Odd regulator for frontend

[gmphadte]

In this schematic for an amp, I found that the 40vac is fed through a capacitor before the rectifier. Is there any specific reason for this type of design.

Gajanan Phadte

[Elvee]

Originally Posted by gmphadte

In this schematic for an amp, I found that the 40vac is fed through a capacitor before the rectifier. Is there any specific reason for this type of design.

Gajanan Phadte

It is a voltage-doubling rectifier.

[AndrewT]

The conventional rectifier gives ~ 55Vdc to 60Vdc at the smoothing capacitor when under load.
The voltage doubler rectifier gives ~110Vdc to 120Vdc at the smoothing capacitor. NO IT DOES NOT !!!.
The doubler is more likely to give 90Vdc to 120Vdc at the smoothing capacitor when under load.

The circuitry after the doubler must be designed to take account of the wide variation of supplied voltage and also designed to reduce the very much higher ripple voltage on the supply.

The regulator (actually capacitance multiplier) is the designer's way of trying to ameliorate that big variation in supply voltage.

[gmphadte]

Thanks and regards

Gajanan Phadte

[gmphadte]

For my Leach low-TIM amp frontend, I wanted to use a separate 2x60vac transformer to get regulated 56V frontend supply. The mains will vary a lot here. May go as low as 170V. I can try the doubler and a 56.6 volt zener in place of R32.

Gajanan Phadte

[AndrewT]

Can someone check the required voltage ratings of capacitors C6, C8, C19 & C21?

I would recommend a separate voltage regulator be fitted after the capacitance multiplier to give the front end voltage you require.
This voltage regulator could simply be a Zener or a transistor assisted Zener.

[gmphadte]

My in-use transfomer is 40 vac, dual secondary.

Gajanan Phadte