DAC i use "denon da300usb", it is quit good, no noise and very very clear sound.
I changed the cap between RCA-GND to AC-earth, from 1uf to 0.1uf. The background noise weak than before, but i can still hear it.
I checked solder joints and re soldering some points like output, input and LED....etc. but the noise issue still have.
I tried changed OP, no difference. now i use OPA2111 KP. PS: i like JRC4562D and NEC 4556, so sweet.
BUT, i observed that, maybe the noise come from "Volume control", because when i touched it, the noise become louder. left hand side is louder than right.
Use HD660S still no noise. BUT 16 ohm headphome (JVC FXZ 100) the noise appear.
Tomorrow i will try to connect RCA to board directly, hope can solve it.
I changed the cap between RCA-GND to AC-earth, from 1uf to 0.1uf. The background noise weak than before, but i can still hear it.
I checked solder joints and re soldering some points like output, input and LED....etc. but the noise issue still have.
I tried changed OP, no difference. now i use OPA2111 KP. PS: i like JRC4562D and NEC 4556, so sweet.
BUT, i observed that, maybe the noise come from "Volume control", because when i touched it, the noise become louder. left hand side is louder than right.
Use HD660S still no noise. BUT 16 ohm headphome (JVC FXZ 100) the noise appear.
Tomorrow i will try to connect RCA to board directly, hope can solve it.
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Noise Reduction
emacs,
Forcing the volume pot anti-rotation pin against the back of the front panel like you have at the moment may not make a good enough contact to earth it (it also doesn't look nice !). As Zenmod and Wayne have already suggested, you need to properly ground the volume pot case. You need to cut off the anti-rotation pin on the Alps pot so the pot goes flat against the back of the front panel (or make a hole in the front panel for the pin). You then need to use a star washer, or something like it, between the pot and the back of the panel. You need something like a star washer to cut through the thin, natural, non-conductive aluminium oxide coating on the panel when you tighten the nut on the front panel.
I also notice you have the RCA input wires very close to, and in one case, on top of the transformer, and running down the noisy mains ac side of the pcb. They could be picking up mains ac noise. You might be better swapping the IEC mains socket to the transformer side, which moves the RCA input wires to the quieter side of the pcb. But there might not be enough space for the mains filter you have built in to the socket you have. Try flipping the back panel 180 degrees to see if it will fit (or try an IEC socket without a filter).
You also have mains ac wires in close proximity to o/p transistors and other components which probably won't help with noise. Swapping the IEC socket to the other side would solve that too.
The apparently unshielded o/p cables to the headphone socket running over components on the pcb may also be picking up noise. Some shielded cable to the headphone socket might help.
Finally, unshielded cable from the pcb to the pot might be picking up noise, although you might get away with it because of the short lengths.
I also have my pot on a pcb, so I will cross-check your wiring when I get a chance.
Mark
emacs,
Forcing the volume pot anti-rotation pin against the back of the front panel like you have at the moment may not make a good enough contact to earth it (it also doesn't look nice !). As Zenmod and Wayne have already suggested, you need to properly ground the volume pot case. You need to cut off the anti-rotation pin on the Alps pot so the pot goes flat against the back of the front panel (or make a hole in the front panel for the pin). You then need to use a star washer, or something like it, between the pot and the back of the panel. You need something like a star washer to cut through the thin, natural, non-conductive aluminium oxide coating on the panel when you tighten the nut on the front panel.
I also notice you have the RCA input wires very close to, and in one case, on top of the transformer, and running down the noisy mains ac side of the pcb. They could be picking up mains ac noise. You might be better swapping the IEC mains socket to the transformer side, which moves the RCA input wires to the quieter side of the pcb. But there might not be enough space for the mains filter you have built in to the socket you have. Try flipping the back panel 180 degrees to see if it will fit (or try an IEC socket without a filter).
You also have mains ac wires in close proximity to o/p transistors and other components which probably won't help with noise. Swapping the IEC socket to the other side would solve that too.
The apparently unshielded o/p cables to the headphone socket running over components on the pcb may also be picking up noise. Some shielded cable to the headphone socket might help.
Finally, unshielded cable from the pcb to the pot might be picking up noise, although you might get away with it because of the short lengths.
I also have my pot on a pcb, so I will cross-check your wiring when I get a chance.
Mark
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In this case, i only connect the AC-earth to chassis, the board no any way to AC-earth, because my mounting screws and screw's stand are plastic. SO hear the noise very louder.
In this case, i uninstall the RCA cables and volume control, then connect the board-GND to AC-earth with 0.1uf cap, the noise become weak, but i still can hear, like my before case.
when i use my finger touch the 7815 and 7915 heat sink, i can hear the noise change "ZiiIIzii". i will try to replace a new one, hope it can solve this issue.
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Many thx mod_sonic,
I will try to swapping the IEC socket (without filter) to transformer side for prevent RCA wires pickings up AC main noise.
Then change all signal wires to shielded wire to prevent picking up noise issue. and make a hole in the front panel for the volume pot anti-rotation pin.
the picture show my shielding wires connection.
For the headphone socket, the shielding should be connect to PCB GND
For the RCA input wires,the shielding should be connect to the RCA plug GND, it can prevent the noise go into PCB.
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Earthing
emacs
It may be something or nothing but I would check for continuity between the earth post/bolt and the black painted rear panel using a multimeter. In theory the bolt should contact the unpainted inside diameter of the hole in the panel, but it doesn't always work like that. I would also check for continuity from the front panel to the earth. Again, the bolts holding the case together should ensure that but it's as well to check.
What sort of shielded cable are you using for the input ?
emacs
It may be something or nothing but I would check for continuity between the earth post/bolt and the black painted rear panel using a multimeter. In theory the bolt should contact the unpainted inside diameter of the hole in the panel, but it doesn't always work like that. I would also check for continuity from the front panel to the earth. Again, the bolts holding the case together should ensure that but it's as well to check.
What sort of shielded cable are you using for the input ?
mod_sonic
I used this shielding cable, it is 3.5mm cable with metal net shielding.
I removed the RCA with volume control and tried to swapping the IEC socket (without filter) to transformer side. The noise less than before, more than half level.
but when i touch the encircle components, i can hear the noise is enhanced. touch 7915/7915, the noise frequency is enhanced
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I feel so sad as i cant kill the noise.
I checked all solder points then no founding and cleaned the board again.
I used shielded cable to headphone socket and RCA.the noise still existing.
shielding cable datasheet
https://catalog.belden.com/techdata/EN/8723_techdata.pdf
As a test to eliminate hum I jumpered from the input RCA ground lugs to case ground bypassing the capacitor. Made hum go away, I then eliminated the cap.
I also rerouted input wiring as far away from the transformer as possible. Eliminated "most" of the noise which is now barely noticeable at full gain with no input. No shielded wiring. If I were to do it again I would definitely use shielded input/output wiring.
I also rerouted input wiring as far away from the transformer as possible. Eliminated "most" of the noise which is now barely noticeable at full gain with no input. No shielded wiring. If I were to do it again I would definitely use shielded input/output wiring.