[auddoc]

The most used were the TLO family, single, dual and quad- 71,72 & 74 respectively, and sometimes the lower noise, lower current but not much better sounding 81, 82 & 84, again respectively. I believe the Trident consoles used the TL chips. The Signetics singles and dual, the ever- popular 5534 &5532, again respectively, were somewhat better sounding..and used extensively- many Brit consoles of a certain era. Occasionally one might see LM318 (a single, not bad sounding at the time, but harder to design with) and duals like the LF353, etc. If you get handy at substituting, you can alway upgrade to the Burr-Brown or Analog Devices line of opamps- low noise, sound good and some, but not all will run at higher supply voltages, where they have a bit more poot. And sound way better, to my ear. They are getting expensive...1-8$ each...ouch! Watch the total current drain when you get a pile of these running, as in a large console. You may stress the PS. The main caveat is that really great wide-band opamps can oscillate when used as plug-in replacements for these older guys. Usually a small cap used in the feedback loop, in the 10-100pf range will reduce the GBP, so that this goes away and you still have actual bandwidth upto 100kHz or better- for those of you with bat's hearing. The monster API at the late lamented O'Henrys, was modified with Video opamps (among other things),with bandwidth out to the moon, BUT these can drive very low Z balanced lines,( 50, 75 oHm) such as the main mutichannel busses. Sounded killer. As far as mods go...Op-amps, caps and power supplies- there is an endless variety of improvements just there.