I was actually "reading" it:)
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 was rading a review of some VH Audio Power Cords" by Jim Merod for Of Sound and Music. I beleive he is a recording engineer - if that matters. in the context of that review he said something very appropos to the LSA experience, I why I love it: "No superior power cord should "enhance" music by adding dynamic slam or transient bloom or etched imaging. Sometimes one may be tempted, hearing such artifacts, to believe that such "more" is good or better...or amazing. Such artifacts are exaggerations that distort or attenuate the relaxed vivacity of well-recorded sound. All audio equipment should be sold with a generic disclaimer: Do Not Be Fooled By Sonic Cartoons!" I think the LSA is a "preamp" Jim Merod could love. |
No need to do the A typical Audiophile thing here, and go overboard. So long as you have 100pf or less per foot, that's fine as this gives with 1mt a -3db 76khz, this is over kill anyway as the cd filtering is lets face it already cutting in the mid 20khz anyway, so you won't gain anything by going even lower that 100pf per foot. No need to waste money, KISS Cheers George |
George - thank you for chiming in. Glad to hear that no sonic purity is being lost at 8-9 o'clock than further around the volume dial. Clio09 - Hemi-cylindrical (polyfuser) diffusers are much easier and faster to make than Skylines of similar size. Email me if/when you wish to consider tackling them. Happy listening all. |
Just looked at the specs of the Sony CDP-CA7es and the 10k for the output is the min load recommended, I would say with this figure it has an output impedance of around 200ohm which is fine. You will not do any harm to anything using the Lightspeed at 8 or 9 o'clock, the only detriment is the range you have is minimised, sound will be the same with good interconects at 9 o'clock or at 12 o'clock and with 180kohms input impedance this is a great high input for any passive. Cheers George |
Clio09 - thanks for taking the time to do your homework before your great answer above. While I intend to purchase the LIO-8 DAC I am currently using an antiquated Sony 5 disk player (CDP-CA7ES) which has an output impedance and voltage of 10K ohms and 2volts respectively. Knowing these specs now, does it change anything in your answer Clio09 or am I still 'safe' in that I'm not missing anything sonically by having the volume control low at 8-9 o'clock? Off topic - was the DIY Skyline Diffuser write-of of mine helpful / useful for you? |
Kevinzoe Am I missing anything by not having the volume at a higher setting (11-1 o'clock for example)? Besides getting louder, will the sonics improve as I turn the volume up louder?Kevinzoe Unless you have very high capacitive interconnects (more than 200pf per foot) you will not hear a difference, even with 200pf per foot = 600pf for 1mt, the -3db point will be at 38khz at the worst position (highest output impednace) of the Lightspeed output impedance. If you use better interconnects 100pf per foot = 300pf per mt, the -3db point will be at 76khz. I use interconnects that are 40pf per foot = 120pf per mt, this with the Lightspeed is -3db at 190khz. and so on. Cheers George |
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. |
Fellow Lighspeed owners - The listening level that I use has my Lightspeed volume at about 8-9 o'clock as my 97dB efficient speakers don't require many watts to crank them up (I'm using an Art Audio PX25 SET amp with 6watts/ch. by the way). Am I missing anything by not having the volume at a higher setting (11-1 o'clock for example)? Besides getting louder, will the sonics improve as I turn the volume up louder? Thanks! |
Lstack, thanks for the write up on the Lightspeed Attenuator in a system that was not a prefect impedance match as this has never been done before. I have listened to it in the same situation and thought it was still better than listening to active pre's and other passives, and this is what I tell customers when they ask. It's just not functioning at 100% of it's capabilities, so when you do manage to listen to it properly matched up you will only then realize it's full potential. BTW there is no problem using it this way, no harm is done to anything. Cheers George |
Yes you did ask. I've gone down this road with George. Bottom line he gave me the schematic, but warned that overall this is an inferior design due to the difficulty in matching the additional LDRs (versus single ended operation). In addition, if you can get one built there could be a higher probability of reliability issues, again due the higher number of LDRs to achieve balanced operation. That being said I recall Audiogon member Dave Garrettson trying to match LDRs for balanced operation to use as a volume control internal to his Atma-Sphere MP-3. He gave up on the effort IIRC. There have been a few people on DIYAudio who have tried to build a balanced unit. I didn't sound like it was a lot of fun. You really should try it single ended into the M-60 amps. You're going to be really surprised. I get the balanced thing, especially with Atma-Sphere components due to their supporting the 600 ohm standard, but the LSA is quite optimal with these amps too. |
As I see it the 10:1 rule will be of no importance if all of the following conditions are satisfied: 1)The output and input impedances that are involved are both essentially resistive, and do not vary significantly as a function of frequency. That condition will usually not be satisfied if the preamp has a coupling capacitor in series with its output, as is the case with most tube preamps and some ss preamps. I'm uncertain as to how often it will or won't be satisfied if no capacitor is present. 2)The component supplying the signal can handle the load impedance without distortion or other signs of stress. I would not expect that to be a problem in most cases unless the load impedance is very low (e.g., 1K or less). 3)The loss in gain that will result is not an issue. For instance, a 1:1 ratio would result in a 6db loss in the maximum volume that can be achieved, in comparison to a high ratio. Also, cable capacitance must not be too high in relation to output impedance, but that is a separate issue. BTW, if the Air Tight's 600 ohm output impedance specification does not make any reference to frequency, and if the design includes a coupling capacitor at its output, the output impedance is likely to rise to considerably greater values at very low frequencies (perhaps 3K or 4K at 20Hz). With a 15K load impedance, that would result in a small but very conceivably audible bottom octave rolloff. A nominal (presumably mid-frequency) output impedance number should be multiplied by 50 to 75x, rather than 10x, to be completely safe under all circumstances, IMO. The 10x number would be appropriate to use if the worst case output impedance is known. Regards, -- Al |
Funny, I've been considering trying an Airtight of late. Guess I'll cross that off my list. I have used the LSA as well with unfavorable impedance matching. Into am amp with 21k input impedance. It did sound good, although you will definitely hear the difference when using it with optimal impedance. The "10 to 1" rule is overrated IMO. |
Just wanted to weigh in on using a Lightspeed in very unfavorable impedance conditions. I have a DAC with an output Z of 10k and an amp with an input Z of 15K . All logic tells you that inserting the Lightspeed between those two devices would spell certain sonic disaster. I had resigned myself to using an active preamp until I could solve the impedance mismatch either by using a buffer or replacing equipment. My active tube Preamp is an Airtight with an input Z of 100K and an output of 600 Ohms easily fulfilling the "10 to 1" rule. Having already pulled the Lightspeed out of the system knowing it could never work anywhere near as optimally as my expensive tube preamp , I suddenly decided to compare the Lightspeed to the Airtight. With only one input it was a simple swap and within the first 30 seconds I realized that the Lightspeed even in a terrible sub optimal impedance match was wiping the floor with my active preamp ANYWAY. Just thought I would give more than a sliver of hope to those who think the Lightspeed won't kick your expensive active preamp to the curb even in a bad impedance mismatch. Yes George warns over and over that the Amp "should be over 50K input Z" and the source "should be 200 ohms". The last thing I ever expected was to hear the Lightspeed be more dynamic , more extended, more spacious and 3D and to basically make a very very fine and expensive preamp sound absolutely woolly by comparison and all this in what was supposed to be a very impedance unfriendly situation. Now all I want is to do is stop slapping Ohms Law in the Face and try to get the impedance matches where they belong so I can hear the Lightspeed in its full singing glory. I can't even imagine how much better it could be , but I will sure try to get the matches right and let the Lightspeed cut loose. SO , for a quick recap, Just because your impedences don't fall in the 10 to 1 rule or better, don't think the Lightspeed won't easily dethrone your expensive active preamp anyway and make what you thought was the best Preamp you ever heard sound broken by comparison. |
Hi Paul, Yes, there are significant differences. An active buffer stage will provide a gain very close to 1, while providing a high input impedance (to the stage itself) and a low output impedance. A transformer or autoformer will transform impedances in proportion to the square of the turns ratio that is selected, while at the same time causing a voltage reduction (or gain) proportional to that turns ratio. Example: If a TVC is set to provide 12db of attenuation, that corresponds to providing an output voltage that is 1/4 of the input voltage. So the turns ratio for that setting would be 0.25. The output impedance would be ((0.25)squared) or 1/16th of the output impedance of the source component. The load impedance seen by the source component would be 16 times the input impedance of the destination component (presumably the amplifier). If the TVC were set for unity gain (no attenuation), there would be no impedance transformation, the output impedance would equal that of the source component, and the input impedance would equal that of the destination component. But as the amount of attenuation is increased, the output impedance will decrease rapidly, since it is proportional to the turns ratio squared. Best regards, -- Al |
The best sounding discrete buffer I have made is a tube buffer called the "SLCF" (Super Linear Cathode Follower). It was first use as the output buffer in the top of thie line Tektronics Ocilloscope, it has the lowest ouptut impedance of any tube buffer, under 100ohms. But it still does'nt sound as good as no buffer. http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp-364.html#post2346943 Cheers George |
Hi George. Thanks for the suggestion. Somewhere I have the schematic for the 8002. Ill take a look. Have you considered creating potted drop-in attenuators so that folks could upgrade their current preamps if so desired? For instance say I have found excellent synergy with amp/speaker but the amp is not remotely passive friendly...or another scenario: I have more than one source to switch? Im thinking that your volume control would ( if pot resistance compatible) be a marked improvement as a replacement for existing traditional pots. In a similar twist any thougts on designing a tube output buffer with your ldr attenuator? |
Yes the Aragon's 22k is the problem you would need a buffer after the Lightspeed, but if your handy or know someone who is you could change the 22k input resistor to say 82k. If the input of the Aragon is fet then all will be fine with the 82k. But if it is bi-polar then the Aragon may give out bit of dc offset with the 82k if switched on with nothing connected to it's input. (just make sure the Lightspeed or something else is always connected) Cheers George |
I'm sure it uses LDR technology. Question is how is it implemented and what parts are being used. Hard to tell as you can't see inside the boxes. By virtue of the fact that Norman previously used the phrase Lightspeed to describe his volume control, do we really know if he is using the same LDR's as George. Since George has made his design and schematic public it's quite possible, but I haven't seen anything that describes exactly what Norman is doing. BTW - I'm pretty impressed with the build of the unit. A couple years back I remember seeing some tube designs from Arte Forma here for sale. They were beautiful units and again appeared to be well constructed. Then they disappeared. Seems like they are back now with a US distributor. Hope they reintroduce the tube amps I previously saw. |
Quick question: would the LSA's full potential be realized in this setup: PS Audio DLIII ( 99 ohms Z out ); low capacitance one meter interconnects; aragon 8002 power amp ( 22k Z in). Speakers spendor s3e. Average listening level : low to medium 85 db ish... I use a buffered passive in same system. Volume range is more than adequate. Somewhat concerned about lowish input impedance of amp...thanks. |
Even if it is a MkI Lightspeed setup and not MkII in those little boxes, they will still sound better than any industrie standard volume pot you can get. I asked him to remove all references to the Lightspeed name because it's the name of my product, and he was trying to capitalize on the name that's all. Cheers George |
So why the heck would he false advertise if he really didn't have the light speeds? There has been info on the net about the new version that said they would have them. Heck I bought one, it sounded good to me(no pun). Don't get me wrong I'm happy with the sound of the integrated, but I guess it doesn't really have the light speeds? oh well. |
Thank you for your appraisal and the pat on the back Brislander. As you have now experienced the no contacts in the signal path sound of the Lightspeed Attenuator, it will be difficult to go back to an active preamp with a normal pot, as I maintain all pots are flawed because of their lightweight wiper contact (diode effect), that's why they all sound different. Cheers George |
It appears the revised version of the I-150 that is coming out does use the LDR modules. You can see a picture here, just scroll down a bit: http://www.audiocircle.com/index.php?PHPSESSID=41nuif7eicssir4e9kk8svclrd1p42r9&topic=87635.20 |
Kcloone, I believe it does have some form of LDR controlled volume in the new version with lcd readout on the front. I did ask Norman the owner of Arte Forma Audio to remove all references to Lightspeed Attenuator which he kindly did, he now calls his ldr volume the Nature Audio Light Sensor Volume Module. I have no idea if it is my old MkI version, easy for manufacturers and much cheaper to implement into an amp. I don't think it's the far better sounding MkII version as this would not be a stable environment for it, as the heat inside would change up to 20c at times inside an amp, and the MkII Lightspeed would go in and out of calibration, it could not be listened to without changing balance calibration every 10 mins. Cheers George |
