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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
georgehifi's avatar
georgehifi
10,312 posts
 
Wow busy while I was asleep.
Pubul57
Anthony, I'm not sure if you would know this, but if a CD player can be switched for output level (The EMM Labs can be switched between 2v and 3.9v)is there any theoretical reason why one should sound better or different, assuming 2v plays loud enough?Pubul57

You have to watch this one, if it changes the gain via the feedback network of the output stage opamp/amplifier then all will remain the same output impedance wise.
But if the highest output of 3'9v may have say have an output impedance of 100ohms then when you push the switch for 2v this could just introduce a simple voltage divider into the output circuit, which is a series & a shunt resistor this then will change the output impedance of the of the unit from the original 100ohms to whatever the series resisitor is of that voltage divider, it may 1000ohms.
Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 
Grannyring
Ok, one last question. If I run my CD player right into my amps, won't that damage the amps or speakers? When this is done will my system play at full volume? Half volume? I can't image playing at full volume as I never go past 1/3 or so right now - to loud!Grannyring

This is why you MUST pick a known quite starting CD like the lead in for an orchestral piece so you can gauge the level. This is a test to show you what the source (CDP) without preamp colourations/distortions sounds like.
You don't hope into a Ferrari for the first time and put the peddle to the floor, you would do it gently at first, then kill yourself when the testosterone takes over.
Cheers George
intactaudio
302 posts
 
Hey Milpai'

you stated: "any passive converts the extra voltage to current"

This is true for inductive based units. Resistive based passives turn the extra voltage into heat.

dave
milpai's avatar
milpai
2,412 posts
 
Dave,
I agree with you that with a resistor-based volume control, the extra voltage is discarded in the form of heat. In addition the more resistance that is applied by the volume pot, the more the signal is compromised – usually in the form of compressed dynamics.
It is important to note that the output voltage specification on a source component represents the maximum output level when playing a disc that is recorded at the very highest possible recording level. Nearly all CDs are recorded at a level where the musical peaks never reach the maximum signal level that can be recorded on the disc. As a result, very few discs will ever result in the CD player outputting its full 2V potential even when playing the loudest passages of music on that disc.
So I believe, even in case of Lightspeed a high output volt from the source is better for the sound quality. I mean, I would any day take 3.9V from source over 2.0V.
pubul57 OP
3,712 posts
 
Actually, the voltage is 2v and 3.6v unbalanced. THe manual says output impedance is 50ohm, the brochure says 150ohms unbalanced - whatever it is, it seems to have no problem driving the Lightspeed Attenuator. Seems that there seems to be no reason not to use the higher output setting, and theoretically a good reason, though it does not seem like they are using a voltage divider (but just in case).
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