MATRIXSYNTH: Analogue Renaissance at SUPERBOOTH - Analog distortion for the TB-303 and pretty much everything else

Friday, May 04, 2018

Analogue Renaissance at SUPERBOOTH - Analog distortion for the TB-303 and pretty much everything else

"TS-303 GT Acid Screamer prototype

Totaly bonkers circuit design with Vbe multipliers, Gyrator, Capacitance multiplier and Negative Impedance Converter in a feedback loop with ridiculously high gain.

- Jumper selectable input impedance 50k - 500k Ohm
- Variable input level: From nothing to +40dB
- Variable output level: 0 to 8Vp-p.
- Tuneable Symetry of the distortion. From perfect symmetric distortion to keeping bottom or top half of the signal intact while obliterating the other.
- Tuneable Dynamics: It analyses the volume enveloppe of the input signal and can restores this on the output signal. This from zero to doubling of the original dynamics.
- Switchable between overdrive and distortion
- Frequency selective distortion: Only distort certain parts of the spectrum, while keeping the rest itact. 2 frequency selection knobs allowing highpass, bandpass, band-reject, lowpass distortion. Do not confuse this with filtering of the input or output signal. It happens in the distortion engine itself.
- Turbo mode: Self-oscillation happening only at the highest clipping levels. Still exploring the posiblities of this one, but it already made me mistake a 606 for a 303...
- A rack version will also be available


Replacement for the IR3109. Sounds and behaves exactly the same.

It even does the distortion that happens in the MC-202 and SH-202 when you run them at low voltage or almost empty batteries.

It's also DC-accurate. So, it also works in the portamento circuit of early Jupiter 4's.
2x1cm 6-layer pcb with plate capacitors to fit everything in the DIL-sized footprint of the original chip


Gravitaional Slingshot upgrade for the Juno-106 (and all other synths that use the 80017A hypbrid modules).
It features a filter pushed far in the non-linear region and Q-compensation placed outside of the Resonance feedback loop. This lack of in-loop Q-compensation makes the signal level in the filter vary with input signal and resonance amount and the non-linearity causes the filter to self-modulate.
Instead if one sharp frequency peak generated by resonance, you now have a multiple. Less squelchy than the original voice chips, but a much richer texture in the lower regions.
See the original as a young soprano and this gravitational slingshot as a old, well trained, voice that has smoked a bit more and drank loads of whisky.

AR662-DOT & AR662-VCA

Exact sounding and behaving replacements for the BA662

There is an entire mythology and cult around the BA662 and I'm still writing a forthcoming article "Fairies, Dragons and the BA662" that should explain a few things... And yes, I have it's design.
Many so called "clones" have surfaced in the past years. From simply replacing it with another OTA, to an OTA with extra current mirrors, to a discrete copy of the LM13700 minus the buffer and linearizing transistors, claiming to be based on a document that simply does not exist.
None of them are even close to the original one and all of them have problems. Some have minor ones, others have thermal runaway that can cause them to self-destruct or blow the power supply of the synth in which they are used.

- AR662-VCA: Replacement for the BA662 'A' versions. This one has an on-chip temperature measurement and compensation circuit to virtually eliminate all control feedthrough. Often called 'offset' compensation, but there are more elaborate mechanisms at work than a simple mismatch of input transistors.
This compensation circuitry is completely isolated from the supply rails, so none of their noise will be added.
Also optimized for ultra-low power consumption (battery operated devices like 303's, 606's and stomp boxes). Works down to about 7V.

- AR662-DOT: Replacement for the factory selected 'color dot' BA662's. For VCF purposes.
In some service manuals it is noted that these were binned on transconductance gain and marked accordingly. But in fact, it's about the I-V curve of it's control port. Mismatch cause filter tracking errors and non-flatness of the resonance level.
The AR662-DOT can be trimmed to match any of those color versions."

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