# DIY Power Supply Thread - Questions and Help

**URL:** <https://lookmumnocomputer.discourse.group/t/diy-power-supply-thread-questions-and-help/117>\
**Category:** DIY STUFF\
**Created:** [January 27, 2020, 6:26pm UTC](https://lookmumnocomputer.discourse.group/t/diy-power-supply-thread-questions-and-help/117 "2020-01-27T18:26:23Z")\
**Posts on this page:** 1\
**Showing post:** 201

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**Author:** ![TimMJN](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/timmjn/32/15227_2.png) [@TimMJN](https://lookmumnocomputer.discourse.group/u/TimMJN)\
**Post date:** [August 28, 2021, 7:05pm UTC](https://lookmumnocomputer.discourse.group/t/diy-power-supply-thread-questions-and-help/117/201 "2021-08-28T19:05:40Z")

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So last week I upgraded my case’s PSU, from 1x [FC microbus](https://frequencycentral.co.uk/product/microbus/) and some passive bus boards to 3x [FC routemaster](https://frequencycentral.co.uk/product/routemaster/). Much to my unpleasant surprise, I got presented a nice fat 50Hz hum after reassembling the whole thing. I noticed the hum emerged whenever I plugged two modules from different PSUs into eachother, so my immediate thought was: ground loops. I also unplugged each individual module to see whether one of them was giving problems, but no difference there.

Here’s a scope capture of a VCA with another (quiet) module plugged into it. The bumps are perfectly at 50 Hz.

 ![2021-08-28 16.17.37](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/c/a/ca5233ce8b44b59b98755073cc589f49de3fa3ec.jpeg)

Before I continue, here’s some info on my current set-up. I use a 230V/12V transformer with a single secondary winding, which is branched to 3 PSUs. See the pictures and makeshift schematic below.

 ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/b/a/bab987965c4a384e56f6bf2d3152a6da2906b3a4.png)

 ![2021-08-24 17.07.39](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/d/3/d3b2eccf61f583865e1037ce3ac1e6f230a66958.jpeg)

 ![2021-08-24 17.07.20](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/e/0/e0dc77b5b9d8ad6fcb233eb18b2548d5bc6fa90f.jpeg)

Now, against better judgement, I had used 22 AWG wires to connect the PSUs to the transformer. This was my prime suspect. I unplugged the top two PSUs, and replaced the bottom PSU ground wire with 10 AWG (ain’t no kill like overkill). Unfortunately, the hum persisted.

I also plugged the supply rails into my scope. These are taken with only 1 PSU connected to the transformer, but that obviously still forms a ground loop between the synth and the scope.

+12V

 ![2021-08-28 17.16.07](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/4/4/444be5d94706804f384ea046e0efbad182828cfd.jpeg)

-12V

 ![2021-08-28 17.09.18](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/5/c/5c9ae936b6c355feafe080169c8292892003275c.jpeg)

Now, I understand why ground loops happen. What I don’t understand, is why they happen now, but not with the microbus. Granted, that was only 1 PSU, but I still connected it to external mixers etc without any problem or hum. Also, is this really a ground loop I’m looking at? Shouldn’t I see a perfect sine in that case? Is this just supply ripple? The routemaster is designed for a centre-tapped transformer, but the build guide also mentions using it with a single transformer.

Here’s the things I will try in the coming weeks:

- replace the transformer with a centre-tapped one
- replace all wiring with 15 AWG
- create more space between 12VAC and GND wires

If there are any more suggestions or ideas here, I’d love to hear them. Thanks!

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