Noob filter question

[dylar]

Hi-
I've built a number of stompboxes and a few simple synths (WSG, Cacophonator). I would really like to build a nice filter that I can feed audio signals through. Though this is probably a dumb question, what kind of signal typically goes into a VCF?
If I build the minimoog clone or a MFOS filter would I be able to send a keyboard output into it?
I am just not sure if these filters can accept a normal audio signal or if there is some intermediate conversion step in between the audio signal and the VCF.
thanks for any help.

[Mongo1]

Hi Dylar,

The filters are set up to accept plain old audio signals - the only possible issue is signal level. Modular synths use higher single levels that a guitar (for example). I have run my guitar into the Yusynth LPF, and it worked fine, although the level was somewhat low.

For that reason, you might want to consider either adding a gain stage before the filter, or modifying the input stage to add some gain. Other than that you shouldn't have any problems.

Gary

[dylar]

Thanks that helps. Looking forward to the build!

[yusynth]

Yes, these filter can be used with a guitar provided you use a preamp befor the filter or do some minor changes of resistor values in the filter circuit. I systematically designed all my clone filter with a buffer input stage which can be trimmed for the input level. If you check the schematics you'll see that some resistor are labelled with a * or a ** which indicate that these resistor values can be changed to modify the gain of the input stage. For example in the Moog filter, this is resistor R5 (56K) that you can increase (say 220K or 270K in order the level up the input signal, you have to try diffferent values), for the ARP filter it is also R5 that you may increase up to 330K, for the EMS and the Steiner filters it is R7.