Tag Archives: preamplifier

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

The evolution of a preamp

Evolution is impossible for anyone to wrap their heads around. Like trying to visualize a billion, or a trillion of anything, our minds are simply incapable of “seeing” this level of complexity. When the numbers get too big, we lump them into groups.

I can remember trying to wrap my head around the complexity of life. It seems impossible we could have started as single-celled critters, yet we see the evidence of how it works all around us. The fact we cannot imagine something doesn’t mean it cannot be true.

Take something simpler, like a high end audio preamplifier. I have designed many so it’s easy for me to imagine starting from nothing and evolving it into a working piece. Only, I don’t start with nothing. I start with a handful of highly evolved parts: wires, resistors, semiconductors, capacitors. Dig deeper. The idea of a capacitor dates back to 1745 when Ewald Georg von Kleist found that charge could be stored by connecting a high-voltage electrostatic generator by a wire to a volume of water in a hand-held glass jar.

You see where this is going. What’s the history of electrostatic generators? Wire. Or, for that matter, glass jars? Or even as far back as the language needed to communicate the ideas. I won’t bother detailing the long thread of what it took for John Bardeen, and Walter Brattain to leverage the work of others to group together enough ideas to invent the transistor.

It is technically possible to drill down far enough to where we get to the beginnings of something but I imagine the numbers and time needed to do that are too big for us to grasp as anything but a group, lump, or concept.

Our brains are incapable of seeing or understanding complex models over a certain size. It’s one of our limitations.

Which is why we accept—have to accept—lumps of understanding in order to function in the physical world. I accept the lump conclusion that a transistor is an electrical valve where a small current manages a big current.

I accept the lump conclusion that one collection of parts sounds better than another.

The fact I cannot break it down into debatable bits does not mean the collection of bits isn’t true.

 

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

Good article explaining phono stages. I’m writing the next one about the audio business!!

Perilous journey

Imagine the tiny signal coming out of a moving coil phono cartridge: 30,000 to 50,000 times smaller than what comes out of your preamplifier. It has come a very long way and through much amplification to become that much bigger. Like a weary long-distance traveler who struggles to stay intact along the way, its journey is a difficult one with detours, traps, pitfalls and dangers aplenty. But sometimes a designer is so adept at navigating the perilous journey that what comes out the other end shines.

The trick to making a successful phono preamplifier that honors and preserves this tiny signal is two-fold: make sure the vanishingly low output from the cartridge is perfectly preserved, then keep the progressively louder signals away from any limiting agents.

The first challenge is often the most difficult. Interfacing with and amplifying without adding noise can often be more art than textbook solvable. For example, most phono preamplifiers use bipolar transistors to interface with the cartridge because they are low noise and easy to work with. Unfortunately, bipolars and their non-linear diode inputs are not the best at working with tiny signals like those coming from moving coil cartridges. A pure voltage device, like a FET or a tube, is a better choice, yet getting these devices to be low noise can be a challenge. In the new Stellar Phono, engineer Darren Myers solved this problem by lining up multiple FETs in parallel. Each added device reduces noise. The greater the number, the lower the noise.

If one manages to get the tiny signal through the input it’s off to the races, though not without challenge. As the signal grows exponentially larger, it begins to approach the power supply limitations of the circuit. When this happens, linearity suffers—which is why Darren uses high voltage throughout Stellar.

It’s often tempting to just meet spec and call it a day, but then you probably won’t get Stereophile’s Michael Fremer to write: “The midrange on this phono preamp is as open, uncongested, transparent, and revealing as that of any phono preamp I’ve heard at any price.”

It’s a rare treat when a designer maps with care the perilous journey of a signal, then clears a free path for it to arrive at the other end unscathed.