level about issues with LDRs. These are things that have been said before by others more knowledgeable than most around here and can be referenced on the DIY site. So nothing new there. I think what many miss is what George does to eliminate the main criticism of LDRs which is the issue of drifting. It is said that when ones work is copied it should be considered a form of flattery. Obviously some serious preamp manufacturers have found enough in George's work to copy it. I trust he is flattered. Regarding the paradigm shift. I for one have tried both and prefer having tube amps to tube preamps (although I will be digressing a bit by the end of the year). In my conversations with some designers the indication was that active preamps are responsible for a larger source of the noise in ones system than amps (assumption is we are talking similar designed equipment). Case in point at least in my system and others that have allowed me to do this simple test. Using shorting plugs on the inputs of my amps I cannot hear any noise (with my ear to the drivers) coming from my Music Reference amps (both sets). With my Atma-Sphere amps I get a minute level of noise from the tweeter. Adding any passive preamp I own (a TVC and the LSA) to the chain and then shorting the inputs on the preamp the noise level does not change (regardless of volume level). I can't say that for active tubed preamps (mine and other's systems), especially those that use tubes. There have been cases as well with noisy amps when I have done these tests outside my system, so that just adds to the noise floor in most cases. Also, from the perspective of the preamp in the chain, I agree with Ralph and his opinions of the volume control. It is nearly always the weakest link in a preamp design and will be responsible for sound deterioration. The LSA and some other very expensive switches will eliminate or minimize this, but even in some expensive preamps you get nothing more than an Alps pot. |
09-22-11: Clio09Interesting, Anthony. I would add the thought, though, that the increase in noise that occurs with an active preamp could often be due in part to ground loop effects occurring between the active preamp and the amp, especially if the interface is unbalanced. To the extent that may be the case, a dilemma would arise, both philosophically and technically, as to which component is really responsible. Paul, thanks for your comment. Best regards, -- Al |
Agreed, Anthony. That certainly reinforces the meaningfulness of the experiments you cited. This Jensen paper may be of interest to others who are following this thread. It explains why unbalanced interfaces between components can be prone to both low frequency hum and high frequency buzz, resulting from ground loop effects. Best regards, -- Al |
Not helping anyone at this point Tony. Just curious. Do you have any current or planned business relationship with George? Teajay asked that of Paul above and it is logical to ask the same of you. I know you are now attempting to design and sell tube amps now. Correct? No LSA users with feedback on its performance with SS amplification? |
