A balanced version could be built and George has a schematic for the design, but he has made it known to me that it is very difficult to properly match the LDRs for operation in balanced mode and the unit would not be as stable.
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
I'm using a content management tool for the layout and publishing. The forum module was very easy to work with. Not as robust as some other third-party options, but since this is the only forum that will be on the site and I don't expect heavy traffic it works for me. Electa-Fidelity is a playground. I don't expect much from it. Just wanted to do something fun and interesting with my spare time, as well as try to help a few friends out. Now I guess on occasion I'm going to have to add disclaimers on my posts here. What a PITA. |
I think you'll be fine. Your CD has a good amount of output voltage and your amp isn't too insensitive. You should definitely be able to swing the volume knob past 12 o'clock which is ideal. I do use my LSA with the S-30 single ended inputs. I've also removed two of the driver tubes and shorted the tube sockets, effectively lowering the gain of the amp 12db. In each case the LSA worked fine. My speakers are rated 92db, but that is conservative. 94 or 95db is probably more accurate. Had they been under 90db I doubt the LSA would have worked well with the S-30. |
Battery or wall wart? If you want a battery PS look here: http://www.sears.com/shc/s/p_10153_12605_02871486000P?prdNo=2&blockNo=2&blockType=G2 You will also need this: http://www.minute-man.com/acatalog/Online_Catalog_Cigarette_Ligher_Plugs_and_Sockets_272.html#a90_2d618 |
The battery I use is the same one the designer of my turntable supplies for the motor pod of the table. It can go days without having to be recharged. In fact I actually went and bought the next model up because it allowed me to run two pieces of equipment on battery power (I have a preamp that could be connected to it too). So far with just the LSA connected I haven't had to recharge it once, and its been 45 days. |
Oh I forgot. I agree with George. I sensed the sound was different using the battery power supply, but can't really pinpoint exactly what it is except to say that I felt the lower frequencies were affected. I know there was no difference in noise level, at least from what I could tell by just placing my ear next to the speaker. With my Music Reference RM-10 it was dead silent either way. |
The only other possibility is to put it inside the actual amp at the input. It would require enough chassis space, but it can be done. This is Ralph's approach with the passive attenuator upgrade for the M-60 amps and up in his line. Unfortunately not enough room in the S-30 or Iwould have opted for it. |
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 |
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. |
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. |
James, I have a few of those Keith Jarret ECM CDs too. I get to about 2 o'clock on the dial using my Music Reference RM-10. Most of the "hot" CDs I have I get to about 11 o'clock. Not an IC issue IMO. George might be on the right track regarding lowered gain on the source. Might want to ask Alex about that. |
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. |
I have the EVS attenuators and the concept is pretty sound in terms of being able to put them at the amps inputs. Not sure you could get the LSA to accomplish the same thing since each unit would probably be larger in size than an EVS or Endler making them a tight or impossible fit on some stereo amp inputs (monoblocks should be much less problematic). Not to mention I assume each will require it's own power supply or share a power supply that sits off to the side somewhere. |
2549 and they are low capacitance. Just a simple shielded cable design. This connects the LSA to the S-30. Roger Modjeski first introduced me to Litz as he uses this geometry in is top line cables. Litz in general yield low capacitance and superior noise rejection. I use a Litz cable between the LSA and RM-10 and EM7 amps. |
I use Mogami: http://www.audiogon.com/cgi-bin/cls.pl?cablintr&1303312915&/Mogami-RCA-1m---studio-standar Alternately I recommend a cable that uses a Litz geometry as it is noise canceling by design. One such cable is the one offered from Q Audio. The TelWire power cords are the best I have found for my systems needs. I use the HC cords on my amps. There are more people who use these cords than you may suspect and for very good reason. Extremely neutral and simple design. Dealer Disclaimer: I resell Q Audio and TelWire cables. |
Thanks George, publishing your IP has been a benefit to many. Although I suppose some of "the many" don't realize how tough it is to match those LDR's. They could sell the circuit for as cheap as they can, but the overall question is can they build it well. I appreciate the efforts of the true DIY'ers that try, but frown upon those trying to cash in on your IP. |
The DAC has enough output voltage, and if the output impedance is less the 200 ohms you should be fine. My understanding is that it uses a tube output stage so I'm guessing that the output impedance is higher the 200 ohms, but you'll have to verify that. As far as the TRL OTL's I've spoken to Paul about them but we didn't talk about specs. I suspect the input impedance should be high enough, that being greater than 47k ohms. I find the sensitivity of the amp to be less of a factor. I run the LSA with my S-30 and even though the amps sensitivity is nearly 3V, the LSA does just fine. Still, you should check on that spec. Being that the LSA has just a single input you should consider the fact that if you have more than one source you're going to have to get used to swapping cables around. Doesn't bother me at all, but I suspect I'm in the vast minority on that. Then again, your TV/BR may not have the proper specs to match up with the LSA anyway. I'll let George address that one. |
Gain of the Audiopax amp is 18dB so that is pretty low. Using my Atmasphere S-30 which is 16dB, depending on the CD, I get to about 3 o'clock or farther on the dial, but I do get more than adequate volume. Some CDs are "hotter" than others, depends what the engineer was doing in the recording/mix process. So it's not uncommon to get different volume levels by CD. What is the output voltage of your source? Being that it is modified does it deviate from the 2.5V stock output. Not sure what you can do otherwise, besides adding gain to your system. |
Banquo363, sent you an email. Not sure why the Mogami didn't work out for you. It is one of two types of interconnects I use with the LSA, and as you know I also have the RM-10 MkII. In reality, the Blue Jeans cable should have been the problematic one. Anything over 2m is definitely pushing it with the LSA. One other note, use shielded or cables that use good noise rejection designs (ex. Litz). Seems to work better than unshielded by my own personal tests and I think George has recommended shielded cables as well. |
Well at least MF is comparing it to something a bit closer in price. Then again MF liked the LSA too, just wasn't high enough in cost to get Class A rating. I'm sure he'd look pretty stupid to the industry if he said a $500 component was comparable to one that cost $26k, but wouldn't it be interesting if that is what he privately felt;) From the information I saw on the Ypsilon PST-100TA preamp it has two operational modes, each with a 150 ohm output impedance. One operates in unity gain and the other 20 dB of gain due to a tube output stage IIRC. Leads me to believe this is an active preamp all around, but I could be wrong, just not that much information to go on. |
The source should put out 2V or there about and less than 200 ohms output impedance. The amp should have an input impedance greater than 50k ohms. As for sensitivity, I'm of the opinion that this is less of a factor. I've used the LSA with amps whose sensitivity ranged from .8V to 3V. Never had a problem. |
My speakers are probably close to 95 dB sensitive even though they are listed at 92 dB. I think Duke is pretty conservative with the rating. Normally with amps that are closer to 1V I get to about 2 o'clock for normal listening. Less if the CD is hot, more if I'm playing vinyl. On the S-30 I get pretty close to 4 o'clock and with vinyl it's wide open, which according to Ralph is an ideal situation. Right now I use the LSA with the Music Reference EM-7 amps and I have a second set up using an Otari MX-5050 direct into the S-30. |
Optically controlled resistors for volume control. See George, if you use fancy language like this you can get a lot more money for your Lightspeed. What exactly is an array of 48 optically controlled resistors and why can't my LSA have this feature? ;) |
Dgarretson - So you finally were able to get it done. I had recalled earlier you were attempting this. I take it the Shallco is the one used in the MP-1 and that is now replaced by the LDR? If you can provide some more details on how you did this I would appreciate it. I've always been interested in building a balanced LDR preamp, but George has always recommended to proceed with caution on that front and I understand his reasons why. |
Well it might be a great suggestion but in the MkII version it appears to be somewhat impractical according to George. IIRC the single ended version of the LSA uses 4 matched LDR modules. In balanced mode it would be 8. It's difficult enough to find a lot of 4 tightly matched, to find 8 would be much more difficult. In addition George feels the reliability suffers. I have the schematic George provided for the balanced version. Just don't think it would be worth building. Perhaps Dave's approach using an existing balanced active circuit and substituting the LDR attenuator into it is the closest we can get. I'm curious though, Burson makes a balanced active buffer, but sans a volume control (unlike their single ended version). Wondering what possibilities exist to take Dave's approach and apply it to the Burson. Could be interesting if it can be done. |
Your many reviews on here aren't free advertising? The comments you make in them aren't a reflection of personal taste and/or results you are hearing from system synergy? Maybe in his old age Sam has had a change of heart and prefers the distortions an active linestage adds to his listening experience. He's certainly allowed to change his mind like any of us. Heck even Arthur Salvatore changed his mind and raves about the new Coincident linestage. Maybe instead of referencing all the techno-babble here you can help Sam out and give us a technical explanation on how an active linestage fills the void in the music created by the LSA, or other passives for that matter. |
I can see the point regarding complications of adding an input buffer to the circuit of an active preamp. It certainly moves away from my simpler is better philosophy. However, I was more curious about adding this type of volume control, or more accurately, attenuator, to the Burson AB160 XLR buffer itself. I run an Atma-Sphere S-30 in one of my systems and currently am using a Resolution Audio Cantata CD/USB source and running it direct into the S-30 via it's own buffered balanced outputs and using its analog volume control. I also run my Otari MX 5050 with volume control direct into the S-30, just swapping cables when I want to swap sources. I can certainly hear the benefit of a balanced set-up in this case. I do feel though that I would like to extend this system to add something in the middle that might provide the opportunity to take advantage of a balanced phono stage. One option I'm considering is the Atma-Sphere MP-3, which can be configured as a buffer. However, I'm open to other suggestions as well, including a modification to the MP-3 taking advantage of an LDR volume control. |