Pedalboard Power Supply Issue

[Bonzai_Musik]

Hi,
I'm making a DIY Pedalboard with an integrated power supply, thought I'm having some trouble with the power supply.
I ordered one from AliExpress (to feed a MXR Mini Iso Brick), it was center positive so I desoldered the dc jack and flipped the polarity.
But now once I plug it in, it keeps flashing I'm guessing because the power supply doesn't feed it enough current ?
Though it is the recommended 2 A and 18V.
If you could confirm, cause this never happened to me.
But it seems strange that it would take up 2 A right away with no pedals plugged in.
Thanks for your help.

 

[ccaudle]

The manual says:
"Each output features a green LED. When lit, this LED indicates
a good connection. If short-circuited or overloaded, this LED
will turn off."

Not sure how to interpret that "indicates a good connection" wording, but it may mean that the LED does not stay on until that output is actually providing power. Have you tried connecting a pedal to one of the outputs to see of the green LED comes back on?

 

[Bonzai_Musik]

Yes, and my pedal just turns on and off, pretty much like the iso block,. But if there isn't a good connection, how come my multimeter reads a steady 18 V ?

 

[AnalogPackrat]

Your PSU may have a minimum load requirement to function. Does the isobrick work with its 18V wall-wart supply? I've never had trouble with mine, but reviews indicate there are some QC issues at times.

 

[CJ]

You can build a battery supply, I have two, a 6 D cell land fill special, and a vape pipe supply which uses 3 batts which are rechargeable but can burn your house down when they go into meltdown while you are watching Adams Family reruns on nick at night,

 

[Bo Deadly]

What is the AliExpress supply? If it's SMPS, they have certain load requirements like a minimum load and maximum capacitance. For example, if the iso-brick think has a bunch of large caps, the SMPS might interpret that as a short and modulate the output off and on which you will see as the LEDs blinking slowly. This is known as "hiccup mode".

Another issue with SMPS is that they can modulate the output at a low frequency of say 2kHz when the load is too low. This can easily create a whistling noise in the supply which may bleed into the signals of devices being powered.

In both cases, the solution is to add a capacitance multiplier to the output of the SMPS. This will slow down the output so that the SMPS does not see a short. And, if designed correctly, it can filter out modulation noise due to underload (the ideal solution is to not underload by adding a shunt regulator).

A capcitance multiplier circuit is very simple but for 2A, you would need a two transistor version like this:


[graphic stolen from this page]

 

[Khron]

... Or same-polarity transistors as in:

https://sound-au.com/project15.htm

 

[Brian Roth]

Keep in mind a capacitance multiplier is generally not "short circuit proof". A short on the output will commonly cause the "pass" transistor to fail....usually as a short between collector and emitter.

Bri

 

[scott2000]

Some of those DC jacks have that 3rd terminal thing that does something...Can't recall what I'm trying to think of.. Anyway, it'll goof things up if the negative supply isn't connected to the correct terminal of those jacks... and it'll show the correct voltage...