Yes this has been covered in hundreds of threads, but I'd like to ask a specific question: TLE2072 or OPA2134? The application is an audio mixer. Not much decoupling to speak of, some many need to be added.
What I am looking to get out of it: lower THD, lower noise floor. I replaced all with 2134's on one board, but there is a lot more noise, even with extensive decoupling. But it's very possible I messed up.
Not sure why it would need to be a JFET type here - the impedances are low. I'd suggest a bipolar - like NE5532. It has way more drive capability than TL072 which is about the wimpiest audio opamp I've come across for load tolerance. 2700ohm is way too low a load to get decent sound from a TL072 but an NE5532 won't much notice providing its well decoupled.
Good point - the 5532 takes more than twice the current of the TL072. In proposing it here I was only looking at the part of the schematic shown - the mic amp section. There will be different trade-offs in the various different sections and some may well call for JFETs rather than bipolars. If current consumption is a major issue, TI make some low noise bipolars with quiescent currents only slightly higher than the TL072. They are significantly more expensive than the 5532 though.
There is a 0.1uF ceramic on every pin with the capacitor close as possible to the IC. Is that ok?
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Soundcraft Delta 200 24 Channel with a CPS450 supply so the extra draw should be ok if I only mod a few channels. They put the 5532 in the output stages and 072 basically everywhere else.
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I do not know. When running a mic through the modded stage and the unmodded stage, the modded one has much more noise.
I replaced every TL072 with a OPA2134 and decoupled each one with a 0.1uF cap on each power legs. That's it.
I suppose I need to find/borrow a scope, because the chips were directly from TI, ordered as samples off their website.
You need to specify what noise. Low frequency hum like 60Hz or 120Hz, or hiss which is high frequency noise. Or it is whistle or with a distinct pitch that indicate oscillation.
They are of completely different mechanism, specify that to narrow down. Better yet, post a recording.
Look at the frequency response of the new amp you put in. If the new amp is much higher frequency, it might just be wide band noise because the amp has much wider band response.
They are of completely different mechanism, specify that to narrow down. Better yet, post a recording.
Look at the frequency response of the new amp you put in. If the new amp is much higher frequency, it might just be wide band noise because the amp has much wider band response.
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It is high freq hiss, I am guessing you are right as far as it picking up those sounds as it is wide-band. I suppose that means I need to improve my cabling.
You need to compare the old opamp and the new opamp. If the new one has much higher frequency response, a small feedback capacitor across the feedback resistor of the opamp will help
Usually, you calculate the max frequency response you need, then calculate a small cap across the feedback resistor of the opamp to band limit it a little.
Do it step by step, a recording can tell a lot. don't blind guess. If it is not oscillating problem, putting 0.1uF bypass cap is not going to help at all. You want to really determine it's not oscillation, then everything else is easy.
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