Quote from: mshilarious on March 03, 2008, 08:33:10 PM
One thing to keep in mind with slew rate is how fast do you need to slew? And that question has to be answered by the application. If you are building a high-headroom pro-level (+4dBu) preamp, then you need more slew rate than for a few extra dB in front of a -10dBV portable recorder. Actually, you'd need something like 8+ times the slew rate.
On the other hand, you have issues like current consumption and noise. But again, what is your application? Most people here are using condenser mics with a reasonably hot output. If you are using small diaphragm condensers, especially the weensy ones, those by their nature will have a higher noise level than nearly any quality opamp you'd stick them into. And if you are powering it with a battery, you'd be more concerned with current than noise. If you are using unbalanced microphones, you might have enough induced noise to not even care.
I am using OPA2277 in a new mic I'm working on that will end up with total current ~2.5mA. If you look at that chip, it isn't the quietest, it isn't the fastest, has a low GBW, but at 0.8mA/channel, it's incredibly efficient. The slew rate is just fine when you consider the capsule's FET can't swing much more than 2V peak to peak before it clips, and the circuit is unity gain. Note that slew rate is measured in microseconds; a 20kHz signal takes 25 microseconds (somebody check that math please) to go from peak to peak.
If I were building a general-purpose pro-level preamp, I usually use OPA2134. OPA2277 uses a little less current, with less noise, but slower. There are even sexier ones . . . OPA211, OPA627, and we still haven't left TI's range; there are a few other well-regarded chip makers out there.
But you could drop any of those in a particular design and not hear any difference, if the application did not test the limits of each chip's strength and weaknesses.
On the other hand, you might drop in OPA627 to a circuit that was designed with a 5534, and it might oscillate horribly . . .
That is one thing I have learned just because its pin for pin compatible does not mean it will work in your circuit.. but thats part of the fun of designing.. Its hard for guys like me and Jon because if your like me your so busy building you dont have as much time as you would like to try new things.. Thats the hard part for me anyway..
I would like to thank you for your contributions here!
Chris
Topic: interesting DIY preamp kit (Read 18,287 times)