Most Telarc recordings I have heard sound bad, so this becomes even more interesting to me. I would have stuck with the analog.
Which would you choose?
Raul Montilla from Puerto Rico sent me a kind note about an interesting experiment from years past. In it, Jack Renner and the engineers from Telarc are said to have recorded the Cleveland Orchestra on both an analog tape recorder and a Soundstream Digital recorder. They then compared the output of the two and all selected the analog tape version as being more musical.
To most of us that doesn’t sound so far fetched. What they did next might stand a few hairs on end.
Curious why their new digital recorder didn’t sound as good as the older analog tape they ran a second set of experiments. In this round, they had the orchestra play again and as they did the engineers switched between the live sound and the output of both recorders. To their surprise, the digital recorder’s output was indistinguishable from the live feed while the analog’s output softened the highs, compressed the strong bass, and added a type of pleasant coloration.
This convinced them to abandon the analog recorder and stick with the Soundstream (and later others) and thus the label Telarc was born. Not everyone would have made that choice.
Which would you have chosen?
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.