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Help cleaning up ripple on 9v 6 channel guitar pedal power supply

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Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Simeon » Fri Mar 29, 2013 7:45 pm

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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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Folderol » Fri Mar 29, 2013 8:42 pm

Those drawings really don't make much sense. I would guess it's on a double-sided PCB and you're not seeing half the trackwork.

Adding rectifiers won't improve the hum level.

Significantly increasing the size of a capacitor (by doubling it up) could put stress on other parts of the circuit - especially at switch-on.

Although I'm always keen to encourage people to get into electronics, mains power supplies are a very bad way to start. You need to have a pretty clear idea of what you are doing to work safely on them.
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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Simeon » Fri Mar 29, 2013 9:08 pm

It's single sided circuit board. Although I just noticed a mistake the ic has 4 pins on the bottom connected to the negative.


Would changing out any parts for better quality parts improve hum?

I think I get what is going on ac gets rectified - hits tranny and voltage is brought down and then the rest of the circuit from the tranny just distributes out the power with some filter I guess to reduce audible noise. That photo coupler I'm guessing is if something over loads on the way back or feedback loop I don't know.

The thing I don't get is those diodes in parallel across the tranny.

That's probably all wrong though.

I just want to improve on noise and make sure I'm not getting ground loop problems.

Would a photo help.
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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Hugh Robjohns » Fri Mar 29, 2013 9:10 pm

Simeon wrote:I want to clean the power up a bit

The diagrams make no sense... But what makes you think the supply needs 'cleaning up' anyway? Have you measured any ripple? A you getting audible hum?

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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Hugh Robjohns » Fri Mar 29, 2013 9:24 pm

Simeon wrote:Would changing out any parts for better quality parts improve hum?


Possibly. Capacitors can dry out after many years and lose efficiency. But usually improving a power supply requires a major redesign, rather than simply replacing components.

That's probably all wrong though.


Yes, I'm afraid so!

It's more likely that the mains 'hits' the transformer first and is reduced in voltage. This lower AC voltage is then rectified (by the diodes, which are probably in a bridge arrangement) to produce 'lumpy DC' which is then smoothed by some chunky capacitors. It would then feed a number of DC regulator chips which produce a clean, stable DC output voltage for each ofthe separate outputs. There will be some additional components around the regulators to set the output voltage and provide further smoothing and decoupling. There could be more sophistication involved -- protection circuitry etc -- but that's the usual kind of arrangement.

There's a typical supply schematic for this kind of application HERE to give you a better idea.

Clearly your understanding of power supply technology is obviously limited at the moment and you really can't afford to mess around with mains power supplies if you don't know what you're doing! I suggest you do some reading up on power supply designs before going any further.

I just want to improve on noise and make sure I'm not getting ground loop problems.


Ground loop problems are to do with the audio wiring, not the power supply. And while a bad power supply can produce audible noise in some cases, it's not just down to the power supply -- the devices running from the supply affect things too.

It's worth asking again: what makes you think the PSU is at fault here.

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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Simeon » Fri Mar 29, 2013 9:41 pm

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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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Hugh Robjohns » Fri Mar 29, 2013 9:43 pm

Links not working.
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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Simeon » Fri Mar 29, 2013 9:59 pm

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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Simeon » Fri Mar 29, 2013 10:12 pm

Like I said I really don't know much about electronics, I'm reading about the basics but still very confusing. I can do repairs, follow instructions and replace parts but I don't really know exactly how things work. I'm pretty sure that single phase bridged rectifier is in front of the tranny.

There isn't loads of hum/ noise not unbearable but by process of illumination it turns out to be the power supply, I was hoping to make some improvements on it.
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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Simeon » Fri Mar 29, 2013 10:15 pm

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.
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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Folderol » Fri Mar 29, 2013 10:34 pm

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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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Simeon » Fri Mar 29, 2013 10:37 pm

Thanks guys for you help. I'm going to plug into my power condition and see if that helps. There is an earth in the box attached to the chassis.
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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Simeon » Fri Mar 29, 2013 11:02 pm

Also did mine second circuit drawing make any sense? Just for peace of mind
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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby ef37a » Sat Mar 30, 2013 7:01 am

Leave it ALONE Simeon!

As Folderol said, that is a switch mode supply and them's evil! At least with a conventional low output voltage supply the dangerous part, mains volts, can and should be made "untouchable", the worst you are likely to do is get burned or bugger it.

Not so for SMPS! The mains goes straight to a bridge rectifier and then a pretty big cap, 220-470mfd often and that charges to mains peak, i.e. some 340volts (cos' we always get 240ish rms?)and that will hurt a very great deal,leave a mark and COULD easily kill you.

If the supply is noisy, bin it and learn from the experience. If you want a DIY pedal power project you could use individual 9V regulators as Hugh suggested and power those from a readily available (and safe!) SMPS "line lump". You will need about 18V at say an amp depending upon the number and type of pedals.

NB I am not agin the SMPSU as a concept. Modern computers could not exist without them. But that is very mature technology and tho' PC supplies are remarkably cheap they are subject to very stringent quality rules. Mind you even so, many computer experts think 5yrs or so is about the lifespan of a PC supply!

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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Hugh Robjohns » Sat Mar 30, 2013 9:14 am

Simeon wrote:Also did mine second circuit drawing make any sense? Just for peace of mind


It's certainly makes more sense... but as others have already said, this is a switched mode power supply, and not the simple linear supply I had previosuly assumed it would be.

SMPS designs are horrendously complicated and fiddly, and massively more dangerous to work on. Like the others I'd urge you to leave this very well alone. There is nothing you can do to modify it in any way whatsoever.

But I ask once again, why you think it is 'noisy' and needs modification anyway? SMPS units can certainly generate and radiate interference if the design is poor, but that's why these things are normally certified.

If you want a decent pedal power supply, there are plenty of quite acceptable designs and kits available on the web, most using the much easier to understand linear supply concept.

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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby The Red Bladder » Sat Mar 30, 2013 11:50 am

I discovered recently that these things have a transient spike protection circuit (a very small cap and a very large resistor) that connects the DC to the AC-in. If the PSU is defective, then this can result in a tiny current, but at full AC being fed to the DC supply. If then the device supplied is not properly grounded, you get mains-hum. It also explains why these confounded things are so very sensitive to a less than absolute earth.
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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Folderol » Sat Mar 30, 2013 8:33 pm

The Red Bladder wrote:I discovered recently that these things have a transient spike protection circuit (a very small cap and a very large resistor) that connects the DC to the AC-in. If the PSU is defective, then this can result in a tiny current, but at full AC being fed to the DC supply. If then the device supplied is not properly grounded, you get mains-hum. It also explains why these confounded things are so very sensitive to a less than absolute earth.
They don't all have that - indeed this one is an example! If you look closely at the two photos of the board itself you will see there is total isolation between the mains and output sides. As a matter of interest if you get one marked as 'medical' there will never be anything bridging the two sides.
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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Simeon » Thu Apr 04, 2013 7:32 pm

Put in 2200uF caps today to replace the 10uF filter caps. all noise has gone almost completely, it's actually very quiet now even with 3 distortion pedals on. There's plenty of room in the chassis for the caps so it was an easy change.
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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Simeon » Thu Apr 04, 2013 7:35 pm

More detail info on these forums if anyone is interested.

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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Hugh Robjohns » Thu Apr 04, 2013 9:25 pm

Ah well... Enjoy the improvement for as long as it continues working...

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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby shufflebeat » Fri Apr 05, 2013 12:00 am

Looks like you're intent on going ahead despite people all over the world saying "this is dangerous, you don't know what you're doing, it's only a throwaway power supply".

All the best, can I have your instruments when you... er, retire from playing?
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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Martin Walker » Mon Apr 08, 2013 1:51 pm

I've just read the Gearslutz thread that Simeon linked to, and it seems he now has another intermittent problem with this PSU, but still seems determined to carry on modding it


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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Hugh Robjohns » Mon Apr 08, 2013 2:48 pm

I wonder how long before it goes bang in a dramatic way, possibly taking out his pedals in the process, and whether he'll then learn the lesson not to play with things he doesn't understand?!

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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby ef37a » Mon Apr 08, 2013 6:11 pm

Hugh Robjohns wrote:I wonder how long before it goes bang in a dramatic way, possibly taking out his pedals in the process, and whether he'll then learn the lesson not to play with things he doesn't understand?!

H
Heh! Bit evil Hugh?
The SMPSU technology has ceratinly "matured". Today I tested two samples of a (nom') 22volt 1.1A supply.
They delivered 21.78volts at 1.09A(just because that was the load I had handy) at all mains inputs from 253 to 90 volts and the voltage did not begin to drop (to 21.56)until the mains in was just 41volts!

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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Hugh Robjohns » Mon Apr 08, 2013 6:27 pm

Good SMPS systems are excellent and I have no problem with them at all. But as you know, they are complex and much harder to understand than linear supplies... as well as being inherently more dangerous to work on.

I am happy to encourage people to 'get into' electronics, but random experimentation with a SMPS isn't even close to being a good idea in my book. Sorry if that comes across as evil...

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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Folderol » Mon Apr 08, 2013 6:39 pm

Any half-ways decent SMPSU has a crowbar on the output to protect against over voltage under fault conditions - at its very simplest a thyristor and zener diode. The above unit doesn't have one, as the O/P is likely to discover if he manages to damage the Optocoupler or associated components.
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Re: Help cleaning up ripple on 9v 6 channel guitar pedal power supply

Postby Simeon » Fri Apr 19, 2013 6:25 pm

Don't worry guys, It's not really happening, I was hoping for a quick fix. Seems to be a intermittent problem depending on the venue, Back to batteries for the time being. You can't polish a turd anyway.
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