D501 – NJM2069

The last D501 NJM2069 VCFVCA modules has now shipped to the USA.
And as promised I wanted to share the schematics and PCB files (KiCAD format) with you.

You can download them here.

The NJM2069 is a fabulous sounding VCF/VCA and I really wish you could still buy these new. not only is a great VCF, but it has a VCA built in and a mixer. It’s a very simple chip to use as well requiring very little in the way of external components. If I could get a good supply of these it would make building poly-synths so much easier!

Anyway, on the PCB you’ll see I bought out the extra pre VCF inputs and the CVs for controlling the levels. Just keep in mind you *must* keep the CVs within -5V to +5V (though they operate from 0V to 5V), going outside of this will damage the chip.

I’ve also added a “Ko-fi” page, so if you feel like buying me a coffee (or in all honesty more likely some chocolate) then you can do so on my ko-fi page here.

Moving Times

A number of things have been going on in the world and in my personal life. So I wanted to give a quick update.

The COVID-19 problems are really worrying and very stressful, to see so many people loosing their lives due a disease that can be stopped simply by avoiding social contact is so saddening.
Even sadder is that a portion of humanity seem to feel they’re immune, it’s a hoax or simple that it could never happen to them. So they carry on as before resulting in more avoidable deaths.
I’m finding the headlines increasingly painful and difficult to read.
I can only hope that the selfish people soon wake-up and start acting like responsible adults.
One thing is certain, this is a world changing event and our lives will never be the same. I my one hope for this crises is that humanity changes for the better going forward.

A personal update, I’ve recently moved home, this resulted in about 3 weeks of downtime for my development efforts and a lot of upheaval, things are almost back to normal for my working environment.

As a result of my move MuSeq work was on hold, I’ve only just started again. I discovered that the MIDI timing was a bit out, MuSeq was slightly ahead of the beat, so I fixed that and now it’s rock solid.
Bad news is I discovered a bug in the MIDI library I was using, it doesn’t run on an interrupt, so any event that happens like say changing from the CVA page to the CVB page means that some MIDI clock ticks are missed, resulting in a massively out of time sequence, which is really annoying to say the least.
I’ve had a look and it doesn’t look like it’s possible to modify the library to do this, so I’ll be writing my own library for handling MIDI using interrupts. Not a big problem, just a lot of code that will need stripping out and refactoring.

I’ve got a new module in the works. This is something I’ve had in breadboard for about 4 months, and I got the prototype PCBs early march (delayed due to COVID-19). You can hear a quick clip of the new module here;

The module is based on the somewhat infamous Korg NJM2069 VCF/VCA chip used in the Poly 800, DW6000/8000 and DSS1, here’s a picture;

This is only going to be available in the MU format because there are a plethora of really great VCFs for euro-rack, but only a limited range in MU format.
Some of the nice things about this module is that it has a built in VCA, so for people with smaller rigs where space is an issue this module works really well as a “dual function” module.
I’ve also added a switch so you can select 24dB/Oct or 12dB/Oct cut off slopes.
Of course, being designed for a poly synth means the resonance is CV controllable which is a real boon (one of my favourite tricks is to route VCF envelope to both cut off and resonance).
Finally on the back there are jumpers which can be opened and a header cable can be added to bring out the extra two pre VCF inputs and VCAs. I may do an expansion module for this to bring those extras in.

Now the catch, I only managed to get 25 of these NOS (New Old Stock) from a retailer who sells NOS chips, I would love to get more and maybe if I can find some I will. However, this run (when I find my oven for baking PCBs) will be limited to 25 only. I’ve tested these chips and they all work perfectly.
However, I will be publishing me schematics, gerbers and front panel design, so you can make your own if you’re lucky enough to find one of these incredible sounding chips.

For now, please, stay safe and look after yourself and your loved ones, humanity has had some major crises in it’s existence, we will get through this one too.