A FE2022 PCB with integrated PSU to fit a specific space

G'day Guys,

I am working on a PCB design to fit in place of a Broskie 12VAC Aikido PCB.
Long story short, I have run out of tubes for the 12VAC Aikido so it is time to pass that sought after board onto somebody else.

It's also a good excuse to use a FE2022 essentials kit I impulse bought from the store a while back.

The catch is that I spent 6 months making a chassis around the Aikido. I spent too much time cutting, folding, drilling, sanding and painting not to reuse the chassis.

The new pcb has to go here:
The goal is to get everything onto one board so that I can simply replace the donut and PCB and button everything back up for immediate use.
Hopefully no drilling into my lovely paint work. Definitely no cutting!
That means a PCB of the same dimensions as the 12VAC Aikido or at least the same hole centers.

I am working off of the V0R1 schematic:
DIY FE 2022 V0R1.jpg
I have removed R14 as it isn't needed.
I have removed the trimpot P1 as I am not worried about DC offset.
I have removed R11/R12 as I am using a bipolar supply.
I have removed R9/R10 as I think these are an RC filter for an external DC brick and I will be using a regulated linear supply.
I have kept C6, just in case.
I have decreased C4/C5 to 100uF which seems sensible to me as decoupling for a regulated PSU.

Thus I have come up with this:
FE2022 V1.0.png
The PSU will be a VRDN. I was going to shoot for +/-24Vdc rails but I don't have any appropriate donuts, so I will run +/-20Vdc rails.
I have applied the changes Mark Johnson recommends for immunity to manufacturer variations in the LM317/337.
Figure1.png VRDN V1.0.png
And here is the first draft of one channel of the FE2022 part of the circuit.
Topside V1.0.png Botside V1.0.png
Shown with the output caps of the VRDN on the left.
I am happy with the parts placement.
The grounding is subject to change as I layout the PSU but I intend to keep the signal ground separate from the PSU ground except for the single point of connection.

I am going to see if I can fit separate regulators for each channel driven from the combined cap bank.
a) LM317/337 and denoiser parts are cheap.
b) This should allow me to get the regulator outputs closer to the FE2022.

I am wondering if with the output of the regulator so close to the FE2022, whether decoupling is necessary at all?
I have managed to get the layout to do what I want it to do:
Top Side V1.4.png
Left channel "complete", Right still pending of course. But I now know it will all fit as I intended.

I managed to fit a pseudo dual mono where by each channel gets its only cap bank and regulator after the first 'C' stage of the CRC filter.
PSU V1.4.png

Prettying up the routing, running the grounds and general prettying of the silkscreen etc to follow.

Layout done:
Top Side V1.4.png
Bot side V1.4.png
Dimensions V1.4.png

A few checks here and there. Check footprints and lead spacing on the caps for example and I should be ready to send this to the fab.

Minor changes include:
-I have used different bridge rectifiers from the standard VRDN to use what I have on hand from salvage.
-I have applied the modifications to the original VRDN to allow the stable use of non OnSemi regulators as I have ST ones on hand.
-I added C6 back into the FE2022 just in case.
-I went with a 1W resistor for R15/R16 as this was an easier footprint to find compared to 600mW.

Last night I ordered a custom donut from Ali express: 2x20V + 1x18V. The 18vac to drive the input selector relays.
I considered just putting an extra secondary winding on the existing 2x18vac transformer that was powering the 12VAC Aikido. But I want he slightly higher voltage for the VRDN and this way is less messy. The custom ali express donut was the same price as ordering one with 2x20v from Element 14 and then I would have to modify it.

All going to plan I should have this sent off to the Fab and a parts order for what I don't have on hand in the next couple of days.
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Pcbs have been ordered.

Mouser is sending me a bunch of fresh parts. Unfortunately I forgot to order 1000uF caps for C19/C20
I might have something of the right diameter and pitch in my stash somewhere. So far the best I have found is 470uF 35v. These might have to do if I can't find any 1000uF 12mm diameter caps anywhere. I don't think the value on these parts is critical anyway.

Mouser was out of stock of the On semi LM317/337 so I will just use the ST parts I have on hand. Good thing I applied the modifications for non-On Semi parts.

BC327-40/BC337-40 were out of stock also. So I will use some ZTX851/951 I have on hand. I will just need to remember to check the pinout when it comes to stuffing time. IIRC the pinout is reversed for the ZTX parts.

For the DIYFE2022 end. I have most of the resistors on hand in RN55/CMF55 form so I decided to order the extra couple of values so everything matches all pretty. I did price up doing the same for the VRDN end but the cost was just a bit silly. Some values were 6x the price of standard metal film and it just seemed a bit silly for a PSU.

All going to plan I can start stuffing parts in a couple of weeks.