SIAM 295b

[fragletrollet]

Fun project! Following

 

[GreyboxAudio]

Update: I've renamed the repository https://github.com/greyboxaudio/SIAM-295b and the schematic has also been updated with some minor changes to the gyrators. I'm also happy to announce that I plan to design a PCB this year

So about that PCB... While I now have enough experience with KiCAD & JLC PCB to order PCBs, I am still struggling to come up with a satisfactory schematic.
- The opamp in the shelving circuit creates a lot of high frequency noise and performs much worse than the discrete class a topology of the original. I'm refusing to accept "discrete class a magic" as the solution and want to ideally fix this issue at the source
- the mid band is weird, because the Q not only varies for each gain setting but is also slightly asymmetrical between boost/cut. This makes it tough for me to decide the right balance between simplicity and authenticity

But I've picked the project back up and will hopefully make some progress over the holidays.

 

[GreyboxAudio]

I rewired one of my PSUs from +/-12V to +24V and built the shelving filters with the discrete amp. I used all BC549C transistors and chose the nearest values for electrolytics (22uF instead of 25uF and 47uF instead of 56uF). It works but I need to put it in a metal case because the lack of shielding is messing a lot with the low end. I've also ordered a used Siemens V2284 card to gut for input/output transformers.