Could also be that your amp is very sensitive and/or has high gain, as well as you source could have a higher output voltage than is the norm.
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.
Showing 50 responses by clio09
LSA at THE SHOW Newport. I forgot to mention for those that might be attending the event I will be using the LSA at THE SHOW Newport to provide attenuation for the analog system we will be using. Our room is #417 in the Hilton. Associated vendors are: Electra-Fidelity FritzSpeakers Resolution Audio WyWires Zesto Audio Please stop in and say hello if you are attending. |
If indeed the EMIA uses the Slagleman autoformer modules with the circuit board designed by John Chapman then the only nit I have is the inexpensive switch used. If they use the OEMed modules that John Chapman offers (which I think is the case with the remote version), then this would change things somewhat. Paul, have you peeked inside yet? Can you tell me what version of the autoformer is being used. I have to admit Jeffrey Jackson does outstanding woodwork. I have decided to have my woodworker build me a nice box and I will re-house my Slagleman modules inside it. |
Paul, yours will either look like this (pic at top of page): http://www.intactaudio.com/atten.html or this (pic at top of page): http://bentaudio.com/index2.html Mine has the first one. The later Tap-X units have the second one. |
There is nothing wrong with the gain structure of your system IMO. As George mentioned get a set of Rothwell attenuators. I believe they come in a 10 dB and 14 dB version. Also, I think Luminous Audio makes interconnects with resistors built in to attenuate the signal. This is going to be the simplest way to lower or eliminate the volume at "0". Do you have a SPL meter? can you tell us what the sound level is at your listening position with music playing and the volume at "0". |
This is quite shocking and sad. My condolences go out to his wife and family. I met Paul here via Audiogon and had the pleasure of meeting him and spending a weekend with him at the RMAF a few years back. He was as gracious a person and as passionate an audiophile as he was here on the forum. In fact, I was just speaking with him last week as we were discussing one of our favorite topics, passive preamps. May he rest in peace. |
Yes, whether it was Bobby, Ralph Karsten, or Roger Modjeski, Paul appreciated designers who refined their original concepts and more importantly stood by their convictions. The first time I met Paul was RMAF and we agreed to meet up in the Merlin room. Sitting there with just Paul and Bobby I had the opportunity to really hear the Merlins properly set up for the first time. At future shows the Merlin room always received a good chunk of my time and always ended up on my top 5 list. Like Audiodynamo I do not own a set of Merlin's, but not because I don't like them, I really do, but because like Paul's commitment to Merlin, I'm totally committed to my Audiokinesis speakers designed by Duke Lejeune. I recall on a number of occasions Paul indicating he needed to try a set, since he and I shared similar tastes and similar equipment. Sadly he never got the chance. While Paul did enjoy his system, he enjoyed music much more. What I also learned from my brief time knowing him and from reading the memorials posted by his family and friends from his obituary is that he truly enjoyed life. |
Are you able to try another preamp in the chain to see if the problem persists. Although it may not be tube related, there could be something else going on in the amp that could cause this issue. Trying another preamp will help you further isolate the problem. If you don't have another preamp let me know as I have a set of EVS attenuators I can loan you. I'll be in Newport Beach next week so you can pick them up in room 417 where I will be exhibiting. |
If necessary I can have my partner look at it but that would mean sending the LSA to me. I can lend you a preamp in the interim. The loose RCA could be an issue, perhaps its shorting due to a bad connection. Maybe we can do some trouble shooting in Newport with assistance from George via email. I will have my tools with me anyway. |
Thanks for the comparison. I have used my LSA with an Atma-Sphere S-30 amp for vinyl playback with great results. Right now though until I get my vinyl rig hooked up again I am running my Resolution Audio Cantata direct into the amp via the balanced outputs and using the internal volume control. It works quite well for my digital needs. Have you tried running the AA direct to the amps? |
You can buy the Lightspeed directly from George. Email him at georgehifi@optusnet.com.au. Also, check out this thread regarding a comparison I did between a few different passive/buffer units: http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1248137240&read&keyw&zzavc http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1286153678&read&keyw&zztruth |
The LSA is not available in balanced configuration. George has stated several times that in his testing a balanced design was not reliable. As Photonman advised just get an RCA to XLR cable, but keep it short, 1.5m at the most and ensure the cable has low capacitance. FWIW I have a Warpspeed optocoupler passive preamp that uses LDR technology. It is balanced but is a more complex design than the LSA. In comparison I found both to provide satisfying results, but overall felt the LSA was smoother and cleaner. |
Get the Lightspeed, get the adapters, and be done with it. Given what you probably paid for those cables the investment here is minimal and the reward factor is very high. I bought a pair of adapters from a pro music store for another set up I have and use them with my second LSA unit. Works just fine. In my system the sound stage varies by recording. Most of the time it is set back, but that also has to do with how I set up my speakers as well. I have never heard a Lightspeed make a system forward sounding. Only way for you to know for sure what it will do in your system is to try it. |
I recommended Mogami which is what I use. I bought mine here from: http://app.audiogon.com/listings/interconnects-mogami-rca-1-meter-studio-standard-interconnect-2013-06-27-cables-80015. You could also try some pro gear stores. Mogami Studio Gold Neglex Quad would be one of the brands to look for. |
The LSA adds nothing to the mix. It will be purer and smother than the Placette if the LSA matches up with your source and amp. Minimum 2V output and less than a few hundred ohms output impedance from your source. Minimum 47k ohm input impedance and a highly sensitive amp. Low capacitance cables kept short. |
Not all linear power supplies are created equally. B_limo makes a good point as to the LSA not requiring a lot of current, and the LSA has it's own regulation, but any power supply can introduce noise into a system. If this Teradac somehow reduces the noise level then it should be quite apparent as Banquo indicates. |
I would though argue that a neutral preamp can be mixed with the widest range of sources and amps, which are then left to present their own sonic signatures. That's exactly why I'll only have tubes in the amp and nowhere else in the chain. Too many tubes, too much coloration/artifact (granted other non-tube components such as transistors and op amps can add coloration/artifact, but IMO tubes can be the worst culprits). Not to mention we haven't even discussed cables and as Ralph Karsten so often states, the coloration/artifact added by cables also has to be taken into account. Too bad the Lightspeed couldn't be developed as a balanced version that supported the 600 ohm pro audio standard. Then we could eliminate the cable from the equation as well. |
Mine was made center pin negative because the wall wart George recommended was set up this way. For the battery power supply you can find it here: http://www.sears.com/shc/s/p_10153_12605_02871486000P This will allow the Lightspeed to run much longer than the Lithium Ion George recommended. You will need an adapter cable that plugs into the 12V DC outlet on the unit. Here is an example of one (although they are sold elsewhere too): http://www.minute-man.com/acatalog/Online_Catalog_Cigarette_Ligher_Plugs_and_Sockets_272.html You need to scroll down the page and look for: Power Plug with 2.1mm X 5.5 mm Coaxial Plug with 18 AWG 8' Cord Item: CA205MCIGF8FT18AWG The cost is $5.95 Just make sure it is center pin positive. This battery power supply and the adapter cable are used to power the motor pods of Galibier Design turntables. These aren't inexpensive tables so I trust Thom's choice in parts. Thom procured my cable and wired it for center pin negative. |
I hope this unit is used by someone at RMAF so everyone can actually hear it and decide for themselves if it provides the type of sound they can be happy with. I'm bringing mine there this year and hope to convince a few people to plug it into their systems for some A/B comparisons. That's if they're brave enough. I too have had what I consider to be some fine preamps by Cary, TRL, Joule, and Berning. The Lightspeed bested them all. Although there is no trial period I can't believe anyone who owns a $5000+ preamp can't spring for this unit to give it a listen. Even if you had to take a loss on resale you could still recoup at least 50%. While I too am disappointed a balanced version is not available, some people have built them and George will provide you a schematic upon request. You could also email me and I'll send you a copy. |
Sorry, itchy trigger finger. For some time I had been a big proponent of transformer based passive designs. The Lightspeed changed all of that and the idea of the thread was to really extol the virtues of resistive designs - done right IMO. Yes they do require more finesse in system matching than a TVC or AVC, but overall I think a well designed resistive passive is truer to the sound. Makes me want to go back and listen to a Placette again, I may have dismissed it to soon. What I find with the LS is that the issue of soundstaging, dimesionality, apparent bass and highs, etc. is dependent on the recording, and for my approach to building as system, this is the way it should be... To Pubul57's point, I've been hanging around a recording engineer of late. His system uses SET amps, a passive, preamp, and some pretty good source equipment and speakers. The speakers were placed against the back wall. One would think sound stage depth would suffer, but it didn't. It was however recording dependent and to his point, much (if not all) of the sound staging comes from the recording itself. I tried this at home with my own speakers and found it to be true. Amazing how much space I've created for stuff other than listening now that my speakers are nearly in the corners of the room. I think equipment that is true to the source will provide the proper sound staging - regardless of whether they are active or passive designs (in the case of preamps). It really does come down to preference, but I know I'm not going back to an active preamp anytime too soon. |
The best sound you will get is to put your (CD DAC or Phono) directly into your power amps with a VERY quite CD track first, this is the most perfect "true to the source" sound you will get... This is the actual test recommended by Arthur Salvatore to determine if your system is passive friendly and if so whether or not you will like the sound. He recommends Ravel's Bolero as the test track since it starts off with very low volume passages. You need to be careful when conducting a test like this because if you use a track that has a loud volume passage, or even an unexpected loud drum kick, you could blow out your speakers. |
Clio9, could you share what those Atma sphere tweaks are? No. Please contact Ralph directly. The tweaks may not be applicable to you and your system. Only Ralph can tell you that. As for a switch box, Decware makes a nice one. I just unplug my cables. Guess I'm a barbarian. The price you pay for the best (IMO) sound. Are you, or could you, consider making a fully balanced version with some sort of remote volume function? LOL. Been down that road with George, except the remote part. It's hard enough matching LDRs for the single ended version let alone what it would take to match them for a balanced version. Not too mention according to George it might not sound as good or be as reliable as the single ended version. Let's bear in mind that the reason the Lightspeed is so good is its simplicity. Adding inputs, remote, balanced design, etc. just complicates things. George addresses all this in detail on the DIY.com site where he has been gracious enough to share loads of information. If anyone wants a balanced version I mentioned in a previous post on this thread that George (or I if you email me) will send you a schematic. You could build one or have one built. There is a site (forgot the name but I think its mentioned in this thread) where you can get matched LDRs, and possibly a completed board, leaving you with just the hardware to sort out. |
Will it work well on speakers that are 87 db efficient like Soundlab speakers and other ESL's? I say this assuming the amps are very powerful and the spec criteria mentioned by the poster are meet by the source unit and amps. I don't see why not, but I'll let George address this. I thought I recalled a conversation where the Lightspeed was being used in a system with Maggies. However, my own personal opinion would be that the amp driving the speakers and the synergy between the two would be the more appropriate matching criteria when determining this since the spec criteria (source output voltage and output impedance/amp input impedance and sensitivity) is met. Last, this LS volume pot has no sound of it's own so I assume you hear the amp speaker combo and it's particular sonic signature and synergy? If so, an active preamp may well act like the hub or heart of a system bringing everything together the way the owner likes. Perhaps the speaker/amp synergy is just a little shy of perfect to the owners ears, thus the active pre is the crowning jewel or the cherry on top. As I said previously, an active preamp is a tone control, or in some systems a band aid. |
Bill - Go to the Arthur Salvatore site and read the instructions for the test (see link). There are test instructions for LP and CDP. Ravel's Bolero is a good track to use because it has low passages at the start that will not cause damage. You're right though, loud passages or even an unexpected loud passage might cause damage. With no volume control on the CDP you wouldn't be able to mitigate damage unless you were to hit the pause or stop button very quickly. If you are still using the TRL Samsom amps IIRC they have an input impedance of around 67k ohm. The sensitivity is just under 1V. Any CDP with 2V or greater output should be able to drive it. The question is will there be enough volume and will you like the sound. Also, perhaps not with the test but if using any passive preamp the output impedance of the CDP will come into play. Typically this should be under 200 ohms, but under 100 ohms is even better. http://www.high-endaudio.com/RC-Linestages.html |
George, maybe you can help me figure something out. I was using the Lightspeed with a pair of monoblocks that supposedly had a 10k input. Theoretically this would not be an ideal match for the Lightspeed, but I heard nothing out of the ordinary. Any explanation for this? The link shows a schematic for the circuit. http://electra-print.com/singleended_a2.php |
From elsewhere in this thread are some of George's comments: Regarding using the LSA with low sensitive speakers, a question/answer: Grannyring: I have a question for you owners of this exciting volume pot. Will it work well on speakers that are 87 db efficient like Soundlab speakers and other ESL's? I say this assuming the amps are very powerful and the spec criteria mentioned by the poster are meet by the source unit and amps. George: My Martin Logan Monoliths ESL's are around 86db, I am never more than 11 o'clock for very very loud listening. I make it a point of asking customers with low efficiency speaker where the position of the volume control is for good loud level listening, and the worst was 82db speakers and he was still only at 1 to 2 o'clock for loud listening sessions. Regarding system requirements George states: If your source output impedance is less than 200ohm and your poweramp input impedance is more than 47Kohm then the Lightspeed Attenuator is a shoe in, no buffer will sound better. I have read where short interconnects are best suited to the LSA, less than 2m. Grannyring has my LSA right now and is using it with his Sound Lab speakers and Atma-Sphere amps. He's given me positive preliminary thoughts on the sound so perhaps he'll weigh in on this later. I personally have tried the LSA with scenarios that are not as ideal as previously mentioned. For example, an amp with less than 47k ohm input and a digital source with more than 200 ohm output impedance. One thing that never happened in my usage was a change to a 2D sound stage, However, I will add that in my system imaging and sound stage are recording dependent. I also now use battery power for the LSA. There is a difference versus using the stock wall wart, but I can't identify it. However, I will say I prefer the battery power method. Just something about it that sits better with me. |
In my system the sound becomes a lot more colorful steeped in more accuracy of the natural tones and timing of real music. Marqmike, glad you're happy with the LSA. I think you really hit on something with this comment. It pretty much describes how I feel about the LSA and IMO it's more evident now that I use it with a battery power supply. While the term "colorful" would not be one I would have thought of using and IMO traditionally goes against how I would describe the sound of a well designed passive, nonetheless I think it makes a lot of sense. To put it another way, I think we sometimes get caught up in how our equipment performs on a linear level. I know I have been guilty of such. Focusing way too much on frequency response, imaging, sound staging, etc. Since I purchased my Audiokinesis Jazz Modules a couple years back they really started opening my ears up to things like natural timbre and timing. Things you could consider colorful versus linear IMO. In fact, the designer of my speakers had his priorities set so that reproduction of natural timbre was a high (if not the highest) priority in his design. He never set out to build a speaker that sound stages well. It wasn't nearly as high a priority. Now you might think that speakers designed in this manner add a fair amount of coloration to the sound. Well most who have heard them, including some well respected experts say they are the least colored horn designs (actually wave guide) out there. I think George may have achieved something similar in his design approach with the LSA. Something pure and true to the source, yet doesn't lose that ability to convey natural timbre and timing. Pubul57 always stresses the importance of system matching with passive preamp designs. I made note in another thread I started as to how creating system synergy with a passive preamp could be one of the hardest things to achieve. Potentially too many variables to satisfy. However, if you can satisfy the variables, then the design of the passive becomes paramount to achieving what we experience from the sound. I was just reading something where the following quote popped up: "I am not so much interested in where the musicians are on the stage, as in why they are on the stage". In my system the LSA enhances that train of thought for me. |
The LSA plays the instruments more up front and forward - and I mean all of them! The instruments play on the same plane at the front of the speaker. Some may like this. However, to others it is a lack of 3D perspective or depth. Bill, was this true of every recording or was it recording dependent? I do find with the LSA in my system it exposes the recordings for what they are. Meaning some have a more 3-D sound stage than others. Some are also more immediate in their presentation than others. However, I can't recall one where all instruments are in a flat plane at the front of the speaker. What specific recordings were you listening to? If the recording offers only a forward perspective for all the players, then the Dude reveals that. If the recording is more layered, then the Dude gives that deeper layered presentation. Exactly how it should be with any preamp, active or passive. |
I don't know of one resistor based passive that doesn't vary the output impedance based on the attenuation level. I think it is just the nature of the beast and as Andrew mentioned the LDR design is not immune to this (Side Note: The Truth Preamp does not vary the output impedance but that is because it uses active buffers on the outputs). It is one of the reasons why it is important to get the right impedance matching and in some cases to pay attention to cabling to attain the best sound from such a design. TVC passives have the same issue (see here, scroll down the page http://www.stevens-billington.co.uk/page102.htm) but are more forgiving. It was one reason I preferred TVCs earlier on before encountering the LSA. Also, Ralph Karsten mentioned a number of times that the best sound from a passive will occur closest to the maximum point on the volume control (least attenuation). That is because the further around the dial you go the lower the output impedance. I'm never at much lower than 12 o'clock on my LSA and with my Atma-Sphere S-30 amps where I can vary the input sensitivity and gain, I'm never at less than 3 o'clock. So it's safe to say I'm operating at lower output impedance running into high input impedance amps (minimum 100k ohm, maximum 250k ohm). |
Interesting comment on the buffered approach Dave. I believe when John Chapman re-introduced the Tap-X with the Slagle autoformers the remote allowed you to choose from buffered or unbuffered (only on the multi-input models though). In his testing he said he couldn't distinguish a difference between the two, but his goal was obviously to allow a user to address impedance mismatches. The Truth preamp I wrote about in another thread uses photo cells and a buffered output. Output impedance is extremely low, something like 2 ohms. It supposedly can drive cables up to 30 ft. in length. It works nicely with my Atma-Sphere S-30, but as Pubul57 mentioned if you don't need the buffer, and my other amps don't, why add anything to the mix. In this scenario the comparison of LSA to other preamps becomes more of a contest between volume controls-- which is a critical and oft-neglected determinant of a preamp's performance. I agree we often forget the impact of the volume control in preamp designs. The concept of removing the volume control from the equation was what got me interested in the LSA to begin with. The LSA doesn't need a high quality volume control since the design eliminates the impact on its performance. |