If we never left home everything would be ok

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In yesterday's post Air Cables I described Stan's invention of the modified twin lead for an interconnect. Made of two identical 20 gauge stranded wires and held apart 3/4" with masking tape, so chosen because it was as close to nothing (air) as he could figure out, this was our first great sounding cable: open, spacious and certainly low cost. Our preamp was nothing more than a single volume control (pot) strung between two short sets of these cables. Our customers were clamoring for us to expand our product line from the single phono preamplifier we built, to that of making a full preamp. They were tired of our little phono box being an accessory and wanted the start of a full PS system. Stan wanted to build a simple box, identical in size to our phono box. Inside we would copy his masking tape wonders, add a pot for the volume and a selector switch for the inputs. Together, we'd have a two box solution. I thought it was a fine idea. To be honest I was relieved that Stan, adyed in the wool minimilist, had readily agreed to have a chassis at all. I don't recall any other "pots-in-a-box" during the early 1970's and we were pretty sure this was a novel idea. We both liked the notion because it was simple, it matched our existing product and it would have been easy to build. Then reality struck. The first problem we encountered was the masking tape itself. Made from paper and adhesive it was certainly a good insulator with very little sonic degradation added to the cable. But masking tape becomes brittle over time and eventually disintegrates. I proposed, as an alternative, a PC board. Stan was horrified. No way, it had to be hand wired with point-to-point contact of the controls. Ok, we weren't planning on building many of these so why not? He was correct, the point-to-point wiring method definitely had a sonic edge. How much of an edge, relative to the easier-to-build PC board option (that all the other manufacturers used), was hardly up for debate. We played with different ideas, including twisting the two conductors together (using a drill to twist them), hand braiding them like the eventual Kimber Kables, but finally landed on single point wiring between the inputs/switch/pot/outputs. The ground would be run separately and would not be near any of the signal wires, thus removing the constriction problem we experienced earlier with coaxial cables. The chassis itself would be the shield and, we discovered, as long as we kept the signal wires away from the metal of the chassis, we'd maintain that open sound we were looking to maintain. A history note here. Years later others, like Counterpoint and Marantz, would resort to making their chassis out of copper to reduce this ground/signal proximity issue that gets worse with different metals in the chassis. Even Stan, after he left PS and started Superphon, used acrylic to build his chassis and called it a "Space Case". We decided to call the product a Control Center rather than a preamplifier. Two lines of thought with the name: it hadn't any amplification stage in it and all it did was control which input was selected and at what volume it would be played so using a name with "amplifier" in it wouldn't be honest. So the Control Center it would be. Then came the next problem, interfacing with power amplifiers. Our reference system was based on our own power amplifier design. In that design we easily controlled the overall gain of the power amplifier and set it so it was a comfortable match to our passive Control Center and phono stage. Worked great. Others weren't on the same page as we and the first time we ventured outside PS Audio to try the new Control Center we were faced with a serious problem: loudness. Of course we'd neglected to consider the efficiency of loudspeakers and the gains of power amplifiers other than out own. That's what happens when you don't get out much. If you've ever seen an efficiency spec for a loudspeaker it's usually something like 97dB/watt. No doubt you've seen this. What it means is that for 1 watt out of your power amplifier, the loudspeaker will produce 97dB of sound. The higher that dB number, the louder your speakers play for the same power amplifier output. Efficient loudspeakers don't take a lot of power, inefficient loudspeakers needs lots of it, all to reach the same loudness level in your room. Then there's the power amplifier itself and its issues are gain and impedance. Power amps do not have consistent gain specs. They are all over the map, certainly back then. Power amp ratings are less obvious than those of loudspeakers. They typically reference a given input voltage to produce full power. It can be a little confusing. Back in those days manufacturers were just figuring out that louder is better when it comes to A/B testing of amps by consumers. If you take two amps and one has a certain gain, the other a few dB more, inevitably people tend to choose the louder of the two. Certainly this was true in the way amps and speakers were sold at stereo stores in those days. Most hi fi shops had large push button panels allowing the sales people to select any loudspeaker in the store and any amp. The idea was that a customer would come in and ask to hear, say a pair of Advents. The dealer would select the Advents with the matrix switcher, play an LP the customer selected and then he could compare the Advents with whatever other choices in the store with a push of a button. Once selected, you could then try different power amps. The louder amps generally won. The problems here should be obvious: none of the speakers pairs were setup for best sound, the switching systems they used were awful and making decisions like these should be done in an environment closer to a person's living room. History note. During this era we saw the rise of the Audiophile dealer who had dedicated living room systems setup to audition speakers and amps rather than the traditional hi fi shops method of pushing a button to select. It wouldn't be until the 1990's that the speaker matrix switchers finally died a much needed death. Our first audition of the new Control Center was a flop. Even with the volume turned all the way up, the music played only at moderate levels. To make matters worse, the power amp we were trying it out on had a low input impedance of 20k, touted by this particular manufacturer as an advantage because it made the amp "faster". There were a lot of good stories amp manufacturers came up with back then. This low impedance was a problem because our volume control was a high impedance one: chosen because we felt it was important to have a high input impedance for the sources we wanted to connect to the Control Center. If you take a high impedance source or preamp output and try and feed a low impedance input, like that of a power amplifier, you get a loss of volume. Not a good thing. In a standard active preamplifier this isn't a problem because of its internal gain stage, which has low output impedance. The story continues tomorrow.
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Paul McGowan

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