Help cleaning up ripple on 9v 6 chnl guitar pedal power supply - diyAudio
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Old 29th March 2013, 08:35 PM   #1
Simbl is offline Simbl  United Kingdom
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Default Help cleaning up ripple on 9v 6 chnl guitar pedal power supply

Hi guys hope you can help me with this one.

I have a Soundlabs six channel 9v dc power supply for guitar Pedals. Pre warning I'm still a beginner, so sorry if the way I explain things is hard to understand, I'm still learning. Also I apologise for my bad circuit drawing. I kinda guessing at the tranny setup up there so ignore my circuit symbol for that.

I want to clean the power up a bit with either some rectification or maybe even a tranny replacement. I have 2X in5817 2x in5816 and 2x in5819 diodes.

-Could I put one in parrallel after the diode (d1) thats already there? then change the 10uf (c1) cap to 470uf so it's the same as (c2).

-There's a resistor (r3) that has been removed from negative to ground? I guess by the manufacturer as a revision. I guess thats got something to do with rfi should I put something in there?.

-Anything I can do to prevent ground loops between pedals?

-would replacing the rectifier with a better one help as well.

Had to draw the circuit in two goes sorry hope it maks sense.
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File Type: jpg pedalpower circuit.jpg (521.5 KB, 123 views)
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Old 29th March 2013, 10:07 PM   #2
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Its hard to tell what's going on there with your diagram. It can't work like that. The bridge rectifier is on the wrong side of the transformer
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Old 29th March 2013, 10:15 PM   #3
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Putting individual regulators on each output can help alot with the noise and interaction between the pedal's power rails. Replacing the transformer and/or rectifier would likely do nothing to help in those regards.
I agree with counter culture, the diagram doesn't make any sense, so it's hard to get specific.
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Old 29th March 2013, 10:31 PM   #4
JMFahey is offline JMFahey  Argentina
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Short answer, don't touch it.
Sorry.

Get help from a friend who has some experience.
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Old 29th March 2013, 10:37 PM   #5
Simbl is offline Simbl  United Kingdom
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Ok I had another go the bits that are shaded in pencil represent the track where it's thicker and has several connections to one place. Seems to make more sense.
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File Type: jpg circuit 2.jpg (851.7 KB, 103 views)
File Type: jpg circuit.jpg (613.5 KB, 108 views)
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Old 29th March 2013, 10:40 PM   #6
Simbl is offline Simbl  United Kingdom
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sorry posted the wrong picture here's the components.
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Old 29th March 2013, 11:15 PM   #7
Simbl is offline Simbl  United Kingdom
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Quote:
Originally Posted by iaxxaxxai View Post
Putting individual regulators on each output can help alot with the noise and interaction between the pedal's power rails. Replacing the transformer and/or rectifier would likely do nothing to help in those regards.
I agree with counter culture, the diagram doesn't make any sense, so it's hard to get specific.
I read in another forum replacing the chip with a lm317 reduced noise. It's a voltage regulator but I can't see where it would go.

Last edited by Simbl; 29th March 2013 at 11:24 PM.
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Old 29th March 2013, 11:23 PM   #8
Simbl is offline Simbl  United Kingdom
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Quote:
Originally Posted by JMFahey View Post
Short answer, don't touch it.
Sorry.

Get help from a friend who has some experience.
I thought that is what this place is for. Sorry I've never traced a circuit out before. I've only ever had to replace parts.
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Old 29th March 2013, 11:40 PM   #9
Simbl is offline Simbl  United Kingdom
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Someone posted this on another forum

"That last photo reveals all. This is what is called a switch-mode power supply. These may look simple but are in fact hideously complex. I've worked in the trade for over 40 years and avoid messing with these things like the plague! It is very unlikely you'd be able to improve it's performance, and the change you suggest would result in a rather big bang! That chip is the switching control chip (which unusually appears to directly drive the transformer).

The input reservoir cap and the output filter cap both look to be in good condition so it's unlikely that there is any mains hum being produced by this unit. Also, like most such power supplies the unit completely isolates the output from the mains - not even earthing it, so it won't be causing any earth loops. That is, unless there is an earth connection elsewhere in the box. "
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Old 30th March 2013, 12:49 AM   #10
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OK, it appears to not have any regulation, just simple RC filters on each output. Is the problem you're having with a bunch of hiss noise in the outputs? Switch mode supplies are sometimes very noisy, though I've noticed most of ones designed to work with guitar pedals (like the Visual Sound OneSpot), seem to not be bad in that regard. If you're having noise problems, I would guess the filtering in this one is inadequate.

You could measure the output voltage and see what it is. To get an accurate reading, you should have a pedal plugged into one of the outputs and powered up so the power supply has a load. Measure the DC voltage across C18, that small cap near the transformer. This should tell you how much voltage is present before the output filters. My guess is somewhere in the neighborhood of 10-12v. If you have in the range closer to 12, you should have enough voltage to work with to be able to stick a regulator in there somewhere and possibly help with the noise problem. If you only get about 9v at that spot, you wouldn't be able to use most regulators to get 9v out of it, because they usually need approximately 1,5v over the desired voltage to get proper regulation.
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