All this power supply talk motivated me to install the cheap-o outdated meanwell clone into my 2nd case:
It turned on without anything going pop and powered a JFET VCA module I had to hand, so it looks like it’s good to go.
Cheers
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I’ve just wired up a new case with a new-to-me PSU:
It’s a Bel Power Solutions HBB15-1.5-AG, a linear power supply capable of delivering 1.5 A each of ±12 V (or ±15 V). These seem to sell for $130 or so new, but I got a used one for $30 plus shipping on eBay.
120 V enters the case via a power inlet with a built in illuminated rocker switch and a built in fuse holder. You DO want a fuse in a setup like this, really. The inlet is covered on the inside with a blue plastic electrical box, and the 3 conductor cable runs to the PSU, entering through a hole in the orange 3d printed piece I made. That covers a slot on the side of the PSU, rendering the 120 V terminals inaccessible to wandering fingers. The open sides of the PSU are up against the wood side and front of the case, and it’s attached with long machine screws to a piece of sheet aluminum on the bottom. Earth ground connects to the PSU chassis. So everything 120 V is contained. ±12 V and ground wires go to a barrier strip nearby, and the bus boards (just one so far, second one later) connect to the other side.
I haven’t used this yet to power anything beyond two LEDs on the bus board and two LEDs in a power display module, so there could be issues I haven’t hit yet. I also haven’t examined the outputs on a scope yet. But it’s up and running at least, and Bel seems to have a good reputation so I have good hopes for this setup.
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Industrial! Nothing says reliable like 100W power transistors.
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Hi everyone,
Would this transformer work to power a MFOS-style power board?
I’d normally use a centre tapped transformer, so I’m just checking that I can use the second VAC as the ground, as you would do in the MFOS board.
The AC-AC 12VAC wallwarts I’ve used are quite noisy (as in you can hear noise from the wall wart itself), so I’d like to try a toroidal transformer inside the case, which is the approach I’ve taken on hifi builds.
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hey yeah! that works. ive used a couple of those befroe! just pulled one out of a diy synth because the power switch was close to a hole someone might have put their finger in haha. so yeah itll be fine.
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Great, thank you.
I’d like to put it in a metal 19” rack case and have the mains earth connected to the chassis for safety.
I’m guessing that means I need to keep the circuit grounds that are returning to the transformer isolated from the chassis to avoid shorting the secondaries?
Hi LMNC Brains trust,
I’ve got my hands on a Meanwell LRS-100-12 powersupply and was wondering if I could use it to power my 6U 84hp diy case. I can see it outputs +12 and -12 (depending on how you hook it up) but it has no COM (gnd) output. Can I use the ground off the IEC to supply ground to my busboard?
PS my busboard regulates 12v down to 5v for the 5v line.
Cheers
Rumble
Nope, that’s a single PS…
You need two of them, one for each side (+12V, -12V).
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Thanks Eric. I’ll look into getting something else.
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Maybe reach out to @TimMJN, he’s developed his own power supply that looks great. I’ve got 2 of his boards in transit to me now!
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Hi, everyone. I have a quick question: I have a standard 24V 15A power source. I was watching this video where the person configures two L7812 voltage regulators to drive the 0, +12V, and --12V.https://www.youtube.com/watch?v=7PJ0lwqZLe4 It seems pretty straightforward, but with your experience, is there anything that could be potentially bad/wrong with the synth application using this approach? Or it’s best to have two Power supplies 12V, connected in series? like this: Get a positive and negative voltage output from power supply - Test and Measurement - Electronic Component and Engineering Solution Forum - TechForum │ Digi-Key
Instant reaction, not necessarily authoritative (also I haven’t watched the video, just looked at the schematic): Won’t work well due to dropout at least, maybe also due to poor design?
An LM7812 has a dropout voltage of about 2 V, which means you need an input of at least 14 V to get a reliable 12 V out of it.
Here they’re using two LM7812 to get ±12 V out of a 24 V source. If that really works at all, I think it’d need at least a 28 V (2 x 14 V) source.
The business of using an LM7812 to make a -12 V output I don’t know about. I’d think using an LM7912 which is designed as a -12 V regulator would be better and maybe safer.
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Thanks for the quick response; it does make sense. Is the approach with two 12V power supplies in series a better option? I appreciate your comments.
That works if the supplies are designed with three terminals, two (+ and -) that are floating 12 V apart (neither being connected to ground internally) and the third being ground; you tie the two grounds together, tie the + to ground on one (then the - is your -12 V output) and tie the - to ground on the other (and the + is your +12 V output). (Or maybe there’s no ground terminals, but the grounds are connected through the wall cords, then you’d tie the - on one to the + on the other and the tied together terminals become your ground terminal — again neither + nor - can be connected internally to ground.) Workbench variable power supplies are often set up like that. But such supplies would be a questionable choice for a synth supply, where variable voltage isn’t needed or wanted — and they’d be too big and cost too much. If you have a pair of cheap fixed voltage 12 V supplies (a couple of Mean Well RS-15-12 for instance) set up like that it could be a decent choice.
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if you crack open a DC 12 v wall wart you can remove the DC circuit and just tap directly to the transformer inside. This only works for the “heavy” wall warts that are just a transformer with a small rectifier circuit.
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Thanks for this helpful thread everyone.
I am about to wire up a system and started to read this make sure I can run 2 FC Power PSUs properly for a 4 panel Serge System (THC stuff). …
I also found this place in Spain for 2-3amp 12VAC supplies: https://www.retroamplis.com
maybe helpful as those things seem a bit elusive.
Question is:
Will a 12VAC 3A 36VA power supply safely power 2 FC Power PSU’s?
I’ll find out when I plug them in (before any modules connected), and from what I read the regulators should be able to handle this.
If any disagree I appreciate being corrected!
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Should be more than good enough. 1A is enough for one FC power, so 3A is plenty for two.
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Thanks! Just ordered too.
Hey everyone, I want to start building a modular synth too. I made a VCO based on CEM3340/AS3340 (and my first professionally made PCB 
) and a power adapter that gives me ±12V and +5V from a 14v ac-transformer:
For the +12V and +5V rails, I used switched step-down converters (rated 1W I think) and for -12V I used the L7912 voltage regulator with a low end passive aliexpress heatsink.
I think, this power supply is ok for experimenting and stuff, but I probably need a better one in the future, so:
I searched around the internet and found the following solutions:
- The RT65B is simple, but not really suitable for audio (noise, low -12V power etc.)
- Linear regulated with 12VAC transformer, L7812 and L7912 is ok, but these voltage regulators are only rated to 1A-1.5A with a big heatsink
- All-In-One 12V DC to ±12V DC modules, like:
https://www.mouser.de/ProductDetail/TDK-Lambda/CCG30-24-12D?qs=Cb2nCFKsA8qvzo4xGj%252BciQ%3D%3D
What do you think of these all in one solutions? There is an Erica DIY Synth Power Supply + Case Kit that uses one of these, why are these not more popular?
Thx!
The linear regulators are cheap ($0.53 at Mouser; parts for a full linear PSU might add up to $5 to $10) and quiet, and 1 A is typically enough to power 10 to 20 modules. They have built in overcurrent and overtemperature protection. The heat sinks are “big” only in comparison to, say, a resistor or something… the filtering capacitors are typically bigger. As in your photo. I haven’t had problems with heat dissipation.
The 30 W converters you link are $37 each, you can build several linear supplies for the same cost. They have no overcurrent or overvoltage protection built in. On quick look at the datasheets I couldn’t really get a feel for how they compare to linear regulators for ripple, regulation, and so on.
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