Super saw analysis ideas

I found a post on Matrixsynth today that lead me to a second paper analysing the JP8000 super saw. 

The post: https://www.matrixsynth.com/2021/07/korg-nts-1-nutekt-digital-synthesizer.html

The project: https://github.com/GrahamJamesKeane/UberSaw

The project page: https://korgnts1beginnersguide.wordpress.com/

Adam Szabo: How to Emulate the Super Saw: https://korgnts1beginnersguide.files.wordpress.com/2021/07/szabo_adam_10131.pdf

Alex Shore - An Analysis of Roland’s Super Saw Oscillator and its Relation to Pads within Trance Music: https://korgnts1beginnersguide.files.wordpress.com/2021/07/ananalysisofrolandssupersawoscillatoranditsrelationtopadswithintrancemusic-researchproject-a.shore_.pdf

This got me thinking - I still think the detune response looks like it consists of three linear components instead of a 11th order polynom like Adam Szabo shows in his paper (I did in 2014 as well when making my analog 7-saw module).

I really want to test my theory in detail, but that requires some automation. Here's my idea:

- Control the JP through webMidi

- Loop through all midi values for detune

- Use a js spectrum analyzer, for example https://github.com/hvianna/audioMotion-analyzer to find the frequency components. We should be able to find 7 distinct maximums (the 7 oscillators). 

- For each maximum, record the pitch and amplitude, possibly as an average over several samples

- Build tables for each oscillator/detune setting and calculate spread and pot response to see what the actual response is.

Edit: I've been looking at the Web Audio API lately, and using it directly could be a good option. It works by chaining nodes, one of them being a FFT node. I assume that can be used for finding the maximums. 

7 saw controller board populated

I finished populating the 7 saw controller board tonight. It has not been tested yet but it looks good :-D

I didn't have any 22k 0204-size resistors, and I can't find any 3M3 or 4M7 resistors anywhere in that form factor, so I used normal 1% metal film ones instead. It looks a bit wonky but will work fine.

I have yet to test both the dual VCA and this board so not sure it works yet...

7 saw controller board

tiny LM13700 based dual VCA

Silk screen looks great :-)

First multi-sub-oscillator board populated

The first 4 x sub oscillator board has been populated. This is the top board, a second pcb with four more sub oscillators will be mounted below it. This time I've made sure connections from the lower board actually go through the top board, so no cables have to be attached to the lower board (as opposed to the oscillator boards where you have to connect cables to both boards.

This is the rev 1 board which has the same bug as the single sub oscillator, so I have soldered 100nF caps to the flip flop feedback lines to make them flip and flop like it should.

Quad sub oscillator

Close up, note the tiny 100nF caps soldered directly onto the smd components' legs.

New panels

This week I've finished five new panels and prepared prints for three more. I've done two more oscillator panels, two sub oscillators and one 7-saw controller. I've also printed two more sub oscillators and one controller. Since the edges of the first oscillator panel didn't get as sharp as I wanted when folding the plastic around the edges, I've decided to cut the foil along the edges this time.

Plexi glass panels before attaching the adhesive film

Three oscillator modules - the first one to the left has plastic folded around the edges while the new ones are square cut for a sharper edge. I've also realized that I will run out of orange potmeter caps. Unfortunately, Re'an has stopped producing these so it's hard to get more. I've found some similar looking ones on Ebay, they seem to be 1mm wider but it may work out ok.

Finished sum oscillator and 7-saw control panels

Close-up of the sub oscillator. Note the input polarity switch, setting this to the opposite of the input wave will give that cool saw-within-saw wave shown in an earlier post

Final (?) Saw mix and detune circuit tested

This week I've spent at least 20 hours recalculating and building the saw mix and detune circuits on a solderless breadboard. I changed the mix and detune inputs to accept 0 to 10V instead of 0 to 5V, and also added an offset input to be able to use -5 to 5V inputs. The detune output still ranges from 0 to 5V, but the mixer slopes are now 0 to 10V as well, as this is what the VCAs I use expects.

I did a lot of up front calculations, but the final circuits were adjusted by ear. I am pretty pleased with the result, enough to go ahead and redraw the PCBs. I have decided to place the two VCAs on a separate, tiny PCB, which can be reused for other projects. I will also try to fit all parts on a single PCB instead of the two that the initial design uses, but this probably requires me to use SMD components again - the prototype uses almost 30 op amps and more than 50 resistors and takes up one and a half proto board :-)

The result is quite good, although not as good as I initially hoped and dreamed about. I am still impressed with the result though, especially at lower frequencies - it will make one hell of a bass sound. I may try to make a "computune"-style automatic tuner, to keep the oscillators better synced. I will also add a chorus, filter and perhaps distortion module, but for now I will focus on making the controller PCB.

The prototype fills two breadboards and includes all the necessary electronics for generating separate detune slopes for each oscillator, mixers to mix the single input pitch CV with the detune CV, mix CV slope generators, two VCAs and two audio mixers. To the right, behind the breadboard, is the 8 oscillator module.

Before protoboarding this circuit, i finished the 8 oscillator module, complete with separate fine tune pots and 8 CV in / 8 saw out connectors. It looks very cool!.

I shot a few videos for a friend of mine - the quality is crap but it illustrates how things work:

Oscillator mixing

Detune