That may be possible. I have been using the AudioQ schematic for a reference but there are several differences.
If I let my DMM probe touch pins 6 and 7 at the same time it reads 14.34vdc.
If I let my DMM probe touch pins 6 and 7 at the same time it reads 14.34vdc.
I remember finding this op amp voltage when I originally was checking it. I have been working on this one on and off for about 3 months or more. I suspected it then. In fact I ordered 4558 op amps just in case.
If you're going to replace it (there are more tests that could be done before), look for traces on both sides of the board for pins 5, 6 and 7.
The noise shouldn't be audible in the other channel of that op-amp but there could be some crosstalk into the other channel. I'd suggest shorting pins 6 and 7 together and connecting pin 5 to either the secondary ground or any non-PS terminal of the other channel of the op-amp. This will keep it quiet.
Connected it to my small power supply with a 2A limit and connected a 15" woofer with no input signal. It maxed out the current, so I increased the current limit to 5A. It still has the static noise through the woofer without an input signal. It was drawing ~4.5A.
No. And I can also hear a hum and a kind of higher pitched whir in the background of the static. The whir sound is like the sound you get sometimes tuning in an older radio.
I was checking the other op amps DC voltages. I disconnected the woofer. The only op amp with a board designation is IC6. I found -13.73vdc on pin 1.
Are you saying that the output of the unused op-amp still looks like the waveform you posted?
Does the noise you hear sound like this:
http://www.bcae1.com/temp/cooleditmixedoscillator01.wav
What's the DC voltage on the pins of IC6?
Does the noise you hear sound like this:
http://www.bcae1.com/temp/cooleditmixedoscillator01.wav
What's the DC voltage on the pins of IC6?
Attached screen shot of pin 7 of the op amp that I shorted pins 6 and 7 together. Pin 5 connected to pin 1.
Yes, the noise sounds exactly like that.
DC voltages of IC6:
Pin 1) -13.73
Pin 2) -.026
Pin 3) -.027
Pin 4) -15.11
Pin 5) 0
Pin 6) -.001
Pin 7) -.001
Pin 8) 14.84
Yes, the noise sounds exactly like that.
DC voltages of IC6:
Pin 1) -13.73
Pin 2) -.026
Pin 3) -.027
Pin 4) -15.11
Pin 5) 0
Pin 6) -.001
Pin 7) -.001
Pin 8) 14.84
Attachments
That sound is due to unsynchronized oscillators (PS and output). There isn't anything practical to stop it.
If pin 5 is connected to pin 1, why don't they have the same voltage?
If pin 5 is connected to pin 1, why don't they have the same voltage?
The voltages listed above are from IC6. The one that I shorted pin 6 to pin 7 and connected pin 5 to pin 1 is a different op amp. The voltages on it before the connection changes is listed above in item #39. The voltages on pins 1 and 5 on it are the same now.
For the shorted op-amp, does pin 7 look the same as pin 5?
I don't know how the op-amp IC6 is being used. The fact that pins 2 and 3 are the same, seems to indicate that the op-amp is doing its job but the voltage on the output pin is odd, being so close to the supply voltage. From the numbers alone, I can't make any definitive conclusions.
If you short pins 1 and 2, does the voltage on pins 1/2 match the voltage on pin 3?
I don't know how the op-amp IC6 is being used. The fact that pins 2 and 3 are the same, seems to indicate that the op-amp is doing its job but the voltage on the output pin is odd, being so close to the supply voltage. From the numbers alone, I can't make any definitive conclusions.
If you short pins 1 and 2, does the voltage on pins 1/2 match the voltage on pin 3?
For the shorted op-amp, pin 7 looks the same as pin 5.
On IC6, I shorted pins 1 and 2.
The voltage on pins 1/2 are -13.77 and the voltage on pin 3 is -.005.
On IC6, I shorted pins 1 and 2.
The voltage on pins 1/2 are -13.77 and the voltage on pin 3 is -.005.
That looks like a defective op-amp unless something external is driving voltage to pin 1. When pins 1 and 2 are shorted, the op-amp is a follower and pins 1 ans 2 should match 3.
I don't have any TL072 DIP8s. I have them on order. Can I use a 4558 just to check it? And should I replace the op amp that I shorted earlier?