Poor Man's Digital PGA - Part 2 of 2

No testing is complete until you try the final configuration. In the earlier post, I had simply grounded the extra resistor R7 to switch in the higher gain. Figure 1 below shows a capture of the signal at its base gain of 2.

In this capture, all extra AVR resistors R4, R6 and R7 are in the tri-state condition. It can be seen in Figure 1 that some noise exists on the output. Counting the bumps, there appears to be 20 per cycle amounting to about 100 kHz. The AVR device here is operating at about 1 MHz, using its built-in RC oscillator.

Figure 1. Noise on PGA Output

For use with the MSGEQ7, this should present no difficulty since the switched capacitance filters will eliminate this. This may present a difficulty when used in other audio work, however.

The good news is that this noise is reduced as the AVR resistors get switched in for higher gains.

You can watch an AVR switch between four gains here:

  https://youtu.be/iqPBaHtLFI0

Thanks for reading!