Tuesday, 28 May 2019

Run a Korg SQ-1 Sequencer from a 9V Stompbox Supply

The Korg SQ-1 is a great little sequencer, and one of my favourite bits of kit for its simple hands-on feel and penchant for lucky randomness (I have 3 of them!)

I tend to use it in a live setup with no computer but with a lot of guitar effect pedals on 9V daisy chain cables. The fact that the SQ-1 can only use batteries or USB power becomes a bit annoying so I decided to hack one so it can run on the same power supply as the pedals.

This is a pretty straightforward mod and I actually did this a couple of years ago (just found the photos again :) so I can say it didn't break the SQ-1, which is still working just fine. Also the SQ-1 still works fine on USB power, this mod just gives you an additional option.

However follow these instructions at your own risk and only if you feel confident making electronic circuits. You might break your SQ-1 if you mess this up!

So you're gonna need

  • A 2.1mm barrel socket with plastic body
  • LM7805 +5V voltage regulator (0.5A rating is OK, higher is fine)
  • 2 x 10uF/35V electrolytic capacitors
  • 2 x 100nF ceramic capacitors
  • 2 x 1N5817 schottky rectifier diode
  • Stripboard
  • Wire


Lets cut off a 9x9 hole piece of strip board and build the regulator circuit

The schematic is pretty simple. The 7805 regulator reduces its input voltage (at least ~7V) down to 5V. The capacitors stabilise the regulator. Diode D1 protects the circuit from incorrect polarity input and D2 prevents backflow of current when the SQ-1 is running from other power sources.


(Note: Click on the photos to see the full image if it is cut off)

Here is how I laid out the stripboard. The black and red wires are connected to the power socket.
No track cutting is needed

Take the SQ-1 apart and cut a hole in the end of the case the correct size for your power socket. Please note that the socket needs a plastic body if you are using a BOSS-style centre-negative guitar pedal supply. This is because the SQ-1 case is grounded and a metal socket wired for a centre-negative supply will short out when the case is put back together again. If you are using a centre-positive supply you should be OK.. I think!

Make sure the socket will fit when the case is back together, and that it will not touch any part of the SQ-1 PCB. See the final photo at the bottom of this post to see where I fitted the socket (and please note that the SQ-1 is upside down on the desk in the photo below, the hole is closer to the base than top)



Connect the 5V output wires to the regulator board as shown below. Do not try connect them to the SQ-1 yet! With the power socket wired to the regulator board and bolted to the case, plug in your 9V supply and use a multimeter check that you have a steady 5V from the output wires



Now the scary bit - we need to solder the 5V wires on to the SQ-1 PCB... make sure all power is off, USB is disconnected and batteries removed.

These are the solder points I used for the 5V

Then I secured the leads with tape

I attached the regulator board to the base of the case with sticky foam pads, making sure none of the stripboard was touching the case.


At this point check all connections look good and (depending on your beliefs) maybe say a little prayer or take a long slurp of beer and power up. Press the SQ-1 power button and check it comes on. If it doesn't, disconnect everything quickly and check it all again.

Finally reassemble and you're good to go!


2 comments:

  1. Hello! I did more or less the same mod, using banana plugs in input and using a step down converter (I can use a transformer from 7 to 25v and it will be kept cool due to nature of these high frequency step down dc-dc converters). Thanks for giving me the idea :)

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  2. For audio the ldo is a better solution, because of the dcdc converter noise

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