V3 Universal Power Supply Circuit Board

[Wessideg]

Thanks, I appreciate it.

[6L6]

The circuit with 7812 is incredibly simple, just a small cap (value not very critical) on each side of the regulator. If you get one in TO-220FP (the plastic insulated version) you can just attach to the chassis floor for heatsinking. The caps and wires can be attached directly to the pins.

[myleftear]

Hello
Uhm, so for the F4 which becomes true, what adjustments should I make concerning the bleeder resistor (R9, R10), and since I‘ll try making the rectifier part too, is the output snubber required? (Not sure anymore about this, whether it is not required because of the constant current draw of a class-A amp?
I‘ll try not to ask too many too basic question (except these 2 for a starters)
Thank you
All the best
d.

[myleftear]

Hello
Uhm, so for the F4 which becomes true, what adjustments should I make concerning the bleeder resistor (R9, R10), and since I‘ll try making the rectifier part too, is the output snubber required? (Not sure anymore about this, whether it is not required because of the constant current draw of a class-A amp?
I‘ll try not to ask too many too basic question (except these 2 for a starters)
Thank you
All the best
d.

[6L6]

Bleeder resistor is there to discharge the capacitor bank after power-off. It’s value is not critical at all. 2.2k is a common value and works perfectly. Anything from 1.5k to 10k is again, completely fine.

Leave the output snubber open. The next PSU will not have one, it’s worthless.

[myleftear]

Thank you, 6L6!

(And you were quite right on the F4/PSU: pretty nice to put together, once the scare is shaken off )

[AddiDub]

I have build a Universal Power Supply circuit board. It seems to work fine and i tested it with my M2x boards, drawing 2,6A per PSU rail. My toroid ist a bit oversized with 500VA.

My negative voltage rail seems to have unmeasurable AC voltage at the output, while my positive rail measures around 50 mV ripple voltage. Measurements are the same with load applied or without load.

I triple checked all solder connections. Does anyone have an Idea how to find the culprit?

[AddiDub]

I will answer my own question. First i realised that i used a wrong range setting for measuring the AC ripple voltage at the output. When i use the "mV" setting my DVM reads around 7mV ripple (not 50mV) between V+ and ground.

My DVM only measures AC voltage when i connect the red clamp to the point with higher DC potential and the black probe to the point with lower DC potential. To measure the positive rail i had to connect the red clamp to V+ and the black clamp to ground. To measure AC ripple voltage on the negative rail i had to connect the red probe to ground and the black probe to V-.

Using this method and the mV range on my DMM both positive and negative rail measures AC ripple voltage around 7mV.
I will repeat measurements next weekends using my CRO. I was too lazy to set it up in my living room workshop that must be cleaned after every DIY session.

[DaveFred]

Question about PI resistors,

Are they recommended for Class AB or just Class A amplifiers?

Thank you,

David.

[Ben Mah]

Class AB amps draw varying amount of current so a CRC filter would vary the voltage available, depending on the value of the resistor. The current could vary from tens of milliAmperes to many Amperes, so the power supply voltage variation due to the voltage drop across the resistor could be quite large.

Class A amps on the other hand have only small current variation so the power supply voltage variation is quite small.

Although a C filter has much higher ripple than a CRC filter, Class AB amps are push-pull and they have high Power Supply Rejection Ratio (PSRR), so higher ripple can be tolerated compared to a single ended amp which has low PSRR.