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Old 19th January 2011, 01:39 AM   #2081
Salas is offline Salas  Greece
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Quote:
Originally Posted by Joachim Gerhard View Post
Rüdiger, this are the improvements i made : i put in two helper resistors. Because they would starve a bit only on the base current i feed them with aproximately 2mA of iddle current. I put in R3. When the same current flows in the left and right side of the mirror no current flows in R3. If there is a mismatch the resistor comes into action and provides differential feedback. i set it arbitrary to 100kOm. In praxis it has to be checked if that value is low enough. It reduces the impedance of the mirror some but it also provides matching and distortion cancelation so i think it is an improvement. I have seen parts of this circuit elsewhere but not implemented in total so i call it a Gerhard Mirror. I have drawn only one side and you have to scroll down a bit to see it. This circuit is much faster and lower in distortion then the simple cascoded mirror and gives an amasing gain in dynamics and slamm.
We had a report from member Stinius about a topological similarity with a drawing of his in another forum and a JG's originally attached above. We let JG know and he answered that he could not have seen it because he is not a member in that forum anyway. Non the less he felt it would be positive we pull his own drawing from the above post too.

Given the opportunity, please notice that people's drawings may not be copied without permission as they are, but any other drawing no matter similar topologically is belonging to the one who draws it, and he may circulate it at will. That's the official thing.

Similarities between circuit drawings from different people are not the concern of breaking any rule here and please don't report such to us in the future again.

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Old 19th January 2011, 01:58 AM   #2082
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Just for completeness i got the idea of the differential feedback resistors from Bob Cordell´s book " Designing Audio Power Amplifiers ", page 139. The rest was playing before a long time ago. There are other ways to reduce distortion in a current mirror that do not require this resistors. The main problem is the limited output resistance. A mirror can be made that has limited, infinite and even negative output impedance. Stinius, you are attacking the wrong person. I am here to put information in this world.
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Old 19th January 2011, 02:30 AM   #2083
Salas is offline Salas  Greece
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Members obviously can claim ideas and ask for public credit and be answered by clarification from other members. That is something different from expecting DIYA to be pulling content of drawings belonging to others without their consent. In this case we had your consent.
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Old 19th January 2011, 11:17 PM   #2084
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It makes music right now with a dual mono salas style shunt supply. Nicer than lead gel batteries...
I'm in luck that my digital photo does not work at the moment so you can't see that mad professors lab mess here...

Rüdiger
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Old 19th January 2011, 11:30 PM   #2085
Salas is offline Salas  Greece
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Congrats. I like mad professors for one.
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Old 20th January 2011, 12:52 AM   #2086
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Your circuit looked certainly very orderly to me Rüdiger. You found your MPP nirvana for sure.
I am currently running a stage with a Salas Shunt too. Yes, sure, it makes batteries obsolete but i whould not say it sounds worse with batteries. I call that progress. Batterie management is no fun most of the time. I have my LFD Batterie stage the third time in England for repair.
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Old 6th February 2011, 12:16 AM   #2087
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It had to happen. After much thought i am back on the MPP thread. Mostly because i got a lot of ecouragement from members and second because several people are building some of my designs and the PM box is flowing over so this is a much better place to discuss and help.
One thing i designed recently is a buffer. It is ready, works well and there are some test PCbs that need some changes. I had a problem with oscilation, that thing is damn fast, but that is solved now. I also designed my first PSU. Usually i am using the LC Audio Low Noise PSU, Salas Shunts or batteries but it was time to design something myself. Actually there was not much to design. I simply decided on a 3 stage topology where i use well known techniques in cascade. First are LM regulators. Then comes a discrete circuit that has a constant current source supplying a TL431 that is noise reduced. That voltage is low pass filtered and taken to a pass transistor. It´s a kind of voltage regulator with a cap multiplier. Then comes a passive C-L-C combination or a Keentoken cap multiplier. I build it this time on a perf board and got it working in two days. I prefer the result to the lead acid batteries i used. It sounds more dymamic and robust without loss of fine details.
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File Type: jpg My First PSU 2.jpg (59.6 KB, 375 views)
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Old 6th February 2011, 12:49 AM   #2088
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Good to see you back Joachim. Picked up phono cartridge from IMMEDIA, yesterday. Saw your loudspeaker prototype, impressive!
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Old 6th February 2011, 02:11 AM   #2089
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Thanks John, what cart did you get ? Was it the new Allegra with metal piece and decouplig between upper and lower cabinet ?
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Old 6th February 2011, 03:05 AM   #2090
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Oh please, I don't "look a 'gift horse' in the mouth". It is a reconditioned Helikon SL. Wanted one for years, even if it is NOW last years model. You must have some idea that I make a serious living in audio. You should know it is almost impossible to do so. I cannot afford my own designs, how could I possibly afford an uptown phono cartridge like you have?
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