That capacitors that are formed inside opamps have many nonlinearities not present in caps like polistyrene ect. There arent any mica or plate like caps inside opamps, they are formed by using BJT or mosfet junctions to serve as caps. There are well known problems like voltage dependance of these junctions serving as caps which are being addressed by analog and VLSI designers. In a normal cap the value of capacitance is not dependant on the voltage accross it, at 10v or at 30 v the capacitance stays the same or very close to it. Now what happens with a junction, as voltage increases and decreases ?? This is all basic semiconcuctor theory so I dont think I have to explain it further.
Would a reference book regarding these manufacturing defects in opamps and in general intergrated circuits help ??
Would a reference book regarding these manufacturing defects in opamps and in general intergrated circuits help ??
Absolutely, and in other ways too, including the caps, heat up a junction and see what happens.
capacitors??
where are the capacitors? In a decent op amp are no capacitors different the parasitic ones....
Herb.
where are the capacitors? In a decent op amp are no capacitors different the parasitic ones....
Herb.
MISSIONCAT
My Take is that vacuum tubes are slightly microphonic, having shaky grids and all. Some manufacturers of solid-state amps try to capture the vacuum-tube thing by putting in large ceramic coupling capacitors at low-signal stages. Ceramic caps are piezoelectric transducers and will capture some of the sound waves and feed them back into the channel, giving mysterious effects.
Vacuum tubes will of necessity introduce low-frequency noise if the grids shake in response to vibrations.
The best op amp I know of is the Linear Technology LTC1250, available in PDIP and also as samples. This is a chopper op amp, with input noise of about 100nV/Rt-Hz all the way down to 0.001Hz (I have measured this). The input bias current is in pA ( same as vacuum tubes) and the input capacitance is in pF also.
My Take is that vacuum tubes are slightly microphonic, having shaky grids and all. Some manufacturers of solid-state amps try to capture the vacuum-tube thing by putting in large ceramic coupling capacitors at low-signal stages. Ceramic caps are piezoelectric transducers and will capture some of the sound waves and feed them back into the channel, giving mysterious effects.
Vacuum tubes will of necessity introduce low-frequency noise if the grids shake in response to vibrations.
The best op amp I know of is the Linear Technology LTC1250, available in PDIP and also as samples. This is a chopper op amp, with input noise of about 100nV/Rt-Hz all the way down to 0.001Hz (I have measured this). The input bias current is in pA ( same as vacuum tubes) and the input capacitance is in pF also.
This low frequency-noise is called: microphonism.
You can not choose an op amp only on their spec! Even measurements will not always give the right solution. Certainly a chopper op amp is NOT a good choice for audio! They are ment for very precise very low frequency measurements as with strech gauges (or wathever they are called).
In my opinion the LT1028 and the OPA134 are the best audio op amps. The LT1028 for virtual ground circuits, the OPA134 for rather high ohmic applications. (See the different articles in pa0su.nl on this subject.)
"In my opinion the LT1028 and the OPA134 are the best audio op amps."
Those are terribly outdated op amps. True Hi-Fi audio needs Analog Devices AD8597/8599 devices. The Burson Audio and Dexa Technologies discrete op amps will simply blow away ANYTHING in A/B comparisons.
Those are terribly outdated op amps. True Hi-Fi audio needs Analog Devices AD8597/8599 devices. The Burson Audio and Dexa Technologies discrete op amps will simply blow away ANYTHING in A/B comparisons.
Groner's meaurements do show that the Burson's blow
opamp_distortion.pdf (big file!) @ SG-Acoustics · Samuel Groner · IC OpAmps
opamp_distortion.pdf (big file!) @ SG-Acoustics · Samuel Groner · IC OpAmps
How else could opamps be compensated ?? Could you reference say a philips opamp that does not have a capacitor that can be used for audio.
Not hardly!
I've been an audio engr for 30+ years who's devoted a lot of time to LISTENING to myriad op amps in all types of circiuts. Test measurements alone always fall short of telling the whole story regarding the sonic characteristics of a device.
I'm with you Atom Shop, I LISTEN and compare IC op amps. I still hear the difference. Rather annoying, really.
John, jcx is talking about actually listening, not "listening." I know, not good for sales in your market niche. But some of us aren't afraid to trust our ears.
I had the rare pleasure of meeting and working briefly with the great Deane Jensen back in the late 70's. He was tinkering with a phono preamp design using his discrete je-990 op amp. I became the guinea pig in playing with it (and discovered an error in the RIAA eq parts values). What an experience that was! But, since it couldn't be DC coupled, it never developed.
Double "bllind" is SO over-rated. Try and and sell that concept to a studio recording engr who does nothing BUT listen through an un-ending variety of gear in their work. I haven't yet met a professional audio person who needs that stupid crutch to determine his/her preference when selecting what box to use in the recording chain. The same idea applies tp playback.
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Audio professionals rely on double blind testing to establish audibility of claimed or suspected effects. Ears only, crazy concept, huh?
Recording engineering is a different profession with different goals- and they get it wrong quite a bit.
Recording engineering is a different profession with different goals- and they get it wrong quite a bit.
Well said, Atom Shop. I wish I had the ----s to say the same thing. It gets tiresome to be accused of not knowing what I am doing, or that I am trying to mislead the public in some way. Recently, I HAD to make a phono stage with IC's, AND it had to work well! MY reputation as an audio designer depended on it.
I was VERY worried at first listen. But with a series of adjustments, NONE easily measurable, I could make it listenable. Ultimately I could compare it to my 'big rig' composed of a Vendetta and a CTC Blowtorch and while the IC version was not as good, it was 'good enough'. Now it has an A rating in the audio marketplace, MUCH to my surprise. During this evaluation I used mini-dip sockets and sometimes, surface mount adaptors to exchange different op amps, and each one had its own 'personality'.
Knowing WHAT to chose is my profession, and I am good at it.
I was VERY worried at first listen. But with a series of adjustments, NONE easily measurable, I could make it listenable. Ultimately I could compare it to my 'big rig' composed of a Vendetta and a CTC Blowtorch and while the IC version was not as good, it was 'good enough'. Now it has an A rating in the audio marketplace, MUCH to my surprise. During this evaluation I used mini-dip sockets and sometimes, surface mount adaptors to exchange different op amps, and each one had its own 'personality'.
Knowing WHAT to chose is my profession, and I am good at it.
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