Author Topic: Op amp swap.  (Read 2702 times)

Guitarist335

Op amp swap.
« on: May 28, 2021, 05:52:51 PM »
For this circuit( the one entitled, IC-based overdrive) can I use a 4558D op amp instead? Will the circuit still work? (Assuming I have made sure I have remapped the pins, if required) ?

Thank you in advance for your help on this. 

antonis

Re: Op amp swap.
« Reply #1 on: May 28, 2021, 06:06:22 PM »
Of course it will work..!!  :icon_wink:

Just make sure for pin right arrangement, like 8 instead of 7 and 1 instead of 6..



470k bias resistor (R3) may be of the same value due to 4558 also BJT bi-polar inputs..

P.S.
You can use the 2nd amp (pins 5, 6 & 7) for a more stabilized VB..
(or properly configure it by shorting pins 6 & 7 and wire pin 5 to VB..)
https://www.ti.com/lit/an/sboa204a/sboa204a.pdf?ts=1622228711500
« Last Edit: May 28, 2021, 06:15:16 PM by antonis »
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

Guitarist335

Re: Op amp swap.
« Reply #2 on: May 29, 2021, 01:22:47 AM »
Thanks Antonis.  I appreciate it.

I am trying to understand what the factor is that makes an op amp swappable with another. Does it have to do with the required bias voltage.  If so, where do I find that value on the data sheet?

Thank you

idy

Re: Op amp swap.
« Reply #3 on: May 29, 2021, 03:21:39 AM »
"...what makes one opamp swappable with another." That's the kind of things you ask engineers... But for most stomp box circuits:

Some have higher input impedence (MOSTET vs JFET vs BJT)
Some have  "faster"  "slew rate" ("slower" might make a "softer" distortion)
Some operate "rail to rail" or very close to the power and ground "rails." (ones that don't might either distort very unpleasantly or be useful for their "gating."
Some use less current, better for battery life or keeping an LFO from being noisy.

Things like offset null on some single pampas...small differences in DC output can build up over multiple stages and you can correct that.

You can read about opamps, somewhere you'll read something like "The perfect opamp has infinitely high inout impedance, infinitely low output impedance, open loop gain of infinity" and other stuff I've forgotten. They're very good, but never perfect.

Guitarist335

Re: Op amp swap.
« Reply #4 on: May 29, 2021, 06:24:06 AM »
Thank you.  Is this a true statement

In the context of building stomp boxes, for the most part, when using general purpose op amps like the 4558d or the 741, or the tl081 or tl082, they should be swappable provided you remap the pins where needed?

duck_arse

Re: Op amp swap.
« Reply #5 on: May 29, 2021, 10:57:20 AM »
true. bipolars and bipolars, fet input and fet input. watch for uncompensated types.
"I'm your vehicle, baby", but go easy on the clutch.

"You've got a suss sus sus sus sus sus sus suspect device."

Guitarist335

Re: Op amp swap.
« Reply #6 on: May 31, 2021, 05:20:42 PM »
Thank you

ElectricDruid

Re: Op amp swap.
« Reply #7 on: May 31, 2021, 05:44:46 PM »
Thank you.  Is this a true statement

In the context of building stomp boxes, for the most part, when using general purpose op amps like the 4558d or the 741, or the tl081 or tl082, they should be swappable provided you remap the pins where needed?

+1 agree. Not absolutely true, but true for most practical purposes. Pretty much all you need to worry about is packages with a single op-amp (741, TL071, etc) versus packages with dual op-amps (TL072, 4558, LF353, etc etc). Any differences you can hear you can call "mojo" and charge double for!