Happy December! I was just watching some silly show last night and was reminded the Mayan calendar says the world ends in 21 days. Let’s make the best of what we have left icon smile Enjoying or working? Sorry, I just couldn’t resist.
We’ve been focusing on the art of listening and the subjects seems to have generated some measure of comment. One of the more interesting points made was the challenge of listening as a designer is different than listening as a music lover. Of course you can have both but if you, like me, make your living designing audio products then sometimes we have to “work” when we listen.
I cannot speak for other designers, most of whom are far more gifted than I, but I can relate to you the process I went through to understand the cause and effect of designs and parts. Indeed, when I hear a Hi Fi system displaying certain character traits I can usually tick off the most likely candidates of why I hear what I do. That skill is something learned over many years of trial and error.
The education started many years ago when were were working on the first phono stage the company manufactured. There are two main schools of thought when it comes to designing a phono stage and both concern the way the RIAA curve is implemented: actively or passively (we’re ignoring digital schemes because in the early 1970′s there was no such thing).
The RIAA curve is a serious bit of EQ, spanning a 40dB range. It’s essentially a huge double low pass filter – meaning it rolls off higher frequencies – starting at 20Hz and reduces everything above that. LP’s are mastered with the opposite EQ: exaggerated highs and reduced lows. This EQ is implemented to reduce noise and increase the playing time available and the RIAA curve in a phono preamplifier reverses this so you get a flat frequency response.
Most phono preamplifiers place this EQ curve in the feedback loop of a single amplifier and this is known as active EQ. Another way to handle the EQ is passively: meaning the components used to roll off the highs are not in an active feedback loop but instead, the passive components are placed between two amplifying blocks.
Because we were using an Audio Research tube phono stage as our reference and it used a single stage active RIAA, we did exactly the same thing in our first designs. We made sure we copied the exact values of the EQ network and even made sure the parts themselves were identical to the ones AR used so there would be fewer differences in our solid state design vs. their tube design. We weren’t even close in the way ours sounded next to theirs despite the fact the measured results were nearly identical and – despite the fact that our little solid state design sounded remarkably good as a simple line stage relative to theirs. It was when we tried to implement the RIAA curve that everything fell apart.
Tomorrow we start to relate what we’re hearing to what’s happening.
Paul McGowan – PS Audio, Intl.