Power supply issue?

DIY STUFF
1

Hi there!

I’ve been building a VCO bank composed of 5 Thomas Henry VCO-01, and a classic power supply unit (220-12V AC + LM7812 + LM7912, big caps, etc).

Schematic_TH_VCO_01_2022-07-24
Schematic_TH_VCO_01_2022-07-241920×1360 150 KB

I have a strange issue with, from what I suspect, the PSU.

When one VCO is plugged on the PSU rail, there is no problem, it always switches on correctly. When two or more are plugged, I get some wrong starts, the oscillation does not occur (I just get a flat minus 8V on the outputs). So I switch off and on, and sometimes, it works on, sometimes not. I kinda have the feeling of rolling a dice here.

I changed the two tension regulators, but nothing really changes.
All the VCOs behave the same: they all work, or the all don’t.

Could this be an inrush current issue?

2

Analog output did a nice job figuring out that the positive regulator needs to be clamped with a schottky diode otherwise can be pulled negative and fail to start

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3

That’s was exactly the solution!

Strange fact is I bought 1N5817 and I am pretty sure I saw the AO video in the past. And totally forgot about it.
I guess I was a bit panicked and tired ^^

Thank you!

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4

That’s assigning me credit I’m not due. @savt22 pointed out a mention of this solution from modwiggler; all I did was to set out to check if it violated any best practices and discovered it was recommended in a more authoritative source.

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5

My apologies .

Your video explaining the issue is an excellent resource

I haven’t extensively tested my new power supply yet but so far it starts up every time with the clamping diode mod

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6

You RTFM for us, poor peasants, and brought it in an easily understandable package.
Huge thanks for that.

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