Hi,
MC33078:- The phase performance of this chip is terrible ?
http://www.onsemi.com/pub/Collateral/MC33078-D.PDF
I accidently had my speakers in reverse phase, and it sounded really strange. Am I right in this op amp will sound a bit odd due to phase change in audio band ?
Also the Lm833 has poor phase performance.
I have looked at the AD712, and this has a 'flat' phase performance in the audio band:-
http://www.analog.com/UploadedFiles/Data_Sheets/288953399AD712_e.pdf
AD797, LM6172 seem to have flat phase.
Should I only select op amps with flat phase in the audio band ?
MC33078:- The phase performance of this chip is terrible ?
http://www.onsemi.com/pub/Collateral/MC33078-D.PDF
I accidently had my speakers in reverse phase, and it sounded really strange. Am I right in this op amp will sound a bit odd due to phase change in audio band ?
Also the Lm833 has poor phase performance.
I have looked at the AD712, and this has a 'flat' phase performance in the audio band:-
http://www.analog.com/UploadedFiles/Data_Sheets/288953399AD712_e.pdf
AD797, LM6172 seem to have flat phase.
Should I only select op amps with flat phase in the audio band ?
I'm sorry to say that but the only terrible thing here is your understanding of op-amps.
These graphs show open-loop phase response, and show it in different ways because AD712 datasheet shows phase margin (that's 180 degrees minus phase shift) while MC33078 datasheet shows bare phase shift.
Also, if you could actually understand a little these graphs and datasheets, you would notice that both MC33078 and AD712 have similar phase margins of approx. 50 degrees around their rated unity gain frequencies. However, these frequencies are 16Mhz for the MC33078 and only 4Mhz for the AD712, thus the former will always show less phase shift than the later at 20Khz in closed loop applications.
There is a lot of op-amp theory published in the web that you could use to gain better understanding about them.
These graphs show open-loop phase response, and show it in different ways because AD712 datasheet shows phase margin (that's 180 degrees minus phase shift) while MC33078 datasheet shows bare phase shift.
Also, if you could actually understand a little these graphs and datasheets, you would notice that both MC33078 and AD712 have similar phase margins of approx. 50 degrees around their rated unity gain frequencies. However, these frequencies are 16Mhz for the MC33078 and only 4Mhz for the AD712, thus the former will always show less phase shift than the later at 20Khz in closed loop applications.
There is a lot of op-amp theory published in the web that you could use to gain better understanding about them.
Phase shift itself is not a problem with music.
If you reversed phase on one speaker only , bass response was cancelling out.If you reverse on both , they should sound the same.
Phase shift also depends on circuit , not only the op- amp.
In active filters , it would look quite different from that you found in datasheet , and will not be linear anyway.
If you reversed phase on one speaker only , bass response was cancelling out.If you reverse on both , they should sound the same.
Phase shift also depends on circuit , not only the op- amp.
In active filters , it would look quite different from that you found in datasheet , and will not be linear anyway.
Of course, there is a lot of people just swapping expensive op-amps (without even reading the datasheets) and trying to find "sonic excellence" that way, but that's quite far from science. No op-amp understanding is required to do that, a gentle budget and a lot of imagination are just enough.
That is good start.
You must keep in mind, the manufacturer's are trying to describe the device itself and NOT the circuit you build around it. You notice the gain is probably 1,000,000 or more for these amps... where would you use that?
The circuit you put around the amp determines (mostly) its final gain & phase response. That is NOT to say the factors on the data sheet don't matter for audio... they do...
Keep doing your homework!
Good luck,
You must keep in mind, the manufacturer's are trying to describe the device itself and NOT the circuit you build around it. You notice the gain is probably 1,000,000 or more for these amps... where would you use that?
The circuit you put around the amp determines (mostly) its final gain & phase response. That is NOT to say the factors on the data sheet don't matter for audio... they do...
Keep doing your homework!
Good luck,
Hi, EVA,
I don't understand, why a "genius" opamp designer said that opamps are not for audio? What is the problem? Too much gain can be burned by feedback, so what is the worst case?
http://www.diyaudio.com/forums/showthread.php?postid=893695#post893695
I don't understand, why a "genius" opamp designer said that opamps are not for audio? What is the problem? Too much gain can be burned by feedback, so what is the worst case?
http://www.diyaudio.com/forums/showthread.php?postid=893695#post893695
this was probably an example of why audio opamps didn't sound good 30+ years ago -- I purchased this back when Harvey Electronics on 45th Street stilll sold electronics parts -- back when I was in college -- 35+ years ago -- never even opened the package. Must be some kind of artifact:
Attachments
jackinnj said:
Well, there were very few "audio" opamps back in 1974. The problem was that the op amps that were available we often used beyond their limitations, particularly in terms of GBW. There was no way of getting 40dB of gain from a single op amp and still have decent audio performance. But split the 40dB over two stages (20dB + 20dB) and it was possible to get gain and performance.
The manufacturers pushed the op amps as "universal gain blocks" which they certainly were not. Not then, not even now (though some come close).
Most op amps did one or two things well and you had understand their idiosyncracies. For example, in 1972-1973, My friend Jim Bornhorst designed the electronics for a 30 channel console with full parameteric eq using the 709 op amp for input stages and the 1458 op amps for the rest. Eight of these were built and used for live performance show between 1975 and 1985 (including bands like Led Zeppelin) and even some revered live recordings (incl. Jackson Browne's "Running On Empty".
So it was possible to design quality audio equipment in the early 1970's but it took brains and effort. Probably not easier than discrete though if you wanted to do it well!
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.