Deciphering the following error correction amplifier overview may require an automated translator (the detailed article was published by the Japanese magazine Transistor Gijutsu in their October 2019 issue), but links to schematics and component lists have been provided.
ゼロディストーション・パワーアンプ
ゼロディストーション・パワーアンプ
With crossover distortion you have some choices.
1/ Use class B and accept the crossover distortion.
2/ Use class A, have no crossover distortion but accept poor efficiency.
3/ Use class AB and adjust bias current until you are happy with it. This is a compromise between crossover distortion % and amount of power lost in the heatsinks due to more bias current.
1/ Use class B and accept the crossover distortion.
2/ Use class A, have no crossover distortion but accept poor efficiency.
3/ Use class AB and adjust bias current until you are happy with it. This is a compromise between crossover distortion % and amount of power lost in the heatsinks due to more bias current.
To the OP:
One striking feature of your schematic is your amplifier uses two input differential pairs, with one for negative going signals, and another for positive going signals. It does this expecting identical amplification for two different differential inputs built out of two NPN and two PNP transistors! Essentially, you have two amplifiers sharing the same output stage, and you are expecting these two different amplifiers to have identical characteristics to get very low total harmonic distortion and crossover distortion.
My advice is to use only one differential input stage for both negative going and positive going signals. I also strongly suggest you to use a current mirror instead of resistors. A current mirror guarantees a differential pair's branch currents are balanced and almost equal, provided you do not load one branch more than the other.
Finally, the VAS, voltage amplifier stage, can be modified to operate from one single differential pair by adding a constant current source. If you are concerned a constant current source may exhibit unwanted constant current modulation, you can reduce this by using a cascode at the current source's collector.
One striking feature of your schematic is your amplifier uses two input differential pairs, with one for negative going signals, and another for positive going signals. It does this expecting identical amplification for two different differential inputs built out of two NPN and two PNP transistors! Essentially, you have two amplifiers sharing the same output stage, and you are expecting these two different amplifiers to have identical characteristics to get very low total harmonic distortion and crossover distortion.
My advice is to use only one differential input stage for both negative going and positive going signals. I also strongly suggest you to use a current mirror instead of resistors. A current mirror guarantees a differential pair's branch currents are balanced and almost equal, provided you do not load one branch more than the other.
Finally, the VAS, voltage amplifier stage, can be modified to operate from one single differential pair by adding a constant current source. If you are concerned a constant current source may exhibit unwanted constant current modulation, you can reduce this by using a cascode at the current source's collector.
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You also have
4/ Use enhanced class AB like double-cross or cube law output stages at the expense of complexity.
For options 3 and 4 (option 1 is a waste of time and 2 does not really need it), if you want to go the extra mile, you can add error correction to reduce the cross-over distortion even further.
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Sliding bias Class A ? look up Elvee’s Circlophone amp, it’s pure genius.
But who cares in real life? not me. The sound quality of SOTA Class AB means you’ll never actually hear cross over distortion.
But who cares in real life? not me. The sound quality of SOTA Class AB means you’ll never actually hear cross over distortion.
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Complementary input diff pairs are pretty common. Some revered amplifiers (Krell comes to mind) use it with quite good result, objectively and subjectively.
Way ahead of its time!
Copied in my library for future reference. Second half of the circuit has been truncated though.
Some people feel that the Ampzilla of 1974 was just a copy of the Tigersaurus of 1973.
https://www.epanorama.net/sff/Audio...near/The Tigersaurus 250W Power Amplifier.pdf
The problem with the online scans of Popular Electronics magazines in 1974 is: the .pdf files are too big for diyAudio attachments. If you want to locate and download the original, big, pdf files ... buy some 7-Up and Pizza for a couple of high school computer wizards and have them search & download the (big) magazine scans.
https://www.epanorama.net/sff/Audio...near/The Tigersaurus 250W Power Amplifier.pdf
The problem with the online scans of Popular Electronics magazines in 1974 is: the .pdf files are too big for diyAudio attachments. If you want to locate and download the original, big, pdf files ... buy some 7-Up and Pizza for a couple of high school computer wizards and have them search & download the (big) magazine scans.