Yesterday I touched on one of the first big learning experiences I had as a designer: trying to sort out what I heard relative to what was happening electronically. It's a very different discipline to try and relate cause and effect with what we hear vs. just knowing whether you like something or don't.
The challenge was with an Audio Research tube phono stage using active EQ vs. our solid state phono stage with identical EQ. You could listen for hours to the AR, but grew fatigued after a couple of tracks with our version - yet they measured identically in terms of frequency response - actually, ours measured a bit better at the extremes. Go figure.
The overwhelming emotional feel from listening to ours vs. theirs was one of fatigue, especially when the music got loud. Because tubes run at a magnitude higher voltage level than do solid state amplifiers we began to suspect overload from the loud passages of music. Cartridges at the time were fairly hot, most were moving magnets and the lower output moving coil cartridges were just getting going. But alas, when we duplicated the maximum outputs possible on the phono cartridges and tested the two units neither were even close to overload - at least as far as the test equipment was concerned - and even real time scope pictures of the actual output never approached clipping. But here's where it gets interesting.
So convinced were we that the scrunched up fatiguing sound we heard at high music levels must have been due to the lower voltages of our solid state design vs. the tube's higher voltages that we went out on a limb and made an experiment. We figured out how to double the voltage of our stage from 30 volts to 60 volts - still way less than a tube - but far greater than any solid state design of the day. Bingo! The music opened up, the fatigue was reduced and we learned that the standard tests of the day really didn't tell the whole story.
So were we done? Nope. Realizing we just discovered something about overload (called headroom) we sought to see how far we could go. Tomorrow we'll finally understand why we went passive.
