From radio case to drum machine case

In the previous post I found the Nordmende radio for housing of the drum machine. It looks like promising starting point for the enclosure, but it will need all kinds mechanical work before it suits to purpose.

When buying the radio, I was hoping the case would have been wood, but it is not, it’s plastic. Everything is a single piece, only the back panel is separate. This does not make fitting the new electronics any easier.

The idea is to attach the sequencer buttons in the lower part of the front panel, where the radio buttons and volume and tone controls have been. All control knobs and switches are located in the upper part of the front panel, where the radio’s frequency scale and dial have been. Because the cast housing has quite complex forms, I modeled it partially in Fusion 360 to get better understanding how to fit the mechanical parts.


The sequencer buttons from eBay fit just nicely to the slot in the lower front panel, but there is one problem: there’s almost nothing where to attach the buttons. The plastic is very thin and missing completely in some areas. This needs something to support.

 

 

 

 

 

I modeled this kind of support bar for the buttons in Fusion. 16 buttons for the sequencer steps + a start/stop button. It is meant to be made from 4 mm aluminium.


Luckily, local Hacklab has a very decent CNC milling machine for this kind of jobs, so the support bar was quite quick to make, with generous help from other Hacklab members who actually can use the machine. I cannot.




The idea is to make an aluminium chassis inside the radio enclosure and attach about everything to it, except the sequencer buttons, which are attached directly to the enclosure front panel. Despite the Fusion modeling, I wanted to do some traditional cardboard modeling also. Here are some basic parts being test fitted to cardboard chassis.


After some sawing and drilling, the chassis parts were ready.


The upper part of the front panel will contain all the pots and switches. They are attached to the aluminium chassis. In front of them will be an acrylic panel, which replaces the radio’s original frequency display panel.

The switches are push switches with 4P2T contacts, because some of the double sound generators need three changeover contacts, as discussed in a previous post. I found nice looking switches from eBay.

 

 

 

Making the acrylic panel is easiest by a laser cutter. The Fusion model contains also the front panel model, it can be used as the input for the cutter. Luckily, local Hacklab has also a very decent laser cutter.




I painted the panel with black spray on one side, engraved the texts and markings with laser and re-painted with green spray. There will be led lighting from the edge, so it resembles the original radio panel illuminated with lamp.


If someone is wondering: the clutter in the edges is not because of bad cutting, it is glue residue, because this panel was already once glued in place, but in slightly wrong place. I was wise enough to make several of these, laser makes them quickly when you get the setup right.


Now that all mechanical parts are ready, next phase is to put everything together and do the wiring.


Comments

Post a Comment

Popular posts from this blog

Secrets of the YM2154

Image
  After a break, I returned to the PSR-70 reverse engineering project: t he YM2154, a.k.a. RYP4 is still an unknown territory. The time has come to reveal its secrets. R YP4 is used a bit more widely than OPQ. Besides PSR-60/70 it is used at least in PSR-80 and RX- 11/15/21 drum machines. This time I did remember to check for service manuals, and found one for RX-11: https://elektrotanya.com/yamaha_rx11_sm.pdf/download.html . This contains a full schematic and other useful information.   T racing register writes Because I had good results with OPQ by tracing what the PSR-70 firmware is writing to the chip registers, this would be a good starting point also for RYP4. The chip has 128 registers which reside in Z80 I/O address space at addresses 80H...FFH. Looking at the disassembly listing reveals quickly that there is no single function which would take care of all the register writes, like OPQ had. There are many IN and OUT instructions accessing the RYP4 register
Read more

Reversing the PSR-70 hardware

Image
  First step in the actual reverse engineering is to start studying the PSR-70 hardware. This is quite service-friendly (meaning hacker-friendly) device: all circuit boards are single-sided and copper side silkscreen has IC numbers and jumper wire positions marked. There are also many useful looking signal names marked, like “D7”, “A12”, “IOWR” etc. It would be possible to draw the whole schematic from one high-quality photo of the circuit board. My intention is not to draw the whole schematic, but at least the address maps should be figured out. It will make the interpretation of disassembly much easier. All address decoding is done with 7400-series discrete logic, no PAL-circuits or other nuisances used, this is very good.   Block diagram Most of the electronics is on the large main board . The other cards are: Power + audio board contains the audio amplifiers, some kind of analog chorus-effect based on a BBD-circuit, power amplifiers feeding the speakers, and voltage
Read more

Digging into YM3806

Image
In the previous post I got the PSR-70 original firmware modified so that it dumps to serial port all register writes done to OPQ chip (YM3806). Now I’m getting the data I wanted and plenty of it! A simple keyboard key-down or key-up produce only under 20 register writes but changing sound from the front panel results in about 300 writes. Why 300, there are only 256 registers? Yes, but there are many registers which are written several times. T he raw dumps from the modified firmware are quite hard to read, they just list the register address and written value in hex in the order they happened: 1F=20 5E=1F 56=1F 4E=20 46=20 5E=81 56=81 4E=81 46=81 9E=1F … To make some sense out of this I wrote a small python script to analyze the dump. It lists all registers in numerical order and all writes done to that register. In the script output the first column is OPQ register number, second column is the number of writes to that register and then a list of the written values.
Read more