diy pedal board power supply question

I built myself a custom power supply for my pedal board. My requirements were pretty specific and nothing on the market met my needs.
I have several 9v pedals, one 18v, and my effectrode tube drive takes 12v and 1200mA on a center positive jack.
So I made it like this: 2 transformers. an 18v 1000mA and a 12v 2000mA.
18v transformer > rectifier > 220uf filter cap > 18v regulator > 100uf filter cap > output.
12v transformer goes parallel to the 12v and 9v "rails", just like the 18v rail only with different voltage regulators to match the desired voltage. Each rail has its own independent ground. So the 12v and 9v rail share a transformer winding, but it feeds independent rectifiers and so on down each rail is all isolated.

I put this all together and it tested great. Each rail with the proper regulated voltage.
Note: I wired all the outputs center negative and got a polarity reverse cable to connect my tube drive (the one that takes 12v center positive).
I find that when I hook it all up the 18v works, the 9v works, but the 12v powers up the pedal just fine, but a massive hum whenever its connected to the 12v. No him when I use the 9v and/ or the 18v. But adding the 12v center positive with the polarity reverse cable, the him shows up. Huuuuge hum.

What should I be looking for? Is there a problem with running two rectifiers from the same transformer winding? Should I have split the 12v and 9v rails after a shared rectifier?
Or could it be something to do with the polarity reversal?

Thanks everyone for advise on this!

jnTracks said:

I built myself a custom power supply for my pedal board. My requirements were pretty specific and nothing on the market met my needs.
I have several 9v pedals, one 18v, and my effectrode tube drive takes 12v and 1200mA on a center positive jack.
So I made it like this: 2 transformers. an 18v 1000mA and a 12v 2000mA.
18v transformer > rectifier > 220uf filter cap > 18v regulator > 100uf filter cap > output.
12v transformer goes parallel to the 12v and 9v "rails", just like the 18v rail only with different voltage regulators to match the desired voltage. Each rail has its own independent ground. So the 12v and 9v rail share a transformer winding, but it feeds independent rectifiers and so on down each rail is all isolated.

I put this all together and it tested great. Each rail with the proper regulated voltage.
Note: I wired all the outputs center negative and got a polarity reverse cable to connect my tube drive (the one that takes 12v center positive).
I find that when I hook it all up the 18v works, the 9v works, but the 12v powers up the pedal just fine, but a massive hum whenever its connected to the 12v. No him when I use the 9v and/ or the 18v. But adding the 12v center positive with the polarity reverse cable, the him shows up. Huuuuge hum.

What should I be looking for? Is there a problem with running two rectifiers from the same transformer winding? Should I have split the 12v and 9v rails after a shared rectifier?
Or could it be something to do with the polarity reversal?

Thanks everyone for advise on this!

Click to expand...

If rectification is done by bridge rectifiers, the 9V and 12V supplies cannot share a single winding. Pls post schemo.

Oh shoot. I sure did use bridge rectifiers. (Learning time)

I don't have a schemo of what I built, but I used this as a guide
https://www.generalguitargadgets.com/pdf/ggg_ps_rps_sc.pdf

Picture three of these and the 9v and 12v fed from the same winding.

Is there a solution like using diodes for one or both of the rectifiers? Or is the only solution to use independent windings for each rectifier?

Thanks!

Or, another idea: what if I feed two different voltage supplies (220uf cap > regulator > 100uf cap > output) parallel from one rectifier?
In that case they would need to have the same ground in order to conduct from the same rectifier, right? But they would not be isolated from each other.

So do I have two solutions here? Either non-isolated voltages from the same rectifier or add another transformer so each of the rectifiers has its own winding.

jnTracks said:

Or, another idea: what if I feed two different voltage supplies (220uf cap > regulator > 100uf cap > output) parallel from one rectifier?
In that case they would need to have the same ground in order to conduct from the same rectifier, right? But they would not be isolated from each other.

So do I have two solutions here? Either non-isolated voltages from the same rectifier or add another transformer so each of the rectifiers has its own winding.

Click to expand...

You can't produce a positive AND a negative voltage from a single winding...well, you can, but they would be single-wave rectified, which I don't advocate.
Anyway, if your effectrode thingy really requires 1.2A, you're already using most of the juice your xfmr can produce; that's because AC amps= 1.4 DC Amps. That means you draw 85% of the xfmr's capacity.
Just buy another xfmr for your 9V rails. That will be safer, cleaner and more flexible.

OK, I actually do have a 9v transformer laying around.

Thought I'd save space on the box.... Oops!

Thanks for your help!

I designed an accessory power supply years ago to replace a bunch of wall warts with a single 1u rack mount supply. The problem when trying to power a bunch of single ended gear with a common power supply often the common ground connection from a common power supply can cause rouge ground currents that inject hum into audio, not to mention some power supplies can use transformer windings differently (I know I did).

My solution was a little too expensive for the market, I used a single custom transformer with 6x 1A secondary windings so each output was fully isolated and worked exactly like separate supplies. Unfortunately this product that everybody loved and said they wanted, was too expensive for everybody to buy. Go figure... that's what happens when you listen to your customers.  8)

Second guessing myself decades later, I could probably make a crude single transformer power supply to mimic the separate windings more cheaply. Still questionable if it's worth the trouble.

JR

so now I added a third transformer.  so each section of the supply has it's own winding.  everything tests out at the right voltage.  I plug in the pedal board and still there is a hum when the 12v is plugged in. it's a lot quieter now.
I tested different configurations: only when the 12v is plugged in is the hum there. any of the other outputs can be used and there is nothing.  also the hum is in the power because if I plug the supply into the wall with the amp but plug my guitar directly into the amp, not going through the pedals, it still hums when the 12v is plugged in. 

i'm starting to ramble here.

any more ideas? maybe I need to shield the transformers from each other? they are bolted to the top of the supply.

Shielding might work, but first you might also simply try rotating the 12v transformer (while it's making the humming noise) and see if that helps.  If the transformer is picking up hum, then there is probably a sweet post where it doesn't pick up hum.

i saw Jason Bonham in a small club a while back, he had a very good guitar player with him that was less sloppy than Jimmy Page, which is not saying a whole lot, so the git player is setting up and i see him stuffing 9 volt batteries into 6 or 7 stomp boxes, i am thinking "what a hassle, does he do this every night?", i guess he had the same problems you have, or maybe the batts give a better sound,

so you might try a rechargeable battery setup, with proper fusing of course,

zero hum from batts, maybe a little shot noise as the electrons hit the plates, but i wonder who many other pro musicians still use batteries,

there might be a way to convert the offending effect into Tip Positive,

when i had a string of Fulltone boxes wired up, i had the biggest hassle with the one effect that had the reverse polarity, i think it sets up a ground loop that is hard to get rid of,

if i had to do it all over again i would get some D cell Sanyo Cadnica's and wire up a wall wart to charge them and have a disconnect switch on the charger,

you would need 2 sets, and those puppies are 15 bucks a pop and they do have a limited life span, but if you are going to be famous, cost will be no object,

now i'm not much of a boozer anymore, but i did get a kick out of Jason hauling a large  ice chest up on stage and setting it next to his kit, i guess Dad did the same thing and he was trying to do everything just like dad, playing 5 sets and drinking 6,

now why would a world famous drummer who many think was the best in rock have a drinking problem?
well, if your guitar player started writing songs like Hot Dog instead of Black Dog,
jus sayin...

jnTracks said:

so now I added a third transformer.  so each section of the supply has it's own winding.  everything tests out at the right voltage.  I plug in the pedal board and still there is a hum when the 12v is plugged in. it's a lot quieter now.
I tested different configurations: only when the 12v is plugged in is the hum there. any of the other outputs can be used and there is nothing.  also the hum is in the power because if I plug the supply into the wall with the amp but plug my guitar directly into the amp, not going through the pedals, it still hums when the 12v is plugged in. 

i'm starting to ramble here.

any more ideas? maybe I need to shield the transformers from each other? they are bolted to the top of the supply.

Click to expand...

Your tube thingy draws 1.2amps; you hav eto size the smoothing cap accordingly. You need at least 1200uF. I would recommend lager (min 2200uF, 4700uF if it fits in).

abbey road d enfer said:

Your tube thingy draws 1.2amps; you hav eto size the smoothing cap accordingly. You need at least 1200uF. I would recommend lager (min 2200uF, 4700uF if it fits in).

Click to expand...

ah, that's interesting.  would that account for the noise it puts in the wall power? because plugging in the 12v pedal adds noise to the guitar amp even when the pedal isn't in the audio path (guitar straight into amp, not through pedal board)?

jnTracks said:

abbey road d enfer said:

Your tube thingy draws 1.2amps; you hav eto size the smoothing cap accordingly. You need at least 1200uF. I would recommend lager (min 2200uF, 4700uF if it fits in).

Click to expand...

ah, that's interesting.  would that account for the noise it puts in the wall power? because plugging in the 12v pedal adds noise to the guitar amp even when the pedal isn't in the audio path (guitar straight into amp, not through pedal board)?

Click to expand...

But the 12V supply is connected to the pedal, correct? And the pedal bord is not connected AT ALL to the amp?

Right. I was testing it. Amp and pedal board supply are plugged into the same outlet panel. When I plug in the 12v pedal the noise starts. (It's a true bypass pedal so I can test out my signal through the board with out the pedal plugged in. )  so then I pull the guitar cable put of the pedal board and go straight into the amp. Pedal board not connected to the amp. Still when I connect power to the 12v pedal the noise happens.
So I has to be putting the noise into the power, not the signal wire, right?

what kind of effect is the offending 12 volt box/

maybe if we can find a schematic we can figure it out,

Your pedal is a=out because of your true baypass, try unpluggin it completle, just leave 12V to the pedal and a wire directly from guitar to amp with no pedals at all in the middle

JS

joaquins said:

Your pedal is a=out because of your true baypass,

Click to expand...

You can't say that. True by-pass does not disconnect the ground. If the ground is heavily polluted by strong rectification currents, true by-pass won't eliminate noise.

try unpluggin it completle, just leave 12V to the pedal and a wire directly from guitar to amp with no pedals at all in the middle

Click to expand...

What I don't explain is that, according to jnTracks, he has completely disconnected the pedal board from his rig, the only remain connection being the power cable...?

abbey road d enfer said:

joaquins said:

Your pedal is a=out because of your true baypass,

Click to expand...

You can't say that. True by-pass does not disconnect the ground. If the ground is heavily polluted by strong rectification currents, true by-pass won't eliminate noise.

try unpluggin it completle, just leave 12V to the pedal and a wire directly from guitar to amp with no pedals at all in the middle

Click to expand...

What I don't explain is that, according to jnTracks, he has completely disconnected the pedal board from his rig, the only remain connection being the power cable...?

Click to expand...

that's right, the amp and the pedal board power supply are plugged into the same wall socket. I tested with the pedal board in the signal chain, and also with no pedal board in the signal chain.

the pedal in question is an Effectrode Tube Drive.  positive tip 12v 1.2A supply, it needs.
so far it's been suggested that I need bigger smoothing caps on the 12v rail of my supply to handle the high current of the pedal, but does that explain why the noise goes into the power line even when the pedal is not in the signal chain? (guitar direct to amp)

the other complication is the tip positive jack on the pedal.  I am using a polarity reversed power cable to connect it to the supply.  that should be right.  it tests correctly with my DMM.  just mentioning cause we seem to be stuck.

JohnRoberts said:

I designed an accessory power supply years ago to replace a bunch of wall warts with a single 1u rack mount supply. The problem when trying to power a bunch of single ended gear with a common power supply often the common ground connection from a common power supply can cause rouge ground currents that inject hum into audio, not to mention some power supplies can use transformer windings differently (I know I did).

My solution was a little too expensive for the market, I used a single custom transformer with 6x 1A secondary windings so each output was fully isolated and worked exactly like separate supplies. Unfortunately this product that everybody loved and said they wanted, was too expensive for everybody to buy. Go figure... that's what happens when you listen to your customers.  8)


JR

Click to expand...

I still have one of those .... 6 x 16.5v ... ?  with lamps to light the rack too.

Marty.

jnTracks said:

that's right, the amp and the pedal board power supply are plugged into the same wall socket. I tested with the pedal board in the signal chain, and also with no pedal board in the signal chain.

Click to expand...

May I assume that both the amp and the pedal board PSU are grounded?

so far it's been suggested that I need bigger smoothing caps on the 12v rail of my supply to handle the high current of the pedal, but does that explain why the noise goes into the power line even when the pedal is not in the signal chain? (guitar direct to amp)

Click to expand...

that's what we're trying to understand, and why we're asking all those nosy questions [/quote] the other complication is the tip positive jack on the pedal.  I am using a polarity reversed power cable to connect it to the supply.  that should be right.  it tests correctly with my DMM.  just mentioning cause we seem to be stuck.
[/quote] Again another nosy question: if I remember well, you opted for a separate xfmr for the 12V rail. Then this rail should be left floating. Then you wouldn't really have to worry about the polarity. You say you use a polarity reverse cable; it shouldn't be necessary. You could use a straight cable and wire the socket accordingly, i.e. with positive tip. I'm somewhat confused and think that maybe you have reversed twice, 1st the socket, then the cable...