You're welcome. Disconnect the green wire. The signal flows from the source to the pot as you have done, from the middle pot terminal to the IN connection on the board, then to the amplifier chip. It returns from the SG terminal back to the pot "earth" terminal (as you have marked it) and then back to the source. This completes the circuit from source to amp.
Still humming and no sound. However, a couple of things I just noticed:
1. My fluorescent magnifying lamp was adding a ton of noise.
(Like I said, I'm new to this). I will have to remember to always unplug it before testing.
2. This was not actually one of the boards I was intending to test right now. But since it was working (measurement and sound-wise) before I attached the POT, I still need to know why it's not working now.
I desoldered the green wire from the POT. I left it soldered at the Chassis Ground end on the amp board.
There is still hum and no music. It sounds like ground hum, but I'm too new to know. I assume the green wire connected only to CHGND is not the problem?
Here are a few scope pics to show what the waveform looks like now. IIRC, this was with the POT turned about half way.
View attachment DS0015.BMP
View attachment DS0016.BMP
If I touch the POT or the output wire from the RCA audio source, the buzzing gets louder.
1. My fluorescent magnifying lamp was adding a ton of noise.
(Like I said, I'm new to this). I will have to remember to always unplug it before testing.
2. This was not actually one of the boards I was intending to test right now. But since it was working (measurement and sound-wise) before I attached the POT, I still need to know why it's not working now.
I desoldered the green wire from the POT. I left it soldered at the Chassis Ground end on the amp board.
There is still hum and no music. It sounds like ground hum, but I'm too new to know. I assume the green wire connected only to CHGND is not the problem?
Here are a few scope pics to show what the waveform looks like now. IIRC, this was with the POT turned about half way.
View attachment DS0015.BMP
View attachment DS0016.BMP
If I touch the POT or the output wire from the RCA audio source, the buzzing gets louder.
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Sorry, my battery died. Then, by the time I could charge it, I hadn't noticed that the cables had shifted slightly and I was once again running out of light. If you zoom in on the full size photo, you can see everything quite well.
So everything is still the way it was, excepted I desoldered the green wire from the POT end. It's still attached to the CHGND on the PCB end.
So everything is still the way it was, excepted I desoldered the green wire from the POT end. It's still attached to the CHGND on the PCB end.
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Have another look at this picture https://qph.ec.quoracdn.net/main-qimg-0034648e79a35431ff0cb9e6cdbbd063-c the grounds need to be connected to the pot as shown
Scott:
Which grounds? I need you to be more specific. Again, complete newbie. Please, spell it out for me.
Also, I started looking at breakout PCBs for POTs. The ones I'm seeing on ebay don't seem to have screwholes for mounting. Don't they usually have screwholes?
Which grounds? I need you to be more specific. Again, complete newbie. Please, spell it out for me.
Also, I started looking at breakout PCBs for POTs. The ones I'm seeing on ebay don't seem to have screwholes for mounting. Don't they usually have screwholes?
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The signal ground/return. The screen of the input that you have connected to one of the white twisted wires, that joint should also go to the "earth" on the pot
The screen from the RCA input goes to the Input AND ground pins on the POT?
If so, should I just join them with another piece of wire? Will any similar primary wire work? Green?
If so, should I just join them with another piece of wire? Will any similar primary wire work? Green?
Solder the joint you have already made to the "earth" pin on the pot so both the input screen and the white wire to the amp are connected to it
Huh? You lost me. You just told me to remove that green wire from the POT.
How about specifying exactly which wire goes where? I have two white wires, please be more specific.
How about specifying exactly which wire goes where? I have two white wires, please be more specific.
That's right, now connect the screen on the input and the white wire you've soldered it to to the pin on the pot that you removed the green wire from
Uh...WHAT? I haven't soldered it to a white wire, I soldered it to the input, nothing else. You've completely lost me.
How about using this format:
X--Y
A-->B
That way, I'll be more likely to understand what you're saying.
How about using this format:
X--Y
A-->B
That way, I'll be more likely to understand what you're saying.
The screen from the source that you've soldered to the white wire with the black negative marking
Add a wire to connect the RCA jack ground to the pot terminal you labeled 'earth'. Do this for both channels.
D'Oh! Sorry, I think I just figured out what you meant. Will try it tomorrow. Thanks for being patient.
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Well, this is embarrassing. It turns out there was no sound cause I hadn't noticed there was a second set of RCA cables attached to the CD player, and the first set I was using were attached to nothing!
Now that the sound is back, I notice that the advice you all gave me has reduced hum to basically zero. I listened to some music, adjusted the POT and it's effect seems to be very smooth. I put a test CD in the player and played a 100Hz square wave test signal.
Here's what I got. Is something wrong? The waveforms look a little rounded off to me.
View attachment DS0017.BMP
View attachment DS0018.BMP
Now that the sound is back, I notice that the advice you all gave me has reduced hum to basically zero. I listened to some music, adjusted the POT and it's effect seems to be very smooth. I put a test CD in the player and played a 100Hz square wave test signal.
Here's what I got. Is something wrong? The waveforms look a little rounded off to me.
View attachment DS0017.BMP
View attachment DS0018.BMP
Nothing is wrong - reproducing a low frequency square wave with no discernible tilt requires exceptional low frequency bandwidth. The waveform might look more square at 1kHz. In any case there is nothing wrong with your waveform.
It seems you have solved all the outstanding problems, so put the amplifier in a case and enjoy the music.
It seems you have solved all the outstanding problems, so put the amplifier in a case and enjoy the music.
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