SOLVED 4 Tap DC Isolator - Help me be smart

[Lytt Effects]

Ok, so I built one of the 4 Tap DC Isolators with the intention of using it as an off-board power supply for my “amp” setup, which is a UAFX Dream and Ox Stomp off-board. When I built the 4 Tap, I made sure to get the highest mA output I could find at Mouser, which was 330 mA, for each output.

Dummy me, I didn’t check the mA requirement for the UAFX pedals, which naturally require more than 330 mA. According to UA, they need at least 400mA, and I did test the current draw on each of them, which ranged from 350-375 mA. Fair enough.

Then, I had the idea that I could just double up the current from the outputs since I really only need two, and I built up some current doubling cables to do so. To do this, I twisted together the + leads of the cables coming off two of the outputs, twisted together the - leads off of the same two outputs, and then soldered them to the single cable + and - leads that go to a single DC power jack. I believe this is the correct way to do this, but please correct me if I’m wrong.

I’m using a OneSpot 9v 1A supply to power the 4 Tap. Each output is working properly, and will power a normal drive pedal just fine. When I attempt to power the UAFX pedals, things get weird. When I power either UAFX pedal with just one output, the pedal will continuously power cycle. This makes sense, as it is just under the mA requirement for the pedal. When I double the current and use two outputs with the current doubling cable, it will power up, but will then power cycle every 30 seconds or so. If I plug in both the Dream and Ox using just the current doubling cables, the repeated power cycling occurs for both pedals.

What am I doing wrong? Is this unit not capable of this, and I’m just dumb and should stop trying? Did I build the cables incorrectly? Any help would be greatly appreciated, and I can take pictures if necessary, just let me know what you need.

 

[giovanni]

In theory this sounds reasonable but in practice you’re probably seeing issues because of the specs of the devices and whatever interaction they are having. I wouldn’t pull this thread if I were you. If you can’t find a chip with higher amperage I would look for a different solution.

 

[jwin615]

For one, you're probably pushing the one spot to its limit.
Probably loosing some current through the isolator via it's effeciency(check the datasheet).
The isolator isn't really the right product to power two high current digital devices either. Gonna put this in the bucket of "just because you can doesn't mean you should". Really more for isolating fuzzes and picky charge pump circuits.

What part did you pick from mouser?
Curious if that 330mA rating is constant or peak.

 

[Lytt Effects]

@giovanni & @jwin615 thank you both. I guess in theory, my thinking was “these are isolated outputs, should work just fine” but in actual practice, not so much. I had a feeling, and I knew going into it that it likely wouldn’t work, but figured I’d come to the actual smart people and see if I was just doing something wrong.

I guess I’ll just have to run two separate wall warts for the off-board instead of one, oh well!

The part I ordered from Mouser was this:

https://www.mouser.com/ProductDetail/490-ITR0305S09

 

[jwin615]

Yeah, those are running ~90% efficient. So, your 9v one spot is getting close to maxed, maybe more on boot. They may be taking turns resetting each other

 

[Lytt Effects]

Yeah, those are running ~90% efficient. So, your 9v one spot is getting close to maxed, maybe more on boot. They may be taking turns resetting each other

Makes sense. I will mark this as solved, and a great success in not damaging anything!

 

[Lytt Effects]

Yeah, those are running ~90% efficient. So, your 9v one spot is getting close to maxed, maybe more on boot. They may be taking turns resetting each other

Just one quick follow up, as I'm learning all of this on the fly and y'all are so very helpful.

So the four outputs are all the 333mA max draw on current. So, I'm guessing that juicing it with the OneSpot is fine so long as I'm running low draw things like fuzzes, drives, etc., correct? Is it an issue that these outputs are rated so high since the OneSpot can only provide 1A max? I'm guessing it's fine, as they will only put out what the circuit will draw, but just want to make sure. Also, let's say I dropped it down to the 222mA output component. Would this help me achieve my goal of doubling the current and joining two outputs to make it work? It'd be an expensive swap, and I really don't feel like doing it, just more curious than anything.

 

[jwin615]

As expensive as those UAs are, I would just use 2x one spots.

Okay. So the ole energy can never be created or destroyed applies here, as always.
A one spot can only output 1 amp at 9v. That's 9 watts.
But, the isolators eat ~10% in efficiency. So you can only have 900mA max out at 9v, or ~8.1 watts.

You could put 1 amp isolators/DC converters in the brick but you can not output more than ~900mA due to the 1amp limit of the one spot. Also, it's not ideal to run any PSU at full output capacity.

To answer your other Q, yes, that isolator would work great for other pedals, as intended by design.
It's value is really in that. Positive ground fuzzes and isolating heterodyning charge pumps is where it's most useful.

Now, if you use a higher wattage PSU and beefier converters(needing a new PCB layout), it's doable.
But this seems like a lot of trouble and costs to have one PSU instead of two.
Something like this mean well converter would work well. Feed them with a medical grade 24V 2A brick.

 

[giovanni]

Just one quick follow up, as I'm learning all of this on the fly and y'all are so very helpful.

So the four outputs are all the 333mA max draw on current. So, I'm guessing that juicing it with the OneSpot is fine so long as I'm running low draw things like fuzzes, drives, etc., correct? Is it an issue that these outputs are rated so high since the OneSpot can only provide 1A max? I'm guessing it's fine, as they will only put out what the circuit will draw, but just want to make sure. Also, let's say I dropped it down to the 222mA output component. Would this help me achieve my goal of doubling the current and joining two outputs to make it work? It'd be an expensive swap, and I really don't feel like doing it, just more curious than anything.

Yeah as long as your total draw is below the 900mA max that the OneSpot can give you in total (you should try to keep it even lower than that), that should work with the 333mA devices. They won’t draw all that current all the time, only what they need. So you could easily plug 4 fuzzes or phasers or probably even analog delays and it should be fine.