|I've always wanted to find a use for that line which comes from a John Lennon song entitled, "Gimme Some Truth." Turns out a little discourse on a preamp would provide the reason to use it.|
Okay, those of you that know me or have followed my comments here know I have eschewed the use of active preamps in my system in favor of passive designs. I still own a couple active preamps, namely a Berning Micro ZOTL and a Silicon Arts Design Si2, but primarily listen to the passive units in my system. I have also owned some fine active preamps from Cary, Joule Electra, Jeff Rowland Design, and Tube Research Labs. Itís not that the active preamps donít work in my system. Itís just the passives work better.
There has been lots of talk here lately about the Lightspeed attenuator that I own designed by George Stantschleff in Australia. Heís known on Audiogon as Georgelofi. If you havenít heard about this attenuator here are a couple links for you to check out:
To recap, the Lightspeed attenuator is basically a resistive passive design with a twist. The uniqueness of the Lightspeed's design is that there are no contact points in the form of a "wiper", as is the case with other passive designs (resistive and transformer) that use a potentiometer or discrete stepped attenuator. The key component in the Lightspeed attenuator is the Silonex NSL-32SR2. The device is a sealed unit that consists of a high performance LED that shines on a light dependent resistor (LDR) thereby achieving proper attenuation.
There has also been lots of talk about the challenges in getting passive preamps to work optimally in ones system. Impedance matching, cable length, source output, and other factors all come into play. In fact, I feel itís safe to say that achieving system synergy with a passive preamp is possibly one of the most difficult things to do. Itís not difficult to find out if your system is passive friendly. Here is a link to a good test one can easily perform:
Just scroll down to the Bolero Test. However, just because a system is passive friendly doesnít mean you might like what a passive preamp does in your system. Many use terms like lean, flat, and lifeless to describe the sound they heard when using passive preamps in their system. Whether this is because of a lack of synergy or personal preference is not relevant to this discussion, but nonetheless passive preamps do get unfairly characterized in my opinion. Of course I have my own opinions too on the subject;)
Okay, so why more blather on a topic that has been discussed at great length of late? A couple months ago I was having a discussion with Steve Eddy, known here on Audiogon as Simply_q. Steve is a designer and manufacturer of fine cables and other things audio. In our discussions I mentioned the LSA and he pointed me to a Stereophile article written by Corey Greenberg many years ago. You can click on the link and read it:
The article discusses passive preamps and describes a means of building one using the Analog Designs BUF-03 buffers. Interestingly enough itís been ďrumoredĒ that the person referred to as Elvis in the article is none other than Steve Eddy himself. So just maybe he deserves the credit for the design. In any event Steve Eddy referred me to Ed Schilling at The Horn Shoppe. It turns out that Ed makes a preamp using these same buffers, but with some new design ideas added to the mix, including the use of photo cells. Ed calls the preamp The Truth. Here is what he has to say about it:
It has an input impedance too high to measure, output impedance is a couple ohms, bandwidth is to 60Mhz, slew rate is a couple hundred V/microsecond.
There are no capacitors or resistors in the signal path. There is no potentiometer in the signal path.
It uses photo cells to control the volume. It does not use optocouplers.
It is an "active" device and suffers none of the "problems" that "passive volume control/pre amps" have. It can drive long (30 feet) cables with ease.
I've had parts of this circuit run for 10 years without failure.
As far as I know there is nothing like it available for any price.....I could be wrong but I doubt it. I looked "pretty hard and long".
The price in a nice natural aluminum enclosure is $825 shipping included. Extra input adds 40 bucks...a third adds 20 more. Anodized black adds $40. It's taking 2-3 weeks right now, this may increase.
You can also go to The Horn Shoppe forum on their web site to read more about this preamp:
Now, getting back to The Truth. First off, youíll note that Corey Greenberg refers to his DIY build as a buffered passive preamp. However, I believe Ed Schilling has more accurately described a circuit that uses buffers as an ďactiveĒ device. Buffers arenít new to preamp designs and have been used by the likes of John Chapman, Nelson Pass, and I believe Guy Hammel among others. In essence the use of buffers in the circuit, if designed correctly, eliminates all the potential system matching issues normally associated with using a passive preamp in your system. As Ed Schilling mentions, cable length is no longer an issue. In addition, the output impedance remains fixed at each point in the volume control.
However, The Truth goes a few steps farther in keeping the circuit very simple and like the LSA design, eliminating the potentiometer from the signal path. In my opinion, one of the keys why these two preamps sound the way they do.
So by now youíve probably figured out that I bought The Truth. Iíve had it in my system for a few weeks and have swapped it back and forth with the LSA. Iíve recently lent the LSA to a friend for evaluation and The Truth is now being used exclusively. I have hooked it up to both my VAC Auricle Musicblocs and Atma-Sphere S-30 driving Audiokinesis Jazz Module speakers. Sources are a CEC TL-51X/Lessloss DAC 2004 MkII digital front end and Galibier Design Serac/Colin Engineering Groove Master Phonostage analog front end. All running single-ended as unfortunately The Truth is not available in a balanced version.
Before getting around to describing my thoughts on the sound I would like to mention a couple things about The Truth. First off, using the volume control might be a little tricky for some folks. You will notice that even though you are rotating it, no music may be heard until youíre pretty far around the dial. In my case this was true regardless of the amps input sensitivity, which are quite different between the VAC (1V) and Atma-Sphere (2.83V). It wasnít until about 1 oíclock that I started to faintly hear the music. However, once you reach that point, the sound level will rise pretty rapidly even with the smallest increments on the non-stepped volume control. Normal listening volume for me is around 3 or 4 oíclock depending on the amp. According to Ed Schilling, one of the benefits of using this much of the volume control is that The Truth operates quieter the further around the dial you go. Not that itís a noisy preamp at lower levels, at least not to my ears anyway. I find like my LSA that The Truth is overall extremely quiet.
Secondly, The Truth does not use an on/off switch. Once plugged in it stays on all the time. No worries here as it does not run hot. However, even though it remains on constantly, Ed Schilling advised that it still takes about 10 Ė 15 minutes to sound optimal after music has been playing. Unfortunately I canít recall Edís explanation as to why this is the case.
Now that thatís out of the way you might be curious as to the sound. Upon first impression the sound with The Truth in my system reminded me of the Wadia digital house sound. It was very fast, detailed, unforgiving, with a little edginess on the top. In fact in a conversation with another audiophile friend who purchased a unit right after me, and who also owns an LSA, we were discussing the possibility that the buffers were adding some coloration/artifact to the mix. Well as it turns out, my unit had a glitch that I stumbled on by accident and was indeed negatively affecting the sound. Upon inspection of a photo of the circuit I sent to Ed Schilling he immediate identified the issue and walked me through the simple procedure to remedy it. One thing I learned about Ed through this process is his customer service is impeccable. With the situation resolved the edginess was gone and The Truth began revealing itself.
Again, The Truth provides a very fast and detailed sound with plenty of dynamics. It is very transparent. Background is black and The Truth presents a nice 3-D sound stage (assuming itís there in the recording to begin with). It will not hide flaws in recordings, or your other components for that matter. It gets out of the way and is quite enjoyable. Iíve found I can listen for extended periods with no fatigue. At its price point you can make the argument that it is a true bargain. For those of you into audio jewelry The Truth isnít going to win any beauty pageants but it is well built in a nice aluminum chassis. The captive power cord may turn off some, but works for me as it does what it is intended to do. I have no desire to switch it out for an IEC.
For those wondering how it compares to the LSA I hate to disappoint but I wonít be making any comparisons. Both units are affordably priced and easy to obtain so try them for yourselves. The Truth is offered on a trial basis so in my opinion itís a no-brainer and worth a listen. I will say three things. First, I do have an opinion on which one I like better. Second, both are staying with me. Third, The Truth provides all the benefits of a well designed passive without the need to worry about system matching issues associated with passive designs. Those who are hesitant to go down the passive road because of potential system matching issues, or their systems may not be passive friendly in general, can find a great no compromise solution with The Truth.