Building an Ambika synthesiser


The reason I decided to build an Ambika synthesiser are probably fairly unique. I had stumbled upon the Shruthi synthesiser by accident and upon a quick read and a YouTube video I was instantly hooked.

I became aware of the Ambika while building and researching the Shruthi but to be honest it looked a bit out of my price range and perhaps a little ambitious construction wise, especially programming the microcontrollers.

It wasn’t until I accidentally acquired an Ambika motherboard that I actually started to seriously consider the possibility. How can you accidently acquire an Ambika motherboard I hear you ask? A long and boring story of problems that I won’t go into, anyway the motherboard was quite a considerable cost to the project, I know if you total up all the components it probably isn’t but it’s the single most expensive so in my deranged way of thinking I could just get the parts as I could afford them and hopefully learn along the way when it came to programming the microcontrollers. So that’s how I came to begin building the Ambika synthesiser.

So as I had the motherboard PCB, that was where I was going to start. After a bit of reading I realised I could build and test the motherboard on its own which for me was a nice surprise. I’m one of those electronic constructors who like to build things bit by bit and test them as much as possible as they go along and getting to the finished tested and working motherboard seemed a realistic target.

building an ambika pcb top side
building an ambika pcb bottom side

Showing both sides of the Ambika motherboard PCB.

First thoughts on components

The first real worry for me was that there were a lot of components that I had not really used before and some were very specific. Like the push button switches for instance, they had to be an exact to fit on the PCB the same as the Midi in and out sockets. I later found out that the ¼ inch PCB mounted audio sockets aren’t the standard ones used on the Shruthi but slimmer and are almost impossible to find.

I keep a stock of common resistors, capacitors and common semiconductors, IC sockets and stuff but it was clear I was going to have to order some difficult and specific parts.

Getting started on the Ambika motherboard

The instructions on the website inspired me with a lot of optimism

1. They are written in a step by step method

2. They are very comprehensive and don’t skip or gloss over anything

3. At the beginning there is a link to a how to solder guide (I liked this as I already felt further along than some who had got this far!)

Something to note early on is that components get soldered on both sides of the PCB and it’s quite easy to end up soldering one on the wrong side (I say quite easy. It’s probably not but I managed it!)

As you might know it’s not much fun trying to desolder from a double sided plated through board especially if you don’t want to damage it and it the cost of the Ambika motherboard I certainly didn’t want to damage it. I have a link here to an article on desoldering if you have to go down that route.

So by following the Ambika website and starting with the motherboard construction I set about the first step on fitting the first few resistors. Check and double check before you solder them in place. I even used a component tester to measure the resistors before I soldered them in place.

There is a note about the 0R resistor on the PCB for the display backlight. Some need a wire link and some need 100R resistor, I couldn’t find anything in the documentation for my display about the backlighting so to be safe I fitted a 100R resistor, having dim or no backlighting as opposed to burning out the display seemed a better option and I could always change it later without removing it as I could just solder a wire link over it.

I just followed along with the instructions fitting the other components step by step, the crystal, the resistor networks, again I used a multimeter to check the values and the fact that the dot was correctly showing the right orientation. Then onto the pre-set resistor and diodes, this lead me to the first unfamiliar components, the 1N5819, apparently they protect the regulators from weird things that can happen during the power on/off phases! I didn’t want anything weird happening so a made sure I got the exact part for these.

Next up were the ceramic capacitors and the IC sockets, the instructions mention that the kits didn’t have sockets for the IC’s mounted on the top side of the board but I decided to mount sockets. I always use them for IC’s! Then some electrolytic capacitors, making sure they go the correct way round and then the 3.3 volt regulator, again an unfamiliar part for me the MPC1700.

Again just following along with the website instructions I fitted the power socket and the other regulators on the required heat sinks. Bear in mind to use the LM2940-8.0 and not a 7808!

I also used heat sink compound on the regulators before bolting them to the heat sinks, something my old electronics boss taught me at Leicester University. I just can’t get out of the habit now. Still not sure if it makes any difference or not!

Then the other larger electrolytic capacitors and then something else I was unfamiliar with that took a bit of tracking down to order, the connector for the SD card. Its surface mounting soldering but not the fiddliest kind. I only tried surface mount soldering a few months before and I didn’t find it as scary as I had thought it would be.

Carry on to the Midi sockets, again check you get the right footprint as there are different ones available and then the header pins can be soldered in. The header pins are the component that I mentioned before that I soldered on the wrong side. So let’s be careful out there!

The ¼ inch PCB audio connectors

I didn’t initially fit these as I couldn’t find the slim one’s that fit on the Ambika motherboard PCB. This won’t be a problem in testing most of the Ambika motherboard PCB functions but I made another mistake in assuming that without the sockets I could just use the main output. You can’t because the PCB mounted sockets are wired in such a way so as if you plug an individual lead into a socket, it takes it out of the main mix so you won’t get any output at the single mix output without either mounting all the individual sockets or linking all the sockets out with individual wires, which is quite time consuming and messy to remove when you get the right sockets. Bear this in mind.

Mount the LCD display as instructed with the connector and spacing nuts and then the dual colour LEDS. I hadn’t used these before but like the instructions say the worst that would happen is that they would light the wrong colour. Not the end of the world for me.

Nearly there now but for a few specifically sized components, I’ve used encoders and PCB mounting resistors before but this time I was hoping I’d got the correct ones to fit the PCB footprint, luckily the potentiometers, switches and encoders fitted, result!

I didn’t do the step of fitting the spacers for the voice cards at this stage because I didn’t have them and they wouldn’t make any difference when it came to the testing.

Testing the Ambika motherboard.

After the usual visual test and multimeter short tests I connected up a 9V AC supply and went through the voltage test as per the instructions, all of the voltages checked out ok.

Programming the ATMega644

It’s worth mentioning at this stage that this took me several weeks to get and solder in the parts although reading it back makes it sound like a few minutes work. During this few weeks I had acquired a Usbasp programmer from Amazon.

 

I had also acquired an ATMega644 and nearly enough knowledge to program it. I say nearly enough because I didn’t quite know as much as I’d thought as you will find out later in this article.

I did my reading up on the internet and connected up my Usbasp, downloaded the software for the programmer and the program for the ATMega and got familiar reading and writing to the chip so I felt confident I could do it. Failing to be able to burn the ATMega meant I would have to source a preprogramed one which could be expensive and time consuming and let’s face it we all want to know how to do it ourselves, that’s part of the fun/torture!

So I programmed my ATMega and plugged it and the other IC’s into the Ambika motherboard having previous checked the voltages I was reasonably confident that I had done a decent construction job and there was a very decent chance it would work.

So I plugged the supply up and no bang. Always a good sign, some LED’s flashed and the LCD lit up and upon twiddling the viewing pre-set, words appeared on the screen. Bingo I thought it’s all working but sadly it wasn’t. Although it started on the correct filter page and the potentiometers altered the values, the push buttons didn’t function so I couldn’t select any other pages.

I mistakenly thought I’d soldered something in wrong and set about checking where I thought the fault would lie.

Push buttons, wrong sort or in the wrong way.

Resistor arrays in the wrong way stopping the buttons from working.

Maybe the ATMega, so a programmed another but with the same results.

I couldn’t find anything wrong that I’d done which was in one way good but in another way frustrating.

I took to the internet to ask questions but the answers just asked me to try the hardware things I’d already done. This went on for several very frustrating days.

I had noticed that when I turned the motherboard on it took about twenty seconds for the display to start displaying the filter screen.

Thanks to the guy on the forum who said it sounds like the ATMega is running too slow, have you checked to see that you’ve set the fuse bits properly.

Set them properly? I didn’t know what they were I hadn’t set them at all.

I bit more reading on the internet and a bit of experimenting and I realised that I had to run another command prior to the one that programs the ATMega to set the fuses, without that the ATMega doesn’t run at the correct speed.

So I quick run through setting the fuses and then the programs, and upon plugging the ATMega644 back in it started up in lightning speed time and all the buttons and controls worked perfectly. So two weeks of head scratching and testing my hardware construction was wasted. I’d just miss understood how to program the ATMega644 properly. Notice the bit at the beginning where I said nearly enough knowledge!

I have now written a full article on programming the ATMega’s for the Ambika synthesiser here. It became so big it needed an article on its own, again not too difficult if you take it step by step.

The bright side was that I now had a fully functioning Ambika motherboard ready to build the complete synthesiser.

Building the Ambika voice cards

I had figured that by now I had done the hardest part. If I could get the Ambika motherboard going a voice card shouldn’t be that difficult. I could just build one little card and get that working and then it was just a case of duplicating that five times.

So here goes building voice card number one.

Again the instructions on the website are great and step by step, I just followed them, starting with the resistors again. Following that the zenar diode and crystal, the ceramic capacitors, the trimmer and two small LEDS.

Next were the IC sockets and electrolytic capacitors. Note that there are two capacitors that are 4u7 C1 and C21. These are values that to me are normally polarised, however the voice cards call for audio non polarised ones. They are available but harder to track down. I don’t know what would happen if you put polarised ones in. Something unpleasant maybe so I didn’t risk it.

I found these ones on amazon.

 

Next fit the film capacitors, the board has holes for both sizes and they are linked already on the pcb so some holes won’t be used, when I checked it at a later date I thought I’d missed some components off, what an idiot!

Finally fit the transistors. I say finally but there are connectors to fit.

Connectors and spacers and nuts and stuff.

I couldn’t find the correct connectors for the Ambika motherboard and voice cards. I spent ages looking at all the major component suppliers that I’d usually used.

I have a link here to an article about buying electronic components here.

I eventually found what I was looking for on Amazon under the title of Arduino shield 2.54mm tall stackable. They seem to be the key words but they don’t mention them in the instructions, that’s what you’re looking for, I’ve put a link in below.

   

I also ended up using Amazon for the hardware stuff. I used black nylon M3 nuts and bolts and the hex threaded standoff spacers again in black nylon all M3. They are spacers hexagonally shaped with an M3 threaded hole on one end and a protruding M3 thread on the other so they can be stacked or have nuts and bolts while holding PCB’s they were cheap from Amazon and I bought loads because I can see them being really handy for future projects, and stuff like that costs a fortune from the normal component suppliers. Using these meant you didn’t need the blank ended ones like you do if you follow the instructions, you just screw one into another with the PCB in between.

 

 

There are three spaces for voice cards on the motherboard and they double up with one on top of another to fit in the full six, but depending on whether they are on the motherboard or stacked they have to be set as either “A”or “B” with a two jumpers on each voice card. I decided just to hardwire a link instead but be careful when you plug them in that they are in the correct place.

When the first board was complete I put all the IC’s in their sockets including the ATMega328p plugged it in to the connector then bolted in in place with the nylon spacers and powered it up. I then connected up the Usbasp with the ISP lead and set about programming it.

I’ve written a complete article about programming ATMega’s for the Ambika synthesiser here. This mentions ISP programming. It was my first attempt at it and it certainly made it easier with the voice cards.

After a few seconds of programming the two LEDS on the voice card changed status to indicate all was well. I connected up a midi keyboard and the midi data indicator on the motherboard display indicated note data was being sent and the voice card LED’s flashed as the notes were pressed but nothing came out of the mix output on the motherboard. If you were reading earlier it was because you need to have all six ¼ inch output sockets wired in. fortunately it didn’t take too long to figure this out.

All was working with a single voice card

I built the other five cards all together and plugged and bolted two more onto the motherboard and programmed each with the Usbasp and ISP lead and each blinked into life shown through their respective LED’s. I then plugged in the three remaining voice cards piggy backing them into the first three and using the M3 nylon spacers and nuts. Then programing them in turn with each blinking into life. When you attach a Midi keyboard you can see each voice card cycling through as you play different keys.

building an ambika mothboard and voice cards

The completed mothboard and voice card assembly.

Setting the filter volts per octave pre-set

The last thing to do is the only setting up you need to do and that’s on each voice card. You need to tweak the one pre-set to set the correct keyboard tracking for the filter. The easiest way to do this is to use a tuner, I use this one for all my tuning needs, cheap and accurate.

   

 

Set the card to produce no sound by turning off both oscillators and then set the filter to low pass and with the resonance set to maximum the filter will oscillate producing a tone like a sine wave.

The filters frequency will alter the tuning and you need to tweak the pre-set on the voice card so playing notes an octave apart on the keyboard produces notes an octave apart on the tuner. You will only get it to track over a couple of octaves, that’s normal and that completes the setting up.

As for the rest of the construction I decided not to follow the design of the case and go with my own.

building an ambika white card panel

This is the printed on white card front panel.

I’ve already done an article on how I make cheap panels here. I decided to mount everything on one panel so that meant putting the output jacks on the front as well so I had to make the panel I bit larger. I did my unusual design the panel and get it printed onto thin white card and then drill a Perspex sheet to go on top, trimming the card behind and using the panel mounting components to hold it all together.

building an ambika perspex panel

The drilled perspex sheet.

 

Incidently, the drill bits above are the ones I use for drilling perspex sheet. I tried various other normal, carbide and high speed drills but still managed to shatter the perspex, the ones shown above have been excellent in use and are esspecially good for larger holes as I needed in my panel.

Then the idea is to fix it in a box with wooden end panels.

building an ambika finished panel

At this stage I hadn't found any suitable knobs.