Eurorack Doepfer A-130-8 Octal VCA Expander (DIY)

I developed this DIY expander for the Doepfer A-130-8 Octal VCA. The expander sandwiches between the main module to add a manual bias control and a bipolar CV control to each of the 8 channels. The total width of the module + expander is 12HP. For more details on the development of this expander, you can search for "Doepfer A-130-8 Octal VCA Expander (DIY)" in the modwiggler forum.

NOTE: I'm selling only the expander here, excluding the A-130-8 module itself.

The expander adds a lot of useful functionality to the module: For example, you will be able to easily

• add bias to your CV voltage
• subtract the CV voltage from the bias for ducking effects
• crossfading of multiple channels to one of the SUM outputs
• panning of a single input to two channel outputs

For crossfading and panning to work, I recommend the following normalization settings:

IN1->IN2, IN3->IN4, IN5->IN6, IN7->IN8
CV1->CV2->CV3->CV4, and CV5->CV6->CV7->CV8,

but other normalization options are also possible to use with the expander. For detailed normalization instructions, see the documentation on the Doepfer website. The normalization options have to be set on the main module with solder jumpers.

The polarity of the CV + bias is indicated by a bi-color LED for each channel. The bipolar CV attenuators have a locking point in the middle. The A-130-8 has a small "dead" zone there, so it is very easy to completely mute the channel by moving the CV knob to the center position.

The factory setting for the A-130-8 is suited for 5V envelopes. If you have trimmed the module to other voltage levels, there is a jumper option on the expander to choose between 5V, 8V, or 10V. For me the 5V factory setting worked best, since the expander adds an attenuator knob for envelopes with higher voltage levels.

For the installation of the module to the expander, you need to separate the two PCBs (same steps as for changing of the normalization). Then simply mount the expander in between, see the pictures for the correct alignment. The expander comes with a cable that can connect to both power sockets (see pictures) so it occupies only one slot in your case.

The front panel is screwed to the Expander and is made from a Doepfer aluminum blind panel. I used good quality label stickers for the front panel prints.

If you want an expander with a black, or customized front panel, please contact me. If you want to make your own custom 12HP front panel, I can also sell you the expander without panel for 130 EUR.

You may wonder why the expander is more expensive than the module itself. Well, I'm doing this as a hobby and this is not a mass production. The price is a balance between offering a fair deal to you and making it worth for me to make the expander available to the community.

Feel free to reach out if you have any questions on the module, or installation of the expander. If you pass by in Utrecht I can also install the expander to your A-130-8. Otherwise you will get the expander shipped for self-installation.