class A eq amp - part 3

Some progress.

I choose to use an output attenuator, the cable to my beolabs measures roughly 1NF cable capacitance and a quick calculation revealed that this should not pose a problem.

With the given values the steps measured: 0 dB, -10.4 dB, -20.15 dB, -30.6 dB, -40.8 dB, -53 dB
The idea is to calibrate the -10dB position for 90 dB sound level.

Although the circuit can easily be built on a piece of experimentors board I still choose to draw a circuit board. It is a very small board(45 x 45). The dimensions fit the cheapest category of seeedstudio pcb service.

I used the online gerberviewer of Paragon to generate the preview.

I also intended to make some form of softstart but it adds a lot of complexity and it would require a bigger circuit board.  I also like a mute function so it occurred to me that it can be kept simple by using a 3 position switch.

I did not yet fix values for the HI filter but I measured the performance of the LO filter.

Values are in dB.

@30Hz	CH1	CH2
1	11,7	11,7
2	6,9	6,9
3	2,75	2,8
4	-0,7	-0,7
5	-4,6	-4,8
6	-7,2	-7,8