Muff's Modules & More

tokyomatik

I watched the video and sound pretty interesting but to see all that wiring involved is a bit spooky,

take a look:
http://ericarcher.net/devices/diy-lpf/

anybody here made a pcb layout for this or tried to add the optional cv? i would really like to have some opinion before to start a knitting work like that eek!

raisinbag · Posted: Thu Mar 08, 2012 9:55 am Post subject:

That looks SWEET!!!!!!! I am looking for a VCF to run at 9v to go into a stand alone box with a VCO/ LFO based around a 40106, so it is perfect! Crazy looking pref board eh? Just have to find those funky ICs close to home (or add to next digi order)

THANKS! Just what I was looking for!

tokyomatik · Posted: Thu Mar 08, 2012 10:00 am Post subject:

more or less i'm also planning a small box with sequencer, 2 vco and a vcf and the fact that u can also add cv controll would make a perfect stepped filter
everithing running at 9v....nice Guinness ftw!

raisinbag · Posted: Thu Mar 08, 2012 9:36 pm Post subject:

Ok so I found where I can get the Virtual ground and Rail to Rail ICs so hopefully I can build one of these up soon.

Seems that if I want to make it VC I have to take the wire from POT and run CV in at that point. My plan is to use a Normalized Jack, going to pot, so when I insert a cable it will activate CV option and disengage pot.

Now there seems to be a WARNING about not running a negative voltage into it, and I want to use this VCF as part of a "Box of fun" for my kids who may not pay attention to polarities, so if I put a Diode like a 4148 in series with CV, do you think that would make if fail safe?

decaying.sine

jumunius

raisinbag · Posted: Fri Mar 09, 2012 10:14 am Post subject:

Ya the wiring doesn't look that bad, maybe not the kind of thing to work on when you are sucking back a few beers and a Sat night!

I am trying to make a few PCBs of my ghetto VCO/LFO so once I figure that out maybe I can make a few of these for fun.

Did you see my question about the diode in series for VC? I figured it would be a small signal one, vs a 4001? series? Or would a Zener be better? Just basically to stop signal from going neg, as my 4 year old will be playing with it!!!!

4mspedals · Posted: Fri Mar 09, 2012 12:01 pm Post subject:

Don't use a zener in series, they have a breakdown voltage that will actually allow negative voltage to pass! A small 1N4001 is great, although will introduce some non-linearity (which probably won't be a problem unless you're trying to track 1V/oct or something specific).

Another option which is commonly used is two Schottky's, one running to V+ and one to GND like this:

The 1M resistor may be unnecessary, but won't be harmful. I have it there because in the circuit I clipped this from, I want to make sure there's 0V when nothing is plugged in the jack.

raisinbag · Posted: Fri Mar 09, 2012 12:17 pm Post subject:

so is the JDIV the jack? just trying to follow the flow

jumunius · Posted: Fri Mar 09, 2012 12:33 pm Post subject:

4mspedals · Posted: Fri Mar 09, 2012 12:34 pm Post subject:

Ah, sorry that wasn't clear. It flows right to left, JDIV is the jack. You could run D5 to +9V if that's what the upper limit on the circuit is.

raisinbag · Posted: Fri Mar 09, 2012 1:29 pm Post subject:

Cool thanks, I have to do a little reading on Schottky's to figure out what is happening exactly. And for the 1meg resistor, I will have to see how I want to add it (if needed), as I was going to use a switched jack going to the freq pot, so when I plug a jack in, it will switch out the pot into CV mode.

Hey your site is really cool 4ms! You have some cool stuff there.

4mspedals · Posted: Fri Mar 09, 2012 1:50 pm Post subject:

Schottky's (such as the BAT85) just have a lower voltage drop than normal silicon diodes such as the 1N914 or 1N4001. So they clamp a little bit "tighter". The difference will be that with a schottky, it will actually allow down to around -350mV to pass, but with a 1N914 it'll allow about -670mV through. Anything more negative than that threshold voltage will force the diode D6 to conduct and route the current to ground (or "from" ground, if you look at it that way). The 350mV/670mV number is called the Forward Voltage Drop. Neat stuff... the wikipedia articles on diode/schottkys are pretty good.

raisinbag · Posted: Fri Mar 09, 2012 2:04 pm Post subject:

ya that whole bipolar way of looking at electron flow has me messed up sometimes. I'll read all about those shots diodes tonight after I finish teaching. AHHHH I have to go out in a big snow storm. Yikes!

Thanks for the help, i''l bug you some more after I do some reading.