Wednesday, 20 July 2011


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.

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