I built this circuit using a 200k log pot. The circuit works as expected, except that when I turn the pot to maximum output a humming noise is heard. The humming is present regardless if there is an input source. Just wondering if someone could shed some light on this issue for me.
Thanks for the help!
Thanks for the help!
broken vol pot?
At full output the wiper sits on, or very close to the connection to the output lead.
There could be a break here that is mechanically disturbed when the wiper hits it.
Alternatively the wiper could be sitting on a dirty/insulating lump that isolates the wiper from the signal track. Again a faulty vol pot.
At full output the wiper sits on, or very close to the connection to the output lead.
There could be a break here that is mechanically disturbed when the wiper hits it.
Alternatively the wiper could be sitting on a dirty/insulating lump that isolates the wiper from the signal track. Again a faulty vol pot.
.
Routing of conductors. Keep the audio conductors away from the power supply conductors.
Route the "ground" side of the audio input circuit to your ground point using one conductor, and the "ground" side of the audio output circuit through another conductor to the same ground point.
Suspect a noisy power supply. Bigger filtering caps? Decoupling caps present?
A 200k pot, are other resistors in the, say, 1/2 or 1meg range? High impedance circuits are more susceptible than others to noise.
Put your finger on the op amp (don't get electrocuted). Careful, it might be very hot. If it is hot then there's oscillation, the hum you're hearing is the lower frequencies of the oscillation.
Did you add 0.1uF (100nF) ceramic capacitors from the op amp's power pins to ground? These are not shown on schematics (usually) because "everybody knows to add them."
Put your finger on things generally, still without getting electrocuted. If the hum stops or lessens then suspect a ground loop. A lowish pitched hum is likely a ground loop.
Or generally, as AndrewT suggests, a poor connection someplace. Is there a screw connection to the chassis? Personally, I always use additional flux when soldering.
Another thing I do is throw the thing away and start over. Usually after hunting the problem for a day or two.
.
Routing of conductors. Keep the audio conductors away from the power supply conductors.
Route the "ground" side of the audio input circuit to your ground point using one conductor, and the "ground" side of the audio output circuit through another conductor to the same ground point.
Suspect a noisy power supply. Bigger filtering caps? Decoupling caps present?
A 200k pot, are other resistors in the, say, 1/2 or 1meg range? High impedance circuits are more susceptible than others to noise.
Put your finger on the op amp (don't get electrocuted). Careful, it might be very hot. If it is hot then there's oscillation, the hum you're hearing is the lower frequencies of the oscillation.
Did you add 0.1uF (100nF) ceramic capacitors from the op amp's power pins to ground? These are not shown on schematics (usually) because "everybody knows to add them."
Put your finger on things generally, still without getting electrocuted. If the hum stops or lessens then suspect a ground loop. A lowish pitched hum is likely a ground loop.
Or generally, as AndrewT suggests, a poor connection someplace. Is there a screw connection to the chassis? Personally, I always use additional flux when soldering.
Another thing I do is throw the thing away and start over. Usually after hunting the problem for a day or two.
.
- Status
- Not open for further replies.