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

[gmeredith]

Your photo didn't seem to attach - can you post it again?

Cheers, Graham

[jepyang]

sorry about that, attached now.

[wax+wire]

building another one of these, cause the first one was so good [and it is now housed in an SK1].

the Jaycar electronics shop down the road from me doesn't have any 100nF/ 0.1uF green cap capacitors in stock. could i swap them for another type of capacitor?

also, has anyone tried a different input resistor instead of 470K.  i feel like something more around 300k or something might be better.  just my thoughts

[gmeredith]

Yes, or another approximate value - it's not that critical.

Same goes with the 470k resistor - they were simply the value I used to get a level input/output response for my sk8, but are by no means critical.

Cheers, Graham

[wax+wire]

So i've built my 2nd QUAD PHAT FILTER and installed it in a Casio SK5 (first one is an SK1)

A few things i did differently this time:

1. Swapped the audio input resistor to 370K.  Probably still a little high, maybe 350K is ideal
2. Put a FILTER BYPASS switch in that switches between the pre-anti-aliasing filter output on the casio, and the post-PHAT FILTER output
3. Used just one single gang 100K pot for the filter cutoff.  When I was testing it I used a 1M pot.  I wonder if a 150K or 250K pot would be best, and drop the resistor on the 'B' lug of the resistor to only 70K or so.
4. Dropped the resonance input resistor to 820Ohms.

What I've noticed is:

1. Audio is still a little lower in volume than the non-PHAT Filter output
2. The Phat Filter output is less bright than the pre-Phat Fitler output.  I really like the digital artefacts of the SK when you bypass the anti-aliasing.
3. The resonance is now too wild and crazy.

looking at the original - http://s1107.photobucket.com/user/joer0952/media/qd.gif.html there is no input resistor on the resonance though.  hm

I actually think ideally a few of the resistors should be soldered onto the lugs of the potentiometers, to make altering the circuit easier as you want to change up some of the resistance and get a better range.

[gmeredith]

I think I added the resistor to control the resonance. Be aware that the different IC's you can use all behave radically different from each other - I designed this one for the NE5534AN op-amp. When I tried a 741 IC in it it squealed uncontrollably at a certain res position. A TL071 behaved differently again. So the values I finally used were for the NE5534AN

[wax+wire]

Sorry for reviving the old thread, but....


I've been using QUAD PHAT Filter's in my SK5 & 8 and gigging with it and loving it ( https://spiritbunny.bandcamp.com/ ) but the filter has been a bit weird/wild/dodgy

So i had a repair day and discovered that the NE5534an chip on one of my channels was to blame.  Simply swapped it and now filter is so much nicer - both with the LFO, by it self, and with the envelope control.

One query/thought - the frequency range of the cutoff still could be better.  The cut off only responds to about the upper 1/2 of the turn on both instruments - and I don't get quite as big a sweep as I'd like.  Ideally I'd like to be able sweep right down into those low frequencies for some rumble and back up again into shrill highs.  Should I look at swapping IC, or is there another option to look into?

Cheers J

[SynthularModulus]

Does the documentation for this mod exist somewhere? I tried following the link to the Yahoo group at the beginning of this thread, but it is a dead link. Would love to do this mod, but I really would like to read through a full walkthrough of the mod before trying it. Links appreciated!

[wax+wire]

Hi all

Anyone interested in doing this, and/or the SLOW AD mod on an SK1 check out this.



There are other images around, but these are correct for the audio outs and the CV outs.

[wax+wire]

oh, and the documentation is here:

http://warningwillrobinson.com.au/index_files/Professor.htm