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[gmeredith]

Well if that's true, that would make a big difference. I just got a handful of quad pots off ebay for my new board I'm drawing up - if you say I won't need them for that control, that is going to be a big expense cut!
 
I'll look into this.

Cheers, graham

[Dj Task Manager]

RE: 2 dual amp chips,

what would be awesome would be to use the spare bit of unused bit of board on the sk5 (just behind where it says CASIO on the back of the keyboard) for the quad filter.  There are two spots that could just about accomodate 2 8pin chips then all other components would have to be carefully placed to best use the other pads and such.  Probs wouldnt work out  but would be a nice if it did!

Maybe some other smaller effect circuit would fit there better...

have a squizz see what you think...

[Gordonjcp]

Could you just squeeze a quad opamp on, for a total of 14 pins and no gap between two chips?

[gmeredith]

So you have an SK5 you're putting the filter into?? That must explain the audio output error you mentioned in my guide. I had assumed from other circuit bender's info that the sk5 and sk8 had nearly identical boards. Seems not...

Cheers, graham

[Dj Task Manager]

Could you just squeeze a quad opamp on, for a total of 14 pins and no gap between two chips?

the available pads that could potentially accomodate 2chips are not next to each other. 
You could cut out the whole area and replace it with a custom circuit board or bit of strip board or something though...

I think thats what i'll do and put a delay circuit on it

[Dj Task Manager]

So you have an SK5 you're putting the filter into?? That must explain the audio output error you mentioned in my guide. I had assumed from other circuit bender's info that the sk5 and sk8 had nearly identical boards. Seems not...

Cheers, graham

yup into a sk5, maybe thats the discrepancy.  
I fired up my squashed fly quad Q&D filter up and it works wonderfully!  a real range of sounds from warm bubbling analoguey bass to the sound of stormy wind*.  I need to try and squeeze it inside now.  Video to follow soon when its installed...  

The res pot does really crank up the wind actually, my sk is blowing a storm, anyone else get this? I do like it but I was wondering if it could be due to a fault? Anyone else get whooshing? I'll put a link to some audio tomorrow...

Another thought (once you get playing with this and making it modular it opens up so many possibilities!)...  It would be neat to sum the envelopes (with diodes) then amplify it with a transistor to drive an LED/vactrol to modulate stuff (delay length etc) ARRGHH so many possibilities!!!

[wax+wire]

some wild ideas out there.

I'm wondering how big the pay off is between 1 and 4 Filters.  I understand the difference, but given my building quality, and difficulty with tight spaces, I'd probably only add a 4 chan filter if i put it out side the box.  a single VCF might fit though....

basically, is it soooo much better to have four channel filter that i should dive into it?

[gmeredith]

Just start with one if you're going to make an external box, then if you want to explore more, build extra modules. Tthe best of both worlds, and you have no risk!

Cheers, Graham

[wax+wire]

Thanks for your work on this.  did some more/started again on this today...

some component questions:

**does the diode need to be N4148 or would N4004 work - i only understand diodes in their most basic form??

**can the metalized polyester 0.1uF cap be a green cap instead?

also, any progress on the other ideas - i.e. using a single gang pot instead of quad?

hoping to build a mono one first to use as an effects pedal/other circuit bent instruments before attempting the quad version.  fingers crossed

[gmeredith]

I think the IN4004 is a power diode - this one needs a signal diode (IN4148) as I understand it - I could be wrong though. Best use the 4148 if you can get them.

Metallised polyester cap should be OK.

Single gang pot should be OK for the cutoff freq knob, but you'll need quad gang for the res. Here are some here:

http://www.ebay.com.au/itm/261215523097?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649#ht_2597wt_1074

These are really small, I bought a few of them a while back.

Cheers, Graham

[wax+wire]

I finished my build (one unit).  without any luck yet.  a few questions to assist with troubleshooting.

1]  The LED - what should it do (always on/flash with audio input??) mine does nothing.

2] the links on the back of the PCB, are they meant to be one point-to-one point (the black + green?) links...

Any other things to look for when troubleshooting.  I've checked my PCB board trace cuts with a multimeter and they seem ok

[gmeredith]

The LED is a power indicator, it should be on all the time. Check it is in the right way.

The green and black wires are point to point wiring.

Cheers, Graham

[wax+wire]

arg. rookie error.

I flipped my LED, and did some more checking.

From my understanding of the circuit (its a bit hard with the front/back PCB) the 7.5+ flows like this (for test) -> to the cut-off pot leg A and to pin 7 of the IC?

*** Therefore, turning the pot should alter the LEDs brightness? (mine does). ***

it looks like it might be working - my next problem is i'm using stereo leads and mono sockets to test - which occasionally cause an issue depending on the sockets - so i'll try to fix that next

[wax+wire]

i got it working *WOOT*
using the type of sockets i had is dodgy when using stereo 3.5mm plugs.

while i've only tested it using iTunes (ABBA's Dancing Queen) through one of those little 1W 4" marshall speaker/amps, I found the cut-off didn't go low enough.  I kind of imagined it would roll all the way down to 20Hz LPF.

Is this normal? design feature/flaw?

I understand with the SK5 you probably would be fine with out rolling off all the way, but i plan to make both a stand alone filter+lfo, and a SK5 built in filter.

[gmeredith]

That's great news! 

The cutoff can be adjusted to go lower or higher by changing I think some capacitor and/or resistor values in the filter network section, but at the expense of top range, if going lower. I think I settled on a value for me that worked in most situations for me. The circuit is very imperfect, it's rough and grungy and lo-fi (many would consider that an asset in this situation  ), don't expect too much out of it. But it's the only filter I ever found that was set up for 6-9V DC battery power - all the other designs out there were for split rail -15V-0V-+15V, which was no good for building into the SK and powering it as well from it. That's why I went with it for the SK.

LED changing - I don't recall mine doing that. I don't think you need the LED - it's just an indicator.

Cheers, Graham