A new Drumulator in the workshop.

This time, it is the machine of a French musical group which made itself known in the early 80s. History does not say whether or not this machine was part of the first successes of this group. Good question, by the way...

I have to admit that of all the Drumulators I have worked on, this one is in the best cosmetic condition. Almost perfect.

Let's go for the identity of the machine:

With the owner's tour of the exterior done, the big question: what about the interior? Because I was given to seeing dramatic things, of the true-false geek type who tried to add sound ROMs but who above all succeeded in crashing the machine by adding an incredible number of wires and modifications to the motherboard etc, which took me hours to remove!

In addition I have doubts about this Drumulator: result of tests or naval battle?

But no, there too, a nice surprise inside. No catastrophe in sight, at least other than a breakdown due to the machine itself and not as a result of outrageous tinkering.

We see very clearly that the machine has been updated with version 3 of the firmware for MIDI management. A MIDI input adapter card has been added as required, and placed/glued correctly. 

It is even possible to say that the original ROM was removed with a screwdriver since we can clearly see the surface condition of the first resistor above the ROM whose coating was burst with the place which served as a support for the screwdriver.

The battery has never been changed. Luckily, it didn't sink. I checked her, she's dead. As a result, sequence saving should no longer have been working for a long time. I imagine it is mainly used in MIDI.

You will have to remove it anyway and place a standard 20CR32 support somewhere on the case.

Little check, at least the voltage selector is correctly positioned on 230V:

Small observation, the motherboard also has an identification number. It is not the same as that of the machine :

The usual checks having been carried out, what is the problem with this machine? At first glance, it seems simple since the machine does not turn on at all.

Power problem or CPU boot problem? Again the first observations are simple, the motherboard does not have any DC voltage. Neither on the analog part, nor on the digital part.

We go back to the source: no sign of alternating voltage either at the two secondaries of the transformer. Hmm... We're getting closer!

The mains voltage nevertheless arrives at the primary of the transformer. No sign of heat or burnt, it does not seem that the machine was connected to 110V.

All that remains is to test the primary windings which are, at 230V, connected in series. The observation is clear, one of the two primaries is cut. The transformer is therefore inoperative.

This is very strange. Transformer connections appear good. No burnt rifle, no burnt marks, no hot smell. What could have been the cause of this breakdown? A manufacturing defect in the transformer?

Now knowing this machine quite well, to further investigate I will connect the digital part of this Drumulator directly to the 5V of a protected laboratory power supply. Even if the processor does not start, this will allow me to check the approximately real 'digital' consumption of the board.

A few days later:

After connecting a direct current power supply directly to the two terminals of the diode bridge of the 5V part: 1.2A at 6V at the output of the power supply, although programmed for 10V, and 0V at the output of the large 5V regulator placed on the metal part of the case:

Simple conclusion: regulator dead. I forgot to specify, but according to tests carried out on different Drumulators, in normal operation, that is to say with the displays on, the average consumption of the digital part of a Drumulator is around 1.2A. So, with the regulator in the regulation loop, I already have the 1.2A consumed and 0V in power on the logic circuits.

But at this stage, I still have to confirm that it is indeed the 5V regulator that is dead. So this time I connected the DC power supply set this time to 5V, directly in place of the Drumulator regulator output. To do this, I cut the three wires connecting the 5V regulator to the motherboard.

And this time, I have consumed 1.2A but with the logic circuits supplied at 5V. Confirmation therefore that the 5V regulator of the Drumulator is indeed dead. But, obviously, the machine does not start.

The design problem of this machine remains for me the detection of power supply operation. EMU has implemented a complex system to ensure that the machine's three power supplies are present in order to authorize the microprocessor to exit RESET. This doesn't do much except make testing the operation of the machine much more difficult. For example, it is impossible to test the digital part if the analog part is not powered. The best thing to do is to remove the power supply monitoring circuit and directly shunt the validation outputs to the desired potential.

All the transistors in this section are used to test the validity of the machine's three power supplies, and also to generate the processor RESET signal. RESET signal that this system generates poorly, which deteriorates over time, and which ends up no longer working at all. This is obviously also the case on this machine.

And I'm not talking about the different power supplies generated in all directions, which must be provided as best as possible during the test phase in order to put the digital part in 'potential' starting condition.

Brief! Having spent some time making the necessary modifications just to get this machine into potential boot condition, I ended up getting my favorite message on the displays:

At this point, I can only confirm that the 'computer' part of the machine is working. I don't know anything yet about the waveform sequencer part, nor about the analog output.

The only thing I can do right away is to change the faulty digit:

I seem to have one or two displays of this type in stock.

I will now pause troubleshooting this machine. To continue in better conditions, I need to redo the power supply, starting by finding a compatible transformer, i.e. with two output voltages available, as well as replacing the original 5V regulator with a switching model, more reliable and dissipating much less heat :

I have made this type of modification on several machines with very good operating results.

Drumulator Clone...

That's it, I've pretty much placed all of my ideas regarding my recreation of the Drumulator. I obviously added some goodies compared to the original machine.

Now I have all these components to place on a PCB:

Hmm, that's not my favorite part of the job...

[06/09] After a few hours of work, here is the general idea of ​​the front panel:

You will have understood, it's new, but old style version, because... I like that too.

[06/15] There's always a moment when you wonder if you're going to make it!

Anyway, I continue to place the components. It only remains for me to place those dedicated to the 'simple' output filters and as well as those dedicated to the commands/display of the machine :

Like that, it seems clear and well arranged, but what will be the routing with all these signals!!!

[06/16] After a few more hours of work, it becomes clearer...

3D visualization, even if it is not perfect, still allows you to get a fairly close idea of ​​what the printed circuit board will look like:

All you have to do is try to route all the connections. It might be 'sporty'!

Drumulator : It's progressing

There it's done. The audio output tests I'm preparing for my Drumulator clone works fine.

I present to you the prototype of the audio output of my new Drumulator:

And, in order to demonstrate the perfect functioning of the board, here are a few seconds of video. 

(Click on Youtube to have more details)

For the moment I don't have a suitable camera but I was able to use DaVinci to select only the clearest part of the video, and export it to Youtube. You have to start by testing the tools at least before embarking on large publications...

Drumulator in FPGA & OMEGA MSX computer.

THE DRUMULATOR

I continue the experiments of recreating the audio outputs of the Drumulator.

At this stage, I know that I am able to read all the Drumulator sounds correctly with the digital/analog converter used, once the data has been passed through the decompression table to the µLAW standard.

But, for the moment I reproduce the sound directly at the output of the audio converter. I now have to test on the one hand the individual volume adjustment part then the sample&hold outputs, in order to verify that the reproduction is going well on all the outputs.

It's a bit complicated because in order to minimize the need for board routing, I opted for serial interfaces for all the commands. Originally, the interfaces are of the parallel bus type with all that this implies of buffer circuits and bus locking.

And above all, I like to condense ;-)

Apart from the analog converter and the serial control circuit, I use the same components as those present in the Drumulator, just to preserve as much as possible the sound signature of this machine.

THE MSX OMEGA

This morning I received a package directly from Poland. Even if I blurred some information on my home address, I note that the French postal service still retains within it, some real clairvoyant eyes. I doubt that it happened correctly in the machine-reading system... Long live to the world of real people!

And what's beautiful inside this 'survivor' package? 

Everything you need to build a great case for the OMEGA board. All I have to do is find the few screws needed to fix the board to the bottom of the case. Interesting thing: I find that my USB to OMEGA keyboard conversion interface fits perfectly inside the box without any problem. I should even have room to attach a USB connector to the front panel. From the cutout informations, I thought my interface wasn't going to fit inside. In fact, it does it very well and I'm very satisfied!

The difference in this version is that there is no cutout for the Omega keyboard as originally planned since I am replacing it with a USB keyboard. I indeed thought that it was not going to be practical to type on the keyboard placed in the high position. I was right. It will be much more practical with a 'normal' keyboard.

So, I'm thinking about building a cartridge to easily develop software for the Omega. I know that there are many solutions, including the one that consists of using a ROM cartridge of the MSXROM512 type from Raphnet, on which we place an EPROM emulator to easily upload the code, once validated in the emulator,

but I am going to try to develop a cartridge that can be loaded natively via a USB port and also equipped with a serial port. 

Because in fact, I'm not very 'games' with computers but rather communication. I would love to connect this Omega somehow to the NET.

Many thanks to Krzysztof Odachowski for the realization of this enclosure...

Drumulator in FPGA & MSX news &...

It's been a few weeks since I posted anything. However, I worked on four simultaneous subjects.

• Troubleshooting the CSQ600.
• The development of the MIDI switch.
• The finalization of the USB keyboard converter for Omega.
• The test of the audio output of my future Drumulator. 

CSQ-600: 

Unfortunately, I couldn't get the machine to work. However, I installed a new processor, but the result is strictly identical to that of the original processor. I just managed to have a different start of the machine by replacing the original oscillator with a signal generator. The result is insufficient for me to get an idea of ​​the problem for now. After a few days of intense investigation, I momentarily put the subject on hold.

MIDI SWITCH :

I made some progress on the subject. I mounted a module with four RJ45 inputs/outputs as well as a small conversion 'pod' to MIDI IN/OUT. I'm currently stuck because I can't get my hands on the small processor used on the PODs. Fortunately, I recently found availability for this processor and ordered a few copies. I am awaiting delivery.

USB KEYBOARD CONVERTER :

I am pleased to announce that the development of this interface is finished. I finalized the code for 'AZERTY' and 'QWERTY' type keyboards. As a reminder, this converter allows you to connect a standard USB keyboard to the MSX OMEGA microcomputer. Also, I'm waiting for some components to manufacture a few copies that I will make available for sale for those who wish to go through this solution rather than building the OMEGA keyboard entirely.

The Omega computer

AUDIO OUTPUT FOR MY FPGA DRUMULATOR :

I completely coded the processor part as well as the waveform sequencer in VHDL. The goal is to fit as many logic elements of a Drumulator as possible within an FPGA. So I still had to study the audio output. 

The problem is of course, that the kind of digital to analog converter used in the Drumulator is absolutely no longer available. The solution adopted therefore consisted in using an available 12-bit converter, and in coding the system making it possible to reproduce the logarithmic transfer function of the original converter.

For this, I started to mount a copy of my analog output prototype:

Quick & dirty test plateform but sound very good!

To do my tests, I used a development board from STmicro equipped with a fairly powerful STM32 processor. This kind of board associated with the ST development software is really ideal. Once the system was set up, I encoded a square signal at 1KHz using Audacity which I exported in µ-LAW format to the development board. The result gives what was expected:

For this kind of test, low precision required and low frequency, the (toy) FNIRSI-1014D is ideal because it does not generate any fan noise. This allows you to leave it on for hours without wanting to throw it out the window at the end of the day ;-).

Finally, I replaced the sinusoid definition file with the one from the copy of the original Drumulator ROM to see the scrolling of all the sounds of the machine, given that I scan the whole 64K of ROM.

In fact I obtained the same result as that obtained by testing the waveform sequencer implemented within an FPGA, by directly sending the addresses to the ROMs present on the motherboard of the Drumulator test:

Basically, I have 'proof' of all the important parts of the Drumulator working. It only remains for me to test the analog output filters, knowing that there are recent components to replace the old SSM present in this section of the Drumulator. Each part works 'in its own corner'. Now it's all about putting it all together on a large prototype board.

I left my job with the madmen of the French national education since a few weeks, and life is much more pleasant now. I develop what I like, at my speed... Peace for ALL!