741 Op Amp Drop in Replacement

Ok. Filter app. What is the highest frequency the filter will output.

OP amps may oscillate from lots of things like impedance on its input , gain / feedback structure & power rail decoupling
to name a few.

I once changed OP amps in a soundcard and it turned into an AM receiver although I checked everything....
 
The '741 was never a high-performance device in audio applications, but it was cheap and easy to use.

15 KHz active filters of any complexity, especially the hipass, are really pushing the limits on 741-class devices. If I had to suggest an alternative without any more information to go on, I'd look at the TL07x family. For truly modern parts check out the (former) National LMExxxx series, or OPA604/OPA2604.

Dale
 
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Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Texas Instruments manufacture a good range of Op Amps with the same pin out as the 741 but using JugFet inputs giving a higher input impedance and better band width.
TL071ID at just over 30pence each or less than 1/2 Euro has excellent characteristics and a slew rate of 13v/uS amd band width of 3Mhz.
A new replacement is the AD8510ARZ and that has a 20v/uS slew rate and even quieter at just 31pence each.
They both can use either single or dual rail power supplies at a voltage range of between 7v and 36v.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Hello. I have a similar question for a 70s mixer I wish to make better.
Each channel has four 5n72741p and one 748cp. Is there anything I could replace with
Where i am sure not to mess it up?
Another forum led me to opa134 as a good replacement. Other opinions would be great.
This is for an sTudio master RSD 12 into 2 mixer channel.

Thanks,
Rodrigo
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Like the original question, we would really need to see the circuit to best advise. The 741's probably would be fine with the OPA134 as a replacement but not for the 748 as it stands. The 748 is an uncompensated opamp which means there will (or could be) additional parts to some of the other pins. Also the 748 is capable of running on 40 volts and it also has a high "common mode" input range. Those two features probably aren't relevant... but unless you are sure.......
 
Like the original question, we would really need to see the circuit to best advise. . . . The 748 is an uncompensated opamp which means there will (or could be) additional parts to some of the other pins.
Yes, the big question regarding the '748 is whether - and how - the compensation and offset pins are being used.

  • If it's being used as a straightforward high-gain (probably 40 dB or more) amp with no external compensation then many IC's are potential drop-in replacements.
  • If it uses a simple compensation scheme to achieve stability at some gain, then a more modern, higher-performance part with no internal connections to the comp pins may be a viable solution.

    In this situation it may also make sense to totally remove the compensation component(s) and find a modern device that can do the job without external compensation.
  • If the original design uses an elaborate compensation scheme or uses the offset and comp pins in a creative way, at the very least you'll have to figure out what the circuit designer was trying to accomplish and calculate new component values, and possibly modify the compensation circuit topology. (Not all opamps that have provision for external compensation implement it the same way.)
Dale
 
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Sorry here is the drawing
That's a balanced-input mic preamp. The 4 transistors create a low-noise front end, and the TL071 provides a moderate amount of gain, differential-to-single-ended conversion, and output drive.

We could start an argument that runs for weeks, but here are a few points to consider:

  • The TL071 isn't a bad choice here if this is for amateur or even semi-pro applications. (E.g., if an SM-58 mic is used as the source, there isn't much point to improving the circuit performance.)
  • The '5534 would provide improvements in a lot of areas - especially output drive - but the gain-setting resistors (100K and 22K) are really too high for it, and they can't be reduced very much without compromising the input stage. On the other hand . . . the '5534A has a decent front end already, and there are other designs floating around that tack a high-performance front end onto a '5534.
  • A modern FET-input opamp, especially one designed for audio applications such as the OPA134 or OPA1641, should have no problems in that circuit.
Dale