Looking for guidance on modifying a midi controller and building a midi thru box

[Fantom_GT-201]

Hey everyone,

I just stumbled on this forum via a google search and it seems a great place to get some help and guidance on electronics and midi.

I've got a project that I've had the concept of for well over 18 months and I've now got the drive and enthusiasm to throw myself in to it and get going.

The project is stripping down a 2 octave midi keyboard and making some modifications then building it into a keytar. Then along with that, use a Behringer FCB1010 to control and perform with my Korg M3 module.

The modifications I want to make to the midi keyboard are as follows:

-original power switch was 3 way, 8 pin. 1=usb, 2=off, 3=battery/dc. I want to change it to a two way rocker switch and eliminate the off position. To turn it off I'd set it to usb without a cable connected.

-remove unwated connections. I have no need for the sustain pedal jack, mains connection or the midi in, so that's just a simple case of solder sucking.

-reposition midi out and power switch.

-wire pins 1 and 3 of the midi socket to the power receiving part of the board.

then electronics aside, build a wooden body for the keytar.

To send power to the keytar via midi I plan to make a midi thru box with one midi in and two midi outs. The in and one out I plan to connect pins 1 and 3 to mains power to send down the midi cables to the keytar and modified behringer fcb1010 (this is a common mod with many guides on how to). The other midi out I plan to be unpowered for instances where I want to use the keytar without the pedal board.

The pedal board has a midi merge out which acts like a midi thru and midi out from one socket thereby combining messages from the keyboard and from the pedalboard both being sent to my korg m3.

Here is a crude diagram showing the end result I hope to achieve:

Now that I've explained my project, the reason I'm posting is because I'm a blank slate when it comes to electonics. I know how to solder, but beyond that, I'm not very keyed up.

The first thing I need guidance on is the replacement power switch for the midi controller. I need the switch to perform the function on the image below and preferably have a build in power led as well.

Can anyone please help me out with the technicals so I can find the right switch to buy and then move on to the next step?

Cheers in advance,

Fantom_GT-201

Edited January 14, 2012 by Fantom_GT-201

[gomiboy99]

Hi, welcome to the forum.

Your concept is interesting.

The switch on the keyboard, I assume it is of the slide type, a simple 2 way rocker switch (DPDT or double pole double throw) would not give a USB position to turn off the power. It would do what you want according to your diagram.

Please watch out for the potential to feed the keyboard electronics with the wrong or too much voltage. If it has an external supply connector for a mains adaptor input then the keyboard probably has its own regulator, but if it only has a USB socket (aside from midi) the it is likely that the keyboard will only work with a 5Volt DC supply.

The midi thru box could be made like this one. Although it shows 7404 chips, 7407 or 74ls07 chips are a better bet.

When feeding power along a midi cable you will need to be careful with the current consumption of the device you are feeding. Most 5 way din cable use thin wires and these will not carry more than a few hundred milliamps, the voltage is also a limiting factor here. Feeding AC alongside a midi signal could cause interference to the midi data.

Hope that helps.

Tim

[Fantom_GT-201]

Hi, welcome to the forum.

Your concept is interesting.

The switch on the keyboard, I assume it is of the slide type, a simple 2 way rocker switch (DPDT or double pole double throw) would not give a USB position to turn off the power. It would do what you want according to your diagram.

Please watch out for the potential to feed the keyboard electronics with the wrong or too much voltage. If it has an external supply connector for a mains adaptor input then the keyboard probably has its own regulator, but if it only has a USB socket (aside from midi) the it is likely that the keyboard will only work with a 5Volt DC supply.

The midi thru box could be made like this one. Although it shows 7404 chips, 7407 or 74ls07 chips are a better bet.

When feeding power along a midi cable you will need to be careful with the current consumption of the device you are feeding. Most 5 way din cable use thin wires and these will not carry more than a few hundred milliamps, the voltage is also a limiting factor here. Feeding AC alongside a midi signal could cause interference to the midi data.

Hope that helps.

Tim

Hi Tim,

Thanks for the reply.

The original 3 position slide switch on the circuit board worked like this:

So in order to modify it I need a 6 pin switch like the diagram in my original post and wire it to pins 1, 3, 4; 5, 8 and 8. I hope that makes sense. I did dismantle the original switch to see how it worked and have since tested that by holding wires from pins 3 and 4, and 7 and 8 with batteries connected and it powered up fine.

Just to re-emphasise, when I want to turn off the controller, I'd set the rocker to usb and have no cable connected. To be honest I don't think I'll use the usb that much, but it's nice to know it's there.

The keyboard does have a 9v dc in socket so I assume by wiring pins 1 and 3 of the midi socket to where the dc in socket was, this would act how I intend?

For now I just want to get the midi controller mods done and dusted, then I'll move on to power down the midi cable.

I don't suppose you know what current I'll be running through the new switch or if there is a way I can provide you with info to help me figure it out?

Thanks Tim,

Fantom_GT-201

[gomiboy99]

To wire the switch you will need a DPDT type, this will have 2 rows of 3 pins.

The centre pin in row 1 will go to your pin 3, the remaining pins, one will go to 1 the other to 4.

The centre pin in row 2 will go to your pin 7, the remaining pins, one will go to 5 the other to 8.

The wires to your pin 1 and 5 should be next to each other on the switch and the the same for 4 and 8.

The bottom of the switch would look like this:

1 3 4

5 7 8

The power supply would probably require about 500mA, that is the maximum load for a USB port, this may be a little too much for an off the shelf midi cable. However, I would give it a try anyway.

You can connect it as you describe, just be aware of the correct polarity.

Tim.

[Fantom_GT-201]

To wire the switch you will need a DPDT type, this will have 2 rows of 3 pins.

The centre pin in row 1 will go to your pin 3, the remaining pins, one will go to 1 the other to 4.

The centre pin in row 2 will go to your pin 7, the remaining pins, one will go to 5 the other to 8.

The wires to your pin 1 and 5 should be next to each other on the switch and the the same for 4 and 8.

The bottom of the switch would look like this:

1 3 4

5 7 8

The power supply would probably require about 500mA, that is the maximum load for a USB port, this may be a little too much for an off the shelf midi cable. However, I would give it a try anyway.

You can connect it as you describe, just be aware of the correct polarity.

Tim.

Thanks again Tim.

I've been looking at Maplins (uk electronics store) and ebay. Seems to be plenty of choice. If I want it to have a built in power LED will it have any extra pins, or would the LED get it's power from the pin arrangement you've explained above?

Thanks

Fantom_GT-201

[gomiboy99]

I had a look at maplin's site, they don't do a DPDT illuminated rocker switch that is suitable for low voltage. A lot of rocker switches have a Neon for mains voltage.

Check out Rapid at http://www.rapidonline.com/ or Farnell at http://uk.farnell.com/

Rapid have a good range and Farnell are excellent but have a £20 ex vat minimum order value but it is free delivery(and watch out for stock from their Newark depot which has a £15.99 delivery charge).

You will have to check the specific switch to see if the illumination is by separate pins.

Tim

[Fantom_GT-201]

I had a look at maplin's site, they don't do a DPDT illuminated rocker switch that is suitable for low voltage. A lot of rocker switches have a Neon for mains voltage.

Check out Rapid at http://www.rapidonline.com/ or Farnell at http://uk.farnell.com/

Rapid have a good range and Farnell are excellent but have a £20 ex vat minimum order value but it is free delivery(and watch out for stock from their Newark depot which has a £15.99 delivery charge).

You will have to check the specific switch to see if the illumination is by separate pins.

Tim

Well going from a cost basis, ebay does look like a good option and there is a lot of choice if you do a search for dpdt.

This switchon ebay looks like the thing I'm after. Comes from abroad but it's free shipping and under £2. Should I be wary of inexpensive parts?

Fantom_GT-201

[gomiboy99]

As with everything, you only get what you pay for.

The switch on ebay is designed for mains voltage, do you require the switch for mains or DC?

If you want a switch for DC e.g. 9Volts, then this switch will work but the lamp will not light.

Tim