Simple Power Isolation circuit?

[nguitar12]

Just wondering if any simple power isolation circuit out there to keep the power of each pedal separated. I am not a big fan of wall voltage so if the circuit work on about 12v will be good. So far I am looking at 555 flyback or self oscillating push pull circuit. Just wondering if they will do the job?

[GibsonGM]

There are many 'power supply' schematics available for running your pedals.  Most of them are just fine, they work well.

You need to define your requirements better...why must you keep each pedal isolated??  If they are properly designed, there is no need to.  A good power supply can easily power MANY of your pedals with no noise, no problems...

You will be using 9V pedals?  Or do you have something else in mind, such as 18V?

Why would you need some kind of flyback or switching supply to get 9V??  Those are more associated with stepping up, for tube circuits, in my experience...

Most people use a line-powered transformer and voltage regulator(s) to obtain their pedal supply.  Some do use a SMPS, although that can introduce noise, but does have the advantage of being smaller and lighter.   Many people just buy one (I did, it is fine and did not cost much). 

So - I think you should define more clearly what you are trying to do, as well as 'why'....

[nguitar12]

There are many 'power supply' schematics available for running your pedals.  Most of them are just fine, they work well.

You need to define your requirements better...why must you keep each pedal isolated??  If they are properly designed, there is no need to.  A good power supply can easily power MANY of your pedals with no noise, no problems...

You will be using 9V pedals?  Or do you have something else in mind, such as 18V?

Why would you need some kind of flyback or switching supply to get 9V??  Those are more associated with stepping up, for tube circuits, in my experience...

Most people use a line-powered transformer and voltage regulator(s) to obtain their pedal supply.  Some do use a SMPS, although that can introduce noise, but does have the advantage of being smaller and lighter.   Many people just buy one (I did, it is fine and did not cost much). 

So - I think you should define more clearly what you are trying to do, as well as 'why'....

I used to get a noisy guitar sound when I use a Y-cable to power up multi pedal with the same adaptor. While most of the commercial pedal supply claim that they are isolated each supply to minimize the noise. This make me curious how isolated power benefit to the sound.

I am not try to get a 9v out of flyback/push pull topology. Just because these topology always involved a transformer. Which is a must for power isolation.

[Phoenix]

Mike's right, usually you don't need isolated power supplies, generally it won't fix problems with a two amp system (which can be remedied with an AUDIO isolation transformer - or plugging the two amps into the same power outlet often solves any ground loop issues too), but it can solve issues caused by digital pedals with noisy internal smps's, or negate the issue of "positive ground" pedals like germanium fuzzes.

But, it also never does any harm, and with the proliferation of "boutique" fuzzes and multiple digital pedals, as well as just bigger pedalboards in general, there has been a demand for larger power supplies, and "multiple isolated outputs" is as much about marketing as it is about actual utility.

Anyway, what you want are monolithic isolated DC-DC converters. These are convient little blocks that can be inserted into a circuit with no more hassle than a 3 pin regulator. Make sure to check the datasheets for their operating frequency - 40kHz or above is recommended. Here's a link: Digikey.

[R.G.]

I used to get a noisy guitar sound when I use a Y-cable to power up multi pedal with the same adaptor.

My day job involves engineering support for pedal power supplies, among other things. As GGM correctly mentions, it is entirely possible to have noise free operation of many pedals on single daisy chain power cable. In fact, the vast majority of setups like this work very well. When they do not, it is for one of a few reasons, mostly:
- the power adapter itself makes noise and passes it on to the pedals; the only cure for this is very careful design of the power adapter
- the wiring carrying the power from pedal to pedal is not well designed for low noise, or the pedal inside wiring is not well designed for such wiring
- the pedals themselves generate noise, and pass it from pedal to pedal on the power supply line, especially the ground wire.

Power supplies with isolated outputs can help with the last two of these, but not the first.

The first one - careful design of the power adapter for low noise - is a tough design problem. There are many simple power designs for making an isolated output - but the details of how to make it quiet are not shown on schematics, as it may involve the number and exact path of individual wires and the exact physical location of the parts.

While most of the commercial pedal supply claim that they are isolated each supply to minimize the noise. This make me curious how isolated power benefit to the sound.

Curiousity is a good thing. Knowledge is valuable. You can easily experiment with how truly isolated power supplies would affect the sound. One 9V battery per pedal is the ultimate isolated power supply. So using all fresh batteries would give you the sound of the best isolated power supply. That is how a good isolated power supply would benefit your sound.

[GibsonGM]

Your problem may be some form of ground loop.   And low-quality cables...

As Greg said, you can use 3 terminal regulators to truly isolate each feed. It is a lot of work, but maybe that is what you want?  Personally, I would locate what is causing the noise before I made my supply that complicated, but to each his own 

Edit: I see R.G. just posted right before this.  He has 100,000 times more experience than I do, and I'd follow his advice, LOL...in fact, I have, on numerous occasions!   

[Agung Kurniawan]

how many pedal did you use? is there any distortion pedal? how many gain stage was the distortion pedal have?
back in time Im using 1 power supply to daisy chain all of my pedal (chorus, delay, overdrive, booster, 2 buffer, 2 distortion). and I get lot of noise when my distortion on. even when the gain pot at 12 o'clock. and I can hear ticking sound when I enggage the chorus.

Then I just discover about isolated power supply through this forum. and then build my own. now my distortion became less noisy and they all work best.

my build:


as everyone say, there is a lot of think to do

[anotherjim]

A hidden flaw with multiple DC-DC converters is that their switching frequencies could all be a bit different. That can lead to audible heterodyne noise, even though the switching frequencies are up around 40kHz or higher. Converters that can slave to a master control frequency would solve that problem. Also, they can be worked in a phased manner, so they aren't all sucking heavy current pulses from the DC supply at the same times.

A Pseudo isolated output can be done with star feed with a small value resistor in each 0v. About 4R7.

[nguitar12]

A Pseudo isolated output can be done with star feed with a small value resistor in each 0v. About 4R7.

That is too good to be true if it really works

[rankot]

- the power adapter itself makes noise and passes it on to the pedals; the only cure for this is very careful design of the power adapter
- the wiring carrying the power from pedal to pedal is not well designed for low noise, or the pedal inside wiring is not well designed for such wiring
- the pedals themselves generate noise, and pass it from pedal to pedal on the power supply line, especially the ground wire.

Is it possible that PS with not enough power can produce some kind of noise? I am having a problem with a pedal I recently built, it works fine when alone or on a separate PS, but when connected with others using daisy chain, it hums. More about it here: http://www.diystompboxes.com/smfforum/index.php?topic=98256.msg1092893#msg1092893