I have a Sansui 5000A. From the factory, it has the 3-transistor preamp below.
The 4-transistor version is improved a bit, it simulates with a distortion floor about 9dB lower at worst-case input (HF signals, large enough to clip the amp) from about -72dB to about -81dB.
To build this, I wired Q703, Q1, and R5 together point-to-point, and then inserted this assembly where the original Q703 was. It doesn't require modifying the PCB at all.
The only other change is the resistor values at R707 and R715. Everything else is the same as the factory. (I also replaced R735 with a 6.8k resistor, but ignore that -- it's no better than the 5.6k from the factory.)
Some component names here don't match the factory schematic; sorry.
Preamp distortion probably wouldn't matter much with the original 0.8% THD power amp section. This unit has had its power amp section replaced with a honey badger clone and converted from AC coupled to DC coupled, so preamp sound quality matters a bit more.
Preamp distortion in this unit also wouldn't matter with the original grounding architecture (or total lack thereof) which this thing left the factory with(out). I did unspeakable things to this unit to introduce a grounding architecture and stop its innate 60/120hz hum. I kept no written record of these things, for my own protection and for the innocent children.
The 4-transistor version is improved a bit, it simulates with a distortion floor about 9dB lower at worst-case input (HF signals, large enough to clip the amp) from about -72dB to about -81dB.
To build this, I wired Q703, Q1, and R5 together point-to-point, and then inserted this assembly where the original Q703 was. It doesn't require modifying the PCB at all.
The only other change is the resistor values at R707 and R715. Everything else is the same as the factory. (I also replaced R735 with a 6.8k resistor, but ignore that -- it's no better than the 5.6k from the factory.)
Some component names here don't match the factory schematic; sorry.
Preamp distortion probably wouldn't matter much with the original 0.8% THD power amp section. This unit has had its power amp section replaced with a honey badger clone and converted from AC coupled to DC coupled, so preamp sound quality matters a bit more.
Preamp distortion in this unit also wouldn't matter with the original grounding architecture (or total lack thereof) which this thing left the factory with(out). I did unspeakable things to this unit to introduce a grounding architecture and stop its innate 60/120hz hum. I kept no written record of these things, for my own protection and for the innocent children.
