I'm kind of at the end of my ability to debug the old version of the Sparkplug, having build and debugged many circuits I seem to be missing something "stupid". There's a horrible "open ground" type noise when adjusting the volume, which turns into an oscillation when adjusting the cut. At maximum volume and gain there is some output and the "open ground" noise and oscillation are minimized but the output is barely there. I've checked the pots, caps and diodes, and have tried replacement ICs, have reflowed and inspected for solder bridges. Any suggestions/ideas on what I'm missing? Note: I wired the pots instead of using PC pin type.
Voltages on IC
1 4.20 8 8.45
2 4.20 7 4.20
3 3.76 6 4.20
4 4.20 5 3.76
Input voltage: 9.20
Voltage post input diode: 8.45 (Vbb)
Voltage at (Vcc) is 4.20
Thanks for any ideas!
Cheers,
Mike
Voltages on IC
1 4.20 8 8.45
2 4.20 7 4.20
3 3.76 6 4.20
4 4.20 5 3.76
Input voltage: 9.20
Voltage post input diode: 8.45 (Vbb)
Voltage at (Vcc) is 4.20
Thanks for any ideas!
Cheers,
Mike