TL081 and TL082 in Mixer

Hi argonrepublic!
Those are operational amplifiers, with standard pinouts. The TL082 contains two seperate op-amps in one chip.
The TL072 is slightly better according to specs than the TL082. It has lower noise. They are cheap, available, and can be changed readily.
But there are certainly many other op-amps you can use such as LM833 for much lower noise. You can try to optimize noise, distortion, or frequency response. They are often trade-offs.

I hope this helps.

(added: I am interested if anyone knows more about the TL082/TL072 story ?? :xeye: )
Those TL072, TL082 have JFET input stages.
When exchanging against other, better opamps
I would first try to stay with JFET Types, such as
OPA2132, OPA2134, OPA 2604 etc.

The LM833 is a great, cheap opamp,
but it has bipolar input stages, resulting in
higher currents flowing through the input pins.
If your circuit uses very high resistances,
additional errors might be included when
swapping JFET against BJT. I use LM833 a lot
exchanging against those 4560, 4558 etc standard

i'm using JRC 072D aka TL072 opamp currently.
I wanted to upgrade to BB OPA2604 or OPA2134.

i) Would like to know what's the difference btw 2604 and 2134?

ii) What are the things that i need to take care off?

iii) I read many sites that recommend to put a capacitor at the V+ and V- pins (pin 8 & pin 4) with a 10uF capacitor. What is the function of these caps? Why we need this?
there are two ways to add caps to the +-V tracks.
One low value cap (10nF to 100nF) directly beside Pins 4 & 8.
And/or caps to ground (10nF to 100nF //10uF to 220uF) from tracks by pin 4 and pin 8. The first should be located as close to pins 4 & 8 as possible and with as short wires as possible and preferably located directly UNDER the chip to minimise the loop between chip current and cap current.
These are decoupling caps to allow fast transients to be amplified by the chip and to prevent interfence from voltage spikes being sent back along the supply rails to other amps off the same supplies.

After a long rest, I have come back to this mixer. It appears that I have two upgrade options. Either the OPA2134 or the AD712JN. Which is the better. Also, what are my upgrade options for the TL081?
Is +/-17Volts OK? The original schematics show +/-15Volts. I am good with solder/desolder and meter but my education is limited to Automotive electronics.
argonrepublic, my advice is since you had a JFET opamp at +- 15 V:

Change to a 10-20 V/us JFET opamp. OPA134/2134 are possible replacements but you have many types to choose from. You might also check the current consumtion if there are many of them so you won't overload the power supply and/or it's become hotter than which is healthy.

The price might also be interesting....
TL071 and TL081 are totally exchangable.
Both take typically 1.4 mA supply current per OP-amp.

TL071 has slightly lower noise.
TL071, TL072 are easy to find.

TL072 and TL082 are dual versions. With 2 OP-amps in one case

If you are building a portable, with battery operation
you shouldnt change to some other than these
that have higher power needs.
You will run out of batteries more often.

TL071/072 is widely used in filters and mixers.
Musicians use them often for guitar effects equipement, filters
and mixerboards.
It is very cheap and have high input impedance,
which often is good when building these things, especially filters.