What are some good replacements for a 741 op-amp?

[Chris Goodson]

I recently built a dist+ circuit and it works well except for having a little too much treble for my taste.  Anyhow, I thought I'd like to see what sorts of different sounds I can get by modding it.
I built it with a socket so I could swap out the chip with others.  I've got piles of scrapped electronics laying around with many kinds of op-amps in them, so I was hoping to get some suggestions of ones that might sound good in it.

[David]

The 5534 is a good 741-pinout style op-amp for audio, in my opinion.  You could also try the TL071 or TL081.

[Manolo Dudes]

I've done a Distorsion+ using Francisco Peña´s layout for a dual op. amp.

Knowing the lore about the 741 being specially adequate for this application I tried the suggested 4558. Then I tried a TL072 but sounded a bit dull to me. An RC4559 sounded much better  but then I tried a 1458 and I have to confess that it sounded the best to me despite its abysmal qualities  :twisted: and it's the one that's still there.

But the greatest difference was not in the op. amps but in the diodes. To my ears, gold bonded Germaniums (AA119) are much better than Silicons in this effect.

[Mark Hammer]

Go to Jack Orman's AMZ site and read the document on warp controls.  Much goodness well-suited to tinkering with the Dist+ there.

The Dist+ does not *depend* on the 741, per se, but part of its tone lies in the weaknesses of the 741.  Although in principle, eliminating the clipping diodes ought to produce a clean tone, in this circuit, with a 741, it doesn't.  Not just in my case.  Many others can attest to this.  The result is that the Dist+ is, in a way, a double-clipping circuit: what comes out of the 741 is already clipped  and then gets clipped again by the diodes.  So, switching to an op-amp that has "better" specs may produce a very different sound.  That may well be the sound you want but it will be different.

Given that the tone of a Dist+ is partly the tone of a 741 breaking up, I think it is worth experimenting with different Vref values, and maybe different resistor values in that divider circuit.  You won't see many op-amp devices with a pair of 1M resistors in the reference voltage circuit so I'm wondering if part of the tone is some sort of current starving, though I'm just guessing here.  In any event, having one resistor be 1M and the other be 470k would bias it weird and perhaps produce an interesting asymmetrical distortion from the op-amp itself.

If the tone is too fizzy for you, the sensible thing to do is to add more capacitance in the feedback loop of the op-amp, and more capacitance to ground just before the output volume control.  Both of those will tame treble.

[Paul Marossy]

Try a Burr-Brown OPA134A. Very quiet compared to a 741.

[aron]

I made a circuit to really test out variable op amp biasing and I came to the conclusion that it does affect the sound, but not really in a positive and useful manner  

Anyway, go for it if you wish :-)

[Ansil]

i know i will be slapped for this, but with another ic socket and a slight moddification to it you could use an lm386,  it makes a great mxr dist sound.  so far i have built a tube screamer a mxrdist + a guvnor and several other opamp type dist's with it.  it is also nice to not have to make voltage bias.

[petemoore]

How do you build a Dist+ using a 386 OA?

[Ansil]

instead of usingthe whole feedback loop thing, set the internal gain to 200by bridging pins 1 an 8 and put the .047uf and 4.7k resistor to ground.

[brett]

Hi.  With reference to Mark Hammer's suggestion of mis-biassing the 741 to get assymetrical clipping, I suspect that you'd need to go wilder (wider?) than 470k and 1M.  The reason being that the clipping will occur out at about 2V less than the supply rail.  With Vref at 3V or 6V (depending whether the 470K is at the top or bottom) clipping will still be about 1V away on one side and several volts on the other.  Unfortunately the diodes will clip at 0.3V for Ge or 0.7V for Si, and so will over-ride the assymetric clipping due to mis-biassing.  

Assuming that you're using Si diodes, you'd need the op-amp bias to be within about 2.7V of ground or the positive supply, so the ratio of the resistors needs to be AT LEAST 2.7/6.3 or 2.33:1.  So 390k (or a bit less) and 1M should do it.  

But I think that an even more interesting idea flows from Mark Hammer's very smart ideas   .  What about replacing the 390/470 k resistor with a 250k resistor and a 500kB pot?  Then you could dial as much op-amp assymetric clipping as you want :!: .  

I'll be modifying a D+ -style distortion next weekend to try it out and let you know how it works out.  

PS I'm no electronics expert, but I think this is roughly right.  Also, I suspect that the clipping will depend fairly strongly on the op-amp used, because different ones get more or less close to the supply rails (ie the 2 V used above is a crude average - some definately get within 1V)