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

My review….. As an ex-owner of many hi-end audiophile hardware from speakers such as Kharma, Dynaudio, Vandersteen, Magnapan, Sonus Faber, to amplifier such as Audio Research, Plinus, Rogue, etc I am experience and qualify to review hifi component, up to S$50K if putting a value to a piece of hardware means anything to you.

Lightspeed is a product that appeal mostly to the diy community. By saying diy community I don't mean only those who seek to build an attenuator only but also those who are constantly searching for tweaks to their hardware such as Caps and tube roll or optimising an amplifier circuit. The writer is one such person.

LS did no active advertising and I chance upon the LDR circuitry in a diy forum only recently while seeking to improve my channel imbalance with the Alps variable resistor swipe type volume control. I assembled a 23 steps attenuator and realised my Alps variable resistor was indeed a bottleneck to my system. The 23 steps attenuator was like from winter to spring in my system. But I believe much can still be done to improve the performance.

Than came the LDR attenuator. A simple and logical concept of using an isolated LED light intensity circuitry to vary resistance in another circuit hence producing a clean signal through the amplifier circuit resulting in crisp, clear, smooth, transparent and quiet layers of music only limited by the quality of the equipment downstream to the LS. The use of the stereotype audiophile jargon such as soundstage height/width, imaging, timbre, etc... is to me irrelevant in describing the LS. I believe an attenuator's aim is not to have a sound but to vary the signal level and pass-through effortlessly and not impeding the potential of your equipment. Any improvement gain is due to your equipment and LS is just an enabler.

But I will certainly get bomb to claim the LS do not have a sound because the signals do run through some circuitry before it gets transmitted to your equipment. My point here is that if the LS produce a negative effects to your setup or swing towards certain attributes that is not to your liking, most likely the cause is a mismatch in impedance or you have a coloured attenuator and not the LS being inferior.

Is the LS a plug and play component? No and maybe. First you need to make sure you don't have an impedance mismatch issue which is rare but not impossible. I have also a tube pre and SS power system and I lost the much preferred "tube sound" by putting the LS in place of my tube pre. This is not to say that it is terrible but not my preferred sound. I have now bypass my tube pre 23 step attenuator and use it as an over glorified tube buffer. If you are using a passive preamp the LS is a no brainer upgrade. If you have and like your SS pre, you will likely like the LS in place of your SS pre. Comparing my Alps to the LS is like winter to summer. It doesn't sound thin or dry on the contrary to some who have reported their experience. I recommend it highly if it fits you bill.

A working LS circuit is available from a diy forum if you are a diy-er or are hell bend for saving up for other upgrade and only if you can find a match pair of LDR out of the many required for a project. I believe I can also make one from the available info from the internet but I choose to support the inventor who is passionate and generous enough to share his circuit and know how to the diy community in the numerous forum in the internet. His generosity proved that he is not a money grabbing person and in today's world such character is few and far between.

The LS is where I stop my search for a better alternative for now. Buy it if it fits your bill before you consider an interconnect upgrade, tube roll, power cord upgrade, component upgrade. Most likely it is cheaper than other conventional upgrade path. DIY if you want and George will throw you his float when you are drowning. I hope the Lightspeed reach commercial success in a huge way in the future not that George care if it did or not.

 PS: I am not affiliated to the Lightspeed product.

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Thanks for that in-depth review water111 .

If any reading who have the skills wish to construct one for themselves as water111 did, instead of purchasing the ready made Lightspeed Attenuator, my first original post is here to do it with.
http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp.html#post924390
PS: you may have to join to see all the attachments, circuit diagrams ect.
 
I’m always available on this Audiogon Lightspeed thread for any help you may need,
PS: I do not sell kits or parts as they are all available for diyers to get themselves.

Cheers George

This is my impression of the Light Speed Attenuator (LSA) in my system that consist of the following equipment:

  1. Amps:  Two Spectron Musician III MKII in mono block configuration with V-Cap Upgrade, Super-Effect Bybee Purifiers upgraded rail and power fuses to Synergistic Research BLACK Quantum Fuses (Outstanding fuse) driving 4 ohms. 

    The Spectron were chosen due to the following capabilities:  (What does the limitation in peak voltage mean? To illustrate, let’s take example of a CD player with typical output of 2.2V rms (i.e. peak 3V), and if you use XLR balanced output then its peak voltage is 6 volts. Let’s for simplicity assume that you are using passive preamp with gain set at this experiment to the unity i.e. 1.0, and finally, let’s take typical amplifier which has usually gain of 26 dB or x20. Thus, you must expect your amplifier to have output peak voltage: 6V x 1.0 x 20 = 120V. This means that when listening to the same music with most other amplifiers, particularly those without output transformers, the signal would be "clipped". These amplifiers would be unable to deliver the transient voltage to the speaker. The effect is that the music loses some of its lifelike qualities i.e. signal is distorted and dynamics is clearly compressed).  The above example represents situation when your preamplifier gain is unity i.e. with relatively efficient speakers. When your speakers (or music) demand your preamplifier to have gain more than 1.0, then even Spectron amplifiers might clip! Fortunately, Musician III MK2 is capable of operating both in stereo and mono (fully balanced) modes. While not necessarily an advantage for highly efficient speakers as described above, less efficient loads will benefit from the fully balanced operation that triples the power and doubles the headroom to  + 240 volts as well as staggering 7000 watts of peak power (and hold it for an extraordinary 500 msec) assuring that no matter what the speaker load, the amplifier will deliver the full dynamics of the original recording undistorted. Number of reviewers observed that Spectron Monobloc’s sound creates noticeably deeper bass, effortless presentation and powerful slam).

     

  2. Usher BE-20 diamond sensitivity: 90 dB @ 1 watt / 1m at 4 ohms

  3. VPI Prime with Dynavector xx-2 MKII cartridge with the Symposium Prime Footer Damping Insert kit on Mapleshade 24 x 24 x 4 Finished Maple Platform with Audience Au24e Low Z Phono cables.

  4. Whest 2017 version of the PS.30RDT SE with the 40 SE series wire loom and 40 SE input modules.

  5. Crystal Cable Reference Diamond Interconnects.

Previous setups:

I was using the Sonic Euphoria Passive Line Controller (PLC), the Sonic Euphoria PLC is a passive preamplifier using an autoformer attenuator. The Purist Audio IRD LLC-P Preamplifier, also the Axiom passive with modifications to the internal wiring with Mundorf sgw110wh wire, a mixture of Silver and 1% Gold.

The closest of the above passives that came close to achieving true non coloration of the sound and delivering only what was in the recording was the modified Axiom passive.

I researched the Light Speed Attenuator and found interesting comments from owners that ranged from outstanding to not a great fit for my system.  Due to prior passives having plenty of gain for my system, I contacted George and made the purchase.  It arrived in Texas within the two week period he stated he needed.  He provided outstanding technical support and even researched the problem I noticed with integrating my Rel R528 SE subwoofer into the system. For some reason using the Neutrik Speakon connector from my amp to the Rel caused issues with the LSA, which to me sounded like an impedance matching issue. (I do not miss the Rel with the LSA, there is plenty of deep articulate bass with my Ushers alone, but will be searching for a fix).

LSA Power Supply:

Adding the LSA to my system was everything I have been trying to achieve in my listening room.  I decided to power it with my HDPLEX 200W Linear Power Supply vs the wart linear power supply due to the fact that it has a dedicated XLR---5.5/2.1mm Connector Cable.  Perfect for the LSA and provides Top of the Line Hi-End Audio ELNA Capacitors, High Quality 200W Silent R-Core Transformer provides clean energy, Separated Ground for Each Output Rail, EMI/RFI Circuit to Prevent AC Grid Pollution, No Humming or Buzz noise for 50Hz and Peak load, 100% Silent, High Quality Neutrik XLR Connector for All Outputs, and Low ripple noise and void of high frequency noise.

LSA Addition to System Sound:

There are details in the midrange and treble that are just more obvious now. The treble seems more extended, but there was absolutely no change in tone from what is on the album.   Vocals are even more realistic, and everything has increased texture and is more palpable. But the best thing of all is the increased speed of transients. Everything has an immediacy to it. This even translates to the very deep articulate bass. Kick drums have speed and an authority that is impressive. The entire sound stage is one cohesive unit now in my system.

There is a tremendous amount of fast energy. This is consistent on all tracks played. The music has real life and intensity. It is extremely quiet, musical, and detailed with a large soundstage and is very well focused. I consider it an outstanding value for its price range.

The best I've heard in my system to date. I perceive no loss of dynamics at any volume. I can load my room adequately at around 9:30 or 10:00 on the dial. I have plenty of headroom and absolutely no distortion at insane volumes. The bass has never been as good and the separation and blackness are vastly improved. You feel the real image of the instrument’s size and acoustic quality with all analogue recordings I have played to date.

Advantages of the LSA:

With the LSA in my system, I have noticed that setting the proper VTA on the fly with the VPI Prime on each record to optimize playback is very easy and the changes are easily heard without the use of headphones for precise imaging.  From https://londonjazzcollector.wordpress.com/for-audiophiles/tonearm-vta-adjustment/ “Precise adjustment of the Vertical Tracking of your tonearm is one of the most significant improvements you can make to your listening experience. It is not as difficult as you may be thinking, and costs nothing. You have already paid for your equipment, and though the turntable may have been set up “perfectly.  In less than 15 minutes, the effect of adjusting, refining the adjustment, and eventually locating the “sweet spot” in VTA – just a turn of the adjuster, listen, turn a little more, listen, turn again until you finally locate it  – completely transformed the performance of the system. The stereo sound stage snapped into focus, the troubling bass lifted, harshness was replaced by sweetness, an extraordinary and unexpected experience.”

 

Please understand that this is my experience with the LSA with my equipment.

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