opamp question

[danwelsh]

Hi, I have a question regarding opamps...I have an english sustain pcb calling for 2 lm741's  ....I only have one but I also have a bunch of jrc4558s, and also have a lm386n, my question is should i use 2 4558s or the 2 lm chips? I'm going to socket anyway, will it hurt the circuit to interchange and try em?

[jubal81]

Neither of those will work. Pinouts won't match. In a pinch you could deadbug the 4558. (flip it upside down and solder wires from the pins to the right spot on the board)

[danwelsh]

Neither of those will work. Pinouts won't match. In a pinch you could deadbug the 4558. (flip it upside down and solder wires from the pins to the right spot on the board)

Thanks a million

[danwelsh]

couldn't i wire them up manually....know what i mean, with wires? and match the pinouts, that would work wouldn't it?

[alanp]

The main issue with regards to 4558/741 interchangeability is that the 4558 is a dual opamp, and the 741 is a single opamp. (The LM386 is something else, but I don't recall. Too much DB Export right now.)

[RobA]

couldn't i wire them up manually....know what i mean, with wires? and match the pinouts, that would work wouldn't it?

It depends on the circuit, and I don't know this circuit. The LM741 has offset null pins on it that might be used in a circuit. I can't see any reason that someone would use two single op-amps instead of a dual unless this were the case. Since this is a sustain pedal, it has high gain? This could be a reason for using the offset feature.

If the circuit doesn't use the offset null pins, then you could wire the pins of the dual op-amp to the right locations. You need to either use both of the op-amps on the dual or terminate the unused op-amp on the dual.

[danwelsh]

couldn't i wire them up manually....know what i mean, with wires? and match the pinouts, that would work wouldn't it?

It depends on the circuit, and I don't know this circuit. The LM741 has offset null pins on it that might be used in a circuit. I can't see any reason that someone would use two single op-amps instead of a dual unless this were the case. Since this is a sustain pedal, it has high gain? This could be a reason for using the offset feature.

If the circuit doesn't use the offset null pins, then you could wire the pins of the dual op-amp to the right locations. You need to either use both of the op-amps on the dual or terminate the unused op-amp on the dual.

How would i terminate the op-amp on the dual?

[RobA]

The proper method and the reasons are talked about in the application note, Op Amps for Everyone, which is a great reference.

Basically, you feed half the supply voltage into the non-inverting input and tie the inverting input to the output. It will eliminate added noise and power consumption from the unused op amp.