Say . . . one last thing (I hope) . . .
Why are the polarities of C1, C2 and C3 situated as - to +?
Why are the polarities of C1, C2 and C3 situated as - to +?
They can go either way around because they see zero DC voltage across them using the opamps shown. If the applied source has a DC offset then that will appear across the caps at a value that depends on the pot settings but there is still no right and wrong way to fit them without knowing if such a condition exists (and it shouldn't)
Well . . . the neon pilot light works . . . but none of the three functions works.
A mono line output was inserted into J1 and J2.
"Zero" pots (R1 and R2) were brought all of the way up.
Headset volume (R19) was brought all of the way up.
The U2 internal volume control was brought nearly all of the way clockwise.
The selector (SW2) was set to CC (Center Channel) and the CC volume pot (R6) was brought half way up.
There was barely a detectable sound. I didn't think the total inline resistances would suppress the (likely) 0.5 volt input so heavily.
Then I switched SW2 to "D-" which is the voice suppression circuit.
When R7ab was at 12 o'clock there was nothing. But when I panned to the left I started to get a very loud squeal!
What the hell am I overloading?
Switching to "D+" (the inverse of "D-") I got nothing.
While I could hear only a very low sound it seemed that the low pass section was doing what it's supposed to do.
If I had any hair I'd have pulled it all out.
(I also noticed that when I inserted those line inputs from my stereo unit into J1 and J2 the stereo's speaker volume dropped.)
A mono line output was inserted into J1 and J2.
"Zero" pots (R1 and R2) were brought all of the way up.
Headset volume (R19) was brought all of the way up.
The U2 internal volume control was brought nearly all of the way clockwise.
The selector (SW2) was set to CC (Center Channel) and the CC volume pot (R6) was brought half way up.
There was barely a detectable sound. I didn't think the total inline resistances would suppress the (likely) 0.5 volt input so heavily.
Then I switched SW2 to "D-" which is the voice suppression circuit.
When R7ab was at 12 o'clock there was nothing. But when I panned to the left I started to get a very loud squeal!
What the hell am I overloading?
Switching to "D+" (the inverse of "D-") I got nothing.
While I could hear only a very low sound it seemed that the low pass section was doing what it's supposed to do.
If I had any hair I'd have pulled it all out.
(I also noticed that when I inserted those line inputs from my stereo unit into J1 and J2 the stereo's speaker volume dropped.)
You need to trace the signal through with an oscilloscope to see what is going on. Apply a sine wave at 1kHz to each input and follow its progress through the circuit. The circuit as drawn does not seem to break any rules and each subsection should certainly work... but tracing the signal will show where it is going wrong.
It is also worth checking the output pin of each opamp is as zero volts DC.
It is also worth checking the output pin of each opamp is as zero volts DC.
That depends on the output impedance of the source. The loading is 10k in parallel with 25k (R1 and R3) with R4 and R6 also contributing. So its going to be around 6k depending on the pot settings.
i can pick up a sig. generator and oscilloscope cheaply enough but while i know what to do with the former you'll have to tell me what i'm looking for on the scope.
i'm also going to rerun my continuity/discontinuity checks - what should be connected is, and what better not be isn't - as well as measuring the DC voltage of pins 1 and 7 on the three ICs. There are caps connected to three of the four opamp outputs. I measure at the pin, right? The cap would block DC, no?
i'm also going to rerun my continuity/discontinuity checks - what should be connected is, and what better not be isn't - as well as measuring the DC voltage of pins 1 and 7 on the three ICs. There are caps connected to three of the four opamp outputs. I measure at the pin, right? The cap would block DC, no?
Yes, you measure the DC voltage at the output pins.
You won't be overdriving it but if the Onkyo has an output impedance of say 2.2k and you load it with 6k then you cut the signal level down a lot. 1 volt output would fall to around 0.7 volts when loaded in that way.
The oscilloscope is just a voltmeter that traces out voltage against time and so lets you see the signal in real time.
You won't be overdriving it but if the Onkyo has an output impedance of say 2.2k and you load it with 6k then you cut the signal level down a lot. 1 volt output would fall to around 0.7 volts when loaded in that way.
The oscilloscope is just a voltmeter that traces out voltage against time and so lets you see the signal in real time.