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Old 7th January 2007, 12:47 AM   #31
Albertb is offline Albertb  United Kingdom
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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!
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Old 16th January 2007, 08:23 PM   #32
Minion is offline Minion  Canada
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Location: Cowican Bay , vancouver island
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....
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Old 30th January 2007, 08:57 PM   #33
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Default 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 !
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Where there is smoke....there is fire. (usually one of my circuits)
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Old 31st January 2007, 03:36 PM   #34
godinus is offline godinus  France
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Minion, is it possible to see a schematic of your amp design?

Thanks
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Old 2nd February 2007, 09:19 AM   #35
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Quote:
Originally posted by Zero Cool
The JRC 4558 is hailed by many guitar FX makers as one of the best. The original ones bring very good money.

FX pedals such as the Tube Screamer and various Distortion pedals use this chip.

Is it really the best for guitar? i dont know. but it seems to be very popular.

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.
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Old 15th November 2008, 07:53 PM   #36
jeghers is offline jeghers  United States
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Join Date: Nov 2008
Default 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
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