Pre-attenuation sanity check

[Bacci]

I'm using the Crack with 150ohm impedance cans (HD700). Apart from lowering the output impedance with a 5998 tube, I would like to increase the usable range of the volume control.

If I understand correctly, there are 2 ways to pre-attenuate the signal if I want to keep the input impedance to around 100K ohm: Using a 100K log pot/attenuator and making an L-Pad attenuation using 2 resistors in order to stay at around 100K ohm, or using a lower value pot/attenuator and a series resistor to get back to the goal 100K ohm.

I read good things about the Valab stepped attenuators. They come in 10K, 20K, 50K, 100K.

If my math is right I then get following values:

10K log attenuator with a 90K series resistor = -20dB
20K log attenuator with a 80K series resistor = -14dB
50K log attenuator with a 50K series resistor = -6dB

Seems like 50K log attenuator with a 50K ohm resistor in series for a nice -6dB is the way to go then if I'm correct?

[Paul Birkeland]

The 20K attenuator with 80K series resistor will be the best solution, and is most comparable to what I recommend in the FAQ.

There isn't a need to change the attenuator to accomplish the modification, you just need the four resistors.

-PB