Don´t forget supply current and the parts around the OP-amp
There might be one additional aspect for stompboxes and for onboard preamps in particular - that is the supply current. All of the above mentioned audio-OP-amps need pretty much current (between 3 ang 6 mA per channel). If you are running on on a 9V battery that is a lot. I am just building a preamp for the Music Man Sting Ray bass - using basicly the original schematic but with much better parts. Musis Man / Ernie Ball used an LM 4250 in the original preamp, mainly for the very small supply current and very low supply voltage. For my upgrade I first selected the OPA132 (low supply voltage, good sound). The OPA 132 however needs about 4mA per channel, which is more than 10 times of the LM4250 in the original circuit. Therefore I finally ended up with an AD820, which is not quite the audio quality compared the real high-end audio OP-amps, but it only requires 0,8 mA of supply current, works with low supply voltage and provides good headroom with rail-to-rail at the output. Slew-rate and bandwidth should be good enough as well.
Another major aspect: A lot of guitar amps and effect pedals suffer from bad capacitors, resistors and diodes.
I highly recommend to replace all polyester caps by polypopylene caps, all ceramic caps by silver mica , polyprop caps or polystyrene caps, all standard electrolytic caps by audio-grade electrolytic caps (such like the Panasonic FC).
This will change the tonal quality at least as much as the replacement of an old 4558 or 741 by a state of the art audio OP-amp such like OPA 627, OPA 134, AD823, Ad825.
Last but not least: Unfortunately learly all standard-resistors have a bad influence on sound quality. I have just used vishay dale resistors in an amp-upgrade for the first time and I could hardly believe the difference. Sorry to say - these resistors are pretty expensive and hard to get. There are only very few suppliers, who sell small amounts to other than industry customers.
There might be one additional aspect for stompboxes and for onboard preamps in particular - that is the supply current. All of the above mentioned audio-OP-amps need pretty much current (between 3 ang 6 mA per channel). If you are running on on a 9V battery that is a lot. I am just building a preamp for the Music Man Sting Ray bass - using basicly the original schematic but with much better parts. Musis Man / Ernie Ball used an LM 4250 in the original preamp, mainly for the very small supply current and very low supply voltage. For my upgrade I first selected the OPA132 (low supply voltage, good sound). The OPA 132 however needs about 4mA per channel, which is more than 10 times of the LM4250 in the original circuit. Therefore I finally ended up with an AD820, which is not quite the audio quality compared the real high-end audio OP-amps, but it only requires 0,8 mA of supply current, works with low supply voltage and provides good headroom with rail-to-rail at the output. Slew-rate and bandwidth should be good enough as well.
Another major aspect: A lot of guitar amps and effect pedals suffer from bad capacitors, resistors and diodes.
I highly recommend to replace all polyester caps by polypopylene caps, all ceramic caps by silver mica , polyprop caps or polystyrene caps, all standard electrolytic caps by audio-grade electrolytic caps (such like the Panasonic FC).
This will change the tonal quality at least as much as the replacement of an old 4558 or 741 by a state of the art audio OP-amp such like OPA 627, OPA 134, AD823, Ad825.
Last but not least: Unfortunately learly all standard-resistors have a bad influence on sound quality. I have just used vishay dale resistors in an amp-upgrade for the first time and I could hardly believe the difference. Sorry to say - these resistors are pretty expensive and hard to get. There are only very few suppliers, who sell small amounts to other than industry customers.
Upgrade on OP-Amp AD820 for Guitar / Bass
Following my previous comment above I would like to enclose some remarks on the AD820. In the meantime I have finished my preamp-upgrade (2-band tone control) for my Music Man StingRay bass it is a real success. Instead of the LM4250 in the original preamp I use an AD820. Input and output electrolytic caps are Panasonic FC as are the decoupling caps, which I have enlarged considerably. All other caps are polypopylene and the resistors are Vishay Dale CMF.
The sound is more punchy, less brittle, very dynamic and it got a better bottom end and and a more balanced sound from string to string and along the strings. The instrument is more responsive and thus easier to play.
I also tried the OPA134, but turned back to the AD820, because the OPA134 sounded too laid back and too hifi-like in this application. The AD820 seems to be well suited for guitars and basses and should be a good choice for stomp-boxes as well.
Following my previous comment above I would like to enclose some remarks on the AD820. In the meantime I have finished my preamp-upgrade (2-band tone control) for my Music Man StingRay bass it is a real success. Instead of the LM4250 in the original preamp I use an AD820. Input and output electrolytic caps are Panasonic FC as are the decoupling caps, which I have enlarged considerably. All other caps are polypopylene and the resistors are Vishay Dale CMF.
The sound is more punchy, less brittle, very dynamic and it got a better bottom end and and a more balanced sound from string to string and along the strings. The instrument is more responsive and thus easier to play.
I also tried the OPA134, but turned back to the AD820, because the OPA134 sounded too laid back and too hifi-like in this application. The AD820 seems to be well suited for guitars and basses and should be a good choice for stomp-boxes as well.
screw opamps and screw tubes!
this is where it's at:
http://www.native-instruments.com/index.php?id=guitarrig2_us
much more tunable to a particular sound than trying your luck swapping opamps
this is where it's at:
http://www.native-instruments.com/index.php?id=guitarrig2_us
much more tunable to a particular sound than trying your luck swapping opamps
Software is the definite wave of the future. There is plenty of free suites that work good also. Here is one
http://www.simulanalog.org/guitarsuite.htm
Now we just need to figure out a small cheap, reliable, powerful enough PC that can be hauled around.
http://www.simulanalog.org/guitarsuite.htm
Now we just need to figure out a small cheap, reliable, powerful enough PC that can be hauled around.
For hifi the AD8620 has a clean sound, but I prefer OPA627. It has a more warm, brown sound to it. OPA2604 isnt very good sounding for hi-fi, but i can see where people would like it for guitar. I actually prefer the clean, neutral sound of the NE5532 over the OPA2604 for hifi.
What does that have to do with guitar? Honestly, I dont think you want to ever hear your opamps distort. That's a job best left to tubes. In the ts808 tubescreamer, sure they use a JRC4558D but somehow I've got to think it's because it sounded good _and_ was cheap. I think you could do better.
I also have a feeling that the pedals would sound better if built with discrete opamps.
A long time ago I built some germanium diode fuzz boxes and the results were very good. I don't ever remember the opamp I used.
That GuitarRig sounds nice.... maybe approaching a TC Electronics G-Force??? Hard to lug a PC over to a friends place though.
I heard a computer VST plugin, a reverb convolver from Voxengo and some models of a vintage tube reverb and was kind of blown away. It is possible to some degree to emulate the sound of about any piece of vintage equipment. The exceptions are tube overdrive and diode fuzz where I prefer the real thing.
What does that have to do with guitar? Honestly, I dont think you want to ever hear your opamps distort. That's a job best left to tubes. In the ts808 tubescreamer, sure they use a JRC4558D but somehow I've got to think it's because it sounded good _and_ was cheap. I think you could do better.
I also have a feeling that the pedals would sound better if built with discrete opamps.
A long time ago I built some germanium diode fuzz boxes and the results were very good. I don't ever remember the opamp I used.
That GuitarRig sounds nice.... maybe approaching a TC Electronics G-Force??? Hard to lug a PC over to a friends place though.
I heard a computer VST plugin, a reverb convolver from Voxengo and some models of a vintage tube reverb and was kind of blown away. It is possible to some degree to emulate the sound of about any piece of vintage equipment. The exceptions are tube overdrive and diode fuzz where I prefer the real thing.
There are lot of superstitious beliefs about sonic quality of opamps. In your application you may use any opamps. Better use them in inverting mode to avoid distortions caused by a differential input pair, but anyway any guitar amp is built to distort musically, so any opamp will fit, except some noisiest vintage devices.
well-made op-amps everywhere
I agree with Vangelis, that the tlo72 works just fine with instrument preamp circuits. One does get something more with newer technology, but its not always what you want. We used a set of ad797 (which I believe I bought at a good price from jack in new jersey here on the forum) for a high fi preamp repair, and those had a noticable clean quality to them. Not sure I'd use them for original instrument signals, a little too much sparkle for my ears.
I agree with Vangelis, that the tlo72 works just fine with instrument preamp circuits. One does get something more with newer technology, but its not always what you want. We used a set of ad797 (which I believe I bought at a good price from jack in new jersey here on the forum) for a high fi preamp repair, and those had a noticable clean quality to them. Not sure I'd use them for original instrument signals, a little too much sparkle for my ears.
Only a little note :
- The famous 4558 is now replaced with 4560 in almost all electronics
devices. (the 4558 descending from uA741)
- The NE5532 have two internal clipping diode, and it work well
only in a linear application. (not use in overdrive circuit)
For 4558 & 4560 look this:
http://www.njr.co.jp/index_e.htm
bye
- The famous 4558 is now replaced with 4560 in almost all electronics
devices. (the 4558 descending from uA741)
- The NE5532 have two internal clipping diode, and it work well
only in a linear application. (not use in overdrive circuit)
For 4558 & 4560 look this:
http://www.njr.co.jp/index_e.htm
bye
Still lots of discussion about which opamp "sounds" best I see. Honestly this is such a blind. Modern opamps produce something better than 0.2% distortion when they are open loop, that is without the feedback which makes them usable in practical circuits. When feedback is applied this distortion drops to below 0.01%. If we are talking about using them in clipping distortion circuits then the massive amounts of distortion produced by the circuit topology, (NOT the opamp!), wipe out any other sources of distortion. Could you hear the 0.01% opamp distortion in amongst the 30% clipping distortion? If you think that the distortion a clipping circuit produces is caused by the opamp then you are mistaken!
My advice to would be designers is to learn to bias cheap JFET and bipolar transistors and do things discrete. You should also design with no feedback. This leaves in the better type of distortions which the single devices produce naturally and does not reduce them with overall feedback. JFETs are very like valves in this respect. If you look at the circuitry of any standard classic valve amp and produce a really simple design based on what you see there but using FETs you will get far better results than with any opamp circuit. You are then producing your distortion by the same methods as those beautiful classics.
The whole point of opamps is that their design requires them to use negative feedback to give absolute minimal distortions in "proper use". They are to all intents and purposes character free in uses like guitar signal shaping. When they go outside of their designed parameters into clipping within themselves they become immediately awful no matter which one you use! I STRESS, NO CIRCUIT SHOULD BE PRODUCED WHERE CLIPPING OCCURS WITHIN THE OPAMP ITSELF. They can certainly be used as the active component in diode clipping circuits, but this sort of design prevents the opamp from going into clipping anyway, and the vast distortion produced swamps completely any sort of character it may give to the sound. The idea of an opamp having a sonic signature in a guitar preamp circuit is a complete no no, it's all down to the decisions made on the circuit topology they are used in.
I have designed and used a number of good alternatives for a few pence which do give the same sort of distortions and responses that valve stuff does, and though I know enough to do this I'm certainly no expert, so think of what an expert could do!
My advice to would be designers is to learn to bias cheap JFET and bipolar transistors and do things discrete. You should also design with no feedback. This leaves in the better type of distortions which the single devices produce naturally and does not reduce them with overall feedback. JFETs are very like valves in this respect. If you look at the circuitry of any standard classic valve amp and produce a really simple design based on what you see there but using FETs you will get far better results than with any opamp circuit. You are then producing your distortion by the same methods as those beautiful classics.
The whole point of opamps is that their design requires them to use negative feedback to give absolute minimal distortions in "proper use". They are to all intents and purposes character free in uses like guitar signal shaping. When they go outside of their designed parameters into clipping within themselves they become immediately awful no matter which one you use! I STRESS, NO CIRCUIT SHOULD BE PRODUCED WHERE CLIPPING OCCURS WITHIN THE OPAMP ITSELF. They can certainly be used as the active component in diode clipping circuits, but this sort of design prevents the opamp from going into clipping anyway, and the vast distortion produced swamps completely any sort of character it may give to the sound. The idea of an opamp having a sonic signature in a guitar preamp circuit is a complete no no, it's all down to the decisions made on the circuit topology they are used in.
I have designed and used a number of good alternatives for a few pence which do give the same sort of distortions and responses that valve stuff does, and though I know enough to do this I'm certainly no expert, so think of what an expert could do!
I am useing an OPA134 and a TL071 as the preamp in my LM3886 Based Guitar amp and it sounds and works great....To tell you the truth it is one of the Best sounding guitar amps I have ever Played and I have been playing for over 20 years....
I have the OPA134 as a Buffer with a Gain of 2.2 and the TL071 with a Gain of 20 and there is a Tone controll circuit between them...
I also have a seperate Over drive circuit before the Buffer that Puts out an AWESOME crunchy guitar sound....
It is a 50w amp into 8 ohms or 65w into 4 ohms and I am useing a 12in 50w Fender Princeton Speaker and it goes so lout that I haven"t been able to get it louder than 5 on the power amp Volume pot because it is so loud.....
It is truely the best project I have ever built and I designed pretty much all of the Circuits myself and I have only been doing electronics for 10 months but it also took a LOT of trial and error to get it working the way it is now but there are still a couple Minor bugs to be worked out.....
Cheers
PS: it also sounds great as a Bass amp....
I have the OPA134 as a Buffer with a Gain of 2.2 and the TL071 with a Gain of 20 and there is a Tone controll circuit between them...
I also have a seperate Over drive circuit before the Buffer that Puts out an AWESOME crunchy guitar sound....
It is a 50w amp into 8 ohms or 65w into 4 ohms and I am useing a 12in 50w Fender Princeton Speaker and it goes so lout that I haven"t been able to get it louder than 5 on the power amp Volume pot because it is so loud.....
It is truely the best project I have ever built and I designed pretty much all of the Circuits myself and I have only been doing electronics for 10 months but it also took a LOT of trial and error to get it working the way it is now but there are still a couple Minor bugs to be worked out.....
Cheers
PS: it also sounds great as a Bass amp....
Best Opamp?
I operate a small repair shop for solid state guitar amps, with accent on small - no expensive test equipmant. I built just a simple little board so I can place an opamp down into a socket and test it. After reading this thread with interest, and having plenty of time to play, I decided to check the sounds of different opamps, so I hooked my little test board up as a guitar preamp, then into a 30W Kustom. I listened to all the popular opamps up thru the years from the vintage 741 to the late model low voltage MAX492. My conclusion - I could not actually recommend any of them as "the best". Plus, my setup would probably sound different than another setup combination. There's so many different sounds, from deeper mellow, to high and bright. I had no real problems with any of them, not even the old 741. I do have my favorites, but my preferences may differ from yours. My favorites would be the 5532, TLO72, and OPA627 - I think ?
If you're a real audio buff, and serious about changing out the opamps in an older amp, or maybe designing something yourself, I would recommend setting up a board like this and listening for yourself.
Also, with repairing several solid state amps, I've found that opamps sound different in different amps. My last repair job was a burned out 1458 in an old Kustom amp. I replaced same - sounded great.
Sorry to add to the confusion, but there's a lot of different ears out there !
I operate a small repair shop for solid state guitar amps, with accent on small - no expensive test equipmant. I built just a simple little board so I can place an opamp down into a socket and test it. After reading this thread with interest, and having plenty of time to play, I decided to check the sounds of different opamps, so I hooked my little test board up as a guitar preamp, then into a 30W Kustom. I listened to all the popular opamps up thru the years from the vintage 741 to the late model low voltage MAX492. My conclusion - I could not actually recommend any of them as "the best". Plus, my setup would probably sound different than another setup combination. There's so many different sounds, from deeper mellow, to high and bright. I had no real problems with any of them, not even the old 741. I do have my favorites, but my preferences may differ from yours. My favorites would be the 5532, TLO72, and OPA627 - I think ?
If you're a real audio buff, and serious about changing out the opamps in an older amp, or maybe designing something yourself, I would recommend setting up a board like this and listening for yourself.
Also, with repairing several solid state amps, I've found that opamps sound different in different amps. My last repair job was a burned out 1458 in an old Kustom amp. I replaced same - sounded great.
Sorry to add to the confusion, but there's a lot of different ears out there !
Zero Cool said:
worst....op amp.....EVER!
My earliest work was pulling the op amps out of every pedal and guitar amp I own, installing sockets and trying every op amp known to man that would work.
I would say the very best overall performer which just so happens to have the closest specs to a 12AX7 is the NE5532. It is hands down the best performer. I can crank my amp a lot louder before it starts to deteriorate and I'm forced to back off the EQ controls. It has the most clarity and the most balanced tone. It just has a very transparent sound compared to any other op amp I've tried in a half dozen pedals and a couple amps.
The 4558 has this richness and midrange to it a lot of people like but it's damn noisy compared to so many others. If you use it to drive your distortion circuit and use something like the 5532, 2604 or 2228 in the other circuit stags, it sounds damn good. It's ended up back in my amps distortion stage a handful of times now. It's the closest to the 5532 but with a bit more midrange, noise of course but a richness as well.
Instead of cream, it's whipped cream.
Top 5 though.... 5532 has got to be the best, then the 2604, next being the 2228 and the 4558 being number 4 out of the top 5. The 082 is crap in comparison to all of them but still lands at number 5.
I guess it really does depend the application and I don't want to keep sounding redundant but the NE5532 is as good as it gets.
Which op-amp is best for neutral tonality?
I am designing a 3-way guitar selector pedal (e.g. an ABC switch) that will use op-amps for buffering (plus a little gain), volume controls for all 3 guitar inputs, and C4066 analog switches for non-pop switching.
I want an op-amp that will not color the tone of the guitar at all -- completely neutral and transparent as far as tone is concerned. Other devices (e.g. pedal/amp) will determine the tone, the selector switch will just select a guitar (and give it a few more db)
Which of these op-amps might be best suited for this?
FYI, here are my design goals, just for clarity...
- 3 guitars selected and routed into one amp or effects pedal (e.g. a deluxe ABC switch)
- Option of selecting guitars in OR or AND mode (e.g. exclusive or combined) -- I'll do some digital logic for this
- anti-pop solid state switching, audio path will not directly use the mechanical footswitches
- built-in buffering for all 3 guitar inputs with gain controls (3 volume knobs, one per guitar), very hi input impedance for guitars, low impedence output to drive pedal or amp
- the amount of buffer gain is not yet decided, somewhere between 3 and 12 db
- LEDs, one per guitar
- Powered by either 9v battery or ext power, so power consumption is an issue (though not paramount)
Thanx for any advice,
/Mark
I am designing a 3-way guitar selector pedal (e.g. an ABC switch) that will use op-amps for buffering (plus a little gain), volume controls for all 3 guitar inputs, and C4066 analog switches for non-pop switching.
I want an op-amp that will not color the tone of the guitar at all -- completely neutral and transparent as far as tone is concerned. Other devices (e.g. pedal/amp) will determine the tone, the selector switch will just select a guitar (and give it a few more db)
Which of these op-amps might be best suited for this?
FYI, here are my design goals, just for clarity...
- 3 guitars selected and routed into one amp or effects pedal (e.g. a deluxe ABC switch)
- Option of selecting guitars in OR or AND mode (e.g. exclusive or combined) -- I'll do some digital logic for this
- anti-pop solid state switching, audio path will not directly use the mechanical footswitches
- built-in buffering for all 3 guitar inputs with gain controls (3 volume knobs, one per guitar), very hi input impedance for guitars, low impedence output to drive pedal or amp
- the amount of buffer gain is not yet decided, somewhere between 3 and 12 db
- LEDs, one per guitar
- Powered by either 9v battery or ext power, so power consumption is an issue (though not paramount)
Thanx for any advice,
/Mark
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