Who knows their Op-Amps

[AFF]

Okay I know the great people of this site are well capable of helping my latest question.

Who can explain the differences in the most common Op amps and the most common Op amp replacements.

For example I know some places swear that the 4885 is the perfect replacement in your new distortion or overdrive pedal.  I have heard the newer Op amps with long number and letter names are more hi fi and better suited.

I have also come across that because the less clean and easier some op amps are the more you would be drawn to place that specific one in the circuit.

The main reason behind my question is a Metal Zone mod. It got me thinking more about the op amps ... the one I am modding has three (mitsu) op amps and I also discovered that Boss has produced 3 versions of the MT-2 and each had a different combination of the three.

I am very interested in the socket that allows you to replace your sinlge inline 8 pin and plug and unplu instead of solder and desolder!!! Great idea by the way ... I would love to start mixing and matching the dual inline pin op amps ... I saw a small board that allows you to place to opamps together and then the board will drop right into the single inline slot. I think Monte Allums offers one of these set ups and I am sure that mouser and other elec suppliers do also.

I know I will have do a little bit of spec research also to know what will and will not work together ... I know some have the 7 pin is hot and the 9 pin if not and then a different op amp is completely backwards.


SO THE QUESTION AT HAND IS : WHAT CHARACTERISTICS CAN BE HEARD FROM THE MOST COMMON OP AMPS AND THE MOST COMMON OP AMP REPLACEMENTS. EXAMPLE : BURR BROWNS DO THEY REALLY ACHIEVE A BETTER TONE THAN THE STOCK TS-9 CHIP? I UNDERSTAND DIFFERENTAPPLICATIONS WILL PRODUCE A SLIGHTLY DIFFERENT OUTCOME SO AGAIN I AM WORKING WITH BOSS PEDALS ONLY FOR RIGHT NOW. THANK YOU ALL SO MUCH!!!!!!!!
-AFF

[Gus]

You need to search this site and other sites for the information you are looking for.

In two words "It depends"

The best thing to do is build a gain stage and listen to the opamp when driven to clipping.  IIRC R.G., Jack and others have posted in the past about recovery from clipping.   If I hear a  difference it often can be due to the specs of the opamp and how I used it.  I will look at the waveforms with a scope sometimes you can see a difference.

You can adjust some opamps.

Some opamps have different output drive capability this sometimes matters.

Take the stock TS circuit.  At lower gain settings and the tone control not at max treble.  I don't heard a difference in opamps in retail TSs and I am not sure if I hear a difference with the gain all the way up and the treble all the way up.  Now if you change things...

In effects like distortions it is all about how you use the opamp and how it deviates from ideal.

Then you have gain bandwidth product that might be a part of the sound in something like a D+ with a 741 at high gains.

Input resistance can matter for different circuit types you would want a fet input for some circuits or a PNP or NPN input for others.

It depends, buy a bunch and try them yourself.

[Transmogrifox]

...It depends, buy a bunch and try them yourself.

That's my advice too.  You're on the right track searching for IC sockets.  These are available from Mouser and others.   The pin-out changing sockets will be a little bit high profile, so you may want to check the dimensions on the data sheets to make sure IC Socket + Pin Changer + Op amp will fit inside your pedal.  Most dual op amps use the Pin 8 for Positive supply voltage and Pin 4 for negative supply, so you will be able to try almost all opamps you want without a pin changing adapter.  Usually the Op Amps that use pin 7 for hot are single op amps, and you won't be able to substitute those for a dual, anyway.

This op amp issue is very subjective.  We can point to specs and calculate what the bandwidth, distortion, recovery behavior and have an idea of the extent of slew rate distortion.  It all makes a difference to the sound, but who's to say that one person won't like an op amp that generates a certain amount of slew rate distortion while another person likes the sound of an "academically correct" circuit?

When you learn about op-amps and study the data sheets you will begin to associate your tastes with certain characteristics in the op amp.  At that point you will be able to better predict what kind of op amps will sound good.

My personal opinion is that changing op amps in a circuit makes such a subtle difference in the sound that I am able to fool myself in a blind test.  For me, it's not worth my time unless the circuit has noisey or really poor quality devices.  There are some op amps which truly are abysmal sounding, but these are few compared to the rest that don't seem to make much difference.  I would rather be playing with diodes, capacitors and resistors where you can make radical changes to the sound 

If you want the op amp to have a small audible effect on your circuit, then use high slew rate, high gain, low distortion op amps that are able to recover from clipping gracefully.  For most applications, something with better than 16 V/us slew rate, and .01% THD will have minimal effect on the sound from one device to another.

If you really want the op amp to color your sound, then you would likely be best suited experimenting with low grade op amps that are pushed outside of their specified range by the circuit in question...but then again, you ultimately will be the judge of whether a subtle change makes it sound "just right".

[fuzzo]

Good thread !

Do you think it's more important to create a good circuitry around an good op-Amp (reducing hiss, noise ect....) instead of changing AOP (for a better one) in a poor conception ?



 

[valdiorn]

Op-amps usually have around 0.03% harmonic distortion or less. The difference you will hear from replacing an op-amp is miniscule, even compared to replacing a 5% value resistor with another of the apparently same size (meaning that the variance between 5% accurate resistors is more of a factor than the op-amp you choose)

[R.G.]

Do you think it's more important to create a good circuitry around an good op-Amp (reducing hiss, noise ect....) instead of changing AOP (for a better one) in a poor conception ?

I personally *think* the moon's made of green cheese.  

The fact is that opamps were designed specifically to make the opamp itself not matter, and to make the overall circuit be completely determined by the parts other than the opamp. The degree to which this becomes true is the test of how good the opamp is.

Opamps do vary in their imperfections. But even the best opamp will not make up for problems with the components and circuit arrangement around it.

[Electron Tornado]

This op amp issue is very subjective.  We can point to specs and calculate what the bandwidth, distortion, recovery behavior and have an idea of the extent of slew rate distortion.  It all makes a difference to the sound, but who's to say that one person won't like an op amp that generates a certain amount of slew rate distortion while another person likes the sound of an "academically correct" circuit?

(snip)

My personal opinion is that changing op amps in a circuit makes such a subtle difference in the sound that I am able to fool myself in a blind test.  For me, it's not worth my time unless the circuit has noisey or really poor quality devices.  There are some op amps which truly are abysmal sounding, but these are few compared to the rest that don't seem to make much difference.  I would rather be playing with diodes, capacitors and resistors where you can make radical changes to the sound 

I agree.

I've tried changing op amps in a couple of circuits with no discernable difference. Have a look at this video:

http://www.youtube.com/watch?v=bpTv2jAree8

[alanlan]

Op-amps tend to be much of a muchness, but they do differ a lot at the extremes where it may matter in certain applications.  An NE5532 is great for driving lower impedance loads at full level, other op-amps have a larger common mode input range, others have better output swing (closer to rails).  Some have lower supply demand.  Some are lower noise and distortion.  Those are the things which tend to make a designer pick one over another.  In 95% of applications, you can use pretty much anything without much difference in result.  It's the 5% that sorts the wheat from the chaff.

[Electron Tornado]

  It's the 5% that sorts the wheat from the chaff.

"Wheat" and "chaff" are in the ears of the beholders.

While DIYers and "boutique" pedal makers may pick nits to get a certain target sound, I have a feeling that designers at the larger production companies tended to use what was readily available and inexpensive.

[AFF]

Great info.

I will look around and buy a few of them cheap and get some sockets also. Then I can plug and play away. SOme of this info will help when I build a DS-1 from the board up.

Now I need to find small lots of op amps cheap!

[andymac1962]

Hi
There are many choices, and it depends if you are talking about an op amp as a buffer, or in a tone stack, or the op amp used in the clipping section.
Tech 21 (Sansamp) use TL074 (TL072) for their tone control section & TLC2262 for their clipping sections. A big part of their "sound" is the op amp.
TLC2262 is a cmos rail to rail op amp, and is not overly expensive. It does however have a Vcc limit of 16V absulute max, so these are great for running from 9V batteries, but NOT from +/- 12V or 15V supplies as they will blow up.
NE5532 are low noise & can drive 600 ohm loads, so are great for mixing boards
TL072 / TL074 are good general purpose low noise op amps, adn can be used pretty much anywhere
LM833 is also good for low noise audio, but i dont know how it sounds in a clipping clipping
LF351 & LF347 are also good general purpose low noise op amps.

Most dual op amps have the same pin out,    so put a socket in & try different ones out.
Pedal makers will generally use what they already use in other pedals, and what is cheap. There is no point putting a $10 burr brown or Analogue Devices op amp in a Tube screamer.....

[brett]

Hi
Holy Deja Vu Batman.  The batclock says it's op-amp discussion time (again).

IMO you'll hear all sorts of complete rubbish written and spoken about this. 

Firstly, for the "there's no difference" crowd.  Take your tubescreamer clone and plant a 4558 in it.  Turn it and your amp way up and listen to that.  It sounds like a waterfall in your living room.  Replace the 4558 with an NE5332.  Do the same.  Now it sounds like there's a waterfall in the next door neighbour's livingroom.  Proof positive that there is a difference.

Now for the "I can tell the difference between op-amps X, Y and Z just by standing in the same room" crowd (and it IS a crowd).  Most people like their favourites just as mosty people think that their baby is cute (but other babies can be kinda ugly).  So do a blind test with at least 3 people, at moderate gain levels, with the amp at moderate volume, and with the TV set going (thereby avoiding the noise test).  Ask which op-amp is which, and which is best.  In my experience, nobody can consistently tell the difference between op-amps, and different people nominate different ones as best, and most importantly - if you stop playing for 30 seconds *nobody can tell whether you changed away from their "favourite" op-amp to another one*.

A consistent side-result of this technique is that the op-amp "believers" blame the chips/guitar/amp/room/electricity supply/ear wax/hangover/cosmic rays/whatever for the lack of results.

just my (evidence-based) 2c....

And don't forget that the Search function is your friend (fact!).

[JDoyle]

Firstly, for the "there's no difference" crowd.  Take your tubescreamer clone and plant a 4558 in it.  Turn it and your amp way up and listen to that.  It sounds like a waterfall in your living room.  Replace the 4558 with an NE5332.  Do the same.  Now it sounds like there's a waterfall in the next door neighbour's livingroom.  Proof positive that there is a difference.

While I agree with you on the noise issue, it is a secondary issue - we care about what it sounds like when the noise is masked by the signal. So while noise is important, the actual tone of the circuit supercedes that. Please note that I'm not saying the NE5532 is a bad chip - it is probably one of, if not THE, best chip out there for audio - and if you are designing or building ANYTHING BUT a distortion circuit, I would use that chip almost exclusively.

I also think that while duals are definitely cost effective, they are also 'closed' in terms of access to their innards - the points in the internal circuit such as compensation or offest adjust pins or even more esoteric points - unlike single opamp packages, and this is where we can make things interesting and mess with the circuit.

Regards,

Jay Doyle

[AFF]

I tried the search function but I never found anything that actually gives a desciption like I found here!

Thank you all for the input and please continue to add to this thread if you know something else you would like to share.


I guess now I know that some will work okay while others would be best not to try. 4558 would probably work better than TLC2262 op amps.

Now that I know this I will soon start to experiment. I appreciate the great post!