Tag Archives: amplifiers

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.

Choosing inputs

We started a little mini-series on how amplifiers work. I know that some of you gloss over these details because you’ve heard them before or you don’t care. Others have large appetites for learning and it is to those hungry readers I continue.

If we look at the block diagram of a power amplifier in this post,  we note two main sections: input and output. The job of the input stage is to take a small signal from the preamp and make it 30 times bigger. Let’s talk about that stage today.

The input stage of a power amplifier is a big preamp. It is also the one stage that makes nearly all the sonic difference in an analog amplifier. This is the most critical stage to get right. Just like a preamp’s architecture has everything to do with its sound, the amplifier’s input stage is where all the magic happens.

If we look at an amplifier like the BHK, we’ve used a vacuum tube to provide the gain. In most solid state amplifiers—those that are not hybrids like the BHK—this task of amplifying the small input signal is handled by any number of clever schemes. I have engineered simple op-amp style architecture with a single diff pair feeding a gain stage, to more complex versions known as full complimentary where there are multiple diff pairs and gain stages. The means to build a high voltage preamplifier are as many as there are amplifiers. Every engineer has their take on what sounds best in this all critical stage.

One technique we pioneered many years ago, though I am sure we weren’t the first, was the use of a separate power supply for this input voltage gain stage. It’s what we’ve done in almost every amplifier we’ve ever built and the improvements are clear to hear. In this scenario, there are two power transformers (or at least two separate windings on the main transformer) inside the amp: a small and a large one. The small transformer and its associated power supply feed the input stage, while the behemoth transformer is kept separated for the output stage. Here’s where we can get tricky. We can easily regulate this input stage, we can make sure it is never impacted by demands for power on the output stage. Thus our internal preamp is pure and undisturbed by our subject of tomorrow’s post, the less important but certainly not unimportant, current amplifier.

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.

Lowering impedance

The lower the AC impedance feeding high-end audio equipment the better each piece sounds. And when the entire system is fed with low impedance power the results can often be breathtakingly better. But, how do engineers lower impedance?

That question’s not simple to answer but I am going to try. Basically, we need a few things: extra energy, a valve to mete it out, and a measurement system to decide how much and when. Definitely not something passive conditioners or simple wires and plugs are capable of.

The easiest way to think of a regenerator’s power amplifier is as a valve in the classic water example. It has a power supply with stored energy and a means of releasing however much of that energy is needed. For our analogy, we’ll imagine the wall AC plug as the main water source, the amplifier’s power supply as a reservoir, and the output of the AC regenerator as a valve. For powering equipment we need 120 volts (or double that outside this and a few other countries). Thus, we turn our imaginary spigot on just enough to attain a flow of 120 volts. Life’s good.

But then, something happens. A big and thirsty device begins sucking water out of our imaginary faucet at a rate greater than expected. The 120 volts of flow we once drops to 100. The system can sense the drop and turns the valve, releasing more of the stored energy and we’re back to 120 volts again. By carefully monitoring the flow, 120 volts can be maintained no matter of thirsty or satiated the connected amplifiers are.

I have just described the mechanisms at play in the power amplifier of an AC regenerator. If we use the term feedback in place of measuring device we exit the imaginary and move towards the real.

Feedback is the essential element in an amplifier that senses change in the output and relays that information back to the control valve for adjustment. The more feedback, coupled with greater energy storage and strength in the valve, is essentially the elements we focused on when we rebuilt the new amplifier for Ps 20, 15, and 12.