Hi,
I wanted to formulate this in a general way, although the original question was in regards to the MF 101
Let's say I would like to achieve a full sweep (on Filter cutoff or any other parameter for that matter) via CV with the physical knob set near or full counterclockwise.
Suppose I amplify the CV signal (with the common peak being 5v) to a value of f.e. 8-12V
Would there be a risk of damaging internal components? If not, would I actually achieve a full sweep, or is there a voltage limiter?
The specification is 5v I know, but I was wondering whether I could go beyond that knowing that a full sweep IS possible.
Kind Regards,
Mike
CV Voltage Tolerance
Re: CV Voltage Tolerance
Although the other CV inputs on the MF-101 seem to sweep the full range of the parameters controlled by the front panel knobs with a 0 to +5 volt signal as described in the manual, I noticed that the Cutoff cannot be swept full range with just 0 to +5 volts. I found this out while using my MF-101 as an external filter module with my virtual modular synth. Check this out:
http://electro-music.com/forum/topic-12266.html
I just tested your scenario of setting the Cutoff knob at minimum and then applying +9 volts to the Cutoff CV input and it did open up the filter all the way, so for example, a 0 to +10 volt CV signal should work just fine. The Cutoff CV input goes through a 100K resistor which will limit the current and help prevent any damage, but of course there is always a point reached where an over-voltage which will cause damage. But, once the corner frequency of the filter goes higher than the highest frequency that you can hear, pushing the cutoff even higher will not cause a perceptible difference in the sound. I would recommend that you not apply CV much greater than what is necessary to fully sweep the filter cutoff.
http://electro-music.com/forum/topic-12266.html
I just tested your scenario of setting the Cutoff knob at minimum and then applying +9 volts to the Cutoff CV input and it did open up the filter all the way, so for example, a 0 to +10 volt CV signal should work just fine. The Cutoff CV input goes through a 100K resistor which will limit the current and help prevent any damage, but of course there is always a point reached where an over-voltage which will cause damage. But, once the corner frequency of the filter goes higher than the highest frequency that you can hear, pushing the cutoff even higher will not cause a perceptible difference in the sound. I would recommend that you not apply CV much greater than what is necessary to fully sweep the filter cutoff.
varice
Re: CV Voltage Tolerance
Thank you so much for clarifying and testing it out varice.
Unfortunately I couldn't do it myself this weekend for technical reasons.
Just out of curiosity, what did you amplify the CV signal with? Or did you use a module that outputs a higher voltage by default? (I know some modulars do).
Thanks again!
Unfortunately I couldn't do it myself this weekend for technical reasons.
Just out of curiosity, what did you amplify the CV signal with? Or did you use a module that outputs a higher voltage by default? (I know some modulars do).
Thanks again!
Re: CV Voltage Tolerance
For this test I simply used a 9 volt battery for the CV source.
An alternative that you might consider is to modify the MF-101 so that the Cutoff CV input is more sensitive. I did this to mine to get it to work with the -4 to +4 volt output of my synth. In my case, I added a 250K trim pot across the 100K ohm R31 (in parallel) to reduce the total resistance. I think that if you reduce the value of R31 to 50K ohms, that would double the CV input sensitivity.
An alternative that you might consider is to modify the MF-101 so that the Cutoff CV input is more sensitive. I did this to mine to get it to work with the -4 to +4 volt output of my synth. In my case, I added a 250K trim pot across the 100K ohm R31 (in parallel) to reduce the total resistance. I think that if you reduce the value of R31 to 50K ohms, that would double the CV input sensitivity.
varice
Re: CV Voltage Tolerance
Oh indeed, a simple 9v battery could do as well. 
The idea with reducing the resistance and increasing sensitivity sounds great as well!
My main concern was of course damaging the components with short 10v bursts, but I guess voltages around 10V will not really be very harmful.
My tech could probably build a small 4 in/4 out box with variable DC amplification and I'd be ready to go, I'm kind of not very comfortable with changing internal components.
The idea with reducing the resistance and increasing sensitivity sounds great as well!
My main concern was of course damaging the components with short 10v bursts, but I guess voltages around 10V will not really be very harmful.
My tech could probably build a small 4 in/4 out box with variable DC amplification and I'd be ready to go, I'm kind of not very comfortable with changing internal components.