To most people, a transistor is just a black plastic thing with three legs. To an engineer working on a high-end audio system's architecture, it can mean the difference between goosebumps and disappointment.
That's because not all transistors are the same. In high-end audio, the two most common types are bipolar junction transistors (BJTs) and field-effect transistors (FETs). They may do the same job—act as a valve for the power supply to amplify the incoming signal—but they do it in very different ways. And it turns out, we can hear the difference.
BJTs are current-controlled devices. They’re fast, precise, and linear. If you want a circuit to measure well on the bench, BJTs will usually get you there. They give you a sound that’s clean, detailed, maybe even a little clinical if you're not careful.
FETs, on the other hand, are voltage-controlled—more like vacuum tubes in how they behave. They have a softer turn-on, a more graceful overload characteristic, and a kind of harmonic generosity that many people call “tube-like.” Especially JFETs. I’ve always loved JFETs for input stages. They bring a richness and warmth that doesn’t smear detail.
So which one’s better? Depends on what you’re after. If you want maximum resolution and control, BJTs might be the tool. If you want musicality and emotional connection, FETs—especially when used with care—often are the better choice.
At PS Audio, we use both. It’s never just about specs—it’s about synergy. About how the whole circuit breathes together. Sometimes we start with a clean, accurate BJT design and realize it’s missing something. Too clinical? Add a FET at the input and let it open up. You get body, air, warmth. That last bit of humanity that helps the music connect.
In the end, it’s not the part. It’s how you use it—and how it all works together. Designing with your ears means listening for that balance, not just chasing numbers. Understanding the differences helps us build better gear.
But it’s listening that makes it sing.
