A few general noob op amp questions and a Probably over asked 4558 question.

[cptnyar]

Hi there, just getting into this hobby.
I was first under the Impression that I could make a "boost"/distortion pedal from any old op amp. Then thought I was wrong, but after further research I'm no longer sure in one direction or the other.

Is it possible to make a boost from an Op07?
If so, how do I calculate what resistors and capacitors I would want to use (haven't seen one used in a schematic yet)?

Also, the suffix on said Op07 is "a", but I thought that the suffix had to do with the layout out of the ic. It's shaped like a D*. So any insight on that is pretty sweet.

Last, has anyone tried the 4558s that sell from AliExpress?
How do they compare?

[idy]

Welcome to the forum.

Why op07? Maybe you already have one? It should work. The things that make the 07 special (it is an instrumentation opamp with some features for engineers designing instrumentation) will not have any effect on typical guitar boost circuit. "Low offset" is important if you have great numbers of op amps in a circuit DC coupled and tiny "offsets" can add up.

That being said, guitarists are often interested in how it will sound when abused, when driven "close to the (power) rails." Some op amps behave badly, latching up or getting stuck when the signal gets too close to the power voltage. Others clip "gracefully." Worth trying. In some circuits where the gain is limited you never even discover this quirk. The 4458 is known to behave acceptably when overdriven.

The LM308 was famous for its use in the Rat. It has a "low slew rate" which means it can't track super fast transients, it has "poor" high frequency response; and guitarists like that. Some do anyway.

The resistors and capacitors you will need will be the same regardless of the model of op amp you use. That is the beauty of op amps. You can make an MXR micro amp with any single opamp, same parts. If the gain is high enough and your guitar is "hot" enough,  the op amp will clip, and you will have to determine if you like the way that happens. (You can even use a dual opamp, but you have to use the other half to either buffer your bias voltage or ground the input so it doesn't misbehave.)

Show us a link to the doc with the prefixes. The important thing is that you get a package like DIP that you can monkey with and not those tiny surface mount parts, unless you are a robot.

In general, any 4558 will work like any other. That's the point of part numbers. It is true some body may be painting that number on a barrel of generic op amps they got cheap.... why not buy from a reputable dealer?

[Jdansti]

The OP07 data sheet can be found here: https://www.analog.com/media/en/technical-documentation/data-sheets/OP07.pdf


It would be interesting to see if you can produce something interesting with the OP07. It appears that it requires a bipolar, power supply. While this requirement isn't a deal killer, it is extra circuitry to deal with.

[Vivek]

Welcome to the group !!

At first sight, looks like the OP07 is fairly similar to all other opamps, the difference being low voltage offset and drift etc (Good stuff for precision and instrumentation applications, but won't hurt us for Audio applications)

Let's me see if I understood some of the specs and differences

Wide supply voltage range: ±3 V to ±18 V  = Great !!!

Input Bias Current IB            ±5.5 nA
This means that the current in the Vref voltage divider better be more than 50nA. That's really easy


Large Signal Voltage Gain AVO RL ≥ 2 kΩ, VO = ±10 V       180  V/mV
741 has 25 V/mv
Hence 0P07 is superior here. It will have greater linearity, Duh its a precision Opamp for instrumentation etc
But we want to make a distortion circuit.


Power Supply Rejection Ratio PSRR VS = ±3 V to ±18 V      7 μV/V   ie -103dB
741 has 86 dB


Slew Rate SR          RL ≥ 2 kΩ3      0.1  V/μs
741 has 0.5 V/uS
This might actually create a sound that you like more


Input Resistance, Differential Mode4 RIN           8  MΩ
741 is 0.3 Mohms
OP07 is superior


Closed-Loop Bandwidth BW     AVOL = 15       0.4  MHz
741 has 0.44 Mhz
hence somewhat similar


Output Voltage Swing VO  RL ≥ 2 kΩ ±12 with ±15 supply
741 has Output voltage swing   ±16    with VS = ±20 V
hence somewhat similar


Power Consumption Pd   VS = ±15 V, No load          120 mW
741 uses 165 mW
That's quite similar


Graceful recovery from rail saturation : I dont know. Maybe better to start with circuits with diodes in the feedback path to avoid rail saturation.


The OP07 has optional null adjust pins 1 and 8. Some clever experimenter will surely find a way to modulate those pins, maybe to implement something like sag or time related distortion via Bias Shift (maybe rectify part of the output and feed it to one of the optional null pins)

[GGBB]

It appears that it requires a bipolar, power supply.

Bipolar supply for OP07 is not required. For almost 20 years now, the OP07 has been used by all RAT pedals which are designed for +9V single supply. In certain applications/conditions (guitar audio is not likely one of them), it may perform better with a bipolar supply, but that is true for most opamps - which are not designed specifically for single supply use.

The primary difference between a 4558 and an OP07 is that the 4558 is a dual (two-channel) opamp and the OP07 is a single opamp. They are not pin-compatible.

If you are looking for a distortion circuit to build with an OP07 - try the RAT:


Pro Co RAT Schematic - "Multi-RAT" Comparison

[antonis]

Input Bias Current IB            ±5.5 nA
This means that the current in the Vref voltage divider better be more than 50nA.

Or else..?? 

[Jdansti]

Thanks, GGBB!

[Steben]

OP07's most notable feature is the rather low slew rate. But it needs a gainy circuit to be of use. No gain = no gain to loose

[Vivek]

Please check my Slew rate calculations :

The Slew rate of OP07 is 0.1  V/μs  = 100,000 V/s

For non slew rate limited sine wave, 2.pi.f.Vp should be below 0.1 V/μs = 100,000 V/s

Where pi = 3.14
f = frequency
Vp= peak of sine wave

if we want frequency response till 10Khz

max Vp for non slew rate limited sine wave can be 1.59 Volts peak

Assuming that guitar signal is 1.2Vp max, it means that a OP07 stage with gain more than 1.3x will be slew rate limited.

Did I calculate that properly ?

[ElectricDruid]

Let's say that the 10KHz is down by 6dB because of the slew rate limiting. Would you care? Would you even notice? If you did, it would probably be an improvement in a RAT circuit.

So yeah, as the gain goes up, the slew rate means the the top end rolls off more and more. But we know about that, and that's designed into many circuits we know and love (ahem! screamer!). It's just that in most of them it's not an intrinsic feature of the op-amp choice!!

[Vivek]

I feel that slew rate limiting of a sine wave creates many harmonics.

It's amplitude might be less than the original non slew rate limited sine wave, but it will have richer harmonic content.


And that would be noticeable.

[antonis]

Are we talking about a boost/distortion effect or a part of Hi-End audio system..??

[ElectricDruid]

I feel that slew rate limiting of a sine wave creates many harmonics.

It's amplitude might be less than the original non slew rate limited sine wave, but it will have richer harmonic content.

And that would be noticeable.

Since it's slew rate limited, it would turn a sine wave into something closer to a triangle wave, but at a lower amplitude. So yes, it introduces distortion and higher harmonics, but rolled off sharply (amplitude of 1/f^2 for a triangle wave) and the overall level is reduced anyway, so the harmonics are even more reduced - 3rd harmonic at 1/9th the level, 5th at 1/25 the level etc.

I'm not saying it's insignificant. Just that it's not huge. "Noticeable" probably depends on who's doing the noticing!

[Guitarist335]

I have used 4558s and tl082s sold on Amazon. I have not had a problem. They worked fine for me and I think 50 of them cost me around $25.