8 Tap DC Converter/Isolator in a 1590B: good idea or bad idea?

Song Naga

Song Naga

Member
Hi all, I need a DC power isolator for my pedals and found the 4 tap DC Converter/Isolator PCB, but it's out of stock and I would actually like to have a few more than 4 taps. So I took a look at the 4 tap schematic, measured the dimensions of a 1590A enclosure, fired up KiCAD, and churned this out over a good cup of joe. My first attempt at designing a guitar pedal!

Does it make sense to mount the jacks on the bottom of the board and the switch and LED on top for this design? I'm planning to support the PCB in the case using standoffs (hence the drill holes). Will one L7805 be able to reasonably support 8x isolators and 'basic' pedals connected? I don't think I plan to plug much that draws a lot of amperage, the worst culprits are probably a Terrarium and a Sea Bed delay (with a PT2399 in it). Feel free to tell me everything wrong with this design before I order some prototype boards in the next few days. Thank you for your input!

Schematic

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Front PCB

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Back PCB

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Pretty renders!

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You may need to separate them into parallel groups each with their own 7805 regulator to handle the current.

And heavier traces, especially on the DC Input branches.
 
Thanks! I was able to cram a 2nd regulator and its supporting caps onto the board and fattened up all the tracks from 0.2mm to 0.6mm.

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Better!

Question: this looks like you're planning on operating the input at 5Vdc. What are you planning on feeding it with?

Each tap is going to be limited to 110 mA @ 9V on the output. At 76% efficiency that means ~263mA on the 5 volt side per output. That works out pretty well for one 78 series regulator per group of 4. You'll need a 5v PSU feeding this thing that can handle a hair over 2A @ full tilt.

C11 and C1 are redundant: you could combine them into a single 220uF, though you could probably get away with a single 100uF. You could always add a 100nf X7R in parallel as well: transients, yada blah, pretend I know what I'm talking about...honestly isn't necessary but see it done all the time so monkey brain takes over and just does it...

Last bit of advice: I'd recommend rotating the polarized caps to all be oriented in similar directions. (Positive up/right, down/left, or any combination that suits the board). Helps with assembly and preventing "Ah, shit" moments.
 
Stickman393 said:
Better!

Question: this looks like you're planning on operating the input at 5Vdc. What are you planning on feeding it with?

Each tap is going to be limited to 110 mA @ 9V on the output. At 76% efficiency that means ~263mA on the 5 volt side per output. That works out pretty well for one 78 series regulator per group of 4. You'll need a 5v PSU feeding this thing that can handle a hair over 2A @ full tilt.

C11 and C1 are redundant: you could combine them into a single 220uF, though you could probably get away with a single 100uF. You could always add a 100nf X7R in parallel as well: transients, yada blah, pretend I know what I'm talking about...honestly isn't necessary but see it done all the time so monkey brain takes over and just does it...

Last bit of advice: I'd recommend rotating the polarized caps to all be oriented in similar directions. (Positive up/right, down/left, or any combination that suits the board). Helps with assembly and preventing "Ah, shit" moments.
Click to expand...
Thanks! The orientation of the caps did annoy me also, but I was being lazy and had not taken that step. The redundancy of C1 and C11 makes total sense now that you pointed it out. I of course just copy-pasted the regulator and its caps when Robert suggested adding a second. I'm sure a few 100nFs could fit on the board yet, especially if we eliminate one of the 100uf caps by combining C1 and C11 into a single 220uF as you suggest. Would a 100nF just need to go parallel to the 220uf or are there other caps in the circuit that should get the same treatment?

As for what to feed power into this contraption, I was planning to try a power brick that I use with Eurorack power supplies, then looking for an alternative if/when that didn't serve the purpose. I'm open to suggestions on this, as I haven't given it much thought. The product I have laying around that I would start with is this:

Row Power Power Brick

4mscompany.com 4mscompany.com

One of these power bricks will power a couple dozen eurorack modules with similiar components to typical stomp boxes, so I figure it's enough juice for 8 pedals at a time. Maybe it's overkill for this project and something smaller and cheaper would work?

Here's a schematic update with what I think you suggested cap wise: C1 is now 100nF X7R and C11 is now 220uF.

1748444937207.png

And I twirled all the electro caps round to make them less crazy:

1748450028096.png
 
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