SSM2015 Mic Pre
This page describes a mic pre I made some years ago. Since the main chip used has been obsolete for many years, it's not really a good DIY project...

I made it for recording some music at the local music school. A couple of days before the recording was to be made, I discovered that the mic pre in the tape deck there didn't work very well (unless perhaps as a noise source). So I had to come up with something quick.

Click for enlargement
I found two SSM2015 chips in a drawer - I had bought them for something some years earlier but never used them. So I built a small mic pre circuit around those. The amp has a variable gain (20-60dB in 5 steps as far as I remember), balanced (XLR) inputs and unbalanced outputs. The power supply is a simple circuit using a half-wave rectifier and LM317/337 regulators.

Since I was in a hurry, I drew the PCBs by hand and etched them in ferric cloride. The pen I used to draw the traces wasn't very good, so the traces are full of small holes... I didn't spend too much time on the front panel, which can be seen in the picture on the right :)

Some pictures of the amp can be seen below. The schematics are also available, in case somebody who has some SSM2015 chips reads this...

LM3875 amp prototype

LM3875 amp prototype

Schematic - amp section

Schematic - power supply

A couple of parts are not shown on the amp schematic. That is the output capacitors and resistors - a 4µ7 film cap and a 100R resistor between the output connectors on the board and the phono connectors on the back panel. One of the output capacitors can be seen glued to the back panel in the photo.


Comments? Questions? Just send me an e-mail!