2. amps-preamps
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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.
pubul57
clio09
3,360 posts
 
I like the idea of blind listening sessions, why are so many audiophiles and reviewers against it, or at least to believe in it as a effective method for assessment? That always seemed odd to me. Yes, it would be a good idea to do such a test absent the knowledge of when one is listening to a particular piece, especially when they have invested themselves in a piece financially and/or emotionally.

Most of these tests as conducted today are flawed to some extent. Unfortunately you can't create an accurate enough control environment. That being said I think they are fun and a method by which opinions can be shared and discussed. Not that we're going to get any definitive answers, more likely the usual subjective opinions.

One thing that would be nice in the LSA, and most modern preamps, though it might "ruinous" or a least "deleterious", is a scheme for balance control to account for recording mixes, room geometry, and human frailty as we age - not sure how many ears are balanced L/R- perhaps than we would like.

Mine technically has a balance control by virtue of it's dual volume controls. I like this feature for all the reasons mentioned above.
pubul57 OP
3,712 posts
 
I should have thought about that, take that over remote cotrol any day.
clio09
3,360 posts
 
I did not realize that the Concert Fidelity pre was a "passive with balls" also.

Not sure what you mean. The CF-080 preamp has a gain stage so technically it can't be a passive. The Si2 preamp which I own and uses the same volume control as the CF-080 is a zero gain device using an active buffer. That could be classified as a passive with balls IMO. IIRC I believe the VRE-1 engages a gain stage when the volume control reaches a certain level. So it too has passive attributes. Quite a nice preamp to boot.

For some light reading on the Si2 lineup look here:

http://db.audioasylum.com/cgi/m.mpl?forum=hug&n=150154&highlight=Silicon+Arts+Design+clio09&r=

I was pleasantly surprised to receive an email from my friend Hajime Sato regarding RMAF and the use of Concert Fidelity gear by Dale Pitcher. It will be interesting to hear with his speakers.
agear
1,362 posts
 
George, for the sake of those who don't want to sift through all the technical particulars and for this thread, what are the salient features of your design? George, as a resister, how does the optocoupler compare to a fixed 1% metal film Roederstein or Vishay in terms of noise?

The actual history behind this device is interesting (and George, correct me if I a wrong). Solar cells that changed resistance with light were developed in the 50s. Audio Amateur articles mentioned the use of these cells in a compressor circuit. Audio Directions ran an article in about '75 about a dynamic range expander based on the optocoupler. This so-called optocoupler was apparently adapted from radio station and recording opto compressors.

Pubul57, so you owned the ARS twice? I was looking at pics of it recently, and it looks like the level of fit and finish is high. I was also looking at the JE Monoblocks and pre further down the road if I had stuck with the Merlins.

Tony, I agree that blinded sessions can be a mixed bag if not set up correctly. In light of the LSAs requirements, it would be easy to tilt things towards an active in a shootout. That being said, it would be fun and informative.

In terms of the VRE-1 and Concert Fidelity, I was simply quoting TVAD from your review/thread of the LSA. I was not aware of these technical specifics. I would be helpful for him to chime in.

Dale is indeed using the CF piece. I believe Hajime Sato has admired Dale's Essence pre-amp designs and speakers. I did not know there was a relationship there. Dale is supposed to have some crazy new speaker at RMAF. TBD....I wish I was going.
clio09
3,360 posts
 
I should know today, but I hope to be going to RMAF. If I attend I will be doing so as an assistant to Hajime Sato in the Concert Fidelity/Silicon Arts Design room. So I will definitely have time to stop by Dale's room as well. Last time I was at RMAF Dale canceled his visit at the last minute, so I never had a chance to meet him. It's something I hope to check off my to do list.

I agree the thread over at the DIY site is a bit winded, but there is a lot of great information about the history and uses of the opto coupler. Nelson Pass even partakes for a bit. In comparison, The Truth preamp I have uses photo cells, but not opto couplers. The idea is basically the same though as attenuation is controlled by an LED that shines light on the resistors. Looks pretty cool in action.
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