Variable Gain

A project log for Muffsy Phono Preamp PP-3

DIY Hifi Phono Stage

skrodahlskrodahl 06/11/2015 at 10:280 Comments

The Muffsy Phono Preamp PP-3 adds one more level of gain, compared to the PP-2.

By doing so, you get more gain levels to choose from. But perhaps more important, it's become more fail safe as you will even have a gain setting with both switches set to "OFF".

The gain is set for each channels with the two-way dip-switches and resistors marked with orange in the picture above.

The default build will give you the following gain levels:

Modifying the Gain Levels

The usual standard amplification of a phono stage is 40 dB (switch 1 set to "ON"). The other gain levels can come in handy depending on the rest of your audio equipment.

Even though the Muffsy Phono Preamp PP-3 has very usable gain levels, they may not be entirely suitable for your needs. Being DIY, everything can be changed. Here's how.

You will need to find the right resistor values, the ones labeled 430 (R1), 180 (R2) and 300 (Rp) ohms in the picture above. Click on the picture to view a high resolution version, if the text is too small to read.

This calculator made in Excel will do all the calculations for you, substitute with the ones that you choose and you're good to go. It should be noted that a gain level of much more than 46 dB can, in some cases, lead to more noise.