protozoid labs

The schematic for the external LFO for synths like the Ensoniq SQ-80 with an expression pedal input, as described in my older post (here) had some minor bugs in it. I fixed these a long time ago for my own use, but never updated the circuit here. Here is an improved version.

Functionally it’s just about identical. However, the power supply circuit is a lot better (and will now do both 5V, 10V without a change of resistor values). The LED now indicates the shape of the LFO waveform rather than just being off/on. Also, there were a few minor bugs like resistor values, or orientation of pots and things like that.

Another Ensoniq SQ-80 project - to extract SQ80 disk images on a PC for the purposes of searching contents and extracting patches.

The project came about because I was organising my patches with a view to distributing some of the better ones. I have been using the wonderful SQ8L VST plugin as a librarian. It is not only an excellent emulation of the SQ80, but loads SYSEX dumps and allows the creation of large libraries. I have a lot of patches on disk, and want to make sure some of the ones that have ended up in my banks are not actually 3rd party. Large disks would have been a lot of work to go through manually, sending a SYSEX dump for each bank over MIDI to a computer one by one. As floppy disks start to fail, and floppy disk drives and the computers that they can be installed in become harder to find this is also an insurance policy for archival purposes.

Enter the sq80toolkit by Rainer Buchty. This works really well at what it does, which is make disk images. However, it didn’t have the functionality I needed, namely extracting individual banks/patches as SYSEX data.

So what I needed was a tool that could read the disk images, extract the needed data from them, and convert it to SYSEX format. I have written a command line tool - extract_sq80 - to do this and have open sourced it. It’s in python and should run on just about any platform.

It also enables just about anyone to use the disk images that are available on Rainer’s page (and possibly elsewhere?) without having access to a floppy drive and the increasingly elusive double density 3 1/2″ floppies.

Visit the github to download the extract_sq80 tool here.

A quick step by step HOWTO:

You need a linux PC with a floppy drive in it to install the sq80toolkit on. I have no idea if sq80toolkit will work on a USB floppy drive, but I suspect it might not. I built a legacy hardware linux machine specially for this (which was a reasonable project in itself given failing hardware etc.)

Install the sq80toolkit. I also needed to install ‘fdutils’, which I did using my linux distribution’s package manager. There is a precompiled version of sq80toolkit, but I compiled the tool from source and had to make one change to the source. This was was to remove the check on line 74 of sq80dump.c which sees if the ioctl call fails. It was failing at run time with it on, but worked fine without it. I’m guessing this is something to do with modern linux kernels?

Once sq80toolkit is installed you can extract a disk image using the following  command:

sq80dump -if=/dev/fd0 -of=IMAGE_FILE.img

/dev/fd0 indicates which floppy drive contains the disk image, the first one in this case.

The extract_sq80.py tool can be downloaded from the github. It needs python to be installed, but should run without any other dependencies.

You can then use extract_sq80.py to list the contents of the image generated in step 3, and extract whatever you need. It currently doesn’t know anything about sequences, but can extract banks or individual programs, either all at once, or individually. It also has a ‘virtual bank’ mode, where it combines all of the individual programs into banks so that you don’t have to deal with lots of individual programs in separate files. Some example commands are:

extract_sq80.py IMAGE_FILE.img bank --dump syx

which extracts all banks from the image in SYSEX format. Without the '--dump syx' option, it will just list them.

extract_sq80.py IMAGE_FILE.img bank --dump bin -n 2

extracts just the second bank from the image in the binary PCB format used by the SQ80 natively.

extract_sq80.py IMAGE_FILE.img prog --list

lists all of the individual programs in a more human readable format (5 programs per line, rather than one).

extract_sq80.py IMAGE_FILE.img bank --list > IMAGE_FILE_banks.txt

lists all of the banks and save the output to a text file. The --list option when used in bank mode will list all of the programs within each bank as well.

extract_sq80.py IMAGE_FILE.img virtbank -d syx

extracts all of the individual programs in up to 4 “virtual banks”, as sysex files.

extract_sq80.py --help

gives full usage information, so please refer to that for a more complete description.

On Linux, it’s very easy to send the resulting SYSEX files to the synth. I do it like this:

amidi -p hw:2,0,0 -s BANK01.syx

where hw:2,0,0 is the MIDI port, and BANK01.syx is the sysex file dumped by extract_sq80 using the ‘--dump syx’ option.

amidi -l

gives you a list of all the MIDI ports available on your system.

Any number of tools (MIDIOx etc) can be used to do a similar thing on Windows. The SQ8L VST plugin will also read in the .syx files as is.

The LFO-1 is now ready for production, and the first production units are rolling out.

There are a number of changes over the initial design, including power supply improvements, a number of minor bug fixes, and a simple but but useful upgrade: The LED now isn’t just on/off, but undulates gradually in time with the sin and triangle waveforms!

A number of further features/improvements are also planned for Rev 2 of the board, coming as soon as the Rev 1.1 boards are sold out. I will open-source that version of the schematic too once its ready.

The LFO-1 can be purchased from tiny.cc/protozoid_lfo1 for $AUD130.

See this previous post for more information and a demo video.

Update (23 Mar 2020) : I have a few of these ready to go now using this design, but if there is a lot of interest I am considering doing a larger run with a powder coated enclosure and silk screened artwork. Please feel free to get in touch if you are interested in this.

This is a stomp box format LFO that drives the CV/Expression pedal input on an Ensoniq SQ-80 synthesizer. It could be used anywhere that takes CV input (many older synths, some stompboxes, modular gear etc.). The LFO is powered by a standard DC wallwart supply, with the output voltage being configurable. It will also take an Expression pedal voltage out from the SQ-80, allowing it to function as an expression knob when without outboard power.

The hardware is open sourced so feel free to use the schematic below as per GPL v3. It works as is, although the power supply regulation needs work.

Note (23 Mar 2020) - This post has been edited a few times for clarity and in preparation for the release of the hardware for sale. This is now available for purchase with a high quality PCB and printed front panel artwork (see here)

Controls:

      On/Off: On turns on the LFO. Off activates Expression Mode 1 if there is voltage input via the 1/4″ input jack.

      Waveform: Sine, Triangle, Square, Expression Mode 2 (see note below)

     Amplitude: LFO amplitude, or direct control of voltage output in the expression modes

     LFO rate: Audio rate 25Hz or so to approximately 20 sec a cycle

Connections:

     1/4″ jack voltage input for Expression Mode 1.

     2.1mm stomp box power supply (centre +ve). 12V supply input needed for 10V output (like the SQ80).

    1/4“ jack LFO/Expression output. Voltage range set by either the input voltage (for expression mode 1), or can be regulated to max 5-10V if running from external power. Generally you would have a 1/4″ TRS jack on the synth that you plug a Y cable into that gives you two 1/4″ mono jacks for the input and output of the LFO.

Expression Modes:

There are two expression modes to allow for different connection possibilities. For these, the amplitude knob controls the output voltage with no LFO engaged to add direct realtime control options to any compatible synth or other device. Mode 1 is available when the device on/off switch is off, and you have a TRS jack from a synth (like the SQ80) that feeds the device an input voltage. Mode 2 uses the maximum voltage set by the regulation circuit coming from the external power supply.

Schematic

Note (3 May 2020) - There are a few minor bugs in this version of schematic. Please refer to the newer version here

Circuit Notes

RP1 is a trimpot setting the operating voltage when running off external power. I run it at 10V for the SQ80.

RV1 is the control pot for the LFO rate.

RV2 is a trimpot setting the sine wave shape. Set it using an oscillocope or by ear.

RV3 is the control pot for LFO amplitude/expression.

SW_SIG is a 3 pole, 4 throw rotary switch knob to control wave form.

SW_POW is the on/off switch.

TERMSIG/TERMSW/TERMOUT are just connections between the circuit board and the panel controls.

A lot of that schematic is the power supply regulation, and the switching network to do the different modes, run the LED etc. The LFO circuit core is defined by the OP1A, OP1B and OP1C op-amps. I took the idea from here.

The Prototype

Works beautifully. The final hardware will have a custom PCB (ready) and graphics for the front panel (not ready):