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Noise figures of some common op amps are as follows:
TL022: 50nV/√Hz
TL072: 18nV/√Hz
OPA2134: 8nV/√Hz
NE5532: 5nV/√Hz
R.
Eqd Speaker Cranker clone
Monte Allums TR-2 Plus mod kit
Trading feedback: http://www.thefretboard.co.uk/discussion/60602/
I mentioned the TL072 simply as an example, there are better jfet op amps now.
You cannot compare the noise performance of jfet and bipolar input chips, the former will be quieter for 'the magic meg' input Z.
NE5532? Yes, excellent IC for everything BUT a high Z input. Has vastly better load driving ability than the 72. The LM4562 is even better but more expensive.
Reliability of buffers? Never had a chip fail in a pedal*. Footswitch yes, but not because of a poor component, built like a BSH. Very obscure problem in production. All fixed by a completely new design. The odd valve but that was very rare.
Anyone interested in OP Amps etc should get Douglas Self's book, Small Signal Amplifiers.
*and that with a 30V supply, at 9V? Avin' a larf. Oh and DS will tell you, unless you use 741s you don't need to worry about slew rate!
Dave.
(741 - 0.5V/uS, 4558 - 1.7V/uS, 072 - 16V/uS, from a quick check.)
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Cheers,
Adam
Eqd Speaker Cranker clone
Monte Allums TR-2 Plus mod kit
Trading feedback: http://www.thefretboard.co.uk/discussion/60602/
The only problem with Google is that it can be hard to find suitable context for information and often asking people with the knowledge is quicker, so perhaps a more sensible question would be : Why is slew rate important to consider for op-amps in guitar pedals?
Cheers,
Adam
If the op amp can't respond quickly enough then the output will not be faithful to the input.
R.
Eqd Speaker Cranker clone
Monte Allums TR-2 Plus mod kit
Trading feedback: http://www.thefretboard.co.uk/discussion/60602/
Oddly some very high speed opamps aren't the best choice for a buffer ... mainly because they don't like running at unity gain and unless better attention is paid to high frequency decoupling they can oscillate well out of the audio range .... sometimes you can detect this with nothing other than your finger feeling one opamp is hotter than another
Either way, the result of a lower slew rate is more harmonic distortion and less top-end response - which for a guitar overdrive pedal is a good thing.
In a buffer it would be a bad thing, except that in a low-gain configuration the unaffected frequency response is pushed much further up, out of the audio range.
This is for the 741, and you can see that the response is greatly affected in the 1-10KHz range at gains of 40 to 60dB which are common in distortion pedals. For anything below 20dB, it's outside the audio range.
https://www.nutsvolts.com/uploads/wygwam/NV_0701_Marston_FIGURE6.jpg
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Adam
Yeah, I was thinking of the buffer use-case rather than overdrive/distortion.
Eqd Speaker Cranker clone
Monte Allums TR-2 Plus mod kit
Trading feedback: http://www.thefretboard.co.uk/discussion/60602/
I know of no modern (or even the 30+yr old 5532!) op amp that cannot produce a full level 20kHz sine signal?
Dave.
But ironically, only when you use them *as* distortion pedals, and not when you use them as is now fashionable, as low-distortion boosts. Even more ironic is that the 'better' ICs usually used by boutique makers often sound *worse* when they're used as actual distortion pedals .
Obviously this doesn't matter for a buffer though, as Robin said.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
It's important for best distortion performance with TL072s that the impedance seen at both inputs is equal.
This can be acheived in a mixer (or TL072s can be employed in parts of the circuit where this is not a problem) where impedances are generally know.
However being used as a buffer for guitar, the impedances are not equal on either input, and I think that this is a cause of the TL072 sounding brighter than an OPA2134.
Yes but the thread IS about buffers! What, BTW are peeps using then at 40dB and more gains?
Dave.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Ok but, what super-slewing chips are they using?
Dave.
R.
Eqd Speaker Cranker clone
Monte Allums TR-2 Plus mod kit
Trading feedback: http://www.thefretboard.co.uk/discussion/60602/
Or rather, some of the boutique builders do seem to use ones that are faster than the JRC4558 and the original Rat's LM308 - which is *really* slow at only 0.3V/uS - on the basis that these "better" chips must be "better". But as we have said many times before, with guitar gear the exact opposite is often true . Using a chip with a faster slew rate should definitely produce more high-frequency gain, even below 10KHz, with these types of pedal.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein