Ambika - no midi when connected to mixer

Hi all,

I’ve built Ambika with 6 SMR-4 voicecards. Motherboard and all 6 voicecards works fine when connected to power source and midi keyboard. All 6 orange leds are lid and green leds are flashing when receiving notes. But when i connect master out or any individual out to my mixer or headphones Ambika is no longer receiving any midi signals. This is same if no voicecards are present. Everything else works as expected.

Any help would be appreciated,

Have you tried different midi controllers? Have you tried another power supply? Are there any other symptoms (LCD getting less bright or stopping to update, buttons or pots not responding, etc.)

Hard to say what it is from the information we have, so it would be good to gather some more information.
I’d guess it relates to grounding issues, but that’s hard to say. You could try to insert a 1/4"-jack into one of the outputs and touch a grounded, conductive surface (e.g. metal on a radiator/heater, tap/valve on your kitchen sink, or best: earth tap on a lab supply or earth tap next to the turntable input on your hifi) with the “ring” of the jack on the other end of the cable. Does that produce the same error?


no i haven’t tried different midi controller or power supply. I doubt they are the issue but i can try over the weekend. Because without plugging Ambika to my mixer everything is working as expected. I also connected some wires from computer speakers directly to jack output on Ambika (individual and master) and i could play and hear sound normally.

There are no other symptoms when connecting Ambika to the mixer, lcd is bright and all the switches and potentiometers are working and updating values. Only issue is that there is no midi signal.

I also tried to play a note while disconnected from mixer and than plug it into the mixer and i can hear that note but after that the synth is not receiving any midi signal (the note is still playing). Also i tried all of my mixer inputs and still no luck. I use this mixer with all of my synths (including Shruthi) without any issues.

It sounds like a very weird problem to me… What happens when you remove some of the voicecards? (I’m thinking that you might be overloading your power supply. Although I don’t think so)

Yes, please try another controller and another power supply. It’s good to remove some of the variables from the equation.

Did you try grounding the synth to something other than the mixer, as I suggested above?

I get the same behaviour with no voicecards, or just one or three or any combination :slight_smile:

I don’t have the synth on me so i will try all of the above over the weekend.

Thanks again!

Ok, i tried another power supply and i get the same results. I tried to ground the synth to the body of korg m1 and i get the same results. When i connect midi cable from my computer (usb to midi) everything works ok.

It could be related to the midi controller then. You can check the resistor values on the midi in part of the main board. Maybe there’s an error there?

I’d check around the opto-isolator. Maybe a solder bridge? seems like the isolation isn’t working right and you might be getting some sort of ground loop issue.

this is also helpful in possibly my issue as well.

I’m having the same issue.

It will work fine with Midi from an rm1x or keystep but if I switch to a pc connected mio10 or the keystep via usb from the pc, midi will stop and hang. It took me some tinkering to realize it only hangs when the audio outs are connected to external units, midi will continue the second I disconnect the audio jacks.

I’ve had other ambikas with no issue in my setup so I will try building another motherboard. It will work fine if I connect through an Art dualRDB passive reamping box which I assume has a transformer in it and is isolated. I have other gear all interconnected with audio/Midi patch bays and the Ambika only shows this symptom.

Did you ever find your issue?


no i didn’t. I couldn’t troubleshoot the issue so i just used another motherboard.