I'm trying to calculate voltage ripples on bulk capacitors of my guitar amp. Here's a schematic of it:


simulate this circuit – Schematic created using CircuitLab

According to formula Vpp=I/fC, that is Vpp = 0.82/(2*50*0.0011)= 7.4V

I = 0.82, transformer is rated 30W, for rough estimation 30W/36.6V, it's going to be less at maximum load.

C = 0.0011, since two capacitors are in series

Aren't 7.4 V ripples way too high for this application. There are planty of information on the internet about ripples. I'm pretty sure I got it right, or am I not?

The main question is 'if calculations are right, are 3.7 V ripples OK considering schematic above?'

But I more inclined that something is missing in calculation, because I can hear 100 Hz hum, but it is hearable only when ear is <10cm from the speaker. Considering speaker is rated 15W, I bet it's OK.

  • \$\begingroup\$ @LongPham, how could they be in parallel if negative lead of a cap is connected to positive one? \$\endgroup\$
    – Qeeet
    Jul 22, 2018 at 8:37
  • \$\begingroup\$ Assuming that the load is symmetrical, you only need to calculate ripple for a single voltage rail. In this case, Ctotal = C1||C3 or = C2||C4. \$\endgroup\$
    – Long Pham
    Jul 22, 2018 at 8:42
  • 2
    \$\begingroup\$ A rough estimation of power supply capacitance for an amplifier is 10,000 uF per ampere. \$\endgroup\$
    – Andy aka
    Jul 22, 2018 at 9:50
  • 2
    \$\begingroup\$ That 3.7Vp-p is attenuated by the power supply rejection ratio of the amplifier, which will be pretty good (and spec'ed in the datasheet). The fact you can only just hear it supports this. But more capacitance would be better as Andy suggests. \$\endgroup\$
    – user16324
    Jul 22, 2018 at 11:51
  • 2
    \$\begingroup\$ They call it "Supply voltage rejection" see page 3. \$\endgroup\$
    – user16324
    Jul 22, 2018 at 16:52


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