Quote:
Originally posted by manning1
jim. i think i have tested every op amp in the market in building my own diy mic pre's. i would appreciate your comments on one op amp type. to my ears the best op amps i found for my little mic pre were op37 and varaietie like max 437.
do you have any comments why - from a technical perspective ? thanks. |
The OP-37 is just a decompensated version of an OP-27 precision opamp. BurrBrown probably makes the best one, and they make a dual version that's used on the lynx cards. Low dc offset and bias current but pretty slow. The OP-37 needs about a gain of 5 to be stable, and any capacitor across the feedback loop will create an integrator and will make the opamp oscillate. Most mic pres use some form of feedback cap, the Jensen transformers require one as it's part of the "tuning" circuit. The OP-37 would cause problems there. In your case it may be the low level oscillation is adding a subtle "aural excitement" to the preamp. Have you seen the output on an 'scope?
Jim Williams
Audio Upgrades