SRC's hardware hacks page

Mods

TEC4 mods

The TEC4 is an economic all-in-one multifx pedal, it has digitally controlled analog distortion and compression circuits, plus a DSP based (TI's TMS57002, which I could not get a datasheet for) effector for the modulation, delay, EQ and reverb effects. The thing is controlled by a Samsung KS88C4116 microcontroller.
TEC4 Compression is a bit flat, doesn't work by itself, just a complement for the overdrive (compression is disabled internally when distortion is set to grunge (9-15)). The compression circuit is based on the THAT2159 VCA (couldn't get datasheet, but I assume it is similar to other 2150 series, as the pinout fits), although the surrounding components don't do a nice job. The DSP software itself corrects for the loss of loudness when the compressor and the overdriver are both activated. I used to have a 4K7 resistor in parallel with R191 to make it sound a bit better, but I decided to get rid of the compression circuit (saving the 2159 for better purposes). See further on TEC4 Overdrive.
TEC4 Distortion: the grunge distortion is too harsh for me, I never did like diodes straight at the output circuit, that was the fuzz in the late 60's. The overdrive is too gentle for a R&R sound, so I tweaked the distortion circuit. I unsoldered D39 and D40 out and put a 8K2 resistor instead (I just lifted one each of the diodes pins and soldered the resistor to two pads on their sides, so I can go back if I wish). Now it resembles more that power distortion I like. Without the resistor, the sound is still great, but the output level is too high, the resistor lowers the output level to reasonable amounts.
TEC4 Overdrive: The overdrive is nice, but it distorts right at the lowest setting with my humbuckers, and I don't like tweaking the guitar volume level, so I went for a mild overdrive option for bluesy sounds, without sacrificing the original tone. What I did was to replace the compression circuit by a 1/2 attenuator, this way the input to the overdrive is 1/2 the signal and it doesn't distort bad, just some tube alike. The DSP software corrects the lower level for me, so the output is still the same. In order to do this, I removed the two capacitors feeding the sound (A) in to the compressor and (B) to its last stage (out from the VCA), then I forced this opamp gain to unity and run a 100K resistor in series with a capacitor from (A) to (B), so this stage gain is 1/2. This way, when I set both overdrive and compression on, the overdriver gets a lower signal, so it is cleaner, but its output is still at the same level thanks to the DSP.
Email me if you want more details.

Interfaces

MIDI interface

The circuit is quite simple, it just converts the EIA RS-232 C voltages present at the serial connector to the MIDI standard and viceversa. You just build the PCB, plug it into the serial and play along with your favourite MIDI software.

Disk interface

This a two floppy interface to adapt any cheap PC floppy (DD or HD) to your Amiga and save a lot of money (in my country $100 dolars). You can see on the schematics that some numbers are in parentheses, these belong to the second unit. This is because the number of gates and flip-flops on the chips is enough to support two interfaces in a single PCB with three chips. I think schematic talks for itself, but you can write to me if in doubt. It's been working for a long time, so I think there's no problem with it.

Interfaces

MIDI interface

The circuit converts the differential RS-422 voltages present at the serial connector to the MIDI standard and viceversa. It also generates a 1MHz clock for the SCC, Macs can't generate a MIDI internal clock as Amigas do.
You just build the PCB, plug it into the serial and play along with your favourite MIDI software.

I'm scanning all my schematics, please be patient and stay tuned.

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