Moog Prodigy Potentiometers

Sourcing potentiometers is not a simple task. When you find something that would fit you also notice that there is no distributor for that specific pot. After spending lot of time in Google I found the Bourns slimline pot (PC Slimline 22mm Square Single Turn Panel Control) from Mouser.

This is the best compromise-pot I could find. It can be mounted on the PCB with mounting brackets and the power rating and size is ok. Resistance range maximum is only 1M (Prodigy uses one 2.5M and 5M pot) and audio-taper (log) maximum is 500k (Prodigy uses four 1M log pots). This is a high quality conductive plastic pot that should last forever. I must check the technique where you can approximate a logarithmic law by resistive loading a linear pot. I assume you can also change the value of the pot with some serial resistance.

Smaller board-2 is now traced and cross-checked. I created the Bourns PC pot part-layout to Sprint Layout. In the picture below I match the pots to this PCB-layout. I have also ordered the DP3T and DPDT switches from UralTone (Finland) and Banzai Music (Germany).

Volumio and HifiBerry Digi+

My CD-collection is digitised on a hard disk and I have built a music-player around Raspberry Pi B+ hardware and Volumio-software (https://volumio.org/). RaspPi was connected to my Cambridge Audio DacMagic Plus DAC with USB-audio connection. Now I updated Volumio from 1.4 to version 1.5 and upgraded the RasbPi with HifiBerry Digi+ expansion board. This board adds SPDIF and optical TOSLINK connections to RasbPi. I have had this HifiBerry expansion for some time but it didn't work with Volumio 1.4/RasbPi B+ combination (at least not as plug-and-play). With Volumio 1.5 this combination works flawlessly. In Volumio's System-settings I choose I2S DAC as Hifiberry Digi. After this Playback-settings shows that Audio Output is changed to sndrpihifiberry. Hifiberry's TOSLINK is connected to Cambridge Audio DAC so the audio-stream is now fully digital from RasbPi to external DAC. Quality difference is not huge but I can hear how the stereo-field is now bigger and deeper than before with the USB-connection.

 I needed also a new bigger case for RasbPi where the HifiBerry-expansion fits nicely. This case is a simple laser-cut case that consists of 6 plastic pieces that are clicked together.

MOOG Prodigy-clone PCB-trace

I have traced the original MOOG Prodigy PCB with Sprint Layout (see BLOG archive 13th of february). Sprint Layout can handle max 500mm wide PCBs. This was not enough for Prodigy PCB so I decided to split the PCB to two separate boards. These boards are connected with multi pin connectors. The bigger PCB-1 board is now fully traced and cross-checked against the schematics. PCB-1 holds all the main functionalities of Prodigy. PCB-2 contains only VCA and Filter envelopes on it. This is a two-layer board with original jumpers on the top-layer (blue color on the picture).

Next I must trace and cross-check the smaller PCB-2. I can also start to source the potentiometers and switches that must fit on this design.

TTSH 2600 mini-plug maintenance

I had the first maintenance session with my TTSH. It has 80 mini jacks from which 40 are normalled. From these 40 ones three didn't work. I think this is business as usual with ARP 2600. Even the ARP 2600 Service manual explains how you can repair these mini jacks when they fail to conduct from the tip to the shunt. On my TTSH the three failed ones were EXT-CLK IN (internal clock is normalled to S&H clock in), filter input-4 (VCO3 saw is normalled to this input) and VCO1 KBD VC input. I ordered new mini-jaks from Thonk.

Here is a picture of the TTSH 2600 VCF-section where RINGMOD, VCO1-square, VCO2-pulse, VCO3-saw and NOISE are normalled to audio inputs. KBDCV, ADSR and VCO2-sine are normalled to control inputs (a normal is simply a connection which is made to one of the ARP’s input jacks from one of the ARP’s outputs even before a patch cord is plugged into it).

TTSH 2600 power supply

I made a box for the external MW RD-3513 +-15V power supply. This is a very compact and efficient switching power supply that can deliver 1.3A to both 13.5V rails. It is also cheap (17.05 USD from Mouser). The +-15V comes to TTSH with an XLR-connector.