Hi Charlie,
Yeah the HF time constants are 70uS for IEC 7.5ips, 35uS for IEC 15 ips (aka IEC1/CCIR) and 17.5uS for AES 30ips. However IEC2 is actually another name for NAB eq, not AES. HF time constant for NAB is 50uS. And of course NAB also has a LF time constant of 3180uS, similar to the RIAA curve for LP playback. To further complicate things you can't just skip having a LF time constant for the first three eqs, that is to say your repro amp's frequency response can't really go to infinity at 0 Hz. So you have to pick a LF time constant for those eqs that won't interfere with the pre eq of the music signal but still allow you the midband gain you desire. We use something around 9100uS for the LF time constant for IEC1, IIRC.