Power Isolation Module

[Big Monk]

I'm looking for a simple module to place inline between my power supply and my digital pedals, such as the Strymon El Cap and Flint and my NuX Roctary. I'm thinking similar to the GigRig Timelord.

I'd like to have a small enclosure underneath the board where I can run cables to from the main supplies and have the 3 outs be isolated.

My main issue is that my Otraki power supplies, while marketed as fully isolated, seem to be allowing digital noise (in the form of a high pitched whine) to leak into the audio path through my Strymon Flint:

https://www.amazon.com/OTraki-Universal-Isolated-Supplies-Protection/dp/B07F69KR6K/ref=cm_cr_arp_d_product_top?ie=UTF8

The supplies themselves are very nice and are very low noise otherwise. I've contemplated simply ponying up the $100 or so for a used Strymon Ojai (5 9v 500 mA, fully isolated outputs) but just wanted to touch base at the forum to see if there was an easier and cheaper solution.

[Kevin Mitchell]

After looking at the product photos, I kind of want to call their bluff on what they mean by "isolated".

Any chance you could snap a photo of both sides of the power supply's pcb? Because I'm not seeing one regulator per channel in those photos.

[Big Monk]

After looking at the product photos, I kind of want to call their bluff on what they mean by "isolated".

Any chance you could snap a photo of both sides of the power supply's pcb? Because I'm not seeing one regulator per channel in those photos.

Sometime this weekend I'll unmount one from underneath and snap some pictures.

I'm not buying that the supply is fully isolated but also it's on $35! It gives me plenty of outputs for my other, non-digital pedals.

Ideally I'd like a DIY option for 3-4 isolated outputs where I could run a power wire from the Otraki into the separate box and then have isolated outputs for those.

Like I said, worst case scenario I'll just pick up a used Strymon Ojai and have outputs dedicated for high current draw digital pedals. That way I can segregate them from the rest of the pedals and my other 2 supplies.

[R.G.]

Your ohmmeter can tell you whether the outputs are actually "isolated". I've seen some supplies marketed as isolated where the isolation was just a separate regulator for each output, but they all shared a common ground. Set your ohmmeter to read ohms and read the resistance between the supposed-to-be-isolated grounds and see if they are high resistance between them as they should be.

As a word of caution, it is not necessarily simple or cheap to design and build a DC-DC isolator module. These will always involve some kind of oscillator and this is nearly always a switching section to make the DC into AC to get across a transformer. That is, it's a switching power supply itself. And this brings in all of the issues with switching power supply noise again. A DIY switching power supply will generally not have the benefit of all the testing and tweaking that make good switching power supplies quiet, so it may not be much help.

There are good, quiet, and cheap power supplies intended specifically for pedals on the market in most countries. Often, these are available for under US$100, sometimes as little as US$25 for a single output.

[Big Monk]

Your ohmmeter can tell you whether the outputs are actually "isolated". I've seen some supplies marketed as isolated where the isolation was just a separate regulator for each output, but they all shared a common ground. Set your ohmmeter to read ohms and read the resistance between the supposed-to-be-isolated grounds and see if they are high resistance between them as they should be.

As a word of caution, it is not necessarily simple or cheap to design and build a DC-DC isolator module. These will always involve some kind of oscillator and this is nearly always a switching section to make the DC into AC to get across a transformer. That is, it's a switching power supply itself. And this brings in all of the issues with switching power supply noise again. A DIY switching power supply will generally not have the benefit of all the testing and tweaking that make good switching power supplies quiet, so it may not be much help.

There are good, quiet, and cheap power supplies intended specifically for pedals on the market in most countries. Often, these are available for under US$100, sometimes as little as US$25 for a single output.

Thanks R.G. I was just reading through your Spyder article for some inspiration.

Frankly, I only need 4-5 300-500 mA isolated outputs specifically for the digital pedals on my board to isolate them. I'm having issues finding pre-built supplies that have more than 2 of these high draw outputs. I'm currently searching for a Strymon Ojai at a good used price as that is really the ideal solution.

Would the Spyder in a truncated 4-5 output size suit me.

[R.G.]

The Spyder concept could do it, but not the actual transformer as shown. The small transformer can't transfer enough power through the small-wire windings.
The article "Power Supplies Basics" runs through some of this. For a 500ma 9V power supply, you need two volts more than that (11V) for headroom on a 7809 regulator, and 800ma to 900ma current rating on the winding. Mouser has the Triad F20-1000 in stock for $11.92. This gives you two 10vac @1A secondaries. Using two full wave bridges with filter caps can give two 14V 600maDC outputs suitable for regulating to 9Vdc at 500ma. I checked for single output trannies but single output 10-12V @1A transformers go for about $9-$10, so if you need multiple outputs, the F20-1000 is a better deal. Four outputs will run you on the order of $30 in parts plus the trouble of building and the required skills of doing safe AC mains wiring.
Remember - it's not worth dying for.

[niektb]

I'm seeing inductors so I think they might as well be switching power supplies... (possibly noisy if filtered improper).
The product you linked to is definitely not isolated. (although the first half may be separated from the second half, as in different regulator)

[Big Monk]

I'm seeing inductors so I think they might as well be switching power supplies... (possibly noisy if filtered improper).
The product you linked to is definitely not isolated. (although the first half may be separated from the second half, as in different regulator)

Those Otraki supplies are convenient and very quiet except for when my Strymon pedals are hooked up.

It became very clear, very quickly that they are not isolated as advertised.

[Big Monk]

The Spyder concept could do it, but not the actual transformer as shown. The small transformer can't transfer enough power through the small-wire windings.
The article "Power Supplies Basics" runs through some of this. For a 500ma 9V power supply, you need two volts more than that (11V) for headroom on a 7809 regulator, and 800ma to 900ma current rating on the winding. Mouser has the Triad F20-1000 in stock for $11.92. This gives you two 10vac @1A secondaries. Using two full wave bridges with filter caps can give two 14V 600maDC outputs suitable for regulating to 9Vdc at 500ma. I checked for single output trannies but single output 10-12V @1A transformers go for about $9-$10, so if you need multiple outputs, the F20-1000 is a better deal. Four outputs will run you on the order of $30 in parts plus the trouble of building and the required skills of doing safe AC mains wiring.
Remember - it's not worth dying for.

I appreciate the words of caution, sincerely, but I have experience building tube amps so I'd exercise the same caution I do with power supply work in those.

Thanks for the info and specifications.

[Big Monk]

I ended up going with this:

https://www.amazon.com/gp/product/B084C33NPM/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

After sourcing parts, building the things, etc. this price would have pretty much been a wash. 10 fully isolated outputs, 7 of which are 300 mA, 1 at 500 mA, and 2 at an adjustable 9/12/18v at 500 mA.

Can't go wrong. If it works out, I'll just grab another and sell off my Otraki supplies.