Hi,
I’d like to use the Moogfooger MF-101 Lowpass Filter with my modular synthesizer system which uses 5V for signals (also audio signals). I know the basics in electronic engineering and would like to modify the MF-101 by my self that it can process 5V signals and also outputs 5V audio signals.
Does anybody of you know how to do this?
I don’t mind about the guarantee thing …
Thank you in advance!
Cheers,
Olbert
What kind of modular do you have?
This should not be a problem at all, especially if you’re just routing audio into the MF-101. But even with CV you should be fine. No modifications are necessary. All Moogerfoogers operate from zero to 5v control voltage.
Some brands of modular synths can put out higher voltages, say 10v, and that is when you need to be careful. Using CV over 5v into a Moogerfooger could possibly damage it. I know the Future Retro XS puts out zero to 10v, and probably some others too.
Line-level audio signals will probably never reach 10v, and very rarely would they reach 5v. The raw oscillator output of the FreqBox is extremely hot but I’d be surprised if it was 5v.
If you want to bring an audio signal (1.25VRms) to 5V, you will need to amplify it. Some modulars have modules to do that. You can use a small audio amp.
Thanks for your replies. I have the Doepfer A-100 modular system.
I thought about to attenuate incoming 5V signals of the A-100 with a potentiometer or so.
I know, I could amplify the output signal, but unfortunately I don’t have such a module and a good one in studio quality would be to expansive for me at moment.
I just thought that, if the audio signal would be processed anyway in 5V inside the MF-101, than it’s just necessary to bypass the internal in- and output components, which would made the audio appropriate for 1V. But when it’s processed in 1V, than it’s not so good for the sound quality to attenuate and amplify in addition.
Again, I don’t think you need to make any modifications at all. Just plug and play. Anything your Doepfer sends out can be processed by Moogerfoogers and vice versa.
Why do you need the audio to be 5V?
The Doepfer modular system uses instead 1V for audio signals 5 Volts like the control voltages (CVs). The cool thing is, that you can use any audio source like a VCO as a modulations source or also any control module lika a LFO as a audio source (if its audible) 
Ok, I didn’t quite get your previous message, but know I did! Thanks, that are really good news! 
I modified my Nord Modular G2X digital synth to use the MF-101 as an external filter module. It works great. Check this out:
http://electro-music.com/forum/topic-12266.html
NOTE: Contrary to what the MF-101 manual says, with the Cutoff knob set fully counterclockwise, a unipolar 0V to +5V signal will not sweep the full cutoff range of the filter. With the Cutoff knob fully counterclockwise, it might be possible to use a unipolar 0V to +10V to get a full sweep, but I have NOT tested this. My testing shows that it is possible to sweep the full frequency cutoff range of the MF-101 with the Cutoff knob set at the midpoint using a bipolar -5V/+5V CV signal on the cutoff input. In most typical cases of filter use this limited sweep with a 0V to +5V signal should not be a problem. It is something to consider though if you want to use extreme filter cutoff modulation that normally can be done with modular filters.
The MF-101 works very well with line level audio input, but a 5V signal level may be too much. Normally though, you have to attenuate your modular audio signal before sending it out, correct? You should be able to use the VCO signal mixer to get the level right for the MF-101 without sacrificing audio signal quality. In most cases, the line level output of the MF-101 should be suitable for use as a modulation source.