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Op amp swap.

Started by Guitarist335, May 28, 2021, 05:52:51 PM

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Guitarist335

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

#1
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
"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

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

"...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

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

true. bipolars and bipolars, fet input and fet input. watch for uncompensated types.
can you counts to 34.

Guitarist335


ElectricDruid

Quote from: Guitarist335 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?

+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!


Jmariner

Without seeing the circuit, another factor is it single supply or dual.
I've read in forum posts it's popular for a lot of designers and builders to split the supply regardless of whether it's limited to single or not. Another designer 20 years ago more knowledgeable than I, also often stressed his favoring of very high bandwidth models. In terms of how one model sounds vs another, this in my experience heavily circles around the particular op amp the circuit was designed around. Swapping some will greatly reduce noise, possibly change texture and the perceived density of a range in the highs and so forth, and some will just straight up be noisy as hell.

Inversely to this situation, designing the circuit around an op amps known traits can fundamentally steer around the variety when swapping them in a defined circuit, and you can obtain the texture and perceived density of a pitch range, whether it's hollow or a large rise in midrange and so forth. I just dropped in the OPA2228 which is now obsolete in a soft clipper I designed around the oh so common 5532, and the OPA has some improved traits that really stand out, but it's not only an expensive chip, it has also reached the end of it's production life. The OPA was always expensive, but I must note it has 3x the bandwidth.

The favored changes it produced can easily be achieved with the 5532 and some minor changes to a design. I suppose that in itself during the prototyping stage is a very powerful tool, especially if you are using an existing design. Hearing and experiencing some better traits and altering or improving the design to your favor but relying on the affordable chip. The cost is an incentive for builders and customers if people like your work.