Lushprojects Blog

Experimental Korg Monotron Filter (Part 2)

Ever since Samuel Freeman produced some great sounds playing his Vibrati Punk Console through a Korg Monotron at Dorkcamp I’ve been mildly obsessed with the Monotron circuit. The heart of the Monotron is the Voltage Controlled Filter (VCF) which is based on Korg’s classic design for the MS20 synth. Korg did DIYers a great favour by publishing the Monotron schematic back in 2010.

To try and understand the filter better I built a VCF “clone” on breadboard and then moved it over on to a perf-board. It has been an experience that is at times fascinating and at times frustrating. Internally the VCF uses some very low signal levels which are then boosted with a monster-gain amp. Net effect of this is to make the circuit very sensitive to component changes and environmental factors. I had to substitute for the transistors and the FET in the original design and this threw out a lot of other things. I found that swapping the three transistors around could make the difference between the circuit self-resonating or not. It seems unlikely that Korg will be selecting individual components on their Monotron production line so I don’t know how they manage to get good enough consistency in their builds.

The final working model is interesting. Perhaps rather noisier and not as musical as the original, but the sound is certainly striking.

For those that like the details here are the mods compared to the drawn Monotron schematic (component designations are Korg’s):

• Q12-Q14 are 2N3904. As noted above the order of selection of these can make a big difference.
• F3 is J112. As this has a different Vgs from the original I then had to add an AC coupling via a 1uF capacitor to the op-amp with the input DC linked to the voltage reference via a 100k resistor.
• D1 and D2 are red LEDs to increase the clipping voltage on the output.
• R60 is 680k to make sure the circuit will self-resonate
• R73 is 680R to reduce cross-over distortion in the Op-amps output. I think the way that Korg bias the op-amp the output doesn’t go in to the cross-over zone so this wasn’t an issue for them. Because I changed the biasing it becomes an issue for me.

Oldest working mobile?

Friends of mine are planning a “who has the oldest working mobile” event. I have an Orbitel 863 from about 1994 [Edit:] 1992? which I reckon could be a winner. With a bit of searching I found a post in German that gave correct pinouts for the battery. In a quick test the mobile powers up OK without a SIM. Given it is a somewhat powerful radio transmitter and it is missing its antenna I haven’t dared try anything else yet. Anyway, here are some photos.

Edit: Another source on the web dates this mobile to 1994 without giving any evidence. From the design and what I know of its history I would say it was a very early GSM mobile and 1994 feels a bit late. There are various date codes visible on the boards and body castings. The latest date code I can see is “21 92” (ie week 21, 1992) on the main circuit board. Therefore I believe that this is a phone from 1992.

Dorklake11 – Vibrati Punk Console workshops ahoy!

Dorklake11 was a nice event. Great job by Alex, Greenman and co. to create organization seemingly out of nothing. We had 12 Vibrati Punk Consoles built in two workshops

Mike Challis did a very nice build of the Vibrati Punk Console as a Coffee Can Synth.

Sam Freeman made some great phat sounds by looping the Vibrati Punk Console through a Korg Monotron.

Thanks to all the builders and all the campers that put-up with the massed bleeping!

Interview! With me?!

Lots of stuff happening so here are the highlights in bullets:

• Interview with me by the charming Josette Garcia about the background to my various projects.
• Look out for Lushprojects.com circuit bending at Brighton Mini Maker Faire and a chance to buy Vibrati Punk Console kits
• Vibrati Punk Console building workshop at Dorklake11 in a couple of weeks
• First batch of Vibrati Punk Console sold out. Working through the second batch now
• Details of a suggested box for the Vibrati Punk Console now available

Vibrati Punk Console featured in Sound on Sound Magazine

I read Sound on Sound so I am very excited that they have reviewed the Vibrati Punk Console.
The Coffee Can Synth!

Vibrati Punk Console with optical control – New video

Lushprojects.com will be at Brighton Mini Maker Faire

We are going off to the seaside in September. Lushprojects.com will be a Brighton Mini Maker Faire with circuit bent electronics to play with and a chance to buy and build the Vibrati Punk Console. Hope to see you there.

Vibrati Punk Console – second boxed version

Just made this at Nottingham Hackspace using a Vibrati Punk Console that Clare soldered and a mini tin box for vodka that we got at Christmas. I rather like it.

Used my own drilling guide to make it.

New lushprojects.com logo

Sneak preview of the new logo. More changes coming soon.

Vibrati Punk Console – First Chance to Build

Retro Electronic Sound
Evening Build Workshop
Tue June 14th, 6:30pm, Nottingham Hackspace
All welcome

The first batch of kits for the Vibrati Punk Console (aka “Atari Punk Console 2.0”) are in. We are going to have a building session at Nottinghack on June 14th. So if you like electronic music or want to try your hand at soldering then come along.

The Vibrati Punk Console is a beginner-friendly electronic music project that can be finished in one evening. The simple circuit generates an amazing range of retro warbles, screams, glitches, fuzzes and tone ramps.

Workshop Cost: £20 includes teaching and all build materials.

For those that can’t make it to Nottingham the kit should be available to buy on the web soon.