{"id":1620,"date":"2021-04-22T16:48:27","date_gmt":"2021-04-22T16:48:27","guid":{"rendered":"https:\/\/maffez.com\/?page_id=1620"},"modified":"2025-07-04T20:15:17","modified_gmt":"2025-07-04T20:15:17","slug":"bass-bot-tt-303-mk2-modifications","status":"publish","type":"page","link":"https:\/\/maffez.com\/?page_id=1620","title":{"rendered":"Bass Bot TT-303 MK2 Modifications"},"content":{"rendered":"
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fresh from the workbench<\/figcaption><\/figure>\n<\/div>\n\n\n

I’ve been curious for quite a while about the Bot<\/strong>, especially with this thread<\/a> in the back of my mind, so eventually went for a second hand Cyclone Analogic TT-303 MK2. As far as I know, nobody offers commercial mods for the MKII, so here are some modification descriptions.<\/p>\n\n\n\n

This page is an *open-source* DIY project, meant for 303 aficionados with a Bass Bot and interest in moding it. If you like this stuff, think about donating a little to a charity helping refugees. If you make money of the info given here, donate to a charity helping refugees.<\/p>\n\n\n\n

who sez that mk2 can’t bite? <\/figcaption><\/figure>\n\n\n\n
various mods and a bit of syncussion kick (all post processed)<\/figcaption><\/figure>\n\n\n
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rough map of various sections<\/figcaption><\/figure>\n<\/div>\n\n\n

I plan on expanding and refining the info given here a tad over time, do also check in with my TD3 and Geosync TB-EFA modding pages, especially if you are a beginner. Part numbers and layouts will be different, of course, yet this can help you gaining some further insights into 303 modding as the principles are the same. As usual, the xoxbox wiki<\/a> very helpful in this context too!<\/p>\n\n\n\n

Very generously, @Green Dino offered their services as a proofreader, which helps in counterbalancing some of my idiosyncrasies or nincompoop spellings! Thanks!<\/p>\n\n\n\n

Some general info<\/strong><\/h2>\n\n\n\n

The revision I have is R2V1.3, designed by Rezonance Labs in 2016. CPU is an STM82S207-R8T6<\/a>, with a 14174 hex flip flop interfacing 1v\/oct and slide\/accent switching. PSU features a sumida coil. Slide, Accent (and I think Hammer and Mute also) are done via 4066 IC switches. VCA is a discrete BA662 replacement. Headphone amp is a LA4140 (with a dedicated +6V supply rail). There are three trimmers: cutoff, resonance, and +5.33v regulator.<\/p>\n\n\n\n

Opening the Sardine Can<\/strong><\/h2>\n\n\n\n

Pull off the potentiometer and rotary switch knobs first; then peel off the sticker of the bottom panel. There are 6 screws at the bottom and 8 on the back. Take these out, then carefully “bend the plastic “unclick” the plastic braces at the back (2x) and front (2x). <\/p>\n\n\n

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Placing Controls<\/strong><\/h2>\n\n\n\n

The MK2 is a tad tight, but there is space on the side panels and in the following pictures you see areas marked under which the PCB is not too busy.<\/p>\n\n\n

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PCB and chassis superimposed<\/figcaption><\/figure>\n<\/div>\n\n
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areas in black squares offer space for additional components<\/figcaption><\/figure>\n<\/div>\n\n\n

VCO<\/strong><\/h2>\n\n\n
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VCO SECTION<\/figcaption><\/figure>\n<\/div>\n\n\n

Some notable aspects before turning to mods: the VCO on the TT303 has an auto-tuning feature (seems TM4 and TM5 equivalents to the TB303 are IC11 and IC15, which are digital pots). Q3 (equivalent of TB-303 Q8) is an 2SA812-M7, i.e. high hfe transistor. Most notably, VCO and audio input are buffered per opamp (IC2) before entering the VCF.<\/p>\n\n\n

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buffer stage before VCF<\/figcaption><\/figure>\n<\/div>\n\n\n

Square PW adjustment<\/strong>: R19 (22k) replaced by trimmer\/resistor. I settled on 25k as a replacement but you might find other values nice(r). NB hollower square = less volume on square. <\/p>\n\n\n\n