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possible to match the solid-state gear in low noise operation. We might believe them, if it were not for counterexample offered by some of the best tube gear: tube microphones, preamps, and amplifiers that do not hum along with the music or hiss like tea kettles. (I built a direct coupled electrostatic headphone amplifier that is so quiet that a friend used to borrow it to evaluate the noise of hand picked transistors for an ultra-low noise preamp he was building. The headphones and amplifier revealed more information about the amount and quality of the noise than did looking into an oscilloscope.) There is simply no excuse for one tenth of a volt of hum from the output of a tube power amplifier.
     We are not saying that the tube is just as quiet as the transistor or FET, as, ultimately, it is not; only that much of what is built with tubes could be much quieter.
      Amplifying low output MC cartridges reveals the absolute noise floor of a tube. The quietest tube is much noisier than the quietest FET. The 2SK147 FET is eerily quiet; after spending years looking at the 6DJ8's hash noise on an oscilloscope, the flat thin line of noise from the 2SK147 makes one check to see if it is actually connected to the probe. This praise for the FET's low noise does not constitute a wholesale endorsement of the FET's use for all audio circuits, only a recommendation for this limited use: amplifying the micro-volts out of an MC phono cartridge sufficiently to give the vacuum tube a chance to take over.
Making tube equipment quieter requires a solid grasp of where and how the noise is interjected into the output signal. Last month's article should how to lower the noise from the Cascode drastically, without having to lower the actual amount of noise at the power supply connection. This month's article tells of a similar technique.

                                     // Editor


Welcome to Issue Two
    This month's issue continues the unbalanced to balanced article and offers a trick for reducing the power supply noise from the output of an SE amplifier. Noise, its causes and elimination, will continue to be explored in future issues. The motive is not hard to find.
    Noise constitutes a large part of what is condemned as the "tube sound," by those who favor solid-state electronics. Few tube supporters would defend hiss or hum as being euphonic. Noise stands guilty as charged, as it robs the musical experience of subtle nuances. Much of what is magical in a great recording is the air, minute details, and weak hall reverberations that make the recording come alive in our living rooms.
    By masking these subtleties, noise reminds us that what we are hearing is not live, but only electronically reproduced. Of course, live performances are often marred by coughing, hacking, talking, creaking chairs, and glass clinking. But this noise is random and sharp, unlike the continuous and dull drone of power supply hum; no one in the audience imagines that he is hearing a reproduced musical event in his living room because of this live noise. (In fact, a few rare recordings so perfectly capture this live noise that its reproduction actually helps to convince us that what we are hearing is live.)
    Given the choice between low distortion and low noise, choose low noise. The difference between .1% distortion and .01% distortion cannot be heard; a reduction of noise from -60 dB to -80 dB can.
If you want to improve the sound of your tube equipment, lower the noise. Of course, low noise and low distortion are not mutually exclusive and it would definitely be better to have both.
     Here is the irony of the situation. Most solid-state gear is very quiet, because of the low distortion race among stereo manufacturers. In order to please the total harmonic distortion meter, an amplifier must be both clean and quiet, as the meter cannot distinguish between distortion and noise. Whereas, the tube audio designer, having no faith in total harmonic distortion measurements, holding to his belief that no meter can beat his ears, forgoes the requirement of extremely low noise operation.
     Some tube audio designers are very pessimistic about the noise given off by their designs. They tell us that the vacuum tube is an inherently noisy device and that it is simply not

In This Issue

   2 Lowering the SE Amp's Output Noise
5 Balancing Acts  -Part 2-
8 Design Idea: SE Transformer Testing 
9 Publishing Information
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