I’m having trouble with a circuit I designed and I would be greatly appreciative if I can get some help here.
The circuit I designed is a buffer amplifier type design intended to take two channels of audio input from a passive monitor controller, sent to either the resistor circuit, or low pass filter (as seen in the schematic), and then to the second opamp (which has a trimpot to control DC offset for each channel), and then sent as an audio output at unity gain (or near unity gain). The circuit is powered with +/-15VDC, taking a 36 VDC power supply and sent through a virtual ground type divider and regulated with 7815 and 7915 voltage regulators (although I’ve tried disconnecting the power section and using a bench power supply setup to provide + and – voltages with the same problems).
I designed the circuit using the falstad applet and I’ll attach the text for the circuit so you can see for yourself how I imagined it would work, and I’m attaching images of my schematic, screenshots of my oscilloscope, and images of my soldered perfboard circuit.
When I try to input a 120Hz, +/- 2V sine wave with my function generator, all I get from the output is a mostly flat voltage. It wiggles and shows occasional noise and whatnot when I try tuning the trimpot, but what you see in my image is basically the gist of it. In addition, the opamps (OPA2604APs) get a little warm, which I don’t think is a huge problem, but the 7815 gets pretty hot.
https://imgur.com/a/Q97WvE3
The following are URLs for the relevant datasheets:
media.digikey.com/pdf/Data%20Sheets/Texas%20Instruments%20PDFs/OPA2604.pdf
hep.upenn.edu/SNO/daq/parts/lm7815.pdf
hep.upenn.edu/SNO/daq/parts/lm7915.pdf
vishay.com/docs/28193/mkt373.pdf
globalsources.com/gsol/I/Slide-switch/p/sm/1142899729.htm#1142899729
Falstad circuit simulation (copy the following and select "import from text"):
$ 1 0.000015625 4.252108200006279 68 5 50
a 448 16 592 16 8 12 -12 1000000 0.000026274481766352875 0 100000
a 1152 32 1296 32 8 12 -12 1000000 -0.000012183066700374307 0 100000
r 448 -48 592 -48 0 10000
w 336 0 448 0 0
w 448 -48 448 0 0
w 592 -48 592 16 0
w 592 16 640 16 0
S 640 16 720 16 0 0 false 0 2
r 720 80 784 80 0 5600
c 784 80 784 144 0 2.2e-7 4.849103899492971e-81
g 784 144 784 176 0
w 848 80 928 80 0
w 976 80 976 32 0
w 976 -64 976 0 0
r 1024 16 1152 16 0 4700
w 1296 32 1376 32 0
w 1152 48 1152 128 0
r 1152 128 1152 192 0 1000
g 1152 192 1152 208 0
r 1152 128 1088 128 0 4700
174 1056 96 1088 160 1 220 0.5 Resistance
R 1056 96 1056 64 0 0 40 15 0 0 0.5
R 1056 160 1056 192 0 0 40 -15 0 0 0.5
R 240 0 176 0 0 1 220 2 0 0 0.5
g 416 144 416 176 0
w 720 0 720 -64 0
w 720 32 720 80 0
w 912 -64 976 -64 0
r 448 32 448 144 0 10000
g 848 144 848 176 0
c 848 80 848 144 0 2.2e-7 4.618125257029856e-81
r 784 80 848 80 0 13700
S 1024 16 976 16 0 1 false 0 2
r 448 -80 592 -80 0 10000
w 448 -48 448 -80 0
w 592 -80 592 -48 0
r 384 32 384 144 0 10000
w 416 144 448 144 0
w 384 32 448 32 0
w 384 144 416 144 0
w 1296 -64 1296 -32 0
w 1152 -32 1152 -64 0
w 1296 -32 1296 32 0
w 1152 -32 1152 16 0
r 912 -64 912 0 0 5100
g 912 0 912 32 0
r 720 -64 816 -64 0 10000
r 976 80 976 144 0 100000
g 976 208 976 240 0
g 928 176 928 208 0
r 928 80 928 176 0 470000
w 928 80 976 80 0
r 1152 -64 1216 -64 0 10000
r 816 -64 912 -64 0 10000
r 1216 -64 1296 -64 0 10000
r 976 144 976 208 0 100000
r 1504 96 1504 176 0 20000
w 1376 -32 1376 32 0
w 1376 32 1376 96 0
w 1376 -32 1504 -32 0
w 336 16 336 32 0
w 336 48 336 32 0
w 240 48 240 32 0
w 240 16 240 32 0
r 336 16 240 16 0 10000
r 336 48 240 48 0 10000
r 336 -16 240 -16 0 10000
r 336 -48 240 -48 0 10000
w 240 -48 240 -32 0
w 240 -16 240 -32 0
w 336 -16 336 -32 0
w 336 -48 336 -32 0
w 240 -16 240 0 0
w 240 16 240 0 0
w 336 -16 336 0 0
w 336 16 336 0 0
g 1504 176 1504 208 0
g 1504 32 1504 64 0
r 1504 -32 1504 32 0 20000
w 1376 96 1504 96 0
w 1376 448 1504 448 0
r 1504 320 1504 384 0 20000
g 1504 384 1504 416 0
g 1504 528 1504 560 0
w 336 368 336 352 0
w 336 336 336 352 0
w 240 368 240 352 0
w 240 336 240 352 0
w 336 304 336 320 0
w 336 336 336 320 0
w 240 336 240 320 0
w 240 304 240 320 0
r 336 304 240 304 0 10000
r 336 336 240 336 0 10000
r 336 400 240 400 0 10000
r 336 368 240 368 0 10000
w 240 368 240 384 0
w 240 400 240 384 0
w 336 400 336 384 0
w 336 368 336 384 0
w 1376 320 1504 320 0
w 1376 384 1376 448 0
w 1376 320 1376 384 0
r 1504 448 1504 528 0 20000
r 976 496 976 560 0 100000
r 1216 288 1296 288 0 10000
r 816 288 912 288 0 10000
r 1152 288 1216 288 0 10000
w 928 432 976 432 0
r 928 432 928 528 0 470000
g 928 528 928 560 0
g 976 560 976 592 0
r 976 432 976 496 0 100000
r 720 288 816 288 0 10000
g 912 352 912 384 0
r 912 288 912 352 0 5100
w 1152 320 1152 368 0
w 1296 320 1296 384 0
w 1152 320 1152 288 0
w 1296 288 1296 320 0
w 384 496 416 496 0
w 384 384 448 384 0
w 416 496 448 496 0
r 384 384 384 496 0 10000
w 592 272 592 304 0
w 448 304 448 272 0
r 448 272 592 272 0 10000
S 1024 368 976 368 0 1 false 0 2
r 784 432 848 432 0 13700
c 848 432 848 496 0 2.2e-7 4.976304002642837e-81
g 848 496 848 528 0
r 448 384 448 496 0 10000
w 912 288 976 288 0
w 720 384 720 432 0
w 720 352 720 288 0
g 416 496 416 528 0
R 240 352 176 352 0 1 220 2 0 0 0.5
R 1056 512 1056 544 0 0 40 -15 0 0 0.5
R 1056 448 1056 416 0 0 40 15 0 0 0.5
174 1056 448 1088 512 1 220 0.5 Resistance
r 1152 480 1088 480 0 4700
g 1152 544 1152 560 0
r 1152 480 1152 544 0 1000
w 1152 400 1152 480 0
w 1296 384 1376 384 0
r 1024 368 1152 368 0 4700
w 976 288 976 352 0
w 976 432 976 384 0
w 848 432 928 432 0
g 784 496 784 528 0
c 784 432 784 496 0 2.2e-7 5.225197196101461e-81
r 720 432 784 432 0 5600
S 640 368 720 368 0 0 false 0 2
w 592 368 640 368 0
w 592 304 592 368 0
w 448 304 448 352 0
w 336 352 448 352 0
r 448 304 592 304 0 10000
a 1152 384 1296 384 8 12 -12 1000000 -0.000012183066700374307 0 100000
a 448 368 592 368 8 12 -12 1000000 0.000026274481766352875 0 100000
207 144 0 16 0 4 Left
207 144 352 16 352 4 Right
207 1520 -32 1600 -32 4 Left\s1
207 1520 96 1600 96 4 Left\s2
207 1520 448 1600 448 4 Right\s2
207 1520 320 1600 320 4 Right\s1
o 23 16 0 21771 5 0.0015625 0 2 23 3
o 59 16 0 21771 5 0.00078125 1 2 59 3
o 79 16 0 21771 5 0.00078125 2 2 79 3
The circuit I designed is a buffer amplifier type design intended to take two channels of audio input from a passive monitor controller, sent to either the resistor circuit, or low pass filter (as seen in the schematic), and then to the second opamp (which has a trimpot to control DC offset for each channel), and then sent as an audio output at unity gain (or near unity gain). The circuit is powered with +/-15VDC, taking a 36 VDC power supply and sent through a virtual ground type divider and regulated with 7815 and 7915 voltage regulators (although I’ve tried disconnecting the power section and using a bench power supply setup to provide + and – voltages with the same problems).
I designed the circuit using the falstad applet and I’ll attach the text for the circuit so you can see for yourself how I imagined it would work, and I’m attaching images of my schematic, screenshots of my oscilloscope, and images of my soldered perfboard circuit.
When I try to input a 120Hz, +/- 2V sine wave with my function generator, all I get from the output is a mostly flat voltage. It wiggles and shows occasional noise and whatnot when I try tuning the trimpot, but what you see in my image is basically the gist of it. In addition, the opamps (OPA2604APs) get a little warm, which I don’t think is a huge problem, but the 7815 gets pretty hot.
https://imgur.com/a/Q97WvE3
The following are URLs for the relevant datasheets:
media.digikey.com/pdf/Data%20Sheets/Texas%20Instruments%20PDFs/OPA2604.pdf
hep.upenn.edu/SNO/daq/parts/lm7815.pdf
hep.upenn.edu/SNO/daq/parts/lm7915.pdf
vishay.com/docs/28193/mkt373.pdf
globalsources.com/gsol/I/Slide-switch/p/sm/1142899729.htm#1142899729
Falstad circuit simulation (copy the following and select "import from text"):
$ 1 0.000015625 4.252108200006279 68 5 50
a 448 16 592 16 8 12 -12 1000000 0.000026274481766352875 0 100000
a 1152 32 1296 32 8 12 -12 1000000 -0.000012183066700374307 0 100000
r 448 -48 592 -48 0 10000
w 336 0 448 0 0
w 448 -48 448 0 0
w 592 -48 592 16 0
w 592 16 640 16 0
S 640 16 720 16 0 0 false 0 2
r 720 80 784 80 0 5600
c 784 80 784 144 0 2.2e-7 4.849103899492971e-81
g 784 144 784 176 0
w 848 80 928 80 0
w 976 80 976 32 0
w 976 -64 976 0 0
r 1024 16 1152 16 0 4700
w 1296 32 1376 32 0
w 1152 48 1152 128 0
r 1152 128 1152 192 0 1000
g 1152 192 1152 208 0
r 1152 128 1088 128 0 4700
174 1056 96 1088 160 1 220 0.5 Resistance
R 1056 96 1056 64 0 0 40 15 0 0 0.5
R 1056 160 1056 192 0 0 40 -15 0 0 0.5
R 240 0 176 0 0 1 220 2 0 0 0.5
g 416 144 416 176 0
w 720 0 720 -64 0
w 720 32 720 80 0
w 912 -64 976 -64 0
r 448 32 448 144 0 10000
g 848 144 848 176 0
c 848 80 848 144 0 2.2e-7 4.618125257029856e-81
r 784 80 848 80 0 13700
S 1024 16 976 16 0 1 false 0 2
r 448 -80 592 -80 0 10000
w 448 -48 448 -80 0
w 592 -80 592 -48 0
r 384 32 384 144 0 10000
w 416 144 448 144 0
w 384 32 448 32 0
w 384 144 416 144 0
w 1296 -64 1296 -32 0
w 1152 -32 1152 -64 0
w 1296 -32 1296 32 0
w 1152 -32 1152 16 0
r 912 -64 912 0 0 5100
g 912 0 912 32 0
r 720 -64 816 -64 0 10000
r 976 80 976 144 0 100000
g 976 208 976 240 0
g 928 176 928 208 0
r 928 80 928 176 0 470000
w 928 80 976 80 0
r 1152 -64 1216 -64 0 10000
r 816 -64 912 -64 0 10000
r 1216 -64 1296 -64 0 10000
r 976 144 976 208 0 100000
r 1504 96 1504 176 0 20000
w 1376 -32 1376 32 0
w 1376 32 1376 96 0
w 1376 -32 1504 -32 0
w 336 16 336 32 0
w 336 48 336 32 0
w 240 48 240 32 0
w 240 16 240 32 0
r 336 16 240 16 0 10000
r 336 48 240 48 0 10000
r 336 -16 240 -16 0 10000
r 336 -48 240 -48 0 10000
w 240 -48 240 -32 0
w 240 -16 240 -32 0
w 336 -16 336 -32 0
w 336 -48 336 -32 0
w 240 -16 240 0 0
w 240 16 240 0 0
w 336 -16 336 0 0
w 336 16 336 0 0
g 1504 176 1504 208 0
g 1504 32 1504 64 0
r 1504 -32 1504 32 0 20000
w 1376 96 1504 96 0
w 1376 448 1504 448 0
r 1504 320 1504 384 0 20000
g 1504 384 1504 416 0
g 1504 528 1504 560 0
w 336 368 336 352 0
w 336 336 336 352 0
w 240 368 240 352 0
w 240 336 240 352 0
w 336 304 336 320 0
w 336 336 336 320 0
w 240 336 240 320 0
w 240 304 240 320 0
r 336 304 240 304 0 10000
r 336 336 240 336 0 10000
r 336 400 240 400 0 10000
r 336 368 240 368 0 10000
w 240 368 240 384 0
w 240 400 240 384 0
w 336 400 336 384 0
w 336 368 336 384 0
w 1376 320 1504 320 0
w 1376 384 1376 448 0
w 1376 320 1376 384 0
r 1504 448 1504 528 0 20000
r 976 496 976 560 0 100000
r 1216 288 1296 288 0 10000
r 816 288 912 288 0 10000
r 1152 288 1216 288 0 10000
w 928 432 976 432 0
r 928 432 928 528 0 470000
g 928 528 928 560 0
g 976 560 976 592 0
r 976 432 976 496 0 100000
r 720 288 816 288 0 10000
g 912 352 912 384 0
r 912 288 912 352 0 5100
w 1152 320 1152 368 0
w 1296 320 1296 384 0
w 1152 320 1152 288 0
w 1296 288 1296 320 0
w 384 496 416 496 0
w 384 384 448 384 0
w 416 496 448 496 0
r 384 384 384 496 0 10000
w 592 272 592 304 0
w 448 304 448 272 0
r 448 272 592 272 0 10000
S 1024 368 976 368 0 1 false 0 2
r 784 432 848 432 0 13700
c 848 432 848 496 0 2.2e-7 4.976304002642837e-81
g 848 496 848 528 0
r 448 384 448 496 0 10000
w 912 288 976 288 0
w 720 384 720 432 0
w 720 352 720 288 0
g 416 496 416 528 0
R 240 352 176 352 0 1 220 2 0 0 0.5
R 1056 512 1056 544 0 0 40 -15 0 0 0.5
R 1056 448 1056 416 0 0 40 15 0 0 0.5
174 1056 448 1088 512 1 220 0.5 Resistance
r 1152 480 1088 480 0 4700
g 1152 544 1152 560 0
r 1152 480 1152 544 0 1000
w 1152 400 1152 480 0
w 1296 384 1376 384 0
r 1024 368 1152 368 0 4700
w 976 288 976 352 0
w 976 432 976 384 0
w 848 432 928 432 0
g 784 496 784 528 0
c 784 432 784 496 0 2.2e-7 5.225197196101461e-81
r 720 432 784 432 0 5600
S 640 368 720 368 0 0 false 0 2
w 592 368 640 368 0
w 592 304 592 368 0
w 448 304 448 352 0
w 336 352 448 352 0
r 448 304 592 304 0 10000
a 1152 384 1296 384 8 12 -12 1000000 -0.000012183066700374307 0 100000
a 448 368 592 368 8 12 -12 1000000 0.000026274481766352875 0 100000
207 144 0 16 0 4 Left
207 144 352 16 352 4 Right
207 1520 -32 1600 -32 4 Left\s1
207 1520 96 1600 96 4 Left\s2
207 1520 448 1600 448 4 Right\s2
207 1520 320 1600 320 4 Right\s1
o 23 16 0 21771 5 0.0015625 0 2 23 3
o 59 16 0 21771 5 0.00078125 1 2 59 3
o 79 16 0 21771 5 0.00078125 2 2 79 3