2. amps-preamps
  3. 1276356977

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
teajay
1,702 posts
 
George,

I'm sure by reading this thread you know my position on your posturing regarding blatant promoting of your piece along with your arrogant know it all attitude towards anyone who does not see the the light of the purity of your passive linestage.

So, when you make another snide remark like,"needs to do their homework before spending the big bucks," it fits into what I would expect from you based on your past posts on this thread. I have no idea how you experience music or how well you hear. All I know is that your LSA for my ears' was no better or worse sonicly then other passives I have owned in the past and came no were near the the performance of my active preamp regardless of your comment regarding the concern over the impedance of the X-over.

Finally, I have never asked for your advise or your opinion, your minions are quite happy to keep asking for it or you provide it on a on going basis to keep promoting on this thread, so thanks for your help, but I'll just keep limping along with my system the way it is. I will also never directly reply to any of your statements that might include me in the future because it would be a waste of my time.

When Paul wrote that one possible position, that is quite rational, " that passives can sometimes be better than actives" a few posts ago I was in total agreement with one qualifier besides system synergy is personal taste. Yet, good old George tells me that I have a bad match and who am I to know better then him how my own system sounds. George you have convinced me, I have changed my mind I will sell off my CF-080 as soon as possible and either call or E-mail you with my order for your LSA masterpiece.
georgehifi's avatar
georgehifi
10,312 posts
 
You do have a bad match Teayjay with or without the use of the Bryston Xover, and what it shows is that when you said you tried the Lightspeed Attenuator you also put it into that same bad impedance matching situation.
With or without the Bryston xover, the Lightspeed saw the 20k input of the Passlabs XA60.5 or it saw the 15k input of the Bryston xover, and your $60k preamp is in the same unfortunate mismatch.
It is well documented that the Lightspeed Attenuator needs to see 47k or more load, and your preamp is even higher at 100k.
You your self said you do not care or know about impedance matching components, yet you think you have cred by just throwing money at components and bagging them if they don't sound right.
pubul57 OP
3,712 posts
 
George, it just does not seem possible that there is a preamp on the market with 33kohm Zout - does it? It would be almost impossible to match with most any amp. Unfortunately, their website does not provide a Zout for the preamp, but as a hybrid design, you have to believe they are doing something to provide buffering for that 12au7. But anyway, clearly you and Terry will never be in agreement, no matter what the Zs say in or out - I think we can all agree on that.

It does seem that the passive / active divide is even more divisive than tubes / SS:) I wonder why.
georgehifi's avatar
georgehifi
10,312 posts
 
Try to bear with me here and let it sink in.

You see this impedance matching goes right through the whole system between components. EG: source to preamp, preamp to poweramp, and poweramp to speakers.
Even the internal stages of the individual components should be impedance matched if the designer is worth his salt.
eg: of a poweramp it's: input stage to voltage stage, voltage stage to driver stage, driver stage to output stage. Same for goes the pre and source.
Hopefully they are done/designed right as the end user cannot do anything about these stages inside the individual components or check them. But at least the end user can make sure the components are themselves matched from each other.
I specify with the Lightspeed Attenuator that it needs to see a poweramp with 47k or higher input impedance, I believe that tube preamp and tube dac/cdp manufacturers should be saying the same, this is why so many high output impedance tube pre's sound bad when they are mated to low impedance poweramps.

Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 
Paul one of the tube guru's on diyaudio said the solid state part is at the input, and it's even stated that the 12AU7 in cascode mode is directly attached to the rca outputs in the manufacturers blurbs on a website.
I asked what other preamps used this cascode output stage, and he said Rouge Audio used to on their preamps but their poweramps are very high, the M120 monoblocks I had here were 1meg! input impedance. And also he said some early Lamm preamps were also cascode output.
It is ok to have this high output impedance if you have over 100k or more on the poweramps, but you do get the problem of having to use low capacitance and short interconnects 1.5mt or less, just like with the Lightspeed.
Cheers George
More to discover