07-24-2014, 07:14 PM
While there may be limitations on the capacitance of the input cap after the rectifier due to peak rectifier current concerns, the second filter cap after R14 is not so limited. In fact the larger the value of the second cap the better as it provides increased filtering.
Most likely, the original limitation was cost and size, and manufacturers used the largest values that they could afford in the design which would also physically fit under the chassis. Today we are not so limited, as larger value caps are both cheap and physically tiny.
I would have absolutely no concerns about using 100uf for the second cap after R14, and as an added bonus, you will experience a lower hum level.
In general, I try to stick to the original value of the input cap after the rectifier, but routinely oversize the caps after the first stage of filtering. This results in better dynamic supply regulation and a uniformly lower hum level.
Most likely, the original limitation was cost and size, and manufacturers used the largest values that they could afford in the design which would also physically fit under the chassis. Today we are not so limited, as larger value caps are both cheap and physically tiny.
I would have absolutely no concerns about using 100uf for the second cap after R14, and as an added bonus, you will experience a lower hum level.
In general, I try to stick to the original value of the input cap after the rectifier, but routinely oversize the caps after the first stage of filtering. This results in better dynamic supply regulation and a uniformly lower hum level.
