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Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

Re: Calculating preamp output cap value

The output cap is typically sized to yield the desired bass cut-off point driving the lowest load impedance the preamp can drive properly. The output impedance (600 ohms in your case) is not part of this calculation. The best cut-off point is a point of discussion but 10 Hertz is the highest frequency for good sound.

The formula to calculate the capacitance required is:

C = 1/(2 x Pi x F x X)

where

Pi ~ 3.14159

F = Desired cut-off point in Hertz

X = Load impedance

C = capacitance in Farads

For your particular situation:

F = 10

X = 100,000

so:

C = 1/ 2 x Pi x 10 x 100,000

C = 1/ 6281835

C = 0.000000159

or 0.16 uF

This will work fine in your system but if you ever want to use an amplifier that has a lower input impedance you will have a problem with the bass response.

You can use about 1.5uF or 2 uF and get good bass response with a 10k load. With your 100k load the cut-off will be about 1 Hz.


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