Harry Klippton
Well-known member
I want to know how circuits use bipolar DC power, and for what reason. I've got a good handle on how AC is turned into DC
Some way to rig up 12v AC?
- Thread starter Harry Klippton
- Start date
benny_profane
Well-known member
To add to that, split rail supplies essentially give you three common supplies (i.e., +, -, and GND at the midpoint) as opposed to two with single supplies. GND is a reference point and isn’t an absolute of 0V. When we take a single supply and create Vref via a voltage divider, we’re creating that third supply and using that like the ‘GND’ of split rail designs.
There’s also considerations with digital logic and muxes where a split rail supply may be a better choice due to the voltage logic.
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Nostradoomus
Well-known member
There’s usually a bunch of laptop power supplies at thrift stores for a few bucks.
Harry Klippton
Well-known member
@JTEX @benny_profane thank you. This was very helpful
Dysvalence
Member
You could use a 9v DC supply with a voltage inverter to get +/-9 then linearly regulating both down and feeding that past the rectifier, but since most AC pedals are pretty old I can't say I would want to do this without first measuring the rectified voltages off a known 12VAC supply, especially if it contains any BBDs or digital components that may be long out of production.
IME those are overwhelmingly AC->DC, with voltages that can easily hit 16-20V. Great way to power cheap TPA3118 power amp modules though.
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Harry Klippton
Well-known member
I probably should have mentioned this isn't a guitar effects pedal. It's a half rack compressor/EQ meant for line level.
Robert
Reverse Engineer
The variac idea will work, just make sure you measure the output and don't bump the dial once it's set.
Also keep in mind, the "cheaper" variacs are not isolated from the mains input.
Speaking of variacs, I really regret selling my Sencore PR57. That was a nice variac... It would measure the input voltage, output voltage, current, and leakage.
Also keep in mind, the "cheaper" variacs are not isolated from the mains input.
Speaking of variacs, I really regret selling my Sencore PR57. That was a nice variac... It would measure the input voltage, output voltage, current, and leakage.
No polarity.
Go with a Jameco. Always a good bet for PSUs.
Those are certainly Ac-Dc
We keep every PSU we've stumbled across. Others keep every newspaper ever printed...I think we may have lost track of what the OP was asking for: a way to power his box without having to buy a new AC wall wart
He's got to have a 12V transformer somewhere around the house though, if it's anything like my house.
I think if OP doesn't have one, they should just ask said friend to supply the PSU or order a new one.
But hey, at least it's not an old piece of Alesis gear that uses a 16vacct supply! Talk about unicorns!
JTEX
Well-known member
Speaking of, the first AC-powered box I saw was an Alesis 3630 compressor. 9VAC input. I doubt it even uses voltage regulators inside at this input voltage.
Nostradoomus
Well-known member
Ah dang, forgot about the DC conversion haha.
Harry Klippton
Well-known member
Something close to this. Luckily I had enough time to pop a couple screws off and open the chassis. There are at least 3 regulators, two with heat fins. But it looks like a few of the caps at the power input blew their load. I was in a rush so I didn't get great pics. Maybe I'll get back to it later
For reference, this is the unit:
Attachments
vigilante398
Authorized Vendor
If you're looking to generate AC from a DC supply you're going to need an inverter, which is not a trivial thing to design and build. There unfortunately isn't a simple way to "reverse-rectify" DC back into AC. You would be better off modding the device to take a DC input (or paying $20 or so for an AC power supply).
EDIT: I found the one I bought recently, I purchased a 12VAC pedal from overseas and needed a US plug adapter for it. $15 and didn't need to modify anything internally.
EDIT: I found the one I bought recently, I purchased a 12VAC pedal from overseas and needed a US plug adapter for it. $15 and didn't need to modify anything internally.
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chris.knudson
Well-known member
Really what you need is this...
regardless of whether you get it through a variac or just a simple transformer. If you know what you are doing, you might be able to use the transformer from a laptop power supply (which should be 18 or 19 V) and remove the bridge rectifier and then use a voltage regulator to regulate the output to 12V.
regardless of whether you get it through a variac or just a simple transformer. If you know what you are doing, you might be able to use the transformer from a laptop power supply (which should be 18 or 19 V) and remove the bridge rectifier and then use a voltage regulator to regulate the output to 12V.
chris.knudson
Well-known member
Looks like you can get a replacement Joemeek power supply for $25.
www.joemeek.com
Joemeek Accessories
Joemeek are the makers of high quality pro audio equipment made with the mantra of their namesake 'if it sounds right, is right!'
www.joemeek.com
chris.knudson
Well-known member
Nothing seems obviously wrong with it with the exception of the three big leaky caps -- probably want to replace all the electrolytics or at least the bigger ones -- as an obvious place to start.
