Hi all.
As many of you, I have had the great chance to become the owner of a dual mono Lightspeed Attenuator (LSA).
I should first briefly describe my system so that you can figure out how I use the LSA. A CD drive (Mephisto I, Audiomeca) feeds a highly modified Behringer DEQ2496, of which I mainly use the internal DAC. The DAC output is made of a pair of Lundahl transformers with an output impedance of less than 30 ohms. The signal then goes (went) to a passive preamp (a Stevens and Billington transformer volume control unit (TVCU) using copper TX102 transformers mk1(?)), and then from the TVCU to 2 amps per channel via a Y cable (bi-amp). One cable goes through a VT25 SET amplifier to a wide range loudspeaker. The other cable feeds an "all in one" commercial [class D amp / low pass filter / volume control / phase control] package (Atohm S300) and then a pair of Eminence alpha 15 A per channel below 150 Hz.
In a first trial, I just replaced the TVCU with the LSA, and listen to the CD I was listening with the TVCU when the LSA arrived. Well, the result was not so good. It resembled the sound my former Alps pot provided: listenable but with rather poor definition. I knew the impedance matching between the LSA and the downstream amps plugged in parallel was not good because the S300 has a 20kohms input impedance, which considerably reduces the overall downstream impedance "seen" by the LSA even if the input impedance of the SET amp was (presumably because I do not know it) most probably 50 or 100kohms. So, I simply unplugged the S300 and listen again to the same CD using the wide range loudspeakers only. In this configuration, the impedance seen by the LSA is only that of the SET amps. The difference was like night and day! Perfect definition, perfect sense of space, perfect timbres, etc.
Not only was the LSA extremely transparent feeding the SET amps alone ("true to the source" to use George’s expression, which perfectly accounts for what it is about), but it now even largely outperformed the TVCU! To be more specific about this important point, the CD I was listening to was Handel’s opera Agrippina by Rene Jacobs. With the TVCU, the sound was very accurate but also very harsh. With the LSA, not only all harshness disappeared (I could listen louder without fatigue) but that was not at the price of lower definition. To be sure this was not unique to the first CD I was listening to, I tried another one and got exactly the same result. This meant that the first listening impression was not CD-specific, but was an actual difference between the TVCU and the LSA.
Surprisingly, although I was listening through wide range loudspeakers only (remember the bass loudspeaker amps were not used anymore to solve impedance matching issue) I could hear very good bass! I conclude that the LSA also improved the bass, a result that could not be achieved using the TVCU, which sounds lean without the support of 15' loudspeakers.
George suggested inserting a buffer between the LSA and the bass amp to solve the impedance mismatch issue. He was kind enough to even propose a link to a very cheap buffer. Unfortunately, the access to the buffer was denied by ebay for some reason. After a very limited search, I found a ready for use buffer sold by Indeed (Hong-Kong), which I bought. Indeed buffer has an interesting 1Mohm input impedance and a less interesting “more than” (?) 5Kohm output impedance. Since the latter was lower than what I read was that of the LSA (7Kohms, is that correct George?), I thought Indeed buffer was worth a try. After a few weeks, I received the buffer and plugged it between the LSA and the bass amp. The result was perfect! Since then, I have not changed anything to the set-up and enjoy rediscovering my CD collection.
As a provisional conclusion, I would say that I am more than satisfied with the LSA, and that George is a great researcher and a great creator whom I thank for making this jewel available to us simple human beings...
Good listening to all,
Christophe.
PS. I would like to specify that the goal of the above review is certainly not to denigrate the Stevens and Billington TVCU. When it replaced my Alps pot a few years ago, it really improved the sound, and I have enjoyed listening music thanks to it.
