It may be friendlier than tubes, but one weakness of the LSA is its one input design. I understand and appreciate the argument that more inputs would be sonically compromising, but if I didn't primarily use my turntable, I would find constantly switching interconnects a serious pain. Like you I also play a lot of vinyl, but do listen to CDs and on occasion my tuner and reel tape deck. At first changing the ICs was inconvenient, but I got used to it. I had done some research on input switchers. You can get them pretty cheap, but if you're concerned about sound degradation Decware makes one for $119: http://www.decware.com/newsite/rotary.htmThis has 6 switchable inputs. You could probably get them to make you one with less. Steve is pretty flexible. I know, another set of interconnects. Well the Decware ICs are fabulous for the price. All told you'd be out less than $300. Consider it the price of convenience. Of course if you want to splurge then the 47 Labs input chooser is the one to get: http://www.sakurasystems.com/products/47selector.htmlA cool $850. |
Let's agree to disagree and move on. Isn't that what we've been doing for the last 8 pages and nearly 400 posts:) Let's face it, we're relying on the recording engineer to interpret the event and put it down in as accurate a means as possible given their hearing skills and the equipment used to mix the recording (the first introduction of tone controls). I agree with Knghifi that most recordings are awful. So the process is flawed from the start. To listen to what the recording engineer intended us to hear, we have to rely on a means to reproduce the sound of the recording. What that means is comes down to preference (and what we can afford). One such preference is to use as few components as possible in the signal path to eliminate unwanted artifacts and coloration. It's not a perfect means (we still have other tangibles to address in the process) and it may not give us the sound we prefer. It's just one means and the one I and others here subscribe to. But I do see an advantage of a passive preamp in an integrated amp. Ralph Karsten has indicated that the best approach to addressing passive attenuation is to implement it at the amps input. He offers such an upgrade for his amps (M-60 and above). It certainly simplifies the process (one less set of interconnects) and I wish more designers would offer this option. Maybe George can come up with a module based on the Lightspeed design he can OEM to amp manufacturers;) |
A couple things. One, the sensitivity of your amp is quite low, 770mV (and if you have the 350mV option extremely low). The input impedance is a very compatible 180k ohm. I looked at your system page and was wondering if you are using the Metric Halo LIO-8 as your source. I did look at the specs of that piece and the output impedance is quite low at 5 ohms, which is compatible with the LSA. The spec I couldn't find is the output voltage of the unit. What I did find was:
Maximum I/O Levels (Balanced)
Peak Line Output @ 0 dBFS (no jumper/low power) +18.5 dBu
Peak Line Output @ 0 dBFS (output jumper/low power) +22.0 dBu
Peak Line Output @ 0 dBFS (output jumper/high power) +24.5 dBu
Analog Send Max Output +21.5 dBu
Line In Max Input +24.5 dBu
Output Impedance 5 Ω
Monitor Controller
Nominal FS output (Balanced) Output Jumper Off -19.0 dBu
Nominal FS output (Balanced) Output Jumper On -12.0 dBu
Maximum Output Same as Line
Gain Range -96 dB to +30 dB
Gain Precision ±0.05 dB
Gain Step 0.5 dB
I'm kind of curious of what the effect of the peak line output and gain range are all about. It's a bit foreign to me but this is a pro audio unit so it appears they are stating things a bit differently. Could be too much output from the source and it doesn't take a whole lot to drive your amp to full output.
The LSA doesn't have the same mood swings as your typical resistor based passive, but it doesn't maintain the same output impedance across the volume control. The big thing in your favor is the 180k input impedance of your amp. You are likely to be well above acceptable ratios no matter where you are on the volume control. I think worse case scenario is the output impedance of the LSA is around 8k ohm, so you have a very good cushion given the high input impedance of the amp. It would be nice to have a bit more flexibility before you hit your desired volume level, but I don't think you are missing anything at the level you're at. |
Clio09 said it way back when. He said something like you really have to build your system around the passive. But to me that is a really good place to start.
Marqmike Just for the record, I built my system around my speakers. I choose amps that have great synergy with my speakers. IMO the amp/speaker synergy gets you more than 80% there. The rest is determined by what your source can deliver in terms of extracting information from the recording. For me the preamp is nothing more that an attenuator. My choice of amps and sources are contingent on their ability to coexist with a passive preamp, but I wouldn't say I build my system around it. |
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? |
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. |
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According to Ralph a line stage has 4 functions: 1) control volume 2) select input 3) add any needed gain 4) control the interconnect cable at its output The last of these is the critical, as well as, the least understood one in his opinion. Ralph feels a *quality* active linestage will control cable artifacts better than any passive (and IIRC he has indicated in this thread the LSA is the best passive he has heard). From Ralph's design philosophy (true balanced differential, 600 ohm standard) I can see his point and even accept it. He's done the research, it's been substantiated, and it's evident when you hear his components working together. Pretty much why I'm willing to get a buffered version of the MP-3 to match up with my S-30. However, high-end audio is more about single-ended than balanced (as well as more about mixing components from different manufacturers than matching them) and in a single-ended environment given some of the parameters discussed here and elsewhere regarding impedance matching and cable characteristics, I believe a *quality* passive linestage can competitively match up with a *quality* active linestage. Additionally, in my case the cost differential being such that money saved using a passive has allowed me to improve other areas of my system substantially. Now as for designers who have spoken on the topic of passives, here is another opinion from Jeffrey Jackson of Experience Music: http://www.jeffreywjackson.com/preamplifiers.htm |
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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. |
What doesn't make sense Andrew?
Seems like it made sense to Al who replied that my methods reinforced the meaningfulness of my tests. I as well as many others around here respect his opinion.
Have you tried these tests yourself?
I sense you're about to start helping your "friends" again;) |
Here is what you are looking for: http://www.jensen-transformers.com/isokit1.htmlIn the photo you will see two plugs in the lower left with orange barrels. These can be purchased separately and IIRC are less the $20. They are diagnostic only, but more accurate than shorting plugs at isolating ground loops. Only other reason I can think of for the noise is RFI. Phono stages and tubed ones especially are notorious for picking it up, cables too. |
Yes 2 dB could be problematic in some instances. The 24 step switches with the S&B transformers wired to them were even more problematic since the first few steps were quite large increments, something like 6, 4, 4, and 3 dB steps before tapering off to 2 dB over the next several steps.
My magnetic line amp uses stepped attenuators with 1.5 dB steps all the way through (41 steps in all). I find these to be useful. The continuous adjustment on the LSA works quite well for me too. Even matching both channels is quite easy. |
There is no way around the lack of muting issue at "0" from what understand, unless you unplug the LSA. |
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Thanks George, what about a battery PS.
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@chakster, what phono sources would you be using? I think this will have some bearing on the result. I have heard the B1 but have not been able to compare it to my Lightspeed. I have compared my Horn Shoppe Truth buffered preamp to the Lightspeed and there is a thread here that discusses the results. Quite frankly, of all passive, buffered, and unity gain devices I have tried, the Lightspeed is the one I still use. Your input impedance on the FW amp is on the cusp, but I have used my Lightspeed with a solid state amp with a similar input impedance and had no issues.
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Well I see no reason why either of those sources would pose a problem for the Lightspeed. Glad to see the JLTi is still around as well. Listened to one a while back and enjoyed it quite a bit. Great bang for the buck.
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Glad someone else is enjoying the Lightspeed. I have owned mine for over 10 years now. I also have the dual attenuators and while they work just fine, I have often wondered if there is a stepped attenuator alternative. IIRC the Lightspeed uses a 10k log attenuator, but perhaps the Khozmo or Goldpoint attenuators can work as well. Any comments from George or others who have done this would be appreciated.
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@georgehifi, I saw both of those links and the reason I want to use stepped attenuators is not because I think it will provide better sound, but just being able to count the steps on each channel for balance purposes. I know it sounds silly but I have some of these lying around anyway, including some nice Noble stepped attenuators from years gone by, so why not give it a shot. If I understand the second link you posted the value is a 100k dual log pot. Not sure if the Khozmo or Goldpoints that I have are log, but the Noble is. If I use dual attenuators I assume the value is the same.
Keep me up to date on all things Lightspeed. I’ve gotten great mileage out of mine. |
@georgehifi, thanks I will give it a try and see.
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@georgehifi, As I review the schematics and look at the actual pots in the Lightspeed I'm wanting to confirm that the middle tab on the pot is the ground and the other two tabs are for the input and output. I ask because the Noble stepped attenuators do not have the ground on the center. I'm not sure it matters as long as ground is hooked up correctly, but just wanted to check to be sure.
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@georgehifi, on a pot the middle tab is the wiper or output if I understand correctly and if I understand you correctly this is positive. Based on the physical layout the positives of each switch are connected with a red wire and then there is a red wire from one of the switches to the board.
Well I installed the stepped attenuators using the same method. I believe I hooked up the other wires correctly as well, but here is my issue. With the original pots the Lightspeed never fully attenuated the sound, the pots in full counter clockwise positions still resulted in some low level sound coming from the speaker. I get the same result with the stepped attenuators, only the sound is much louder, in fact I could just listen to the music without moving the switch clockwise. If I do move the switch clockwise the volume does increase, but not very dramatically. In full clockwise position the sound level is still reasonable.
Something is amiss. Any ideas?
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@georgehifi, after fudging around with it some more the wiring was not the issue, the amp was. I pulled one off the shelf that I thought was good but is actually in need of repair. Pulled another one out and all is well.
Great news about the Lightspeed. Looking forward to Scott keeping this legendary attenuator alive.
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I own an Atma-Sphere MP-3 and while it is quite a fine preamp the Lightspeed is right there with it. In fact in some of my system set ups I prefer the Lightspeed, while others I prefer the MP-3.
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There are some instances where additional gain is needed, namely analog sources, so the MP3 comes in handy for that. On the digital side the Lightspeed is the solution. Like our old friend pubul57 (Paul, RIP) who started this thread years ago one of the best setups for the Lightspeed was digital source > Lightspeed > Music Reference RM-10 (or RM-9SE). Tough to beat that combo and an incredible value too.
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Good to see the website is back up and the product is available again.
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