Update September 9, 2021. The construction thread is located here: The construction thread for the Mid Side Mini is located here: viewtopic.php?f=7&t=1272
I've had a basic MS board on my list to replace the original I did over a dozen years ago.
The "MS Mini" incorporates the Mid Side gain offset capability of the MSII.
Using jumpers, Mid Encode level can be attenuated 6 dB [(L+R)/2] and an offset gain of +6 dB applied on decode to maintain MS ratio.
Using a jumper and an IC change (IC6 1240 or 1246) Side Encode level can be boosted 6 dB with a decode offset of -6dB.
Gain offsets in the Mid, Side or both Insert Sends present more-balanced levels to outboard gear.
Side is particularly level-challenged often being 10-20 dB below Mid.
The MS-Mini's decoder, identical to the MSII also prevents M+S and M-S from producing 2L and 2R.
This avoids having to incorporate a -6dB stage to maintain unity gain.
MS-Mini PC Layout
The board is about 3.7" by 2.75".
I'll be ordering them in the next day or so and should have a small run in about 10 days.
