class A eq amp - part 5

I finished the little tone control box. I also changed the values in the low filter resistor devider to correct for a little (.7dB) bump in the 'flat' position.

Obviously I made a lot of measurements but creating graphs by hand requires a lot of data points so I tried a few programs that use the sound card as a measuring device.
The best free one in my opinion is the one from RightMark.

measurement results

The response in the 'flat' position. The roll-off is caused by the sound card (ESI U24XL). The -3db point is actually at 81kHz.

The software can also measure THD and reports 0.005%

lo filter

The blue curve is rather extreme and is used for speech.

hi filter

It really pays off to match the capacitors and resistors of the filter components as can be seen in this graph.