Hadley holds US patent 3,631,357 on the design which you will find referenced in the Manantz 500 service manual. It is his design.
The 622 has basically the same circuit as what Nelson Pass patented 30 years later. So it is quite elegant.
There are many people who have made careers based on Dawson Hadley's work, not just in audio. When you die young like Hadley, you don't get to protect your legacy I guess.
Your link is dead. I tried. Having a patent that relates to the amplifier does not mean he designed it. I would be interested in reading the patent though.
I am extremely familiar with the 500 and am currently working on one. I have worked on these amplifiers since 1983. I have had to put them back together after hacks have been inside for years on end. Most technicians can't even manage to do the DC offset alignment properly. As for repairs, I rarely see one that was repaired properly and most people are only dimly aware the transistors need to be matched. Never mind, how to actually match them!
As I said earlier, each Marantz model designed was a team effort. Hadley was the chief engineer but I am pretty convinced he didn't design the 500. The 500 was extremely advanced, but too expensive to manufacture. Lovely amplifier.
-Chris
I am extremely familiar with the 500 and am currently working on one. I have worked on these amplifiers since 1983. I have had to put them back together after hacks have been inside for years on end. Most technicians can't even manage to do the DC offset alignment properly. As for repairs, I rarely see one that was repaired properly and most people are only dimly aware the transistors need to be matched. Never mind, how to actually match them!
As I said earlier, each Marantz model designed was a team effort. Hadley was the chief engineer but I am pretty convinced he didn't design the 500. The 500 was extremely advanced, but too expensive to manufacture. Lovely amplifier.
-Chris
Look what it is. It is missing an ":". Our browsers know that and try to fix it with another http, but wrong.
https://patentimages.storage.googleapis.com/5b/92/1e/cca3a1e9089267/US3631357.pdf
Or attached.
There's a page with 11 'I Claim's, many quite general, though perhaps novel for 1969. It would take considerable time to work out which parts were new inventions and which are just general background.
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Hmmm, not much like the 500.
The basic 500 has an input buffer (important, Nakamichi called it "HTA" many years later) that drove a bipolar diff pair. This drove a pair of diff pair stages, one for positive, the other for the negative. Each of these diff pairs controlled each half of the waveform to minimise distortion in these stages. The diff pair at the front knitted everything together and operated as you would expect. Each diff pair were nulled for a balance, then the primary diff pair was nulled for balance and zero DC offset at the output.
So if we call the op amp in the diagram in the patent a differential pair, it still is miles away from what makes the 500 special. One amplifier I am familiar with that springs to mind when reading this patent. The BGW 750 series is pretty close to this conceptual diagram. Really almost identical. It uses an LM318 for the op amp while the patent calls out an LM741. I strongly doubt the 741 has a high enough slew rate for the job, an LM301 would be far more suitable.
To be honest, this patent really describes the common, basic amplifier, and I am not sure it is different enough from prior art to deserve a patent. I'll read it over again, but this patent does not describe the operation of the Marantz 500. I didn't even have to refer to any documentation to see the differences being I am so familiar with the 500.
The basic 500 has an input buffer (important, Nakamichi called it "HTA" many years later) that drove a bipolar diff pair. This drove a pair of diff pair stages, one for positive, the other for the negative. Each of these diff pairs controlled each half of the waveform to minimise distortion in these stages. The diff pair at the front knitted everything together and operated as you would expect. Each diff pair were nulled for a balance, then the primary diff pair was nulled for balance and zero DC offset at the output.
So if we call the op amp in the diagram in the patent a differential pair, it still is miles away from what makes the 500 special. One amplifier I am familiar with that springs to mind when reading this patent. The BGW 750 series is pretty close to this conceptual diagram. Really almost identical. It uses an LM318 for the op amp while the patent calls out an LM741. I strongly doubt the 741 has a high enough slew rate for the job, an LM301 would be far more suitable.
To be honest, this patent really describes the common, basic amplifier, and I am not sure it is different enough from prior art to deserve a patent. I'll read it over again, but this patent does not describe the operation of the Marantz 500. I didn't even have to refer to any documentation to see the differences being I am so familiar with the 500.
This is all your opinion. The facts are that the patent matches the number present within the service manual and Hadley was indeed the lead designer for Marantz at the time. While I'm sure other engineers contributed (obviously), there is no evidence or discussion anywhere with any kind of basis that this design is someone else's.
Now with all of that being said, I would like to keep this topic on the Hadley 622 amplifiers I'm working on, and not have you derail this thread with a mostly unrelated discussion.
Cool, but my opinion is fact since I compared and understand these schematics and designs. Your comment simply proves that you do not understand how these work. Simple.
Anyone can look at the schematic of the 500 and clearly see it isn't related beyond the fact that it is an amplifier. Big deal.
If you want to believe that Mr Hadley designed the 500 for the most part, go ahead. I don't know to be honest. However, from what I see in his design, and the patent, there is no connection between them. Have any technician or engineer familiar with how the 500 works look at your information and comment. Same for the other Marantz products, and I am intimately familiar with all of them.
The lead engineer guides the overall development of products and jumps in to solve problems. Look up the other engineers he was working with and you will see they are much better known and went on to have successful careers after they left Marantz. I'm not saying that Mr. Hadley had nothing to do with the 500, but the basic design does not appear to have come from his way of thinking, and I see more similarities from the other engineers whose work I am also familiar with. Not putting Mr. Hadley down at all, I just don't see his hand in the 500. That amp is unique in the way it is designed.
The patent is so general that it could be listed as applying to almost any amplifier design. But as I said, the BGW 750 is almost a direct copy. Look that model up and you will see what I mean. The BGW 750 is a pretty good amplifier and very robust, and excellent design. I would not be surprised at all to find that Mr. Hadley had a hand in that design.
Anyway, you made a claim about the 500 which puts it in the line for discussion. Now its time for you do to a little research yourself. Look at the 500 and the BGW 750 and tell me what you think. I did look up Hadley, the 500 history, read the patent and suggested the BGW 750 for you to learn with. The schematic you presented for Mr. Hadley is unlike anything in the patent or other Marantz products except for the very low powered ones that used quasi-complimentary output stages. Heck, the amplifier you presented doesn't even use a differential pair! One might argue it is closer to an NAD on that basis.
-Chris
Anyone can look at the schematic of the 500 and clearly see it isn't related beyond the fact that it is an amplifier. Big deal.
If you want to believe that Mr Hadley designed the 500 for the most part, go ahead. I don't know to be honest. However, from what I see in his design, and the patent, there is no connection between them. Have any technician or engineer familiar with how the 500 works look at your information and comment. Same for the other Marantz products, and I am intimately familiar with all of them.
The lead engineer guides the overall development of products and jumps in to solve problems. Look up the other engineers he was working with and you will see they are much better known and went on to have successful careers after they left Marantz. I'm not saying that Mr. Hadley had nothing to do with the 500, but the basic design does not appear to have come from his way of thinking, and I see more similarities from the other engineers whose work I am also familiar with. Not putting Mr. Hadley down at all, I just don't see his hand in the 500. That amp is unique in the way it is designed.
The patent is so general that it could be listed as applying to almost any amplifier design. But as I said, the BGW 750 is almost a direct copy. Look that model up and you will see what I mean. The BGW 750 is a pretty good amplifier and very robust, and excellent design. I would not be surprised at all to find that Mr. Hadley had a hand in that design.
Anyway, you made a claim about the 500 which puts it in the line for discussion. Now its time for you do to a little research yourself. Look at the 500 and the BGW 750 and tell me what you think. I did look up Hadley, the 500 history, read the patent and suggested the BGW 750 for you to learn with. The schematic you presented for Mr. Hadley is unlike anything in the patent or other Marantz products except for the very low powered ones that used quasi-complimentary output stages. Heck, the amplifier you presented doesn't even use a differential pair! One might argue it is closer to an NAD on that basis.
-Chris
Cool, but my opinion is fact since I compared and understand these schematics and designs. Your comment simply proves that you do not understand how these work. Simple.
Anyone can look at the schematic of the 500 and clearly see it isn't related beyond the fact that it is an amplifier. Big deal.
If you want to believe that Mr Hadley designed the 500 for the most part, go ahead. I don't know to be honest. However, from what I see in his design, and the patent, there is no connection between them. Have any technician or engineer familiar with how the 500 works look at your information and comment. Same for the other Marantz products, and I am intimately familiar with all of them.
The lead engineer guides the overall development of products and jumps in to solve problems. Look up the other engineers he was working with and you will see they are much better known and went on to have successful careers after they left Marantz. I'm not saying that Mr. Hadley had nothing to do with the 500, but the basic design does not appear to have come from his way of thinking, and I see more similarities from the other engineers whose work I am also familiar with. Not putting Mr. Hadley down at all, I just don't see his hand in the 500. That amp is unique in the way it is designed.
The patent is so general that it could be listed as applying to almost any amplifier design. But as I said, the BGW 750 is almost a direct copy. Look that model up and you will see what I mean. The BGW 750 is a pretty good amplifier and very robust, and excellent design. I would not be surprised at all to find that Mr. Hadley had a hand in that design.
Anyway, you made a claim about the 500 which puts it in the line for discussion. Now its time for you do to a little research yourself. Look at the 500 and the BGW 750 and tell me what you think. I did look up Hadley, the 500 history, read the patent and suggested the BGW 750 for you to learn with. The schematic you presented for Mr. Hadley is unlike anything in the patent or other Marantz products except for the very low powered ones that used quasi-complimentary output stages. Heck, the amplifier you presented doesn't even use a differential pair! One might argue it is closer to an NAD on that basis.
-Chris
What didn't you understand about my last post? Your baseless opinion about someone you don’t know has literally no value to me or anyone else. You are wasting your time and as I previously mentioned, I want this thread to be about the Hadley 622s I am working on, not you, not your opinions on these amplifiers, and not the Marantz 500. We really have nothing to discuss and I really do not have any kind of desire to read another word of what you have to say. I would appreciate if you’d respect that and move along.
I point you to Rule #1 if you’re at all confused. Mods should follow the rules just as other members should.
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...
Heck, the amplifier you presented doesn't even use a differential pair! One might argue it is closer to an NAD on that basis.
-Chris
If you refer to the schematic in post 1, it has a differential pair.
Hi as_audio,
I'm missing it completely. Please point out the diff pair. It's possible I am completely blind, but I do not see a diff pair in the input at all.
Hi hadley,
We do follow the rules every member does.
My comments are arrived at from fact and observation. However as I said, I did some research and merely requested you do the same. If you can't, or unprepared to then you are unable to make the comments you have made from a standpoint of real knowledge. If you don't understand the technical points involved I can't see how you can support much.
I'm not out to disprove what you have said, and I did look at the information you offered. What I found out does not support your stance. I explained why. Since I took an honest look at what you offered, why not show me the same respect and look into things yourself?
-Chris
I'm missing it completely. Please point out the diff pair. It's possible I am completely blind, but I do not see a diff pair in the input at all.
Hi hadley,
We do follow the rules every member does.
My comments are arrived at from fact and observation. However as I said, I did some research and merely requested you do the same. If you can't, or unprepared to then you are unable to make the comments you have made from a standpoint of real knowledge. If you don't understand the technical points involved I can't see how you can support much.
I'm not out to disprove what you have said, and I did look at the information you offered. What I found out does not support your stance. I explained why. Since I took an honest look at what you offered, why not show me the same respect and look into things yourself?
-Chris
Q1 is a 1 : 1 phase splitter, and Q2, Q3 are the diff pair with current source Q4.
Collector load for the pair is a bootstrap combination that was in fashion at the time.
In fact this is an exemplary realisation of a differential amp with inputs of both
polarities, feedback from both outputs and dc adjustment between bases.
Apart from that current source Q4 has common mode adjustable dc feedback.
This is a very clever and instructive circuit, albeit drawn in a slightly clumsy way.
Output follower, in quasi complementary style, is double for a true bridge operation.
Collector load for the pair is a bootstrap combination that was in fashion at the time.
In fact this is an exemplary realisation of a differential amp with inputs of both
polarities, feedback from both outputs and dc adjustment between bases.
Apart from that current source Q4 has common mode adjustable dc feedback.
This is a very clever and instructive circuit, albeit drawn in a slightly clumsy way.
Output follower, in quasi complementary style, is double for a true bridge operation.
Hi as_audio,
Yes, I see it now, many thanks! I could see Q1a was a phase splitter, but why feed the diff pair with a push-pull signal? That doesn't seem to be necessary but is an interesting application.
I see they tried to make the impedance equal as well. Drawn in a way it isn't easy to spot, but not uncommon for schematics of the time.
Interesting circuit, but all the various power supplies could have been done better. Anyway, now it makes a lot more sense.
-Chris
Yes, I see it now, many thanks! I could see Q1a was a phase splitter, but why feed the diff pair with a push-pull signal? That doesn't seem to be necessary but is an interesting application.
I see they tried to make the impedance equal as well. Drawn in a way it isn't easy to spot, but not uncommon for schematics of the time.
Interesting circuit, but all the various power supplies could have been done better. Anyway, now it makes a lot more sense.
-Chris
Zeners they will remain then.
I can't seem to find these zeners so I calculated them from the power supply on the schematic.
-D5 appears to be a 6.8V zener
-D6 appears to be a 30V zener
-D7 appears to be a 51V zener
-D8 appears to be another 30V (ideally ~30.6v) zener
If someone could check my work, I'd appreciate it. These numbers makes sense to me, but I wouldn't want to end up getting anything wrong and this info may ultimately end up helping someone else.
I can't seem to find these zeners so I calculated them from the power supply on the schematic.
-D5 appears to be a 6.8V zener
-D6 appears to be a 30V zener
-D7 appears to be a 51V zener
-D8 appears to be another 30V (ideally ~30.6v) zener
If someone could check my work, I'd appreciate it. These numbers makes sense to me, but I wouldn't want to end up getting anything wrong and this info may ultimately end up helping someone else.