Thursday, January 17, 2013

A-128 Modification by Ernst van der Loo

Dutch Sound Designer, Engineer, Composer & Performer Ernst van der Loo posted a few pictures of his latest DIY-project in the Doepfer A-100 Facebook group.

Tools of the trade and lots of wire
The project involved creating 15 individual outputs for his Doepfer A-128 fixed filter bank.

Module A-128 (Fixed Filter Bank) is a filter bank, made up of 15 parallel band pass filters, all with fixed middle frequencies and bandwidth.
Each band pass filter has its own amplitude control knob, with which that frequency band can be attenuated. 
The bandwidth of each of the filters is approximately half an octave.
The signal at the original output of the A-128 contains a mix of all the filters, depending on the position of each one's amplitude control knob.

Finished project 
Ernst used an 8HP blind panel to create the expansion board for his A-128, drilled 15 holes, mounted the mini-jack-connectors and connected them with the correct terminals/outputs on the A-128 PCB board.
There is even the choice between pre-attenuator terminals (fixed volume) or post-attenuator.
You can find the document that shows how to add these single outputs to the filter bank A-128 in THIS PDF (from Doepfer's DIY page)

Ernst commented on the end-result:
 "Not too happy with the alignment of the mini-jacks yet. Maybe I'll need a new drill exercise..."

Maybe he should have saved himself the trouble, because if desired Doepfer can carry out this modification in the factory  (price for blind plate 8HP + 15 sockets + about one hour working time) for about Euro 100 altogether.
Pictures used with kind permission by


  1. Hey thanks Pierre! Nice!
    I'd like to comment that the costs of this mod were around 20 euros in material. Taking that, and the fact I already owned an a128, in account it is a steal. Especially if shipping it to Doepfer and back to me would probably also would have set me back between 20 and 30 euros..
    Anyway keep up the good work!

  2. That does make sense Ernst. I just wish i had the time and patience for that kind of work.
    Thanks for the feedback!