Well that's a nice story, but I have a 1954 electronics book that explains the concept of slew rate in amplifiers and how to design for high SR. Written by a US Naval Captain who taught at the Naval Tech University. What were you guys doing 20 years later???
So if you guys say things were not obvious probably means you read the wrong books
Anyway, we know that 'just degenerating the input stage' does NOT increase SR. Increasing the Iq in the input stage does. However, that might require a larger comp cap due to the increased transconductance, undoing the rise in SR you try to achieve. Fortunately, you could degenerate the input stage to lower transconductance again so you got your increased SR.
Agreed?
jan didden
Last edited:
I'm not an expert on PIM, but I have always wondered how something that modulates the PHASE of a freq component could lead to additional harmonics?
jan didden
Moving on, Otala had published some theoretical papers starting in 1969 that promoted high open loop bandwidth and this tended to give high slew rate. BUT slew rate limiting is NOT TIM, it is the clipping that is caused by the TIM producing cap charging, the cap current being non-linear. In fact, a high slew rate op amp can have lots of TIM at much lower levels, IF a class B input stage is used. This is what Matti Otala wanted to include: The exceptions to the general rule, for example the uA741S, a high slew rate 741. Find one and measure it. You will find high TIM(SID) at moderate operating levels. So much for slew rate being the ultimate and complete measurement necessary. (more later)
Well that's a nice story, but I have a 1954 electronics book that explains the concept of slew rate in amplifiers and how to design for high SR. Written by a US Naval Captain who taught at the Naval Tech University. What were you guys doing 20 years later???
So if you guys say things were not obvious probably means you read the wrong books
Anyway, we know that 'just degenerating the input stage' does NOT increase SR. Increasing the Iq in the input stage does. However, that might require a larger comp cap due to the increased transconductance, undoing the rise in SR you try to achieve. Fortunately, you could degenerate the input stage to lower transconductance again so you got your increased SR.
Agreed?
jan didden
Hi Jan,
Yes, slew rate and how to control it was fairly well-known for a long time. Unfortuantely, it was not considered adequately in the early power amplifier designs. Matti deserves credit for helping to shine the light on the need for high slew rate and good input stage linearity. As you point out, degenerating the input stage is a very effective and popular way to increase slew rate. The degeneration decreases the input stage transconductance without reduce input stage current capability. With reduced input stage transconductance, a smaller compensation capacitor is needed, which results in a higher slew rate. Input stage degeneration also linearises the input stage, greatly reducing "soft-TIM" (sub-slewing HF distortion).
Where Matti went off the tracks was in blaming high TIM on low open-loop bandwidth. It is very easy to show that when things are compared on the proper basis, apples to apples, low open-loop bandwidth does not decrease slew rate and does not increase TIM.
The important thing to keep in mind is that for a given loop gain at 20kHz, a smaller open-loop bandwidth simply corresponds to a higher feedback factor at low frequencies.
Cheers,
Bob
Sorry it's not there either, frankly I don't see what the fuss is about.
No I won't. SR is well understood and it has been explained again and again how Barrie viewed this, and your misunderstanding of it.
jan didden
Hi Jan,
Every 6 months or so the PIM thing gets brought up again and everthing is thrashed out on both sides again. Those who want a good explanation of PIM, what causes it, and how NFB is involved, just need to go to my web site and read the JAES paper on PIM that I wrote. While Barrie Gilbert's long-subsequent paper is technically correct, it is really not a complete treatment. Moreover, John is putting words in Barrie's mouth when he asserts that Barrie's paper shows that low open-loop bandwidth exacerbates PIM.
The conclusions in my paper are:
1) PIM does indeed exist.
2) It is basically what has been known by video engineers forever as differential gain and phase.
3) One form of PIM is indeed "caused" by NFB and I show the math for predicting it.
4) the PIM generated by NFB depends on the closed loop bandwidth of the amplifier, NOT the open-loop bandwidth.
5) the PIM caused by negative feedback depends for its creation on the conversion of amplitude intermodulation distortion to phase intermadulation distortion. PIM from this mechanism cannot exist without substantial amounts of AIM (which is easily detectable).
6) Amplifiers without negative feedback have PIM as well, from numerous sources, only one of which is nonlinear junction capacitances.
7) Negative feedback actually REDUCES the PIM from #6.
In any case, those who want a fairly decent coverage of PIM should check out my paper, to at least understand the arguments. They certainly don't have to agree with me.
Cheers,
Bob
Moving on still further: It might be noted that a 'bible' of amplifier design was written by Dr's. Cherry and Hooper in about 1969. It is about 1000 pages, AND there is NO mention of slew-rate, rate of change, or any such term ANYWHERE, yet it was the best, most up-to-date book on the subject. Find a copy and see for yourself. Yet, while we all knew what slew rate was, mostly from IC op amp spec sheets, we did not have the insight yet to improve it significantly.
Now the years pass, remember, the problem first came up in 1966. By 1972, several papers were available from Otala, promoting high open loop bandwidth in audio design.
So in 1973, when working for the Grateful Dead, I designed what later came to be the Levinson JC-2 line stage, and the JC-3 power amp driver stage, which had about 100V/us slew rate, AND about 20KHz open loop bandwidth. The GD were happy, as was Mark Levinson, and I had found a SUCCESSFUL formula for making amps, and preamps.
These designs still sound good, just try them. Perhaps not perfect, but remember, they were designed 38 years ago. Perhaps we can do somewhat better, today, especially with faster output devices, and better jfets.
John Meyer and I worked together in making a super 3 way driven all horn loaded loudspeaker design in 1974. We tried all kinds of commercial power amps, Marantz, SAE, etc. and they worked pretty well up to about 5KHz or so but a better tweeter amp was necessary. That is when I coupled a JC-2 line amp to a class A complementary symmetry output stage, and got a satisfactory solution. Later, I gave this design to Mark Levinson to make a small power amp, and unfortunately Mark and I fell out, mostly over royalties for this amp, and he marketed it under the name of ML-2, with a few revisions of the circuitry.
However, about the same time (1973) or so, Matti and jan L. made an amp together at Philips Research and published a paper on it. This amp had the same overall specs of the JC-3 that I made later, including 100V/us and 20KHz open loop bandwidth. Both sounded great, and I actually bought the first prototype ever made by Electrocompaniet, and used it, off and on, for 15 years, until it was destroyed in a firestorm, in 1991. I have another, and it sounds good, even today. This amp is NOT special because of the amp topology, it is successful because of the high open loop bandwidth. Some similar designs of mine, even with a more linear topology, do not sound as good as this little Electrocompaniet, and I keep it in service as a constant reminder. (more later)
Now the years pass, remember, the problem first came up in 1966. By 1972, several papers were available from Otala, promoting high open loop bandwidth in audio design.
So in 1973, when working for the Grateful Dead, I designed what later came to be the Levinson JC-2 line stage, and the JC-3 power amp driver stage, which had about 100V/us slew rate, AND about 20KHz open loop bandwidth. The GD were happy, as was Mark Levinson, and I had found a SUCCESSFUL formula for making amps, and preamps.
These designs still sound good, just try them. Perhaps not perfect, but remember, they were designed 38 years ago. Perhaps we can do somewhat better, today, especially with faster output devices, and better jfets.
John Meyer and I worked together in making a super 3 way driven all horn loaded loudspeaker design in 1974. We tried all kinds of commercial power amps, Marantz, SAE, etc. and they worked pretty well up to about 5KHz or so but a better tweeter amp was necessary. That is when I coupled a JC-2 line amp to a class A complementary symmetry output stage, and got a satisfactory solution. Later, I gave this design to Mark Levinson to make a small power amp, and unfortunately Mark and I fell out, mostly over royalties for this amp, and he marketed it under the name of ML-2, with a few revisions of the circuitry.
However, about the same time (1973) or so, Matti and jan L. made an amp together at Philips Research and published a paper on it. This amp had the same overall specs of the JC-3 that I made later, including 100V/us and 20KHz open loop bandwidth. Both sounded great, and I actually bought the first prototype ever made by Electrocompaniet, and used it, off and on, for 15 years, until it was destroyed in a firestorm, in 1991. I have another, and it sounds good, even today. This amp is NOT special because of the amp topology, it is successful because of the high open loop bandwidth. Some similar designs of mine, even with a more linear topology, do not sound as good as this little Electrocompaniet, and I keep it in service as a constant reminder. (more later)
Last edited:
Let's see, where were we? It is about 1976, I have designed the JC-3, Electrocompaniet has started making JL and MO amp, and everybody else is doing what they always do, for the most part, except for Electro Research that made a fast amp too.
I was working for Gale in London at the time, when I was invited to Finland to work with Matti Otala for about 1 month. I did so and we made hundreds of measurements. I concentrated on phono stages. Later in the year, Matti gave the paper we are talking about at the AES-NY in 1976, and we were first introduced to the 5534 OP AMP at the time.
Audio narvina? We hoped so.
Now let make something very clear. I am a distant colleague of Matti Otala, I can't even say I am a close friend. I think that Matti might of thought me a potential 'threat' back at that time, and decided to put me 'close' rather than distant. Matti, did have a problem with directly relating slew rate to TIM, and he STILL insisted that open loop bandwidth was important, even though, by that time, we knew that we could make high enough slew rates, without having an extra high open loop bandwidth. It embarrassed me when Matti would use arguments similar to what is put to me here by some people in order to keep a topic from being discussed. One time I wanted to pin a BS button on him, and I would have, if I would have found Paul Klipsch soon enough. I found Matti to be more 'political' than I cared for, BUT at least he was trying to make progress. Later, I realized that he was probably disappointed in the overall improvement that raising the slew rate and lower TIM to virtually unmeasurable. Just like devices today, by 1978 or so, TIM in op amps became very low. Still, many power amps were made, like Bob Carver's and even Audio Research, that could use a higher slew rate at the time. We measured them, just to be sure.
So was this all there was? No, OR we would have shifted to IC op amps decades ago. As I said before, I got my first 5534 (TDA1034) in 1976, but when I tried it, and compared it with a discrete design that I had made for mixing consoles, the IC fell short. So back to the drawing board. Later, Matti and I worked together for a short time, but he got me in trouble with HK by asking me to put in extra time on a power amp project, and then not backing me up when it came to billing for it, making me look like I was overcharging them. I left HK and never worked with Matti again. However, he did take and use my comp diff fet input stage without ever telling me. I just found that out recently.
So, why do I defend Matti Otala's work here? Because his work is not necessarily the man, and he is not in a position to defend himself. You might think of me as his advocate, rather than his friend. And so it goes.
I was working for Gale in London at the time, when I was invited to Finland to work with Matti Otala for about 1 month. I did so and we made hundreds of measurements. I concentrated on phono stages. Later in the year, Matti gave the paper we are talking about at the AES-NY in 1976, and we were first introduced to the 5534 OP AMP at the time.
Audio narvina? We hoped so.
Now let make something very clear. I am a distant colleague of Matti Otala, I can't even say I am a close friend. I think that Matti might of thought me a potential 'threat' back at that time, and decided to put me 'close' rather than distant. Matti, did have a problem with directly relating slew rate to TIM, and he STILL insisted that open loop bandwidth was important, even though, by that time, we knew that we could make high enough slew rates, without having an extra high open loop bandwidth. It embarrassed me when Matti would use arguments similar to what is put to me here by some people in order to keep a topic from being discussed. One time I wanted to pin a BS button on him, and I would have, if I would have found Paul Klipsch soon enough. I found Matti to be more 'political' than I cared for, BUT at least he was trying to make progress. Later, I realized that he was probably disappointed in the overall improvement that raising the slew rate and lower TIM to virtually unmeasurable. Just like devices today, by 1978 or so, TIM in op amps became very low. Still, many power amps were made, like Bob Carver's and even Audio Research, that could use a higher slew rate at the time. We measured them, just to be sure.
So was this all there was? No, OR we would have shifted to IC op amps decades ago. As I said before, I got my first 5534 (TDA1034) in 1976, but when I tried it, and compared it with a discrete design that I had made for mixing consoles, the IC fell short. So back to the drawing board. Later, Matti and I worked together for a short time, but he got me in trouble with HK by asking me to put in extra time on a power amp project, and then not backing me up when it came to billing for it, making me look like I was overcharging them. I left HK and never worked with Matti again. However, he did take and use my comp diff fet input stage without ever telling me. I just found that out recently.
So, why do I defend Matti Otala's work here? Because his work is not necessarily the man, and he is not in a position to defend himself. You might think of me as his advocate, rather than his friend. And so it goes.
Nobody of us has issues with Matti the man, there's only discussion about his work. Is that OK?
Apparently, YOU are the ONLY one here to criticise Matti the man. Why do you do that to a man who can't defend himself?
jan didden
Stylus Thread
Hi Flavio,
Thanks for making that thread, it is fantastic. The phono playback systems I maintain at home and at the station have greatly benefited from the info here on phono preamp design and your stylus thread!
Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
1st on the Internet
Hi Flavio,
Thanks for making that thread, it is fantastic. The phono playback systems I maintain at home and at the station have greatly benefited from the info here on phono preamp design and your stylus thread!
Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
1st on the Internet
Jan, I think the 'truth' doesn't need defending. I was there when Matti took me aside and asked me to put in extra time. I was there when the VP at HK got really mad at me for 'double charging', I am the one who openly invited Matti to work at HK, and I was gone in a couple of months. I think that it is important to tell the story as it really was to get my perspective on why I support Matti Otala's ideas, not out of excessive personal friendship, but because they are worth supporting.
http://www.diyaudio.com/forums/solid-state/189150-what-happened-digital-amp-revolution-25.html Post 246 should make John's holiday weekend.
To be honest with everyone, this was 'water under the bridge' until recently. I already had another business proposal available, at the time, that made me president of my own corporation doing audio design with Japanese money backing. I didn't need the HK job anymore, but I had hoped to work with Matti on a power amp. I knew that TOGETHER we could make a superior power amp. He had the theoretical knowledge, and I had the BETTER topology (the complementary differential jfet input stage). When I was 'phased' out, I lost that opportunity, except that I recently found that Matti had 'acquired' my topology, anyway, just like Ortofon (who, that very year, 'acquired' my patented topology). I was doing 'great' in other peoples projects, but with not re-numeration or even credit for my efforts, from my 'colleagues'. That really is bothersome!
When I first worked with Matti on the power amp, he had a completely different topology, based on a video amp design, and it looked pretty good, but I knew that my topology was better. Of course, the same topology was in the ML-2 (formerly the JC-3) and I didn't get any credit for that either.
IF I had not spent years developing these designs, making dozens of prototypes, and I had not conferred the essence of these designs to the people who 'acquired' them, then OK, but I was back-stabbed on 4 separate occasions within 5 years. AND people wonder why I don't publish my schematics!
Now when it comes to general 'badmouthing' of others. I don't like it either. I resent the fact that Jack Bybee can be 'trashed' on this website without any proof, just speculation, or that I am considered 'impaired' in some way for expressing my design ideas here.
However, this seems to be the best opportunity to make it CLEAR what the relationships were between Matti and me, over 30 years ago. The only time that we ever worked together again was to put out the rebuttal to Bob Cordell (10+pages) were I contributed my high dV/dT measurements and my support for the general opinion about Bob's work at the time. We never worked together, thereafter, but Matti had plenty of chances to tell me that he used my topology in the HK power amp. Oh well!
When I first worked with Matti on the power amp, he had a completely different topology, based on a video amp design, and it looked pretty good, but I knew that my topology was better. Of course, the same topology was in the ML-2 (formerly the JC-3) and I didn't get any credit for that either.
IF I had not spent years developing these designs, making dozens of prototypes, and I had not conferred the essence of these designs to the people who 'acquired' them, then OK, but I was back-stabbed on 4 separate occasions within 5 years. AND people wonder why I don't publish my schematics!
Now when it comes to general 'badmouthing' of others. I don't like it either. I resent the fact that Jack Bybee can be 'trashed' on this website without any proof, just speculation, or that I am considered 'impaired' in some way for expressing my design ideas here.
However, this seems to be the best opportunity to make it CLEAR what the relationships were between Matti and me, over 30 years ago. The only time that we ever worked together again was to put out the rebuttal to Bob Cordell (10+pages) were I contributed my high dV/dT measurements and my support for the general opinion about Bob's work at the time. We never worked together, thereafter, but Matti had plenty of chances to tell me that he used my topology in the HK power amp. Oh well!
- Status
- Not open for further replies.