So, I have an SX-780, which sounded terrific until the left side speaker bank developed distortion. Traced it to a failed STK, and decided to replace both STK in the short term with a replacements bought online. I WILL be purchasing, assembling and installing the much-better replacement discrete circuit solution in the near future, mentioned often here on AK.
But for now, I'm having difficulty adjusting the DC offset to zero without driving the input voltages up on each STK (Pins 1 & 0)
With DC Offset at 0mV (+/- 3mV), adjusted with VR5 & VR6 :
STK1/STK2
Pin 1 = -1.05 v
Pin 0 = +0.56 v
With DC Offset at 230mV, adjusted with VR5 & VR6 :
STK1/STK2
Pin 1 = -0.81 v
Pin 0 = +0.82 v
The SX-780 will play adjusted either way, but I have kept volume low to avoid pushing it, without knowing the effects of having it set either way. I don't have a scope and signal generator, but wish I did, so I could see waveforms of signal and output.
My question is.....which trade-off is better (safer) in the short term? Balanced inputs levels to the STKs or no DC Offset at output? Thanks in advance for the advice!
But for now, I'm having difficulty adjusting the DC offset to zero without driving the input voltages up on each STK (Pins 1 & 0)
With DC Offset at 0mV (+/- 3mV), adjusted with VR5 & VR6 :
STK1/STK2
Pin 1 = -1.05 v
Pin 0 = +0.56 v
With DC Offset at 230mV, adjusted with VR5 & VR6 :
STK1/STK2
Pin 1 = -0.81 v
Pin 0 = +0.82 v
The SX-780 will play adjusted either way, but I have kept volume low to avoid pushing it, without knowing the effects of having it set either way. I don't have a scope and signal generator, but wish I did, so I could see waveforms of signal and output.
My question is.....which trade-off is better (safer) in the short term? Balanced inputs levels to the STKs or no DC Offset at output? Thanks in advance for the advice!
