tmbg
Well-known member
CMRR of 120dB, noise of 9nV/Hz, these sound like happy things!
But a 0.2V/us slew rate, is that prohibitive? :/
But a 0.2V/us slew rate, is that prohibitive? :/
LM725
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tmbg
Well-known member
LM108 looks promising too... CMRR 100dB, 30nV/Hz noise, 3nA input bias current, external compensation.
Bit pricey though
Bit pricey though
peranders
Well-known member
Are looking for something special and for which application? If you ask me nicely you can even have a couple of opamps for free plus postage. :grin:
tmbg
Well-known member
Oh no, not looking for anything in particular, was just browsing sites looking for fun samples to order.
I'd really like to put together a nice collection of opamps to play with... I know the tl072 and 5532 are popular, but I'd love to know what other opamps are respected for audio, and why.
I'm wanting to do some simple mic pre design, thinking about the front end now, which is why I was focusing on CMRR and noise figures.
As per your offer, I appreciate the gesture immensely! I'm not really hard up, but thanks!
I sat down and played with my few I had on hand the other night, and it was pretty interesting... set up a 10x gain and unity gain circuit, fed it with a signal gen and scoped the output, sweeping it and seeing how different op amps react in the upper frequencies. I have some old old 4558s that I stole out of an old peavey guitar amp, and they did very poorly compared to the TL082 I tried.
They all did very well with regards to triangle in = triangle out... I seem to remember reading that if you get bowed sides on a triangle wave, that's harmonic distortion. Gain dropped below unity on the 4558 at around 100KHz, whereas the TL082 made it all the way to 1MHz before slipping below the input signal. It's also interesting the way square waves turn into triangle waves as the upper harmonics are attenuated.
So basically, I've just been having a great time
I'd really like to put together a nice collection of opamps to play with... I know the tl072 and 5532 are popular, but I'd love to know what other opamps are respected for audio, and why.
I'm wanting to do some simple mic pre design, thinking about the front end now, which is why I was focusing on CMRR and noise figures.
As per your offer, I appreciate the gesture immensely! I'm not really hard up, but thanks!
I sat down and played with my few I had on hand the other night, and it was pretty interesting... set up a 10x gain and unity gain circuit, fed it with a signal gen and scoped the output, sweeping it and seeing how different op amps react in the upper frequencies. I have some old old 4558s that I stole out of an old peavey guitar amp, and they did very poorly compared to the TL082 I tried.
They all did very well with regards to triangle in = triangle out... I seem to remember reading that if you get bowed sides on a triangle wave, that's harmonic distortion. Gain dropped below unity on the 4558 at around 100KHz, whereas the TL082 made it all the way to 1MHz before slipping below the input signal. It's also interesting the way square waves turn into triangle waves as the upper harmonics are attenuated.
So basically, I've just been having a great time
> 0.2V/us slew rate, is that prohibitive? :/
Yes.
That 4558 that turns everything to triangles at high level and frequency? It is 5 times better than a 725. The 725 is very much a low frequency low level chip. (And isn't it just an input stage, not a full amplifier?)
Same for the 308. Groundbreaking bias current in its day, but slower than my old dog. Handy for offset-nulling servos (we can do much better now), not for audio. Oh, there is a complicated way to improve the 308's slew, but I don't see any point when TL072 is a dollar a dozen.
If you like slew-distortion, it is reasonably easy to build an adjustable slewer out of common chips. You guys who remember the 1970s fondly (I don't remember them at all) might want such a thing as an FX box, to get that old-time 741 sound.
> I seem to remember reading that if you get bowed sides on a triangle wave, that's harmonic distortion.
Yes, except if the amp is slewing, you will get beautifully straight sides on triangles no matter what the input signal really is.
> Gain dropped below unity on the 4558 at around 100KHz
Uh, no. Unity-gain on 741/4558 is 1MHz at very low signal level. What you must have measured is the maximum output, which IIRC for 10V signals starts dropping before 10KHz. Try running 10mV through and see if you can't get to 500KHz. Also try big square waves: above a few KHz they will be more triangular than square.
> some simple mic pre design... which is why I was focusing on CMRR and noise figures.
Forget CMRR!!! In most small-studio work, you do not need any CMRR at all. Youse guys is spoiled having XLR everywhere. I did a LOT of good work on totally unbalanced mike inputs.
Noise is over-rated too.
You want simple? You can do a fine mike-amp with a 5534 working transformerless unbalanced. All the slew and most of the gain you should ever need. Noise not that far above theoretical, and lower than most home studios. Phantom is a minor problem. You may run into problems when unbalanced (but "XLR") mikes don't pick the same XLR pin for "hot" as you do: if you have such mikes in your stable, you will either have to wire the amp to work with your mikes, or have a hot-select switch.
Yes.
That 4558 that turns everything to triangles at high level and frequency? It is 5 times better than a 725. The 725 is very much a low frequency low level chip. (And isn't it just an input stage, not a full amplifier?)
Same for the 308. Groundbreaking bias current in its day, but slower than my old dog. Handy for offset-nulling servos (we can do much better now), not for audio. Oh, there is a complicated way to improve the 308's slew, but I don't see any point when TL072 is a dollar a dozen.
If you like slew-distortion, it is reasonably easy to build an adjustable slewer out of common chips. You guys who remember the 1970s fondly (I don't remember them at all) might want such a thing as an FX box, to get that old-time 741 sound.
> I seem to remember reading that if you get bowed sides on a triangle wave, that's harmonic distortion.
Yes, except if the amp is slewing, you will get beautifully straight sides on triangles no matter what the input signal really is.
> Gain dropped below unity on the 4558 at around 100KHz
Uh, no. Unity-gain on 741/4558 is 1MHz at very low signal level. What you must have measured is the maximum output, which IIRC for 10V signals starts dropping before 10KHz. Try running 10mV through and see if you can't get to 500KHz. Also try big square waves: above a few KHz they will be more triangular than square.
> some simple mic pre design... which is why I was focusing on CMRR and noise figures.
Forget CMRR!!! In most small-studio work, you do not need any CMRR at all. Youse guys is spoiled having XLR everywhere. I did a LOT of good work on totally unbalanced mike inputs.
Noise is over-rated too.
You want simple? You can do a fine mike-amp with a 5534 working transformerless unbalanced. All the slew and most of the gain you should ever need. Noise not that far above theoretical, and lower than most home studios. Phantom is a minor problem. You may run into problems when unbalanced (but "XLR") mikes don't pick the same XLR pin for "hot" as you do: if you have such mikes in your stable, you will either have to wire the amp to work with your mikes, or have a hot-select switch.
