counter culture has just earned himself a short break for commenting on moderation.
Yes, its internally a current feedback opamp disguised as VFB. They've done this by adding in an extra buffer prior to the (normally low impedance) inverting input. Stability is indeed a little more tricky than a 5532 but not too difficult, its unity gain stable.
The biggest issue to check on is the input bias currents - around 10X greater than for the 5532, so definitely check over the resistor values in the biassing and feedback networks. Other than this you'll be good to go. Its 3kV/uS incidentally and 36V absolute max supply.
Yes I've been using it for some time in active XOs and like the sound I get.
The biggest issue to check on is the input bias currents - around 10X greater than for the 5532, so definitely check over the resistor values in the biassing and feedback networks. Other than this you'll be good to go. Its 3kV/uS incidentally and 36V absolute max supply.
Yes I've been using it for some time in active XOs and like the sound I get.
Not "self-published," Bruno doesn't have anything to do with publication other than as an author (as am I, Doug Self, Ed Simon, Dick Marsh, and several other diyAudio participants). The publisher, Jan Didden, has Bruno's article available on the site for free download.
Ok thanks for the info. There are a couple of sections in the preamp where the offset resulting from higher input bias currents could be high enough to reduce headroom, so might require more extensive mods to make it work ok. I'm interested though and will order some to try.
Ha ha, that is so true. You can even hear a good mix from a bad one on a mid fi tabletop stereo.
I will say the same thing about the 5532 that I said about capacitors. If you design the circuit to work with the device, it will provide excellent performance. And the limitations of the 5532 vs discrete or more complicated op amp designs is a no brainer. For line level signals, you can make it do whatever you want.
The use of parallel buffers offers greatly enhanced performance at very low cost. I applaud this design.
I'm curious to know why you think the design is so praiseworthy when as far as I can see you're implying that all recordings are already so degraded by lower performance (than this design) mixers etc and as such nobody needs to listen to them on anything other than mid-fi gear. According to your logic there is no need for the higher level of performance provided by this design over any other bog standard opamp mid-fi preamp. I mean what's the point of going to the trouble of paralleling 5532s to get higher SNR and/or better driving ability when single 5532s already provide adequate performance by comparison with the recording chain? 
Presumably you have built it and listened to it then?
Paralleling 5532s might offer significant cost vs performance benefits to manufacturers, but for hobbyists buying only a few opamps this simply not the case - eg taking Element14 as an example supplier and ordering in qtys of < 25 pcs:
1 x On Semi 5532ANG: $2.60. 4 in parallel brings the cost to $10.40
1 x Nat Semi LM4562: $6.37.
This does not look like "very low cost" to me.
Presumably you have built it and listened to it then?
Paralleling 5532s might offer significant cost vs performance benefits to manufacturers, but for hobbyists buying only a few opamps this simply not the case - eg taking Element14 as an example supplier and ordering in qtys of < 25 pcs:
1 x On Semi 5532ANG: $2.60. 4 in parallel brings the cost to $10.40
1 x Nat Semi LM4562: $6.37.
This does not look like "very low cost" to me.
Abraxalito, what sort of decoupling did you use with those super fast beasties? This preamp has 0.1uF across the supply rails (not to gnd) and not one for every opamp package so I'm wondering if that will be adequate. I did use polypropylenes instead of polyester, though suspect it doesn't make much difference...
That could be the mistake.
esr has a big bearing on the damping provided by the local decoupling cap.
What you must not have is oscillation due to a fast change in current demand.
That oscillation is damped by the esr.
A low esr cap like a polypropylene could be allowing a corrupted signal to pass.
Hi-K ceramic are usually good for local decoupling. An alternative could be a high esr polyester !!!!
That's not the main point that I'm making. In fact, the quality of recordings varies from absolutely awful to squeaky clean and dynamic. Anybody that listens to music on a decent system and has any kind of ear knows this. Some recordings are so awful that they sound subjectively better on a "mid fi" system.
My point is that if you design a circuit with the parameters of a 5532 in mind, you can get excellent performance out of it. It can certainly be improved on. The point of diminishing returns is a subjective thing.
The 5532 can't do everything. It would be a poor choice for a microphone preamp. It would make a poor instrumentation amp (the lowly TL072 would be better). But for low impedance (less than 500K) line level circuits, it is right at the sweet spot for cost vs performance.
I wholeheartedly encourage you to design higher performance circuits. I would never argue with advancing the state of the art.
I said the same thing about capacitors. A properly designed circuit will give excellent performance with cheap electrolytic coupling and bypass capacitors. Marginal and somewhat subjective improvements can be made by employing fancy pants capacitors.
I mean what's the point of going to the trouble of paralleling 5532s to get higher SNR and/or better driving ability when single 5532s already provide adequate performance by comparison with the recording chain?
Actually, I explicitly praised the parallel buffers. I have used such schemes myself. It is a simple way to improve performance.
Have you ever looked inside a typical mixer? It has 5532s out the ying yang. A typical headphone amp inside a mixer is parallel 5532s. It works great! But of course we can do better with the resources we have here.
There's nothing earth shattering about this circuit. It is just an optimisation of everyday circuits. It is well thought out. And I have built most (if not all) of the circuits contained in it at one time or another.
Well do it then. This is a website where we try different stuff and compare notes. Go for it.
One thing you must understand is that I studied electrical engineering before op amps were used in industry. Op amps like the 741 only existed on paper. All we had was the 748 which isn't even worth using. When the 741 and the 709 came out, it was the advent of practical op amp circuits. When the 3140 came out, it was considered the very best op amp for most audio applications. We have come a very long way.
Engineers are trained for cost vs performance objectives for industry. I personally applaud all the efforts here to extract the last little bit of performance from circuits. I've learned a lot here. Don't think I'm a hater.
Engineers are trained for cost vs performance objectives for industry. I personally applaud all the efforts here to extract the last little bit of performance from circuits. I've learned a lot here. Don't think I'm a hater.
You sound like a knowledgable chap AndrewT, and I see your point. However several well repected designers have recommended the use of polyprop over polyester for decoupling in their designs over the years. I don't have any data handy for comparison, but is the ESR very different between the two dielectric types at the frequency range of interest? I didn't think it was, and as polyprop are superior in other ways I figured it shouldn't do any harm to use them and potentially some good.
I used Evox Rifa PHE426HJ6100J which have a 5mm lead pitch so I think we can at least discount a potential reduction in effectiveness due to higher lead inductance had I tried to cram bigger caps in by bending leads. There is no sign of any oscillation on the CRO at various signal levels with sine and square signals BTW.
Does anyone else with experience in this area and this specific sort of application agree they could be a problem? I would like to think there was some sort of consensus before going ahead and replacing a whole stack of them in the DSPT board...
One thing you must understand is that I studied electrical engineering before op amps were used in industry. Op amps like the 741 only existed on paper. All we had was the 748 which isn't even worth using. When the 741 and the 709 came out, it was the advent of practical op amp circuits. When the 3140 came out, it was considered the very best op amp for most audio applications. We have come a very long way.
Engineers are trained for cost vs performance objectives for industry. I personally applaud all the efforts here to extract the last little bit of performance from circuits. I've learned a lot here. Don't think I'm a hater.
If you'd read any of the rest of this thread you'd know that I'm an EE also. Many of the guys I graduated with could not design a circuit that works, let alone assemble it, if their life depended on it. From my experience an engineering degree means that you have above average capabilities in maths and the determination to survive 4 years at the bar interspersed with some studying
. It does not make you an automatic expert in anything. I do not recall any training on cost vs performance objectives - this comes from experince and via the bean counters that run the companies where engineers get employed (by which I mean stressed out and generally trampled on
) doesn't it?Again if you'd read my earlier posts you'd know that I also respect the designer Douglas Self greatly and have expressed my gratitude several times for his generosity in sharing his wisdom by publishing his many designs. However I have reconfirmed recently by building the predecessor to this preamp design that I don't share the views expressed in his published work that any audible degradation in a piece of audio equipment only exists if it is measureable using the standard set of measurements in an AP2 or whatever. Luckily I live in a free country where it is still ok to have an opinion on things
I'm posting here because I think the preamp I've built is subjectively "mildy strangling" the music. I find this interesting and was hoping to learn something by working out why. After all, this is a forum for DIY, not manufacturers, is it not? The recent spate of last minute comments implying that I have no basis for this opinion is pointless as everyone here must be aware of the debate over subjective vs objective and no matter which part of the spectrum you sit in no single person has all the answers. No one could prove that I can't hear what I'm hearing any more than I can prove that I can. The design must be audibly perfect as it measures so well.
This is good science for anyone who uses an amplifier to display waveforms on a 'scope or generate impressive looking specs on paper, but for the rest of us who use them for enjoying music I think it's pretty questionable science. Stay human 
Fast Eddie and Owdeo,
I wouldn't dare to take sides in your back and forth here. You are both EE's and obviously there are others here also and some who are just very knowledgeable in electronic circuit design. I agree Owdeo that some things measure great and still we can hear a difference between circuits that appear to have the same measurable response characteristics. It would be great if some of you great minds could also design test equipment that finds out what are some of these differences, what are we hearing, and how can you measure and quantify these subtle changes. I know you are here to design audio circuits and trades ideas, perhaps there could be a thread on possible directions to improve the test equipment that could solve some of the mysteries involved here?
I wouldn't dare to take sides in your back and forth here. You are both EE's and obviously there are others here also and some who are just very knowledgeable in electronic circuit design. I agree Owdeo that some things measure great and still we can hear a difference between circuits that appear to have the same measurable response characteristics. It would be great if some of you great minds could also design test equipment that finds out what are some of these differences, what are we hearing, and how can you measure and quantify these subtle changes. I know you are here to design audio circuits and trades ideas, perhaps there could be a thread on possible directions to improve the test equipment that could solve some of the mysteries involved here?
Thanks Kindhornman. I agree wholeheartedly
I can't claim to have a great mind but at least I try to keep it open...
Many other engineers I've worked with over the years seem to have a "knowledge is power" mentality and feel threatened when they might appear not to know everything. For some this seems to develop over the years into a genuine belief that they do know everything and hard line rationalism can be a convenient tool to dismiss any suggestion that they don't.
This is absolutely what's needed IMO too - the problem is I think it would take a massive investment of time and resources to get anywhere in this direction. You would think commercially there would be a great incentive to improve the correlation between measured performance and listener satisfaction, but there is probably no incentive to make the upfront investment in such an undertaking when corporations can make profits by sticking with known formulas and tweaking these instead. Besides person taste still comes into it. You have to convince the bean counters (good luck), and they decide everything these days...
Audio is unique in that is for entertainment and involves emotions. Focussing on design techniques that optimise conventional performance measurements sure makes the design engineer's job more manageable - if you start allowing subjective evaluation to enter the process the whole thing becomes incredibly complex and presumably often not economically viable in today's world.
I don't hold out much hope here - many of the great minds seem content to stick with conventional methods and advance the art by improving those. Or if not they aren't sharing their findings in the public domain. In a way I think a good analogy is medicine - the western scientific approach to it has resulted in incredible advances in life expectancy and general treatment of pretty much everything, and yet as it only considers symptoms and not causes it's quite possible to suffer serious health problems for which it has no solution, and so many people turn to alternative medicine that may or may not help, but for which there is little incentive for research as natural remedies that can't be patented cannot be profitable enough to justify the investment. Unversities are just profit-driven corporations these days after all. Research doesn't get funding just because it might benefit the common good.
I can't claim to have a great mind but at least I try to keep it open...
Many other engineers I've worked with over the years seem to have a "knowledge is power" mentality and feel threatened when they might appear not to know everything. For some this seems to develop over the years into a genuine belief that they do know everything and hard line rationalism can be a convenient tool to dismiss any suggestion that they don't.
This is absolutely what's needed IMO too - the problem is I think it would take a massive investment of time and resources to get anywhere in this direction. You would think commercially there would be a great incentive to improve the correlation between measured performance and listener satisfaction, but there is probably no incentive to make the upfront investment in such an undertaking when corporations can make profits by sticking with known formulas and tweaking these instead. Besides person taste still comes into it. You have to convince the bean counters (good luck), and they decide everything these days...
Audio is unique in that is for entertainment and involves emotions. Focussing on design techniques that optimise conventional performance measurements sure makes the design engineer's job more manageable - if you start allowing subjective evaluation to enter the process the whole thing becomes incredibly complex and presumably often not economically viable in today's world.
I don't hold out much hope here - many of the great minds seem content to stick with conventional methods and advance the art by improving those. Or if not they aren't sharing their findings in the public domain. In a way I think a good analogy is medicine - the western scientific approach to it has resulted in incredible advances in life expectancy and general treatment of pretty much everything, and yet as it only considers symptoms and not causes it's quite possible to suffer serious health problems for which it has no solution, and so many people turn to alternative medicine that may or may not help, but for which there is little incentive for research as natural remedies that can't be patented cannot be profitable enough to justify the investment. Unversities are just profit-driven corporations these days after all. Research doesn't get funding just because it might benefit the common good.
hi owdeo, you need not go far, in Australia, you have Hugh Dean, Greg Ball, Rod Elliot and Patrick Turner to look up to for some great ideas....suit one to your taste.....
no one can fault you for your opinions, after all they are just opinions.....keep on building and who knows, you may find what you seek...
no one can fault you for your opinions, after all they are just opinions.....keep on building and who knows, you may find what you seek...
Fast Eddie and Owdeo,
I wouldn't dare to take sides in your back and forth here. You are both EE's and obviously there are others here also and some who are just very knowledgeable in electronic circuit design. I agree Owdeo that some things measure great and still we can hear a difference between circuits that appear to have the same measurable response characteristics. It would be great if some of you great minds could also design test equipment that finds out what are some of these differences, what are we hearing, and how can you measure and quantify these subtle changes. I know you are here to design audio circuits and trades ideas, perhaps there could be a thread on possible directions to improve the test equipment that could solve some of the mysteries involved here?
You might find something here. Walt Jung analyzed op amps more thoroughly than anyone else I know of. Services
Check out how he tests capacitors. He measures the distortion that nobody can measure but some people insist they can hear. He separates the woo from demonstrable results.
I was reading a link here yesterday where a "high end" amplifier designer was applying similar test procedures that show the different artefacts of various amounts of negative feedback. It was quite illuminating. And the procedures to measure these artefacts that many can hear but so many people (like me) have a hard time quantifying is so simple that it was a facepalm moment for me.
I need strong empirical evidence to be convinced. It is how I was trained. Jung quantifies what everybody else argues about.
There are a lot of op amps that I don't know about. I learn a new one just about every day. I plan to do some experimenting in due time.
If you'd read any of the rest of this thread you'd know that I'm an EE also. Many of the guys I graduated with could not design a circuit that works, let alone assemble it, if their life depended on it. From my experience an engineering degree means that you have above average capabilities in maths and the determination to survive 4 years at the bar intreconfirmed recently by building the predecessor to this preamp design that I don't share the views expressed in his published work that any audible degradation in a piece of audio equipment only exists if it is measureable using the standard set of measurements in an AP2 or whatever. Luckily I live in a free country where it is still ok to have an opinion on things
I do know that you're an EE. I was not trying to appeal to authority. I was trying to point out that I learned about op amps before they were in practical use. All the stuff I studied on my own through the years, and a lot of stuff I have learned right here, simply did not exist in the 70s. I've done my best to keep up and just recently I started to really look at "state of the art" stuff. I actually designed and built "state of the art" stuff in the 70s while I was in college. It's crap compared to what I can build for peanuts today.
I built my first amp when I was in high school. It was an ultralinear 6CA7 circuit, from mostly salvage parts. I used an active high voltage power supply (like TVs had at the time) for the low level circuitry. I used some fancy pants caps that I bought new. The result was an amplifier that had a very low noise floor, comparable to modern solid state amps of the 70s, and the softest clipping I have ever observed. It didn't IM real bad or regurgitate nasty feedback spike artefacts. It just quit getting louder. If I still had it today, I wouldn't want for anything more. It got stolen decades ago.
So I am not the EE guy that can't wire a light bulb. That being said, my long term career was in finance.
Again if you'd read my earlier posts you'd know that I also respect the designer Douglas Self greatly and have expressed my gratitude several times for his generosity in sharing his wisdom by publishing his many designs. However I have reconfirmed recently by building the predecessor to this preamp design that I don't share the views expressed in his published work that any audible degradation in a piece of audio equipment only exists if it is measureable using the standard set of measurements in an AP2 or whatever. Luckily I live in a free country where it is still ok to have an opinion on things
Walt Jung has demonstrated how to measure some of these "unmeasureable" artefacts. I linked to some of it earlier in this thread.
I am not too quick to agree with Mr. Self's comments either. I can hear too.
I'm posting here because I think the preamp I've built is subjectively "mildy strangling" the music. I find this interesting and was hoping to learn something by working out why. After all, this is a forum for DIY, not manufacturers, is it not? The recent spate of last minute comments implying that I have no basis for this opinion is pointless as everyone here must be aware of the debate over subjective vs objective and no matter which part of the spectrum you sit in no single person has all the answers. No one could prove that I can't hear what I'm hearing any more than I can prove that I can. The design must be audibly perfect as it measures so well.This is good science for anyone who uses an amplifier to display waveforms on a 'scope or generate impressive looking specs on paper, but for the rest of us who use them for enjoying music I think it's pretty questionable science. Stay human
I would like to know why you think it's "strangling" the music too. I wholeheartedly support your quest to improve this circuit. I haven't built it. But I've used some of the concepts employed in it. And these circuits worked very precisely too.
I am working on improving my "state of the art" too.
I will take a second look, and see if I see any room for improvement.