Doug Irwin said:The Pulsecomm PCAUs actually work really well. I have 10 pairs of them in New York for backup STLs. They have razor flat frequency response and the necessary amount of headroom all the way out to 15 KHz, which is something you rarely, if ever, got with the 'older' style of 15 KHz lines from Telco (using Telabs 4008 cards on either end). They actually sound pretty good too.
If you saw the schematic of a 4008, you'd puke. Current boosting output transistors located outside the feedback loop of the output opamp (how do you say .8% THD/IMD?). The equalizer is a 741 opamp, as is the virtual ground driver. Just replacing both 741s with 5534s compensated for unity gain make these sound like a FAR better unit. Put the output transistors in the feedback loop and then listen to the bass! You'll never want to go back to stock 4008s again!