I have tried the following things to reduce the noise:
1, used copper foil to shield two 310A
2, tried two kind of GND method
3, used a 1K VR paralleled to the cathode of 300B and connected the CT to here
noise reduced a lot compare with the previous one, but still too much, is there anyway I can try?
1, used copper foil to shield two 310A
2, tried two kind of GND method
3, used a 1K VR paralleled to the cathode of 300B and connected the CT to here
noise reduced a lot compare with the previous one, but still too much, is there anyway I can try?
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I like you customized shields. They look great and are really unique!
By using a 1k VR you have changed the cathode resistance by adding ~500 Ohms. That's the reason why your B+ has increased by 20V because the current through the 300B is much lower now.
You should use a 50 or 100 Ohm VR which can handle some current (>= 1W)
I also wouldn't add a 50uF to the PSU. Stick to the original one since it's influencing the sound of the amp.
In the end your biggest issue will be AC filament supply. If you want to reduce your THD further you have to switch to DC.
And you should measure your frequency response...
By using a 1k VR you have changed the cathode resistance by adding ~500 Ohms. That's the reason why your B+ has increased by 20V because the current through the 300B is much lower now.
You should use a 50 or 100 Ohm VR which can handle some current (>= 1W)
I also wouldn't add a 50uF to the PSU. Stick to the original one since it's influencing the sound of the amp.
In the end your biggest issue will be AC filament supply. If you want to reduce your THD further you have to switch to DC.
And you should measure your frequency response...
If you can live with this AC hum it's fine. It depends on the sensitivity of your speakers at 50/100Hz and how loud it is on your listening position.
I have 3 different 91A clones, all with different filament supplies:
1. AC (5V)
2. simple DC (5.3V AC - bridge rectifier - 10000uF cap - 5V DC)
3. Tentlabs filament supply (6.3V AC input - 5V DC)
AC sounds best (if you ignore hum), second is Tentlabs, last is simple DC.
I have 3 different 91A clones, all with different filament supplies:
1. AC (5V)
2. simple DC (5.3V AC - bridge rectifier - 10000uF cap - 5V DC)
3. Tentlabs filament supply (6.3V AC input - 5V DC)
AC sounds best (if you ignore hum), second is Tentlabs, last is simple DC.
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