David Gilmour’s guitar tech, Phil Taylor, was on the line. David wanted a compressor, but not just any old compressor; he wanted something special… Let me guess: Like an LA-2A in a pedal. “No problem,” I gagged, not sounding cool, calm or collected, “we’ll get a PC-2A pedal to you”. Gilmour is a god in the guitar world: if he decided to use our compressor, it would put Effectrode well and truly on the map, big-time.
We posted the pedal to David Gilmour’s Astoria studio in Hampton Court. But a few days later I received another call from Phil. As he spoke, I got that sinking feeling. Apparently the PC-2A was not cutting it in the studio: the attack was too slow. He suggested he send back for modification, to see if I could somehow accelerate its compression performance. I was smart enough not to argue with him about it at the time: when the Floyd speak, you listen.
After all these years in audio industry you’d think I would have gotten used to it; but you never do. Knock-backs: I was back at square one; and this time I had the Floyd on my case. Not good; not good at all. I put my social life on ice, what little there was of it, and prepared to spend some long, lonely nights burning the midnight oil in the Effectrode workshop. It was business as usual: trying to solve the unsolvable.
The problem was parts. They just don’t make things like they used to, and that includes photocells. There used be hundreds of different photocell variants for different applications. Now there are just a handful, and there was nothing on the shelf that would do the job. So I ended up fabricating my own custom opto-coupler, from a vintage light dependent resistor and a 3mm red LED. These old LEDs from the late 1970s weren’t very bright, not like the hyper-bright LEDS we see today: my thinking was to create a subtle compression effect using low light levels. And it did work. The compression effect was smooth and transparent: firstly, because the compression ratio was low; and secondly, because the attack was slow.
Great, but Phil noticed that my homemade photocell wasn’t catching fast transients from David’s solo playing. How do you speed up a photocell? Well, you could bias it so that a tiny amount of light is falling on photo-resistive element at all times. This overcomes the sluggishness (time constant, or hysteresis to be technical) inherent in the photo-resistive element. However, it does mean that the resistance is much lower when there’s no compression happening. Tube circuits are high impedance circuits by their nature: they don’t operate well with low resistances. We needed a photocell with an intrinsically high resistance, even when light was falling on it.
I dug deep, searching through vintage datasheets and parts suppliers for a device that would fit the bill. There were a few promising candidates, but they were obsolete; long out of production, as no one used this stuff anymore. But then, I found a cache of new old stock selenium opto-coupler devices. Samples were ordered, and I made a few adjustments to the side-chain circuitry. How did it sound?
Well, “toneburst” tests on my ‘scope revealed that the PC-2A was kicking-in much earlier and limiting the input signal cleanly. In a word: it was “fast”. Impatient to hear the fruits of my labours, I connected the newly modified PC-2A to an amp and a guitar, and gave it a test drive. It was a completely different animal. Still transparent, but more responsive and musical. We shipped the pedal back to Phil, and the rest is history. Over a decade on, that PC-2A is still on David Gilmour’s pedal-board today.
