Clio09,
I hope to stop by :-)
Best regards,
Sam
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
Don't do face book, not into it at all. I joined it ages ago and got bombarded with all these strangers wanting to be my friend. Being homophobic (not really) I ran for the hills and instantly cancelled my face book account. He will eventually sus out what happening, get to me, probably after calling me and arrogant s.o.b for not answering so far 3 of his enquiries. Cheers George |
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 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. |
Well, I spent the day learning how to solder and fixing the detached wire. While it was fun, it didn't help. The very first track I played after all that revealed the same problem. So, I dragged out a beater preamp (thanks for the suggestion, clio09) I had stored in the garage and hooked it up and listened for 45 minutes: no issues. Afterwards, I immediately plugged in the LSA and replayed the same cd: problem returns. So, it's not the amp after all. It must be the LSA. I tried a different wall wart and the problem persists. I tried a different outlet and the problem persists. As I noted above, the problem is not channel specific: imaging is centered as usual. Perhaps there's a power regulation problem in my unit? I should note that one of the output rca jacks is loose, but that's been that way ever since I've had the unit. By loose I mean I can rotate it a quarter turn back and forth with little resistance. If I try to go past the quarter turn, there's resistance. Anyone else experience these symptoms? Clio09: do you or your tech know the insides?; I'm loathe to send it to Australia but it'll be easy to carry it to Newport Beach :). |
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. |
I've been having issues with the sound out of my system and finally had some time to diagnose. I've narrowed it down to the LSA or my tube amp (music reference rm10). The symptoms are the following. I'm getting diminished power/volume and muffled sound quality. Every other track or so the volume and sound quality will briefly return (the volume will suddenly shoot up) and then go back down after a few seconds or so. It's not isolated to one speaker or the other, so I'm ruling out an interconnect or wire issue. I've changed all the tubes on the amp and the problem persists. So I'm suspecting the LSA. I'm using a wall wart power supply and not battery pack. But what in the LSA could cause the symptoms I'm hearing? More importantly, how can it be fixed? Preferably without having to send back to Australia? Help. Thanks. |
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. |
Thank You Bobby and everyone else posting on this board and the Pubul57 board on Best Of. I'm blown way by the beautiful humanity of the audiogon community. Not to diminish the any other posters in the least but I am glad to hear from Bobby. Paul talked about you all the time, Bobby, and no matter how hard I tried he would never listen to another speaker. It wasn't that I didn't love your work as well, we spent many afternoons listening to his Merlins. I was always focused on trying hear as many pieces of equipment as possible. I do think that what he appreciated in you and all great designers was that you took a idea and kept working at it and refining it. He definitely appreciated thepursuit of perfection as you do Bobby and I know many of the other members and manufacturers on Audiogon as well. 'Philes of every ilk search for these ideals, its something Paul helped me focus on in audio and life, most of all he taught me not to fixate on the equipment and to always make time to listen to the music. |
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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. |
This thread truly has a life of its own! I regret to inform all those who may have followed this discussion for the past two years that my friend and fellow Audiophile Paul Rosenthal who is known to you as Pubul57 has passed away suddenly earlier this week. I was happy to know him for the past ten years in Baltimore and he exposed me to a plethora of equipment, advice and insight during that time. Paul loved many fine things and had many great friends. I know he cherished the time he spent on Audiogon with all of you. I know I cherished the time I spent with him, he was like the big brother I never had. I hope you will continue debating what the best source is, or when is absence presence and remember our friend Paul; audiophile, philosopher, and friend. May he rest in piece. |
Wow this threads been active since I went on an outback holiday to the deserts of Australia for the last week. As for some of the questions asked. When the power is disconnected from the Lightspeed Attenuator both the series and shunt ldr's go high in resistance to around a few megohms they never go open circuit, so even with power disconnected they still allow some small amount of signal to pass through. As for never being able to go to zero volume, most do not find this a problem as if they want zero they can mute,pause, or stop the source with the remote. If the source is vinyl the gain of phono stages are quite small compared to a cdp and is never a problem either but a very small signal can be heard through the speaker if next to them. Saying this if someone has one of the many clones getting around, most use the NSL32SR3 led/ldr combo, these do not go as low in volume as the NSL32SR2S that is used in the Lightspeed Attenuator because the minimum resistance is higher on the NSL32SR3, and cannot be shunted to ground as well as the NSL32SR2S. Also some clones are using the MkI Lightspeed circuit which I first used 25 years ago, which has one a fixed value resitor for the series component and a ldr for the the shunt component, these are far cheaper and easier to make but are quite high in volume at minimum and also don't sound as good because of wildly differening I/O impedances. Cheers George |
Yes, the transport has no relation to the issue. The problem is that DAC's (and also CD players) usually have maximum output levels of 2 volts or more, which is unnecessarily high. Stereophile measured the maximum output level of your particular DAC as being 2.17 volts. As a rough approximation the outputs of tuners and other analog sources are often just 1/3 or so of that amount, which is about 10 db less. Regards, -- Al |
04-12-12: AlmargI should add to this statement, though, that since on occasion you have used your volume control as high as the 2 o'clock position, I'm uncertain as to whether or not the 20 db attenuator would still allow you to reach those same maximum volume levels, even at the maximum setting of the volume control. Regards, -- Al |
If I knew about the Rothwells I might have kept the CAT pre/amp combo. Even though the pre and amp were "made for each other" I could not go much beyond 9-10:00 with digital sources, and with a stepped attenuators to boot! If George, Al, and Anthony all vouch for the Rothwells to solve the "problem", it seems it is a safe bet, and easier than changing amps:) |
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". |
04-12-12: GooddominoSensitivity (the input voltage that will result in the amp putting out its maximum output power) is not directly relevant. What is relevant is the gain of the amp (the relation between output voltage and input voltage). Comparing sensitivity numbers is only meaningful if put in the context of the power capability of the amp. For example if two amps both have an input sensitivity of 1 volt, but one of them is rated at 50 watts and the other at 500 watts, the 500 watt amp will produce much more volume in response to a given input signal than the 50 watt amp will produce. The suggestion George made earlier about trying a pair of Rothwell attenuators seems to me to be well worth trying. They would be connected directly to the input jacks of the amp, with no intervening cable. In conjunction with the 47K input impedance of your amp, the 10 db version would result in the LSA seeing a load impedance of about 30K, which is on the low side but I suspect would still be ok, given that it won't vary significantly with frequency and given the 620 ohm output impedance of your source. I am not familiar with the characteristics of the 20 db version, but I would guess that it would present a load impedance that is significantly higher (and therefore even better). Regards, -- Al |
I don't think it has much to do with impedance. It is the input sensitivity of your amp, it gets to full power output too easily. For example, my amp I use with a passive only needs .8v to reach max. power output. My other amp that I use with an active line stage requires something like 2.8 v to reach max. output, and in most cases requires the gain provided by an active line stage. The other side of the chain would be to reduce the output voltage of your source so the overall gain structure is lowered. I have no idea how you do any of that. No matter why you do, the LSA in any system that it is appropriate for will still produce some volume a zero setting, and just should not be that intrusive, except with high sensitivity amps and speakers combined. |
I see that George recommended lowering my gain of the amp or source. My amp input impedance is 47k ohms and output impedance of my DAC has been confirmed at 600 ohms by Rega. What numbers do I need to look for in an amp or source to match with my 98 DB sensitive speakers so that I achieve lower volume in the "0" volume setting? |
