Tag Archives: analog

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

Noble experiment

I’ve been noodling a lot lately on my “live” experience at the airport. I’ve even awakened in the middle of the night with an aha! but then fallen back to sleep with a no, can’t be that.

But it’s something.

Several of you have suggested it is the recording process where the damage happens. This is a noble thought because it’s somewhat obvious. Like Occam’s Razor, simpler theories are preferable to more complex ones because they are more testable.

I wanted to share with you an interesting test I performed some years ago. Working, as I did in recording studios with fine analog tape decks I had the ability to easily switch between the tape recorder input and output. Here’s what I found. On simple single feeds, like a bass guitar or a microphone, it was very difficult to tell one from the other. If I listened closely I could hear a slight roll off of the highs—normal for those days of analog tape.

In later years I performed a similar experiment with our A/D converter the NPC. Feeding the analog output of a phono preamplifier into the preamp on one input and then the gain matched digital version on another, the differences were even smaller—essentially non-existent—as long as the source was a single voice or instrument.

In both cases (analog tape and A/D) when the music’s complexity increased to multiple voices or instruments the differences became clearer.

So, for me, the mystery continues. What I heard was only a few musicians and though they weren’t recorded I’d bet good money that if they had been I wouldn’t have been able to tell the difference.

Which leaves the system…or something else…