The Casio SK sampler PHAT PHILTER BANK mod has arrived!!!!

[wax+wire]

Pretty sure the LED is designed to match the cut-off amount, as it even matches my LFO.

I'd be keen to know if anyone has changed values for more extreme settings, including more resonance.  I like the idea of it 'taking off'/self-feedbacking.

well, now i've built one, I'll house it as a standalone fx and start on the quad!

J

[wax+wire]

What circuit did you use gareth for the LFO?  I've used casper's 555 LFO circuit, though find the shape+depth knobs a little strange/fiddly

[wax+wire]

Finally (been re housing things/repairing an MT-46 and rehearsing music) put my mono filter in a box and added a dedicated LFO (555 circuit).

Working nicely, though it is a lot greater range from the LFO than when just using the freq. and res. knobs.  Maybe I need to alter some of the resistors that are trimming the range?

Also, I've used a real basic LFO circuit this time, as I just want one knob, rate and one switch, Triangle - Off - Square.

http://getlofi.com/control-voltage-output-from-555-timer-circuit/ -> is this the circuit you used Graham for that?

J

[wax+wire]

So I dropped the 1K Resistor that is connected to the resonance pot A down to 500Ohms and the resonance is able to get really nasty (maybe too nasty for some people - maybe somewhere in between??)

Still no luck finding the best way to increase the cut-off frequency's upper and lower limit

[wax+wire]

i'm finishing off my 4 channel version of the phat philter! (the mono version is working nicely - it even has CV in from my MT-60 casio).

however i forgot to pick up enough 10nF (103) green capacitors today :-(

Can i swap one green cap for a ceramic 10nF capacitor and not cause any issues?

[wax+wire]

I finished!!! well not totally, still got to put it in side but i'm stoked it all works.

I was wondering would it have any advantage to make some sort of simple distortion circuit and make it 4 times before the filter, so each channel is distorted before being shaped???

[wax+wire]

All working and housed.

initially forgot the comment about audio line 1/2 being wrong, but with that fixed it is much better.


main issue stopping it from being amazing is the LFO.

i use a basic 555 LFO (http://www.tradeofic.com/uploadfile/ic-circuit/2009624221917817.gif) but the triangle wave is way too weak.

should i work out a way to boost the triangle wave's amplitude, or build a better LFO all together?

[gmeredith]

Hey sorry I haven't caught your updates - don't seem to be getting any reply notifications to this thread 

That's great you got the quad working - again I severely regret designing the board layout so tiny - it has caused no end of problems building it. Maybe you could draw up a PCB diagram of the quad circuit for those who want to make up a proper board? I wish I had time to revisit the pat philter design but between family, band, music and work I just don't get long spans of time on my own to tinker with project reviews - plus there is the lure of new projects 

[wax+wire]

i did mine on a vero board.

I can confirm though you don't need a quad gang pot for the cut-off. (and you could probably remove the 100K resistor just after the pot's wiper and have just one straight off the pot.

strange thing is that the cut off is brightest at 2/3s full turn.  maybe might pot is dirty/dodgy, or maybe it doesn't go beyond there in cutoff

[gmeredith]

quad pot -  that's great - that cuts down the cost greatly 

[wax+wire]

yeah, and now i have a spare quad pot.... thats why i'm thinking about some sort of quad distortion pre-filter?

[gmeredith]

Try the DOD 250 overdrive circuit:

http://music-electronics-forum.com/t17025/

I've copied my mate's pedal and it's dead easy to make - and that link someone has already drawn up a circuit diagram. It's a good bitey distortion pedal - a bit tube screamer-ish in sound, not dull. It sounds good on bass synths sounds to squelch them up a bit. It has drive and volume controls. I made mine on cardboard and wired up the components with copper wire - easy as that! It uses a 741 IC - you could probably find a quad version of it and make up a quad board without too much trouble.

Cheers, Graham

[wax+wire]

Thanks.  I'll look into a distortion unit shortly

for now, i'm trying to improve the LFO section.  I really am not liking 555 based LFOs.  on mine the triangle is much quieter than the square, so it doesn't really drive the filer.

I've used this until now:


but i've been looking at a LM324 based LFO over at electro-music:



(i had to turn a single supply 9V power into dual supply 4.5+/- V

however the voltage output swings from -3 to +3v where i suspect the filter you've designed expects a + voltage only??

is that my problem?

or should i try a different 555 circuit like this:

[wax+wire]

going to finish off the 2nd LFO (sorry my pictures are so massive in the thread) and put it in today hopefully.

I've noticed the volume after the filter is considerably lower than before.

any thoughts on a simple circuit to boost the volume?  or should i look at changing the input resistors?

[wax+wire]

So today, after having gigged a number of times with my SK5 post-Phat Philter mod, and found the need for more gain needed, i opened it up to adjust the gain on the post-Phat Philter channels

1st up i tried swapping the 470K resistors that are set the input volume for something lower.  I only had a pack of 100K, so I tried that, and while it was much lower, it was considerably more distorted.

so i went back to 470Ks and then put a transistor preamp i had built years ago at the output.  much better.  now the gain on the four voice channels is greater than the drum loops (but with a potentiometer, to pull it back it in)

much better.