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Old 25th August 2012, 02:48 PM   #531
redjr is offline redjr  United States
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Has anyone actually built this new pre-amp and has it functioning in the real world yet? It would be nice to have some subjective comments based on listening to this new design. Pics would be good too if you've created a snazzy enclosure for it. Thx.
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Old 25th August 2012, 11:29 PM   #532
owdeo is offline owdeo  Australia
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Originally Posted by AndrewT View Post
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 !!!!
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...
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Old 26th August 2012, 12:16 AM   #533
owdeo is offline owdeo  Australia
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Originally Posted by Fast Eddie D View Post
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
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Old 26th August 2012, 01:08 AM   #534
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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?
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Old 26th August 2012, 02:12 AM   #535
owdeo is offline owdeo  Australia
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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.
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Old 26th August 2012, 02:23 AM   #536
AJT is offline AJT  Philippines
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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...
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Old 26th August 2012, 03:48 AM   #537
jcx is offline jcx  United States
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...only exists if it is measureable using the standard set of measurements in an AP2 or whatever...
any idea how old the AP System 2 is??

have you really worked though all the menu items on a 2010 model?

you can get 2.5 Msample, 1 MHz signal bandwith audio analyzers today from AP

care to hypothesize what exactly they miss - in enough detail that you could write a measurement script?
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Old 26th August 2012, 05:40 AM   #538
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Originally Posted by Kindhornman View Post
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.
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Old 26th August 2012, 06:49 AM   #539
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Originally Posted by owdeo View Post
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.

Quote:
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.

Quote:
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. Click the image to open in full size. 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 Click the image to open in full size.
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.
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Old 26th August 2012, 07:26 AM   #540
AndrewT is offline AndrewT  Scotland
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Originally Posted by owdeo View Post
................ 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 ...............
You have modified the design and complained about the sound quality, all on the basis "I didn't think it was" or "it shouldn't do any harm" !
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