LN1176 Stereo Peak Limiter

I just finalized my 1176 Peak limiter clone, with version J PCB’s from mnats.

Custom made Frontpanel from Schaeffer, Lundahl Output Transformers and large Sifam Vu-meters.

As it is a stereo unit, I tried to match the FET’s responsible for the gain reduction as closely as possible.

Here some pictures of the finished unit:

Now, how it looks inside:

For the bypass switches, I did built a true bypass switch with 2 relays per channel on breadboard.

Top view:

Fetmatching Curves:

As can be seen, the Ugs vs. Ids curves from the tested devices spread quite a lot. Fets number 7,12, 15 and 14 have been selected for the job as they come quite close together. The Fet’s with the closest’s matching have been used as the main compression element, the two other ones for the VU-meter.

First Results:

My first ratio measurements on both channels resulted in following curves:

All measurements have been done for unity gain setting.

The curves look quite similar, but I think I should redo the measurement with the same input level settings.

Second Ratio Measurement:

I swapped the FET’s for a pair which I believe is better matched.

This time I chose FET 13 and 14 as the gain responsible parts, recalibrated both channels and went through the compression ratio measurements once more.

Here’s the outcome: