The inevitable 'State Variable Filter not working' thread...

[patrick398]

So amidst all the excitement of planning how i'm going to mount the FSR i overlooked one crucial factor in this project; i'm still pretty crap at building.

For some reason i can't quite remember, i got it into my head that i needed to horizontally flip the vero image i was working off so that my build is now a mirror image of it. It had something to do with me reading the pinout of the ic wrong or something, i don't know, i think i was just being an idiot. Anyway, after soldering everything in i realised this so had to desolder the ICs and solder them on the reverse side of the board. That's calamity number one sorted but i fear there are more to come and they are going to be varied and numerous.

IC reading look ok to me. The only difference between the readings here and the ones i took when i was debugging it on the breadboard is that  pin 3 of IC1 is now sitting at 4.58 where as on the breadboard it was at 2.36. Someone suggested that this breadboard reading was down to meter loading but i can't see why it would happen on the breadboard but not on the vero.

IC1
1- 4.81
2- 4.81
3- 4.58
4- 4.72
5- 4.57
6- 4.72
7- 4.78
8- 4.78
9- 4.79
10- 4.59
11- 0.00
12- 4.58
13- 4.81
14- 4.81

IC2
1- 4.89
2- 3.23
3- 2.35
4- 0.00
5- 4.44
6- 4.44
7- 4.45
8- 9.72

Aaaannyway, all i'm getting is static noise, changes slightly with adjustments of the attack and decay knob. If i probe at the 'input' of the board i get high pitched whine which can then be found pretty much throughout the board.
What i'm wondering, before i have a proper look at it tomorrow is, is there anything that would obviously be dumping this whine into the circuit? I realise it could probably be caused by a million different things, i was just hoping it was indicative of a short or wrong component at a specific place.

Let's be honest, we all knew this thread was coming haha

[ElectricDruid]

Where's the 9V supply to IC1?

If IC2 is a dual op-amp, the first amp looks a bit suspicious to me, too.

HTH,
Tom

[patrick398]

Whoops sorry that's a typo. Should read 9.75v on pin 4. Thanks Tom!
Sorry i should have included schems and images of vero layout originally.

Vero Layout: http://www.sabrotone.com/?attachment_id=3193
Original Schematic: http://www.sabrotone.com/wp-content/uploads/2012/12/EnvelopeSVF.png
My Schematic with changes:

(note that the parts numbers in my schematic don't match up with original or vero layout)

Component Changes:
R9 is now 100k
R10 is 220R
R12 is 1k
C3 is 100n
FSR is not yet connected

I've not included Q or Sensitivity pot so on the board Sensitivity 3 is jumpered to Sensitivity 2 and Q 3 is jumpered to Q 1,2.

[Kipper4]

Is the FSR/ LDR on a switch?

You likely made an error with the layout. Since your svf is oscillating.

You wont need C5 and you can likely make c6 much smaller.

you can probably get away with just D3 shining on the ldr's and do away with D4. less parts.

I'll take a closer look at the schematic as soon as i get a minute.

I'd put D2 inside the NFB loop too.

[EBK]

Anyway, after soldering everything in i realised this so had to desolder the ICs and solder them on the reverse side of the board.

Come on now, don't be shy.  Show us your work. 

[patrick398]

Today i discovered an incredibly good method for debugging. First i took my board that wasn't working. Then i went over every connection. Then i threw it in the bin. Then i built another one and hey presto it works 
I still might go through the other one and try and find out why it's not working, it kinda feels like cheating if i don't fix it. Otherwise how will i learn eh?
FSR is all up and running too, it sounds great!
Plastic keyring cases arrived today too so on i crack...
Peace

[patrick398]

Hey guys, couple of questions if you don't mind. I'm waiting on a new FSR (i fried the other one  ) so i've been tinkering around a little bit in the meantime.

Basically i had an enclosure i drilled for the Mutron III lying around so thought i'd make use of it for my SVF. As i had three holes for toggle switches drilled i thought i'd just chuck three toggles in there to fill the holes but then thought i may as well put them to some use.

Two are taking the place of the Sensitivity pot and Q pot (never did really work out what Q pot did). Both have a 2k2 resistor wired to one side but effect is minimal annoyingly. For the other one i wanted to add a kind of bandwidth switch. Am i right in thinking C6, the 470n cap is setting the bandwidth? I tried wiring a 2.2u cap to one side of a DTDP toggle so that it would be in parallel with C6 but if there is any difference i can't really hear it. Maybe i've wired it in wrong. What would be the correct way to wire this (and the other two actually) soldering Rs and Cs directly to the switches ideally.

Thanks :

[Kipper4]

The 470nf is for the rectifier only. Not in the audio path. It determines what frequencies go to the envelope detector.

Sent from my SM-G920F using Tapatalk

[patrick398]

The 470nf is for the rectifier only. Not in the audio path. It determines what frequencies go to the envelope detector.

Ok so more likely C2 and C3?

[Kipper4]

Look how the mutron iii does // caps in the filters

Sent from my SM-G920F using Tapatalk

[patrick398]

I was basing my initial assumption on the lovetone meatball schem which has the same set up leading to the second IC. 10u cap into sensitivity pot into 4k7 resisor into switch between 22n and 470n labelled 'bandwidth'

http://www.experimentalistsanonymous.com/diy/Schematics/Filters%20Wahs%20and%20VCFs/Lovetone%20Meatball%20McMeat.pdf

[Kipper4]

The bandwidth cap determines which frequency that the envelope detector responds to. If you want to change the filters response change the cap in the filter c13 meatball.

Sent from my SM-G920F using Tapatalk

[patrick398]

Ok great, thanks Rich

[duck_arse]

on the meatball circuit, C13 and C12 set the band. on the sabro circuit, C2 and C3 set the band.

patrick - are you building to the sabro circuit? do you have two leds running off a single R22, or do you have the proper CLR per LED?

[patrick398]

Sorry i didn't see this last post! Yeah i did think it was C2 and C3 so nice to have some clarification
I was working off the Sabro schem and do indeed have two leds running off R22. I played around with a few leds and strangely found the ones that work best are ultra bright pink pre wired ones which each have a 4k7 resistor wired on them.

All boxed up now and sounding fantastic. Fitted the FSR and it's strange casing. Looks a little unusual but hey it works haha.
I used a square plastic keyring frame, drilled out the front and epoxied it around the FSR then put a square of felt/foam (type for putting under furniture legs) on top of the FSR itself. The removable back plate of the keyring frame now functions as a lid for when not in use.

As usual you guys were fantastically helpful throughout this build and i thank you all sincerely for your patience and knowlege

FSR and felt:


FSR and felt with lid:

[Fancy Lime]

Hi Patrick,

remind me, what was it again the FSR is controlling? I've been fiddling with an autowah for a few days and finally got the controls right when I stumbled upon your thread again, reminding me that there are always more things one could tag on

Thanks Andy

[Kipper4]

IIRC Patrick is controlling the brightness of the led that light up on the ldrs in his schematic reply 6

Or he replaced the ldrs with the variable resistance from the fsr.

I'm interested to know which output he's using.
With my set up I'd probably go with the lpf output.


I could be wrong.

[patrick398]

Hi Patrick,

remind me, what was it again the FSR is controlling?

Hey
I think i've got the FSR in parallel with the 220k resistor and second LDR between Pins 8 and 13 of the TL074 so it's increasing the lower limit of the filter sweep? the 220k sets the lowest point, any actuation of the FSR reduces this resistance massively to around 100ohms...i think haha.
Approach this schematic with caution. I think it is correct but it was drawn retrospectively from annotations i made on the Sabro schem so i guess it's unverified.  Made a few changed by ear which may or may not be significant to you but they're here if you need them

I'm interested to know which output he's using.

I'm pretty sure it uses the bandpass output...if i understand you correctly 

Interested to see what you guys are up to as always!

[Fancy Lime]

Hm, very intriguing. I've tried incorporating a momentary switch in my current autowah (DOD FX-25 type) that sets the filter sweep to a positions that can be fixed by a pot. So as long as I stand on the switch, the filter is static. Or I can give it a kick to go up or down before returning to wherever the envelope says it should be. Turned out not quite as amazingly useful as I imagined it to be for my style of playing. I'd be very interested in a sound demo of your thing.

Cheers,
Andy

[Kipper4]

You may never have know if you hadn't tried it though Andy.

If someone asks you about the mods you will know what effect they have.