@Biasrocks That's interesting yes.. there's quite a few changes on that version compared with the original schematic.. It differs quite a bit.. I've stuck to the original schematic...
http://www.gyraf.dk/schematics/Sontec_MEP250a.GIFIn regards to bypassing, I've done ceramics (100nF) on every IC power pin to ground. And also an extra 2 larger low impedance electrolytic/tantalum on +V & -V to ground on each filter / and the 2 main amp opamps. (47uF)
The layout can also have a big impact on bypassing needs too. As this is very compact, I was able to keep power rail impedances very low throughout..
On the rails going to the filter section, there's also space for a bit of extra filtering (resistor/inductor/ferrite etc) if it needed some extra filtering/isolation, however I've not found it needs anything so jumpered them.. the footprints are still there though..
How does that compare with your findings?
Opamp wise, I've stuck with NE5534 & TL071 for the filters, as I know for certain these were in the original.. However I'm sure curiosity will get the better of me at some point and I'll try some more modern ICs here..
Regarding the two main amp opamps, I tried to keep as close to the written specs as possible but with an IC, and I think I chose ones too similar, as they all nulled around the same level as a second pass with the same IC did.. They were OPA134, O1641, OP827.
Which did you try?
@pvision I think the flash hit the switch and made it seem more prominent than it is real life.. The bushing is recessed behind and doesn't reach the front of the panel.. and the metal shaft only extends around 5mm.. so it quite tight to the panel to not get in the way.. It being diy of course.. experimentation is the spice of life! Nothing to stop you say using the hole as an LED and wiring the switch somewhere else...
Regarding kits! Ok.. well it seems there's quite a lot of interest.. So I'll order a batch of PCBs & metal.. and I think what could be best is if I stocked the knobs too.. and the centretapped pots.. So that you would only have to purchase one order from Mouser, and one order from Omeg, (they have a minimum order of 10 which is perfect for a pair) Also I have a part number with them, so it's easy to order.
I forgot to mention power.. ! Current draw is about 50mA.. and it can either use solely 16V rails.. or 16V rails for ICs and 24V rails for DOAs... or if you use a zener to drop the voltage a little, it can use solely the 24V rails.