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Old 12th August 2011, 10:28 AM   #1
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Default Odd regulator for frontend

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
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Old 12th August 2011, 10:34 AM   #2
Elvee is online now Elvee  Belgium
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Quote:
Originally Posted by gmphadte View Post
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.
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Old 12th August 2011, 10:52 AM   #3
AndrewT is offline AndrewT  Scotland
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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.
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Old 12th August 2011, 10:59 AM   #4
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Thanks and regards

Gajanan Phadte
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Old 12th August 2011, 11:12 AM   #5
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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.

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Old 12th August 2011, 11:13 AM   #6
AndrewT is offline AndrewT  Scotland
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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.
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Last edited by AndrewT; 12th August 2011 at 11:15 AM.
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Old 12th August 2011, 11:20 AM   #7
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My in-use transfomer is 40 vac, dual secondary.

Gajanan Phadte
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