Pioneer SX-750 amplifier board replacement available

[mikebeth]

Hello all,
Would anyone be interested in a replacement amplifier board for the Pioneer SX-750?

As a design exercise I designed and built a PCB to replace the stock amplifier board with the aim of improving the less than stellar performance in as close to a "drop in" package as possible. As benchtested, the board has met my design goals.

• Slew rate is 15V/us into 8ohm at 40W which is fine for a 50W/ch amplifier.
• THD+N (1kHz, 50W, 8ohm) has improved by a factor of 20X from 0.082% to 0.0038%.
• Bias is maintained by a VBE multiplier rather than the original "rubber diode" STV4H.
• DC offset measured ~1mV using beta matched input transistors

I know there it not a huge demand (if any besides me!) for this board, but I thought I would float it out there if any other Pioneer fans have an interest.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[rsavas]

Links do not seem to work, might need to change the permissions.

 

[mikebeth]

Links do not seem to work, might need to change the permissions.

Sorry about that. Will have to look for how to do that. Obviously I don't have experience posting pictures in here.


Was just testing a new pair of TO-3 output devices in place of the 1970's devices and am very surprised by the improvement in performance. Did not expect to see any change to be honest. I will sort out the picture links in case this is of interest on here.