The Gristleism is a LO-FI audio loop player from the designers of the Buddha machine FM3. There are 13 audio loops based on samples of the electronic group TROBBING GRISTLE. The unit comes with a pitch range control which can easily be increased to slightly higher (faster) and a lot lot lower (lower). I have placed the pitch and volume controls on to the front of the unit for easier control. The speaker is taken from a Furby and the loop advance button is on the front of the speaker this made more room inside for the added pots and switches. I have also added LDR (Light Dependant Resistor) light control the pitch (brighter light = higher pitch and vice versa) to create a sort of optical ambient theremin.

The increased pitch range mod is easy to implement. The original pitch control VR2 (top left of circuit board) has been removed. On my unit VR2 measured 500k simply replacing this with a 1meg pot would increase the low range a lot but does not allow you to increase the pitch. The volume pot can be replaced with a 1k or 10k pot with an on/off switch.

To increase the pitch range first solder a wire across R2 labeled on the board and remove VR2 from the Gristliesm (It is best to cut VR2 out with wire cutters rather than heating the solder to remove it). Then wire up a 100k trimmer pot in series with the 1meg pot as shown above my trimmer pot was set to 80k which gave the highest stable pitch range. If you don't want to add a LDR optical control to your circuit wire the centre pin of the 1meg pot directly to P2 on the diagram above.

For the optical light control you need an LDR with a low minimum resistance (in bright light) of about 1k and a high resistance (in darkness) of about 1meg or more. The popular Norps-12 LDR can be used, i get mine from Rapid electronics UK.