Constant impedance attenuator

To provide attenuation for balanced input of my power amplifier I have to use constant impedance logarythmic attenuator. I decide to use relay switched resistors for best performance.

In the Internet there are a lot of relay attenuators, but they aren’t logarythmic or with constant impedance. After hours of thinking I found the solution of the problem and I made simple calculator for my attenuator.

Here is the result for 6 bit 600 ohm attenuator with smallest step of 1dB:

att_log_6bit

The main problem of the circuit is that signal passes through several relay contacts. This leads to usage of relays with maximum possible wuality (and price) to provide best performance.

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