Does the current draw change when you connect/remove the load?
What's the resistance between the high-side output source and the input of the output relay?
What's the resistance between the high-side output source and the input of the output relay?
The current draw increases significantly when a load is attached. I say "significantly" because I now have a 2A current limit on it. When I attach the load it maxes out and the supply voltage drops to ~9vdc. When I had the current limit set to 4.5A, it maxed that out.
The resistance between the relay input and the high side source is .1 - .2 ohms. I have to hold the probes there for a few minutes to get it to steady reading.
The resistance between the relay input and the high side source is .1 - .2 ohms. I have to hold the probes there for a few minutes to get it to steady reading.
As long as the resistance is very nearly 0 ohms, it's OK. It should never read much more than the resistance you read when you touch your probes together.
The current limiting may be an issue. The amp is going to try to draw much more than 4.5 amps at that power level.
The current limiting may be an issue. The amp is going to try to draw much more than 4.5 amps at that power level.
Wow! I connected my larger power supply without any current limiting and using the 50Hz input signal and the amp draw first jumped up to ~16A and then fell and stayed around 9 - 10A.
The output signal looks good at the speaker terminals. Looks like that op amp at U13 was the problem. Before, when using my large power supply is when I originally discovered the problem.
I am going to mount it back into the heat sink and see how it does unless there is something else I should check first.
The output signal looks good at the speaker terminals. Looks like that op amp at U13 was the problem. Before, when using my large power supply is when I originally discovered the problem.
I am going to mount it back into the heat sink and see how it does unless there is something else I should check first.
Yes, with the load. Thanks Perry! I will let you know how it goes. I guess I should have checked the new op amps instead of assuming they were good just because they came from a quality distributor.
Got it into the heat sink and connected everything. The only problem is a constant noise ( snow, white noise or something) in the background. The noise is there with or without an input.
Can you see the noise at the input of the driver board (or any other point in the circuit)?
Does the noise change with any combination of switch/pot positions?
Does the noise change with any combination of switch/pot positions?
I believe that I can see it when I change the scope to 100 - 200mv/div.
The noise remains constant regardless of position of pots.
I attached a screen shot of the noise at the speaker output.
There is one of the op amps in the pre-amp section that has 15 vdc on pin 7. None of these op amps have board designations that I can see.
The noise remains constant regardless of position of pots.
I attached a screen shot of the noise at the speaker output.
There is one of the op amps in the pre-amp section that has 15 vdc on pin 7. None of these op amps have board designations that I can see.
Attachments
Pin 1) .000
Pin 2) .002
Pin 3) .002
Pin 4) -15.11
Pin 5) .787
Pin 6) .757
Pin 7) 14.36
Pin 8) 14.85
Pin 2) .002
Pin 3) .002
Pin 4) -15.11
Pin 5) .787
Pin 6) .757
Pin 7) 14.36
Pin 8) 14.85
Is it possible that that half of the op-amp isn't being used?
If you short between pins 6 and 7 of the op-amp with the probe when measuring voltage, what's the voltage go to?
If you short between pins 6 and 7 of the op-amp with the probe when measuring voltage, what's the voltage go to?