If the inputs of the lowpass filters have 100 ohms to ground then your signal source might not be able to drive them. Without a signal then the 100 ohm resistors will cause the inputs to be 0VDC then the outputs of all 4 opamps should also be 0VDC and have no signals. Then did you measure the DC voltage at the outputs of the opamps?I tried 100 ohm or 22k resistors between input and ground and it does not help.
Look again. He is using an ICL7660 IC to convert the USB +5V to -5V and since it operates at 10kHz he is using the 10uF filter capacitors that are shown on its datasheet.You need a negative power supply and USB gives only 0-5v. try simulating your design in proteus or other simulation tool, carefully see the supplies, mostly softwares provide supply to ICs by default.
If the inputs of the lowpass filters have 100 ohms to ground then your signal source might not be able to drive them. Without a signal then the 100 ohm resistors will cause the inputs to be 0VDC then the outputs of all 4 opamps should also be 0VDC and have no signals. Then did you measure the DC voltage at the outputs of the opamps?
Did the 100 ohm resistors stop the " loud high frequency noise (like a couple of ringing tones)"?
Hi,
Capacitors.
If you want low voltage ripple (low switching noise at the supply rails) you need low ESR capacitors and the ESR needs to be rated at the switching frequency (consider the overtones also).
Your capacitors are specified for mains frequency applications (120Hz), so I'd say they are not suitable for switching in the kHz range.. Adding ceramics capacitors may improve overall performance. Besides the device selection a good PCB layout is essential. Don't expect good results with a breadboard. Especially with this switching frequencies.
Klaus
Then maybe the input wiring is not shielded audio cables so it is picking up mains hum and all kinds of other interference including some 10kHz radiated from the ICL7660.No, it did not stop it, it made the sound quieter along with that high frequency noise.
The person who posted about adding ceramic capacitors did not know that the ICL7660 operates at only 10kHz. It would need ceramic capacitors if its frequency is much higher.That means adding ceramics parallel to the electrolytics? Which value?
yes, that is important.Important thing may be that when there is no input (input jack is unplugged, USB voltage source plugged) there is the noise, and when
I plug in the input jack, it gets louder.
1) What is the signal source? A cell phone? MP3 player?
2) Do you have shielded audio cable between the signal source and the input of your circuit? The shield connects to the ground at both ends and blocks interference pickup from the air.
3) Try it replacing the USB +5V with a 9V battery to test for "a ground loop". The battery should have a 100uF capacitor across it and the USB must be completely disconnected..
The person who posted about adding ceramic capacitors did not know that the ICL7660 operates at only 10kHz. It would need ceramic capacitors if its frequency is much higher.
You said. Although others claimed that the 7660 noise can be filtered, there are no effective filter means implemented in the circuit. The usual bypass capacitors are insufficient to achieve the signal to noise ratio required for an audio circuit, it does probably work for simple digital designs. The suggested LC (or even RC) filters can help, but surely not with the bread board wiring shown in post #43.Over 2 and a half months ago in my post #15 I said, "Many people say the ICL7660 causes noise if used to power an audio circuit". Instead, I should have said the details that it causes a 10kHz whistle in the sound.
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