Building a 12VAC 1A Power Supply for stereo compressor?
« on: December 28, 2020, 08:07:29 PM »
Hi folks,

I'm slowly putting together my stereo Weak Joe compressor build by Mnats (find here: http://mnats.net/what_compressor.html) but supplying the power for it has me stumped.  :-\ 

It asks for an AC supply of 10-25V alternating current, so my initial thought was to get a toroidal 230VAC Primary - 2x12VAC secondary (so each board would receive it's own 12v supply).

Would I need anything after the transformer (some kind of buffer), or can I simply solder the secondaries straight into the PCB?

The other thing that is confusing me is that the schematic has a +15V and a -15V (there's an error on the schematic that shows V2 as positive, but it should be negative). Isn't that irrelevant with an AC supply? I'm familiar with the idea of phase, but it should work whichever way it's connected.. right?


I've attached the schematic below.


abbey road d enfer

Re: Building a 12VAC 1A Power Supply for stereo compressor?
« Reply #1 on: December 28, 2020, 11:25:17 PM »
This schemo does not show a PSU section, which consists in, in addition to a transformer, a rectifier, smoothing caps and regulators.
In order to supply the necessary +/- 15 V rails, you need at minima a xfmr with a 12Vac secondary, two diodes and two smoothing caps, but that would not be a very clean PSU.
Typically you need a xfmr with two 15Vac secondaries, a bridge rectifier, two smoothing caps and two regulators (e.g. LM7815 & 7915, ot LM317 & 337) plus a few resistors and caps for good measure.
Schematics of dual 15V PSU's float around.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

scott2000

Re: Building a 12VAC 1A Power Supply for stereo compressor?
« Reply #2 on: December 29, 2020, 12:46:37 AM »
Could  grab a psu board from members here who sell them to make things easier... Maybe silent:arts or fripholm for example...or just post a wtb in the black market....if that's an option....

fripholm's ttx op76 thread has details on various options including using a wall wart..
« Last Edit: December 29, 2020, 12:55:09 AM by scott2000 »

Re: Building a 12VAC 1A Power Supply for stereo compressor?
« Reply #3 on: December 29, 2020, 07:57:50 AM »
Thanks for the replies guys.

I think the thing that confuses me is that in the project notes it specifically says:

"This should be provided by a 12 volt 1 amp ALTERNATING CURRENT adapter. Do NOT use an adapter that supplies DC - only an AC output of 10 to 25 volts will work"

But surely the dual +/-15V power supply you're suggesting is a DC supply?

That's what I can't get my head around. Are AC adapters not actually providing 'AC' but instead a dual DC supply?

Furthermore, Dual power supplies seem to have a +15V a -15V and a 0 output, but there isn't a place for this in the schematic?

I'm just trying to understand it with my thick brain.
« Last Edit: December 29, 2020, 08:04:44 AM by swilliman »

scott2000

Re: Building a 12VAC 1A Power Supply for stereo compressor?
« Reply #4 on: December 29, 2020, 08:39:07 AM »
Like abbey mentioned, that drawing leaves out the (separate) power supply for some reason. Those little lines coming off the op amps are representations of where the + & -supply voltages should be. And ground is shown. Looks like the pcb component layout has where the +&- go but there is no power supply on that board....

Some adapters/warts put out ac,

 some put out dc.....

The notes are saying to use that ac supply but fail to mention or include the power supply section in the drawing I guess ....which is a bit goofy.....

Hard to see everything on my phone though so maybe there's a clue somewhere else....

« Last Edit: December 29, 2020, 08:48:34 AM by scott2000 »

JohnRoberts

Re: Building a 12VAC 1A Power Supply for stereo compressor?
« Reply #5 on: December 29, 2020, 08:48:31 AM »
Thanks for the replies guys.

I think the thing that confuses me is that in the project notes it specifically says:

"This should be provided by a 12 volt 1 amp ALTERNATING CURRENT adapter. Do NOT use an adapter that supplies DC - only an AC output of 10 to 25 volts will work"
incomplete information.  The circuit obviously needs a split supply, +/- 12 to +/- 15V DC, The note calling for 10-25V AC implies rectifiers and reservoir capacitors to convert that AC to usable DC.
Quote
But surely the dual +/-15V power supply you're suggesting is a DC supply?

That's what I can't get my head around. Are AC adapters not actually providing 'AC' but instead a dual DC supply?
AC adapters provide AC voltage, They make DC adapters but they generally only supply one DC voltage at a time to work with typical 2 circuit connectors.
Quote
Furthermore, Dual power supplies seem to have a +15V a -15V and a 0 output, but there isn't a place for this in the schematic?

I'm just trying to understand it with my thick brain.
You understand enough to question the incomplete advice, a good first start.

JR
It's nice to be nice....

ruffrecords

Re: Building a 12VAC 1A Power Supply for stereo compressor?
« Reply #6 on: December 29, 2020, 09:52:21 AM »
In think there is an error in the schematic. V2 should be -15V.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: Building a 12VAC 1A Power Supply for stereo compressor?
« Reply #7 on: December 29, 2020, 01:52:35 PM »
Ian - you're right, V2 should be -15V.

Thanks JR that makes a little more sense - so the circuit runs on the DC split supply, any AC wall plug adapter would have to be rectified to DC first. That clears that up.

So I've just purchased a +/- 15V regulated power supply - my last question is:

Obviously it's clear where I connect the +/- 15V leads, but where am I going to connect the 0V neutral lead? Would that be to the ground plane?

I thought there would be a difference between signal and earth ground here?

Re: Building a 12VAC 1A Power Supply for stereo compressor?
« Reply #8 on: December 30, 2020, 05:46:40 PM »
Anyone have any thoughts?

 

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