SM042 V. 1.2 TG issues and solutions

The last PCB version of SM042 Kotlenikov module, revision 1.2 was reported by significant amount of users to have various issues with the TG. This applies only to DIY kits, since all retail modules are based on revision 1.1, and only recent units are made using the same PCB.

However, it has has several important updates, which improve the overall performance:

  1. New jumper, disconnecting TG output from internal link to the FM and WM inputs
  2. Better quality switches
  3. Better quality bypass capacitor and also included Epcos film capacitor for C27, which stabilize the high-rate timing in the TG.

Some of the kits, supplied in the 2018, were shipped with the following integrated circuits:

  1. ST TL074CN, datecode GK08B4.
  2. TI LM393P, datecode DN711

Those chips are considered partly compatible fakes, which operate a bit different from the original chips, and prevent TG from cycling in the LFO mode in some TG settings. Also, when Int. Mod jumper is disconnected, TG do not cycle when Attack is set above 9.00, Release is set below 9.00, and TG rate is set to Fast. (Generating a fast up-ramp)

There is a tested working solution for this issue:

  1. Replace IC1 (LM393) with LM358 . This will stabilize behavior of the circuit with disconnected jumper and improve the waveform.
  2. Add a piggy-tailed 5 V zener diode (e.g. 1N4733) between pins 1 (Output) and 4 (GND) of the IC1, Cathode (Stripe) to the pin 1. This will protect CD40106 from overvoltage, since LM358’s output is not an open collector type and pull-up 3K resistor, R4 will no longer define the output voltage in the logical High state.
  3. Replace IC3 (TL074CN) with another one. ST TL064CN is confirmed to operate properly.

We apologize for putting untested chips to the kits and will make all efforts to avoid this situation in the future.