Milbert Amplifiers


The Most Musical Amplifiers. Made in USA since 1986.

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We think tubes in general and in particular our BaM-235ab are superior because:

1. Tidy & Graceful

Passing audio through circuits having fewer components generally sounds cleaner and yields pure, lifelike sound quality as compared to complex circuits having more parts to distort, color, taint, or otherwise degrade signal purity. Simple circuits are inherently more reliable. Tolerant of circuit and part variations, tubes work well in simpler circuits.

Music is dynamic, and in a real tube amp like the BaM-235 any onset of overload is gradual with low, even-order harmonics. This sounds much less offensive than the harsh, sporadic, odd-order harmonic distortion of transistors, even though tube distortion figures can generally measure higher. Tube distortion can measure higher while still sounding less objectionable than transistorized distortion.

In a sense, transistors can inherently tend to "play out of key" by literally creating dissonance in the music: Transistor amps generally distort by introducing odd and spurious harmonics often unrelated to the fundamental pitch that can be quite unpleasant to hear. Moreover, transistory clipping and distortion is abrupt, resembling a square wave, and often comes with DC which can destroy speakers.

2. Highly Linear

Whereas transistors saturate and simply clip and produce odd and unrelated distortion, noise or shrillness, tubes overload on a gradual exponential curve, being by nature relatively linear voltage amplifiers.

Negative feedback is a portion of the output subtracted from the input, and it is widely used to help correct non-linearities and distortions. But all amplifiers exhibit some delay and by the time the negative feedback "correction" arrives back at the input it's a bit late, a different signal is usually present at the input, and the initial signal is already playing at the speakers (negative feedback corrects the next signal for what the current signal has done). This is okay for steady-state signals, like a test sine wave, but it is terrible for fast-moving transient signals like music. In general (and not surprisingly), negative feedback tends to decrease responsiveness and consequently "suck the emotion and life out of music." Expect sterile and boring, lifeless sound as negative feedback increases. Given adequate linearity, less feedback is always better.

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Transistor amps generally need more than 50dB of negative feedback overall, either globally or within local circuits. Transistors inherently resist linear operation as they intrinsically prefer to work as (non-linear) switches and not as linear valves. Incidentally, valve is the European name for vacuum tube, describing rather well how a tube works.

In a tube amp, between zero and 20dB of negative feedback usually improves linearity and reduces output impedance. The BaM-235 uses a trifling 6dB of negative feedback.

Another benefit of the BaM-235 is wide and accurate frequency response. As Rupert Neve (pro audio fame) and others * have pointed out, many people can hear the difference between a sine and square wave at 15 kHz which means they are hearing at least the first harmonic of the square wave; at 30kHz, that's well above what is commonly considered the upper limit of hearing. Tubes love to work at high frequencies, and the BaM-235 plays well out beyond 50kHz with a natural, gradual rolloff.

* Tim de Paravicini notes the importance of frequencies outside the conventional 20Hz-20kHz range. He points out that one can sense the standing wave of a large cathedral which is below 5Hz. A body senses sound through more than the ears (can anyone name a famous deaf composer?). "This traditional notion of the hearing stopping below 20Hz is absolutely rubbish. We detect sound down to the resonant frequency of the body, about 3Hz", argues de Paravicini. Deaf people certainly seem to hear through the body. Likewise, the high frequency notion of 20kHz is also rubbish. We detect audio up to about 45kHz, not as a tone but a certainty that something is going on. My method of demonstrating this was several years doing work on ultrasonic bath cleaners. Everybody in the room suffered the after-effects of tinnitus, aware of something going on. Moreover, playing a 20kHz tone through suitable speakers puts listeners in discomfort. So traditional myths have to be thrown out the window."

Nelson Pass explains: "Although human hearing is generally very poor above 20,000 Hertz, ultrasonic frequency roll-offs produce phase and amplitude effects in the audible region; for example, a single pole (6dB/octave) roll-off at 30 kHz produces about 9 phase lag and 0.5 dB loss at 10 kHz. The effects may be subtle, but their audibility is undesirable in a piece of equipment whose performance is judged by its neutrality."

3. Patented Technology

Real tube amps like the BaM-235 use generally high voltages (200 to 400 volts), versus transistor amps which operate at maybe 60 volts. Our higher working voltages allow much bigger voltage swings and headroom while also tremendously increasing local energy storage. The BaM-235 does not readily "run out of steam" or "hit the rails" thanks to its great headroom and energy reserves. Listeners frequently report that the BaM-235 sounds much more powerful than its 35 watt per channel rating.

We use transistors and semiconductors how and where they are naturally best suited: as switches and diodes in the power supply. Again, the inherent bipolar nature of a transistor predisposes it to operation as a switch and we apply that to best advantage.

As perhaps millions of musicians, engineers and audiophiles will attest, tubes have always bested transistors for sound quality. The BaM-235 car tube amplifier applies patented technology to bring the best possible sound quality to the automobile.

Material herein added and updated constantly; presented for inspirational and educational purposes per Fair Use.

Last modified 7 Aug 2019

Milbert Amplifiers, The Most Musical Amplifiers. Made in USA since 1986.
Milbert Amplifiers
The Most Musical Amplifiers
Made in USA since 1986