Pre/Power Amplifiers

PS Audio's 'Gain Cell' aims to better the performance of a conventional potentiometer in setting the volume, or gain, of a preamp. Inside the Gain Cell's blue boxes, a brew of IC op-amps and discrete FETs are configured into a Gilbert-style mixer. However, instead of combining two audio feeds, a variable DC feed is 'mixed' with the audio to increase or decrease its level.

The linearity of this technique is influenced by the matching of the transistors in each half of the cell, so we asked Paul McGowan, PS Audio's owner, to shed a little extra light on the thinking behind its latest innovation.

'We knew that potentiometers and stepped volume controls impacted sound quality as much as the circuitry supporting it', says Paul. 'We had to find a better solution! It occurred to me that we could eliminate the need altogether by directly changing the gain of the preamp's line stage.

'Over the course of the next year, I played around with various Voltage Controlled Amplifier (VCA) topologies that all showed promise but were difficult to build and harder still to consistently manufacture. Then I stumbled upon some op-amp ICs from a small design house (THAT Corp).

'Another six months of design work later I had what we call the "Gain Cell" an amazing sounding variable gain amp. That circuit, which requires a number of peripherals and hand tuning to get right, solved our volume control dilemma and serves as the basis of our Stellar Gain Cell line, including our upcoming Strata – a new integrated amplifier.' PM