erratum: Both AM-U5 and AM-U7 open loop amplifiers had separate windings, rectifiers, filter caps and also higher voltage rails (regulated!) for the VAS. AM-U5 had +/- 50V for the VAS and AM-U7 had +/- 65V. Both enough for shocks when measuring. Unfortunately the low voltage phono stage did not get separate windings so its +/- voltage was derived from the VAS regulators. This was very often done at various brands but dropping +/- 65V to +/- 24 and even +/- 15V causes heat. The AM-U7 therefor had way hotter PSU transistors that died from the heat certainly when the upper cover was covered with stuff. No product is without imperfections, never take remarks by techs too serious as these usually see mainly defective stuff. It becomes interesting when there is a repeating pattern. The beautiful large volume controller WAS such a pattern.
These examples of fine Japanese engineering were, when the blue "Line Straight" button was pushed, fully DC coupled. Although the complex phono amplifier was excellent some connected an external phono amplifier. Now when that one was also DC coupled and the subsonic button was deactivated (user error) one could see the woofers going up and down. We demonstrated with an AA battery what DC coupling was. Also as DC coupling was rarely understood sources with fluctuating DC offset that normally no one would notice could make the servos go wild in these.
Needless to say that when one knows these many modern class A/AB designs usually do not impress that much. At all really. These fine Akai were just way ahead of their time. Do you want one now? No you don't. The plastic is brittle as are the PCBs as these have seen heat for decades. The switches fail too as they were not designed for a 38 year long use and an alternative to the volume controller is unobtainium.
These examples of fine Japanese engineering were, when the blue "Line Straight" button was pushed, fully DC coupled. Although the complex phono amplifier was excellent some connected an external phono amplifier. Now when that one was also DC coupled and the subsonic button was deactivated (user error) one could see the woofers going up and down. We demonstrated with an AA battery what DC coupling was. Also as DC coupling was rarely understood sources with fluctuating DC offset that normally no one would notice could make the servos go wild in these.
Needless to say that when one knows these many modern class A/AB designs usually do not impress that much. At all really. These fine Akai were just way ahead of their time. Do you want one now? No you don't. The plastic is brittle as are the PCBs as these have seen heat for decades. The switches fail too as they were not designed for a 38 year long use and an alternative to the volume controller is unobtainium.
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You know, everything can be restored now! Solder the annular cracks on the boards, disassemble and clean the switches, regulators, connectors... There would be a desire and a goal. BUT.... Many people don't need it. After all, there are headphones and MP3🙂.
Oh I have tried and I can do it now just as I could do it then (after all I was an Akai tech) but time, costs of parts, availability of semis and reliability together remake it an awkward affair today (2024). I notice a handful of parts nearly always exceeding 50 Euro at Digikey, Mouser etc. Also high prices of even defective devices with a nice label "Vintage!" will make it less attractive. It is a choice but there is enough affordable new stuff to be tried out.
Those Akai are older but they eat the Sony for breakfast 😀
Those Akai are older but they eat the Sony for breakfast 😀