Would you be so kind to describe the "star point manner" please? I'm looking online but there are many examples for other kind of equipments and applications and its confusing to me. Logic tells me that I should add one extra cable to every ground connection that there is in the circuit, and join them all together in one mesh and connect them to the ground terminal on the PCB? and also the wire that runs from the ground terminal of the PCB to the metal plate?Hi,
To reduce noise:
There are at least 5 GND connections on/to the PCB. Please use only one PCB GND connection and connect here all periferal GNDs with extra wires..in star point manner.
Additionally connect the cases of the pots to the star GND.
Klaus
Did you try a search (forum, internet)?
Klaus
Hi,
Reread post #40.
Klaus
The red wire from the input jack to the pcb is not shielded so it is an antenna that picks up hum.
All the wires from the volume control and tone controls are also picking up interference because the pcb was designed to have the controls mounted directly with no wires.
I agree that the cases of the pots should be grounded (mounted on a grounded metal box or plate).
...join the club, as they say, that's completely normalI try to inform myself, but the more I see the more confusing it gets.
... this forum is for people who have advanced knowledge in the field.
Maybe the unshielded wires connecting the bass pot are very sensitive to picking up hum.
Maybe the bass pot is connected backwards then turning it "down" boosts the bass (hum).
Maybe the unshielded wires connecting the bass pot are very sensitive to picking up hum.
Maybe the bass pot is connected backwards then turning it "down" boosts the bass (hum).
Hi,
The star point in best case is very close at the PCB. But no need to change this now.
But - very important - really all GND signals go to the star point. No other GND wires are allowed.
Check these: LED_GND, signal_input_GND, master_volume_gnd, DC_input_GND... really all.
And check that there are no other GND wires. Especially check DC input..
--> Star wiring ensures that all parts in your circuit refer to the same reference voltage.
But star wiring can't suppress power supply fluctuations coming from the power supply. It can't replace a bad power supply.
Star wiring here just can reduce the effects of heavy supply current to cause GND bounce.
Now one may say there is no heavy supply current. Yes and no. If the power supply voltage is clean, the current will be clean, too.
But when the power supply goes into burst mode it will run and push the supply voltage to a desired level...then it will stop working (maybe for a couple milliseconds) ... during this time the supply voltage will drop a litle ... then it starts to run again to push the supply voltage..
But this "push" may create relatively heavy currents (peaks) ... to charge your 1000uF capacitor.
Did you try "base load" recommended in post#7? Please give feedback how this changes th noise.
Try a 1ohm series resistance in the "+" power supply line from connector to PCB. Give feedback.
Klaus
Maybe the unshielded wires connecting the bass pot are very sensitive to picking up hum.
Maybe the bass pot is connected backwards then turning it "down" boosts the bass (hum).
The red wire from the input jack to the pcb is not shielded so it is an antenna that picks up hum.
All the wires from the volume control and tone controls are also picking up interference because the pcb was designed to have the controls mounted directly with no wires.
I agree that the cases of the pots should be grounded (mounted on a grounded metal box or plate).
The AC-DC adapter is a switching one but the line hum is passed over. The line hum you are hearing is most likely 100-120Hz, the filter capacitor is likely to be under value. In other words, the adapter is unable to provide the
Quick attempt: try to add a 2200 uF capacitor to the DC supply jack of the amplifier. Does the noise disappear? It may not completely disappear but may reduce substantially.
Another: use a 9V 2A rated adapter and see whether the noise goes away. How to test whether the adapter is the culprit? Use the adapter to drive a small speaker with a 1 uF capacitor in series . If you can hear the hum, the adapter is not good (do not do this without the series capacitor because the speaker will be cooked!).
Another: make a pi filter for 100 Hz and use the output for the amplifier. The amplifier assumes that you have a decent power supply. It does not work well with a noisy supply.
As far as I see the negative speake is not GND .. instead it is one side of the LM386 bridge.I realize that I didn't connect the speaker negative wire to the star point
Standard formula: fc = 1 / ( 2 x Pi x R x C)So, I calculate what kind of Resistor would I need to work with the 0.1mF capacitor to cuttoff freq of 60hz
The thing that I'm worried about is that the guitar signal is compromised if I add something to quiet down the noise.
Yes, the bass pot is used as a rheostat. Usually, a rheostat has its unused pin connected to the wiper (the middle pin) so that if the wiper gets disconnected by some dirt in the track then the total resistance of the pot is there. It has no effect on how the pot works.
You connected the negative speaker wire to ground without seeing on the schematic that it connects to the output of one of the LM386 power amplifier ICs?? Then that LM386 is probably destroyed, even if it was not playing sounds. I spoke earlier that both LM386 ICs are already overloaded
since they are connected in a "bridged" mode. Modern amplifier ICs are designed to be bridged and are shown bridged in the datasheet. Not the old LM386.
You talked about using an LC lowpass filter. It is wrong because it passes low frequencies like hum but cuts all the high frequencies that you want to hear. A highpass filter would cut the hum but it would also cut all low frequencies that you want to hear.
Do you know if the hum is 50Hz from stray pickup or is 100Hz from the rectified power supply? It sounds like a 100Hz buzz to me. Maybe the main filter capacitor C24 (1000uF) or bias filter capacitor C23 (10uF) is defective or is mounted backwards.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?