sunnuntai 26. maaliskuuta 2017

Sigma and Lovi-club instruments

We are preparing 50min of new music to our gig in Lovi Ambient-club (Kansallisteatterin Lavaklubi) 29.3. 19:00. Here are some pictures of our setup. Hopefully we can fit all this stuff to Lavaklubi's stage with Esa Kotilainen and Unfound.

Tower of synths! Korg MS10, SEKU and TTSH ARP2600.

Roland SH101, Eurorack Moog Prodigy and Nord MicroModular.

Another SH101 and Crumar Performer.

sunnuntai 5. maaliskuuta 2017

Sigma Live in Lovi Ambientklub

Sigma will play in next Lovi-klub in Helsinki Lavaklubi 29.3. with Unfound and Esa Kotilainen. Here is the link to Facebook event https://www.facebook.com/events/392320714472417/
We are going to play for about 50min floating soundscape with mostly analogue synths.


EWI and Mutable Yarns

I wanted to put my Moog Prodigy clone to one portable case where is everything necessary to produce sound with my EWI-controller. So I ordered from Thomann a custom case with their 3D configurator application https://www.thomann.de/fi/casefactory.html#suitcase. It holds one 6U-frame from Clicks & Clocks.
I ordered Mutables Yarns MIDI2CV module so that I can have that also in this portable case. Until this I have used my trusted Kenton Pro Solo MIDI2CV-box for this application.



Yarns have one assignable CV-out from where I can control Prodigys filter with how hard I blow from EWI. Yarns can convert this MIDI-controller information to voltage between 0-5V. That's not enough for Prodigy where I need double of that. So I built a CV Processor module where you can offset the CV and/or amplify it with maximum gain of 2.






sunnuntai 19. helmikuuta 2017

OTA HPF Proto

This is a reference to my previous article about 24dboct-high-pass-filter. I built this two-layer proto of that circuit and it works great. Front panel layout is different because here I have a dedicated layer for pots, switch and connectors where I have more freedom on placement of components.



maanantai 6. helmikuuta 2017

Crumar Performer

I have been repairing my Crumar Performer string/brass synthesizer. One zener-diode was dying and made the master-oscillator to change the pitch randomly. Now this is fixed and it's time to make some modifications. I replaced the MK50240 top-octave generator with FlatKeys replacement box FK50240. This box has 12 synthesizers that create the desired notes from the master clock with a worst case error of 0.00005 Hz. There are also some extra features switches (scale,transpose,octave) that you can activate if you want.



Other modification comes from SoundDoctorin in this "Crumar Performer easy modification for release envelope" video. In the original Performer when you switch the brass-section on it kills the sustain on both brass and strings. With two switches you can choose from three options:

1. original setup where brass-section kills sustain on both brass and strings
2. Sustain works for brass-section but kills the strings sound
3. Sustain works equally for brass- and strings-section

I think the third option is most useful. Brass section adds nice fatness to the string sound.

P621-board where is the brass-switch. The white/black/red cables goes to the both separate switches.

Explanation of what to cut and where to connect the switches.

maanantai 16. tammikuuta 2017

LM723 heater circuit

I have been breadboarding several different heater-circuits for temperature stabilisation of LM3046 transistor array. They all use the same principle of comparator circuit that compares the measured temperature against the desired temperature set by a trimpot. Comparator then works as an on/off switch for heater-transistor that keeps the 3046 chip in steady temperature. I must say that I haven't found an bulletproof circuit that could accomplish this basically simple task. Until now that I found this LM723 based heater circuit.





LM723 is a voltage regulator designed primarily for different power supply applications. But it can also be used as a temperature controller. I have these great McGraw-Hill Publications books "Circuits for Electronic Engineers" where from I found this "Using transistor arrays for temperature compensation" article by Mahendra J. Shah. With 15V power supply it worked right from the box very good indeed. With only one heater-transistor it could rise the temperature from 30°C to 50°C in 5 minutes and reach the final 50.5°C temperature in 10 minutes.


LM723 has also some kind of comparator inside it called Error Amplifier. It seems to work more smoothly than just an on/off switch. There is also a reference voltage generator inside this IC that generates a constant voltage of 7.15V from where the desired temperature CV is adjusted with trimpot R1. I modified this circuit a little to be used from 12V power supply. The pin numbers of LM723 in my schematic refers to PDIP version of this IC. The original article claims that with this heater circuit the LM3046 array exhibits a temperature coefficient of -3.1 ppm/°C from 33°C to 50°C. Peak current that this circuit draws from 12V is about 80mA where from it comes down to 52mA when the circuit stabilizes. In Moog Prodigy you need two of these with total current need for 104mA.  I haven't compared this current consumption to Prodigys original heater circuit. But that's sure that it is a better circuit than the original. Next I must try this inside my Prodigy clone.


tiistai 3. tammikuuta 2017

24db/Oct High Pass Filter

Most mixers have that fixed 75/100Hz high pass filter for cleaning audio from extra low rumble. What I need is an sweepable HPF covering at least 10Hz - 1kHz region. The slope should be quite deep so that I can make the sound lighter without totally killing it. CEM3320 (http://electricdruid.net/cem3320-filter-designs/) would be ideal but I don't like to use this now obsolete part. So here is my LM13700 OTA-based 24db/Oct HPF. It's made from four serial 6db/Oct OTA-filters. With a switch you can choose between 12db and 24db slope. I have simulated it with LTSpice and it seems to work. Here is my preliminary front-panel and PCB for Eurorack. Here you can find some interesting stuff about OTA's in two parts (Understanding and Using OTA Op-Amps.pdf, Understanding And Using OTA OP-Amps PartII.pdf).