Success at last!

Finally! The hihat started working five minutes ago :-)

I did a lot of debugging on the circuit itself:
- touching up on all solder joints in the HH circuit
- checking every single path in the HH circuit (measuring conductivity)
- checking every solder joint through a magnifying lense
- measuring every resistor value
- checking that no electrolytic capacitor legs had broken off

Through all this I found a few suspicious solder joints, as well as created (and later discovered) a short circut. I also found three errors in the 9090 Hihat schematics, two of which does not matter and one that certainly do - however, the PCB is the correct one...

Anyway - I am not sure of any of this actually had much to do with the error. After taking a very close look at the various connectors involved in the HH, I discovered that a crimp in the HH tune connector was bent out of shape. It makes sense if this was the error, as it would affect both the closed and open hat. After replacing the crimp, I put the PCB back in the box and hooked up all cables - and whaddaya know, it works! :) Now, this was the last known HARDWARE error (excluding the rotation encoders that are just anoying, not really an error).

I also tried moving the headphone amp away from the circuit board to remove the noise (after all the previous supply line tricks failed to do so), however, this did NOT work. The noise in the stereo mix main out is not that bad though.

Now all I have to do is put everything back together again, and pray for everything to work once that is done :)


The bent crimp is seen through the right hole.

Output working

No idea why, but when I switched back to the old output stage, it worked perfectly fine. Some loose connections somewhere, bad solder joints or something maybe.

However, this means that untill the problem comes back again, I will leave the circuit board in the box. This also means that I won't replace C6 and C7 (changing from 1uF to 10uF would have improved the bass responce as the 1uF filters away anything below 140Hz, greatly impacting the bass drum when tapping the signal from the stereo mix jacks).

Now, if I could only get that Hihat working again. Tried swapping U42 for a new, known good opamp, but no luck.

Also, I will try moving the headphone amp away from the box to see if I can get rid of some noise.

New output mixer tested

Instead of unmounting the entire circuit board from the machinebeats, I decided to make a new output mixer on a prototype board. The output mixer consists of 7 components - four capacitors, two resistors and an TL072 opamp (+ the necessary connectors), which means that I only need to check a very limited amount of circuitry on the original board if the new one works.

Well, after 1 1/2 hours of building, and 10 seconds of testing, I conclude that it is indeed one of these 7 components or attached solder points that don't work as intended. I still have to remove the circuit board, but at least now I know where to look :-)

Cymbals fixed

The cymbals and hihat have never been loud enough, rather, they've been much quieter than the rest of the voices.

Today I searched through the archives at yahoo groups, and discovered that this is a well known problem that has a known fix. After replacing three resistors, the cymbals are much louder :)

However - the stupid silent hihat is back. Earlier this year I had problems with the hihat not triggering (or not making any sound at least). When I put a probe from my oscilloscope to either the collector of Q73 or pin 2 of U42, it worked, but when removing the probe it stopped working again. Somehow I managed to make it stay working, but now it is broken again. No idea why, this really frustrates me!

Also, the main output is way too low and the main output pot is working the wrong way, turning DOWN the sound when moving to the right. Strange.

Modding the power wiring

Just finished rewiring the internal power lines tonight. I have had some serious problems with digital noise in the headphone stage. The headphone amp drew power from the same board as the midi controller and other digital electronics reside on. I have changed this so that it now draws power from the card closest to the transformator. Also, I have re-added a 5v voltage regulator to the controller board and added a separate ground wire. I hope this fixes some of my problems.

While having the lid off I've also added the missing 500ohm (or actually dual 1k in parallell) pot to BD Accent, so now I thing everything except for the too-low samples/output levels are fixed. Fingers crossed, will test tomorrow!

Progression

So, I got several things fixed friday.

One led had actually broken (though only the red part, the green was still working), one had been short circuited by solder (very strange!) and one was simply working but since the key didn't work it was not possible to activate the step.

As for the keys, after unsoldering the left-key I discovered that one of the pins had been bent on assembly. Bending this back out and resoldering the key fixed the problem. I also remembered that, since this key has always been broken, I did a work-around in software to be able to complete the code - I remapped the first step key to work as the left-key. This, however, means that I have to build a new version of the firmware to fix this.

Now, the sampled sounds are another strange case. As no sound could be heard, and it has been working previously, I tried swapping in the old sample ROMs for the new ones (Crash cymbal only). This worked! But even stranger, when the crash started working, the ride cymbal also seems to work. Hi hat is still broken though. I will try swapping in all the old chips to see if they work. If they do, my conclusion is that there's something fishy with the new chips.

When it comes to the output mix, I did some testing with a stand alone headphone amp circuit, and could clearly hear the sound playing - but at a very low volume. I tried swapping the mixing OP-AMP, but this didn't do the trick. However, at the same time I noticed that the separate outputs are very clean and free from digital/powersupply noise! This means that the noise heard when using the headphone output is either introduced in the mixing stage or in the headphone amp itself. I have to investigate this further.

Yesterday I also managed to put together the front panel inner/outer assembly for the first time. After trying several ways to get things together, I came to the conclusion that the parts have to be put together in the following order:

- First, insert the upper part with the display and pots.
- Then insert the lower aluminium plate, but without the circuit boards.
- The keypad then has to be wiggled into place from the right, between the top plate and the spacers extending from the lower plate.
- Now, screw the two plates together using two countersunk screws.
- Connect the keypad to the main keyboard and the main keyboard to the controller
- Slide the keyboard under the front 'lip' of the box and screw it to the bottom plate.

Voila! Everything should be in place :-D

Today I will hopefully start attaching the new wires for the potmeters. I will use a technique called wire lacing to keep the wires together, instead of using plastic strips. This will make the bundle less rigid and saves a lot of room since the thread used (waxed linen cord) toes not protude from the cable bundle :-D (Thanks dad, for learning me how to do this back in the early nineties :-D)

Still pushing for a July deadline, but some issues may have to be worked out in September. Here is a shortlist of what I think is missing:

- Rewire pots
- Change the power for the backlight and side lights
- Recompile the code
- Fix the samples
- Fix the output stage, check introspectiv groups to see what they wrote about the output level being too low
- Get a stereo 1k pot for the Bass drum attach, solder the channels together to make a mono 500Ohm pot.


Also, it would be nice to do the following:
- Figure out where all the noise comes from. Will be a bit hard though.

Yesterday was a great day...

So, what's the news?

Well, assembly is going great, and yesterday I powered up the machine for the first time after wiring it up. At first nothing happened. After a few scary minutes I figured I forgot to put the fuses in the power entry connector :-)

Next problem - nothing showed up on the screen, and something smelled funny... The keyboard and sequencer seemed to work though, but no sound could be heard.

After a bit more debugging, and an hour of work, the following was fixed:
- New cable for the display - six of the wires had snapped!
- The smell came from the display backlight overheating, I have to switch to a less powerful current source or something
- The missing sound was due to the two midi wires going from the controller to the analogue parts being swapped.

So, after working for a couple of hours the machine actually works!

It does however have some errors:
- The sampled sounds (Hi hat, cymbals) don't work
- The main output doesn't work (though the headphone amp works very well)
- The first step key and the left-arrow key are mixed up somehow
- Four leds are either broken or a data line is not working as intended.
- The software is slightly buggy, it crashes sometimes. No idea what causes this.

Also, the wires from the pots have to be replaced as they are too big, and the spacers between the keyboard and the aluminium back plate are too short, making it impossible to mount the display and keyboard at the same time.

All in all I'm quite satisfied with the result. I brought the machine to work today for a little demo, and my colleague rocked away ;-)

Fall is here

Fall is here, and it's time to get this thing working! Today I've found the last (?) glitch in my PCB design - I've forgotten to connect the mixing bus'es to the headphones amplifier. This was the reason I could not get any sound. Fixed that and it works perfect.

Also, I am getting some noise from the crash symbal. Tried to switch the crash and ride cybal rom chips, but the noise still came from the crash. Thus, I believe I need to get a new rom chip.

This means that I have to purchase:
1 head phones pot
1 rom chip, 24c256.

As for other electronics, I think the only thing missing is the red backlight for the LCD screen.

The bottom part of the box is (hopefully) on its way from the US now. Next up is a silk screen set...

Oh, and I've soldered several of the modular synth modules too - still need to make a Midi2CV converter though, in order to test them.

Finished programming (!?)

This is a great day. The sun is shining, it's about 29 degrees outside (This is Norway and it's not even June yet, so that is pretty good). And the drum machine code is now ready for extensive testing. I guess there are still some small bugs in there, but now all major and minor functionality is finished and the machine is playing cool rythms :-D

Next up will be to get some silk screen equipment and start work on the box. Also I've had to come to terms with a few shortcomings with the current controller design. The LEDs flicker a bit while the sequencer plays, and the encoders are a bit unstable. To overcome this I will have to build a completely new controller again (v5), with a separate led controlling circuit, and with dedicated encoder chips. However, everything works ok, so this wont happen for a while.

I had to re-make the ribbon cables between the controller and the keyboard as well. Half of the numeric keyboard didn't work due to some stupid wiring mishap. Now the only key that doesn't work is the left-key. I'm not sure why yet, have to get my multimeter out and start measuring :-D

I guess this wraps things up for summer, have fun untill the cold winds of fall makes it possible to be inside coding again :-D

Encoder experiences

The encoders on the drum machine keyboard are working now. The missing leads discovered earlier were not the only obstacles I had to overcome. After fixing the circuit, the encoders still didn't work properly. For some reason, I had not thought about what would happen when the encoders stood still and did not have a connection to +5v. This, of course, would lead to floating inputs on the direction-detection flip flops, and no clear readings from the circuit.

I then added 10k pull down resistors to all the inputs, this fixed most of the problems and made it possible to detect encoder clicks.

However, if the encoder is turned slowly, one click of the dial leads to multiple detected clicks, as the circuit keeps outputting clicks, as the flip flops are not reset.

To fix this, I've added a state check in software. Clicks will only lead to events if a 0 has been read in between two reads of 1. This fixes most issues, but quick turns of the dial will in fact give fewer clicks than slowwe turns. Also, I've experienced a few 'backward' clicks in between the forward clicks, not sure what causes this.

But, all in all, things are looking very bright. The mode selection leds light up and respond to the encoder. Now I'll just have to get the rest of the keyboard up and running againg. And fix the head phone amplifier and get a license file for my compiler...

Oh, how I hate hardware bugs...

I must have misplaced my head while designing the keyboard PCB.

The last two days my girlfriend and I have

1) Checked all the ICs involved in the rotary encoder circuit
2) Checked the functions of the rotary encoders
3) Checked the PCB routings for any errors or broken paths.

We didn't find any errors on the ICs, they all performed flawlessly on the bread board.

As for the encoders, they seem to be of different kinds. The tempo encoder seems to stay permanently connected to +5v and send out pulses of 0V (or rather, it varies with the position of the encoder), while the mode encoder stays at 0 and sends out pulses of +5v. Not sure if this is a problem, but it has to be checked.

The routing, however, is a different story. First of all, although it is not possible to see why when inspecting the PCB, the connection between the tempo encoder and pin 5 on the left flip flop IC is broken! This may have happened when the IC overheated earlier.

More important though, I have not routed +5v and ground to the ICs! This is a mistake made in Gschem, the software I used when designing the circuits, I simply must have forgotten to attach the necessary pins to the power connector :-(

So, right now I have to:
1) swap the tempo encoder for one similar to the mode selector one.
2) connect pin 5 on the left flip flop to pin 1 of the tempo encoder
3) connect pin 14 on the right flip flop to pin 2 of the tempo encoder (5v)
4) connect pin 7 to pin 8 on the right flip flop (ground)

...then we'll see what happens.

Success!

Everything works like a dream now :) I've implemented all commands and tested the keyboard using the second controller as a loopback. It looks so good I can hardly stop working on it :-D

I may have to simplify the transfer protocol a bit though, to get increased throughput. Hopefully I can skip some error checking if I just make sure that no invalid state leads to a deadlock.

The remaining work on the keyboard is now:
- Glue some of the perspex pieces in place so they don't obstruct the keys
- Drill holes for the rotary givers and implement the necessary code
- Cut and solder the paths for the second row of instrument select buttons
- Fix the keys on the keypad that are not working (two signal paths)
- Fix a problem with S528 - it seems one of the switches does not work very well (a key release is send immediately after key press). I suspect this is a hardware error.

And then - onto coding the controlling software! Can't wait!

Low sound level fixed!

I have found the error in the amp circuit, and I am rather embarrassed about it... Take a look at the pictures below to see if you can spot the mistake faster than I did. the components and input signals are fitted closest to the camera:

Before inserting a jack

After inserting a jack

So, what is it? I soldered the components to the wrong pins! When inserting a jack, the connectors are lifted, and there is no more connection between the jack and the signal pins. Why I could get any sound at all is beyond me!

mark: I will not use this crappy thrown together output circuit in my final design, but it's nice to have while waiting for the real thing.

Good news everybody!

I have worked out nearly all the errors now. The single-channel problem was due to a broken down line mixer in my rig. The low output level must be somewhere between the output from PCB005 and the stereo output (i.e. in the mix amp) as all separate outputs have a very high output level :-)

As for the two missing sounds (hi-hat and crash cymbal), I DID partially break the PCB while trying to de-solder a socket (stupid, I know, and I promise I've learned my lesson: NEVER try to de-solder a $1 part if you may break a fully populated rare PCB... *sigh* - and I was very much aware of the risk beforehand, but it was late and I had misplaced the DIL socked).

Guess it should be possible to fix both errors shortly!

Ahh... :-)

On another note - the sounds are rich and beautiful. Big thanks to Trevor Page and everyone else involved in creating the clone!