I've never turned my volume past 12, and most often have it at 10. Both vinyl and CD. What is responsible for having to turn it to 2-3? My ear drums would rupture at those levels. |
What I find amusing are these threads where people complain they can't get past 9 o'clock on their volume control. They're looking for a way to get more control over the range. In some cases they end up buying Rothwell attenuators to get a 10db reduction that gets them to 10 o'clock instead.
Several posts above I quoted what Nelson Pass had to say about the psychological dimension to the perception of power and drive. Seems he figured it all out a while ago. |
sensitivity of amp, sensitivity of speakers, size of room, how loud you like it, and hearing acuity. now, if i switch the cd players gain to 4v, i never go above 12. |
WTF... Is all this about short single ended interconnects.
I'm running 6 meters (18 feet) of Crimson cable from my BENT NOH Passive to vintage VTL Compact 100's without any problems. And unlike the Lightspeed the Bent (using S&B 102 mkII) has 6 inputs, 2 balanced and 4 unbalanced. Additionally I can add 6 db on the fly (which works well for my phono preamp).
As much as I would like to try the Lightspeed, with only one input it would never work for me.
So will someone please tell me why interconnects need to be under 2m.
Thanks
Tony |
Cables of capacitance and you need a buffere or a TVC like your Bent (which I once owned)to drive cables with acculmulated capacitance. With your set up, the LSA won't work, it will become bandwidth limited, most noticeable in the bass. And the LSA is certainly not as convenient or flexible as your NOH - you are better of with what you have as long as you need to run those cables and need the connection flexibility you are already getting - but you are certainly enjoying the benefits of not having all the added complexity of a gain stage if you don't need gain. The BENT is an excellent preamp, so.... |
Cables add capacitance and you need a buffer.... |
Yup.
If you are running a passive volume control, it does not matter how neutral the control is (and the Lightspeed is one of the more neutral ones we have seen), the problem is the interaction of the cables, the source impedance and the input impedance of the amplifier interacting with the resistance of the volume control setting.
That's a lot of variables, and what you can draw from it is that the higher the volume setting on the passive, the more the source impedance is what determines the sound. At full volume you get the least interaction- its the source impedance vs the cables at that point.
IOW, as you reduce the volume, **no matter how good the passive is**, you will loose bass and impact. This is why a buffer between the volume control and the interconnect cable is so important; as you reduce the volume setting the bass and impact is not affected. |
First, for fun:
Saint George continues his holy mission to slay the dragon of active linestages that spit forward the devilish sounds of "colourations/distortions" towards us poor audiophiles who have not seen the holy grail of sonic purity and truth!
I have finally seen the "light" of Saint George's gospel, thank God , therefore will burn my active linestage to cast out the devil's of "colourations/distortions" out of my home forever. Thank you Saint George for saving my sonic soul!
Now a serious question for my friend Paul:
If your goal is to have a volume control that adds or subtracts nothing to the signal passing through it, what Saint George refers to as "colourations/distortions, why do you use before and after the Light speed Attenuator in your system some of the most euphonic/colored IC's and speaker wires in high end audio, instead of very neutral/transparent wires just to pass on this "pure" signal?
I'll give my opinion, even Bobby recommends Cardas for his Merlin speakers because they are just a touch "lean" sounding, so to give them a touch of the body of the harmonic or so to speak a little meat on their sonic bones the Cardas adds that to the mix. Wow, you mean a tone control or adding some kind of colouration to the sound, the highest order BLASPHEMY, according the the holy gospel of Saint George. It's personal taste and system synergy, this fiction that there is an objective standard to what music really sounds like is so silly.
I will stick to one of my original assumptions regarding George's position, any volume controls that are not his Lightspeed are for shit, along with being "dinosaurs" and that his veiwpoint is the only valid one on the topic. I still think he uses this thread to try to sell his piece. Can't wait for Saint George's apostle the honorable Fiddler's attack on me for sharing my opinion. It should be fun what he says about me now.
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Teajay and the rest of this thread have made me do some soul searching regarding my audio system. I am going off the grid and there will be no more electronic colorations for me! I am buying a Victrola. This should "Wind Up" this thread ~! |
"It's personal taste and system synergy, this fiction that there is an objective standard to what music really sounds like is so silly." That is true and I'm not sure anyone, or even George, has spoken about what music really sounds like, his claim is that the LSA will permit the signal to go from the source to the amp with minimal distortion, whihc seems to be a measurable claim beyond subjectivity, which is a different statement, he is not making claims about musicality or what you will like, it seems like a more objective statment that the signal will be less adulterated, unless you have impedance matching issues which will be a distotion of its own, as Ralph points out.
I am somewhat agnostic about the issue of neutrality versus color, I just want my system to sound good and I find the $450 LSA sounds as good with my Music Reference amps as with the much more expensive and complex linestages I have used; that is why I think others should try it if they have a sensitive and high-input impedance tube amp with short ICS, they can get great sound for little money. And, I continue to use my Atma pre with Atma amp because nothing has sounded better with my Merlins and the warm Cardas cables - a great match for an VSM owner. |
Ralph, why have gain with a CD player with 2v or more output? Any reason? You make a good argument for why you might need a buffered linestage (though Roger Modjeski still advised me to avoid a buffered stage in my setup with his amp - he was perfectly willing to build me one if I insisted), but gain? What for? |
Atmasphere IOW, as you reduce the volume, **no matter how good the passive is**, you will loose bass and impact. This is why a buffer between the volume control and the interconnect cable is so important; as you reduce the volume setting the bass and impact is not affected.
Atmasphere
Not totaly correct sunshine, the ear becomes less linear at low levels and this is why the "loudness switch" was invented to boost the bass quite a bit and the highs slightly also, but these circuits like all active circuits, introduced too much of their own colouration/distortions as well for high end audio use. So now you'll only find them in car stereos and midfi home equiptment. |
And here is the Flecher-Munson 1933 study done, for percieved frequency loudness at different db levels. As you can see at low levels one needs to boost bass quite a bit to remain flat to the ear. Half way down the page is the graph everyone can understand.
http://www.jimprice.com/prosound/db.htm
Cheers George
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Georgelofi "So now you'll only find them in car stereos and midfi home equiptment"
And certain speaker manufacturers (who shall obviously remain nameless here), that like to boost those frequencies for the "startle factor" in demos .... seems to work too, as people are still paying the big $$'s for their products ? |
George, you and Ralph are talking about two different things. You are referring to the Fletcher-Munson effect. Ralph is referring to the increase in output impedance of a passive preamp that occurs as the volume control POSITION is reduced from maximum, to achieve a NORMAL listening volume. That increase in output impedance increasing the effects of the cable that is being driven.
That said, it's not clear to me why high output impedance + high cable capacitance would affect bass frequencies. Certainly if both parameters are extreme enough upper treble response could be affected, due to the two parameters combining to produce an RC low pass filter effect. And if the input impedance of the destination component varies significantly with frequency, or is too low with respect to preamp output impedance, bass performance could conceivably be affected. But I'd be interested in further explanation of how high output impedance could interact with cable parameters to affect bass frequencies.
Regards,
-- Al |
Almarg Ralph is referring to the increase in output impedance of a passive preamp that occurs as the volume control POSITION is reduced from maximum,Almarg
This higher output impedance will only roll off the highs and won't touch the bass if and I state "if" the interconnects are extremmly high in capacitance, above 300pf per foot, and if they are that high they should not be called high-end, they need to go into the bin.
I belive what Ralph is hearing is the Flecher-Munson effect, in the F&M graph I have posted the link to.
Cheers George
. |
Yes, Al, George seems to have missed my point entirely.
If you think about what happens when you install a resistance after a capacitor, then you have a start at what is happening with any passive system. The cap has a variable impedance vs frequency, which changes depending on the time constants in the system that it is part of. At some low frequency the impedance will be seen to increase. This is how capacitors are used to roll off low frequencies in equalizers and how the low frequency poles in active electronics are set up.
When you add to that impedance, you are changing the timing constant. This is simple math. In effect you are increasing the output impedance of the source. When that happens, you get a bass rolloff when that resulting composite source interacts with the input impedance of the amp.
The thing to note here is that none of this has anything to do with the *quality* of the passive control. It can be the best out there (and the Lightspeed is certainly on the short list in that regard) and this will still happen because these effects arise out of simple physical laws **not the quality of the control**. |
To give some measured examples of interconnects
1: With IC's at 100pf per foot a 1mt = approx 300pf
this with the Lightpeed at it's highest output impedance has a HF rollof of -3db at 76khz
2: Same with 200pf per foot 1mt = approx 600pf
this with the same gives HF rolloff of -3db at 38khz
3: At 300pf per foot same gives a HF rolloff of -3db at 25khz.
Good interconnects are usually below 200pf per foot. As not to create low pass filters with passives and quite a few tube preamps.
Cheers George |
Teajay,
I may indeed craft a scintillating response if you have anything of significance to add here. However, at the moment the motivation is absent. |
Saying all that now if you have a series output cap on your source that is too small it can rolloff the bass with the combination of the Lightspeed and poweramp input impedances, to give an example for this.
1: Source series output cap of 10uf into the combined 7k Lightspeed & 47k poweramp = 6k the cap is seeing which gives a LF rolloff of -3 at 2.6hz
2: 5uf series source output cap will be double that at -3db at 5.2hz
And so on. 2.5ufwill equal -3db at 10.4hz
I like direct coulpled source outputs as this then is not an issue, as well as the best sounding cap is NO cap.
Cheers George |
Ralph is a very sharp mind and I am sure that he is not confusing Flecher-Munson for something else. It does seem however that in the real world with low capacitance IC (my total capacitance with 2 meters is 72pf) that the impedance impact is true, theoretically correct, but inaudible under these circumstances, especially since my hearing is proabaly down 20db at 15khz:) But, obviously with very long cable runs it might very well be the case that buffering is called for. What I still don't understand and would like to hear from Ralph is why gain is of any value except in the obvious cases where the source output is very low and perhaps with some sources and his amps which are 2.83v sensitive. One of the reasons I think his OTLs are among the finest sounding amplifiers of any kind is that he eliminates the complexity and distortion inherent in output transformers, so the tube is directly coupled to the driver in the speaker. A philosophy of less is more, less complexity (in parts and wires)more purity in sound. In some sense the very same thing that is appealing about a passive, bufferless linestage. In the same way that a transformer leads to distortion and bandwidth limitations, it seems to me that the electronics neede for gain in a linestage has some of the very same "problems" as a transformer has in a tube amp. But I do realize I know close to nothing about electronics, and this may be a false metaphor, but I don't understand why. |
01-13-11: Georgelofi
To give some measured examples of interconnects
1: With IC's at 100pf per foot a 1mt = approx 300pf
this with the Lightpeed at it's highest output impedance has a HF rollof of -3db at 76khz
2: Same with 200pf per foot 1mt = approx 600pf
this with the same gives HF rolloff of -3db at 38khz
3: At 300pf per foot same gives a HF rolloff of -3db at 25khz.
Good interconnects are usually below 200pf per foot. George, from those numbers I infer based on bandwidth = 1/2piRC that the maximum output impedance of the Lightspeed is around 7K (which I see is confirmed in your post immediately above). Other passive preamps may be considerably higher, however, at worst case settings. And the issue concerned compatibility with long interconnects, not 1m interconnects. 15K ohms, for instance, in combination with 15 feet of 50pf/ft cable results in a -3db bandwidth of only 14kHz. Ralph & George, thank you for the explanations concerning bass effects. Just to clarify, though, it should be noted that those effects are essentially unrelated to cable capacitance or cable length. Best regards, -- Al |
01-13-11: Almarg Ralph & George, thank you for the explanations concerning bass effects. Just to clarify, though, it should be noted that those effects are essentially unrelated to cable capacitance or cable length.
Best regards, -- Al Almarg
If it's not the Fletcher Munson low level listening curve, that your bass deficiency is stemming from, then I would seriously look at the value of your source series output cap, and make sure it is
1: That is at least a good quality polyprop cap
2: That it is at least 5uf or bigger.
Cheers George |
Wow did you guy's ever loss me... But it gives me something to learn about.
Tony
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George has pointed to exactly what the problem is. In order to produce proper bass, there can be no phase shift above 20Hz. Fletcher-Monson has nothing to do with it. If it were F/M at the heart of this, the same loss of bass phenomena would be heard by lowering the volume on any active line stage, yet that does not seem to happen. The loss of bass is unique to passives.
To eliminate phase shift at 20Hz requires a cutoff frequency of of 2Hz. IOW, the cutoff has to be about 1/10th the frequency to be amplified. So if the cutoff has risen to 5 Hz, effects will be heard at 50Hz- audible on most speakers. This low frequency phase shift is interpreted by the human ear as a loss of bass impact.
Note that the phenomena will not be had if the source has no output coupling cap. In such conditions there will be no low frequency pole and so no loss of bass energy or phase shift. But the vast majority of sources *do* have output coupling caps, and quite frequently, especially in digital gear, the output levels are so high that any amplifier will be driven into clipping by the DAC or CDP. So any passive used in this case will manifest the loss-of-bass problem. |
Some sources that have output coupling caps (series caps) and are in the order of 10uf, and are usually bi-polar (2 x 20uf electros back to back), but these sound like cr-p, better to use plastics (polypropylene) but good ones of this size are expensive, and big. All these caps are there to stop dc offset, which if gets through can take out amps and or speakers.
In my view the best source output stages are direct coupled (no cap) this is harder for the designer, as usually they need to also to design a DC servo to keep the dc offset at a minimum 1-5mV, but when done right sounds the best as they are more transparent and have less colourations of a cap coupled output, and have none of the low frequency limitations.
Then there's transformer coupled output stages, don't even get me started on those, with high and low frequency limitations, ringing and well as current limitations.
Cheers George |
George, does that mean that with some sources, Ralphs aregument is correct due to the coupling caps?
Ralph, what is your view of the argument that complexity required to add gain in a linestage does more harm than good when gain is not needed? |
Wow did you guy's ever loss me... But it gives me something to learn about.
Tony
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Pubul57, there are 4 functions of a line stage:
1) add any needed gain- not all sources are able to drive an amplifier to full output.
2) provide for input and volume control- this function is shared by most passive and TVC systems.
3) buffer the volume control from the output- this prevents the load from interacting with the volume control setting, and prevents the control from exercising a tonality.
4) control the interconnect cable- which is done by having a low output impedance which swamps (makes negligible) the capacitive, inductive, resistive and other aspects of the cable.
Of these four, the latter is least understood, even by the industry that makes active line stages. This issue though is so profound that it is arguably the most important beyond actual volume control.
Its been my experience that if the line section controls the interconnect cable, then it has a good chance of outperforming a passive control or TVC. The reason is that the interconnect cable will cease to be an important part of the system sound. I'm pretty sure just about anyone who has set up a system using single-ended cables is aware of how much difference the cables themselves can make.
With any passive volume control, the cables are paramount and must be kept short for best performance. OTOH if the line stage is designed properly then you can run cables of nearly any length and the difference between the most expensive and the least expensive will be hard to hear. This latter fact is one that most cable manufacturers would rather you not know.
IOW if you can hear differences in the cable between the line section/passive and the power amp, then the cable is not being controlled.
A barrier to performance in many preamps, particularly tube preamps, is the output coupling capacitor. It must be made large enough so that phase shift is not evident in the lower frequencies (no loss of bass, IOW) and it has to do this with a transistor amplifier since the manufacturer has no way of knowing what amp the preamp will be connected to. Since transistor amps have a lower input impedance (usually 1/10th that of tube amps) this forces the output coupling cap to be a rather large value.
There is no way you can make large coupling caps sound right- they introduce coloration out of inductance and other well-known artifacts of larger capacitors. IMO, direct-coupling is the way to go. This allows you to bypass a primary concern of most tube preamps. Once this is done, the circuit has only to be merely competent and it will outperform any passive or TVC made.
It comes as no surprise to me that passives and TVCs are as popular as they are. What this tells me is how poorly active line stages are at the functions I outlined above. But just because *some* are bad at it, does not mean that *all* are. |
A good argument for getting a preamp and amp from the same manufacturer that knows what they are doing and optimized to work together. |
Simply on the issue of gain (not impedance matchin and IC ocntrol)It seems two pretty good designers, Roger Modjeski and Nelson Pass, have said that having gain in a linestage will not make things better when a source component has adequate voltage (Roger more vehment that it will make things worse), and I can't imagine it can do any good to have the signal go "through all that" when it isn't necessary - like a transformer in a tube amp. Whatever the theories, my LSA/RM10 and MP3/M60s sound fantastic, the M60s being the best amps I have heard with my OTL friendly speakers. |
4) control the interconnect cable- which is done by having a low output impedance which swamps (makes negligible) the capacitive, inductive, resistive and other aspects of the cable. What would be a low output impedance (and how would the base measurement be determined, ex. at 1k ohms)? How would one design a preamp to achieve this? I can think of those active preamps and even zero gain designs that use active buffers. Perhaps using negative feedback? Of course if you're designing a true balanced preamp having it support the 600 ohm standard would be the best way to ensure the cable is removed from the equation, assuming the amp on the other end is of the same design. Also, I don't believe my DAC uses coupling caps, but how would I know how to determine that for sure. What would I be looking for in the circuit? |
01-14-11: Pubul57
George, does that mean that with some sources, Ralphs argument is correct due to the coupling caps? Pubul57
Yes, as I pointed out in my last post, but I will say that the said caps are usually big enough, not create any problem, except colourations, it's the moded one's that have had their caps and output stages modded that have to be sometimes questioned, are they large enough?
And Ralph's answer to your line stage question is answered with diplomacy, looks like he has the same view on coupling caps, (the best cap is no cap), Except still I do not believe anyone has yet built the transparent active preamp, as they all sound so different, more so I believe than the sound of different interconnects.
Cheers George |
Since I haven't been able to understand a word of the recent postings (you all lost me at 'caps'), let me change direction a bit.
IF we assume that a straight line from source (phonostage) to amp is the best/least colored way to get at the information on the source (vinyl), then can we assume that finding an amp that has a volume control built into it would be a good way to go? Since it would allow for direct connection and also allow for volume control. In such a scenario we would bypass the LSA (or any preamp) and any colorations it may add. And also bypass a set of IC's and whatever potential issues it raises.
I take it that the answer depends upon the nature of the volume pot design/quality on the amp?
Differently, remaining with this type of amp (with volume control), if we use it in conjunction with the LSA:
1. could we use the amp's volume control to mitigate any impedance mismatches between the two? I understand that these are two different variables, but they are physically related.
2. and, what adverse effects can we expect to remaining faithful to the source?
I'm wondering about these questions because I see that David Berning and Paul Grzybek have amp designs with volume control as an integral part, and am curious as to what the (dis)advantages are. |
Clio09 a low output impedance will mean that the preamp can drive a load of less than 1000 ohms without loss of bandwidth, voltage or increase in distortion. You don't need negative feedback to do that. In the old days, tube circuits did that with an output transformer. You can imagine, being an OTL manufacturer, that we use a different technique (which is patented). If your DAC uses coupling caps, they would be fairly close to the output of the unit, but there is no set rule on that. You might ask with the manufacturer. Except still I do not believe anyone has yet built the transparent active preamp, as they all sound so different, more so I believe than the sound of different interconnects. George and I feel very much the same way in this matter, which is to say that many line stages do seem to fall well short of the ideal. But at the same time it is apparent that George has not heard *all* the line stages out there. |
I think Ralph also makes a high quality volume control as an option on some [?] all of his amps. I suspect this is the very best way for an amplifier, but for the fact that audiophiles tend to like to mix and match gear and this has the sort of perceived limitation that you have with an integrated; in that sense. I would love to have an LDR volume control on my M60s, and or a Pass B1 with an LDR, as I think the LDR is this best method for building an attenuator (without mechanical contacts, wear and tear). I suspect if the Built-in volume control was available with the M60s when I bought them, that is the path I would have take, but Ralph's preamp undoubtedly works brilliantly with his amps. |
01-14-11: Banquo363
Differently, remaining with this type of amp (with volume control), if we use it in conjunction with the LSA:
1. could we use the amp's volume control to mitigate any impedance mismatches between the two? I understand that these are two different variables, but they are physically related.
2. and, what adverse effects can we expect to remaining faithful to the source? 01-14-11: Banquo363
To your top question, yes if the volume control was 50kohm or more and there were no resistors to ground after it before the first active input stage. But saying that it will still be better if the pot was removed completely and a say 100kohm input resistor was inserted to ground.
Q1: No, not with the Lightspeed
Q2: If just using the pot on the input (no Lightspeed)it all comes down to the quality of the pot, as I say even the top ones Alps, Bournes, Penny @ Giles ect, all sound different because of light wiper pressure, materials used eg: wiper being metal on carbon or plastic conductive track, it is lightweight contact that mimics in a small ways a diode, (a proper diode in the signal path would try to rectify and AC music signal into DC), very bad. And it is this that a soldered in resistor gets rid of, the lightweight contact.
Cheers George |
The best possible way of getting the best transfer from source to poweramp is to have a cdp with a digital domain volume control, and have no preamp Lightspeed or whatever. This would be the ultimate, however a digital domain volume control in the cdp usually at less than 75% of full output starts to what's called "bit strip" and instead of getting full 16 bit resolution you start to loose resolution to 14 bit and so on the more you attenuate. I have yet to see one that doesn't "bit strip" at 75% or less level.
Even a question I emailed DCS (on behalf of a Lightspeed customer who believed his Puccini and Elgar did not "bit strip") about these very expensive units, and I asked "do these units bit strip at half volume?"
David J Stevens (of DCS) reply was.
"Hi George
Thanks for your interest in dCS and your questions.
As for the digital volume control, provided that you perform the volume adjustment at the correct point in the processing chain and you do it with sufficient precision then there is no reason to lose any signal.
Best Regards
David
Now this reply says to me that they do "bit strip"
Cheers George |
George, I know you have worked on the LSA for a long-time, so I imagine it is very well "sorted", is there conceptual room for improvement (sound side, not aesthetics)with the LSA that you have in mind or is a MKII not likely, other than possibly offering more inputs/outputs/balanced if you chose to expand the product line? Frankly, I think if there is a patent involved, licensing would make a lot of sense, more time surfing:) |
Pubul57
The one you have is already MkII. The only way I could improve to a MkIII is the versatility of the unit, that would be to have a discrete unity gain buffer (like Nelson Pass designed for the Lightspeed) on the output to lower the output impedance so it could then drive poweramps of lower than 47Kohm input impedance, and of course longer IC cables. But this would be a compromise as they would never sound as good as the MKII, I have done it, and would cost more, this is not what I'm about.
As for the switching for multiple inputs this is also not the purest way for me. If someone needs multipule inputs I suggest one of these.
http://www.decware.com/newsite/rotary.htm
That way you can still go direct to get the purest best sound when needed to show off your system.
The whole reason is to get the signal from the source to the poweramp with the least amount degradation.
And in case your wondering, all MkI's were converted to MkII years ago.
And if your wondering.
MkI = series resistor and shunt LDR "very good" still better than the best pots.
MkII = series LDR and shunt LDR "even better" more consistent i/o impedances, better bass and dynamics were noted by all previous mkI owners.
Cheers George |
"best transfer from source to poweramp" - they key to it all. |
Digital volume controls have always been an irritant. As far as I am concerned, they are a failed concept. Given the brilliance of the Lightspeed system, it would seem a natural in a DAC or CDP. |
Atmasphere, you are echoing what has been said many times, that digital volume control is "bad", which is always perplexing to me. By contrast, once a system is of sufficient resolution it is actually quite obvious the distortion all conventional volume controls add to the sound, as George states.
Yes, digital attenuation is a no go if you then follow that stage with another variable gain stage which you use at times to boost the signal. But that's a silly thing to do! The digital attenuation must be the one and only gain control in the system and then it works perfectly, because the loss in bits is always well below the audible level, unless you want to jam your ear against the tweeter while doing serious listening.
I have a 25 year old CD player with pure digital volume control on it; I play a test music track that's recorded with an attenuation of 60dB -- that's effectively the dynamic range of a very good quality master tape -- and with my ear pressed against the tweeter, can JUST hear the effect of the digital volume control ramped to maximum gain on this almost super quiet signal.
Frank |
IF we assume that a straight line from source (phonostage) to amp is the best/least colored way to get at the information on the source (vinyl), then can we assume that finding an amp that has a volume control built into it would be a good way to go? Since it would allow for direct connection and also allow for volume control. In such a scenario we would bypass the LSA (or any preamp) and any colorations it may add. And also bypass a set of IC's and whatever potential issues it raises.
I take it that the answer depends upon the nature of the volume pot design/quality on the amp?
Banquo363 I have to say that the idea of a volume pot in the amp is a pretty good idea. Of course, implementation is everything in terms of quality. At THE SHOW we were running a 45 SET amp with built in volume control. THE CDP we were using was the very reputable Resolution Audio Opus 21, that also has a very nice analog volume control. In the best scenario the volume control on the CDP had to be pinned and we had to use the volume control on the amp to attenuate. Now I have heard Ralph state the best means is to have the volume control at the amps input if you do not wish to use a preamp. He does offer this as an option on his amps, unfortunately though not my S-30, else I'd take him up on the option. However, one of the things about the LSA that I believe is overlooked is that the use of the LDR's takes the switch right out of the equation. No wipers or contacts of any sort to interfere with the signal. You could use the best switch out there (the custom Shallco's in the Atma-Sphere MP-1 are quite impressive BTW) and it's going to impart a sonic signature. With the LSA it wouldn't matter, a Radio Shack switch would work as well as TKD, Alps, Seiden, Shallco, etc. |
I'm guessing here, but I would imagine the only concern would be the linearity of the LDRs, proper matching, and performance over time (George has had these in the field quite along time). The brilliance of the LSA is that it takes away the need for a very high quality, and usually expensive switches, which no matter how good, can't overcome the laws of physics, the diode thingy George talks about. |
To all who are not very technical, try to bear with me here.
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.
When we view a static (constant) 1k-10k square waves on an ocilloscope all looks fairly fine going through a good pot (Alps Bournes ect).
But it's when you pulse the waves at micro seconds (transients) an then store it on a very good super fast digital storage ocilloscope play the micro second pulses back frozen in time, and magnify the corners of the waves it's then you see the ringing/occilations effect of the light wiper contact on the conductive track of the pot, (I have named it for want of a better word, "dynamic contact bounce")It's the wiper being ever so slightly bounced on the track.
When pressure is applied to this wiper (with in my case a wooden skewer) so the wiper presses down hard down on the conductive track, the ringing occilations stop when doing the same test. When a soldered resistor is in place of the pot it's not there either, when a Lightspeed Attenuator is in place of the pot it also is not there either.
All pots no matter how good bounce to a certain degree this is why they all sound different, they are all fundamentially flawed.
Cheers George
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Sorry I should clarify a bit better the first paragraph above, the figure 100's of volts per micro second, is in reference to "rise time" in volts per micro second of musical transient figures, not what a cdp or dac can put out of it's output in volts, but rather the speed at which they can happen.
Like when very fast opamp specifcations of some of the better opamps, they can have rise times of 1000's of volts per micro second, but they only have 18v rails, these are very good for the i/v (current to voltage) converters after digital to analogue chip before the ouput stage in cdp's
Cheers George |
Clio09, 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.
Like any passive I have heard, it had less bass impact than the preamp, which as I have already mentioned is mathematically unavoidable with a passive if you have a coupling capacitor at the output of the source (in this case a DAC). I contest the idea that *all* switches will have issues relative to a light-activated device (my concern would be the linearity of the light activated device...); obviously in practice both can be quite good.
FWIW the Shallco uses gold contacts, with a double-spring-loaded wiper.
However the preamp in this comparison had not only the Shallco switch (custom-built) but a stage of gain, a set of coupling caps and then a direct-coupled vacuum-tube buffer. It was also driving 24 feet of cable, where the passive was driving 3 feet. The two were gain-matched to avoid Fletcher-Munson errors.
The big difference was in the bass as I mentioned. If you go with the idea that the preamp was hampered by its active circuits, then the idea that its volume control is audibly inferior falls apart.
Its my contention that one of the biggest failings of many tube line stages is the coupling cap found at their outputs, so we found a simple way to get rid of it in out designs. Apparently, that is a bigger deal than I had thought. |
Capacitors on output stages of dacs and cdp's are evil necessity with tube output stages, and yes they will not be a suitable match for passives, not only that, the tube output stages on dacs & cdp's are usually too high in output impedance (more than 200ohm) for passives, being sometimes 2kohm (2000ohm).
As for really good multi (24 or 36) position switched resistor "double leaf contact" volume controls that Ralph uses. These are way ahead of quality high end pots (Alps Bournes Penny ect)
But with the single leaf switched resistor, I did also confirm contact bounce, as you can imagine there is no second leaf on the other side of the wiper to clamp it, like squeezing your fore finger and thumb together with the wiper between them like Ralph's double leaf does.
Cheers George |
