EDP Wasp VCF as a Pedal...WOH!!!

[snk]

Hi,

Is there a schematic that the layout was for certain derived from?

I don't know, the original poster didn't mention the source...

I'm not sure if I trust that layout.

At least two people in this thread built it and reported it to work fine.

Where is the signal input meant to be?

The input signal goes to gain knob's lug 3.

Is the 78L05 regulator the right way around?

I don't know  (you mean : on the veroboard, or on my build?)
On my build, i have put the 78L05 in the same orientation than the layout. And no one who built it from the layout picture reported it to be in the wrong way.

[anotherjim]

Well, if the layout shows the view looking down on the top component side, that voltage regulator supply input is at the bottom pin and the +5v output is on the top pin.

If the regulator is working right, there will be 5v on pin14 of the 4069. Note that both chips will work happily on 9v supply, so I'm puzzled as to why 5v regulation has been provided. That said, if you drive the 78L05 backwards, it will probably just fizzle out quietly and supply the original 9v through to the rest of the circuit. And yes, it might appear to work.

[anotherjim]

Ah, but this one...
http://modular.fonik.de/pdf/Wasp%20Filter%20clone.pdf
Used a TO-220 7805 regulator (but note also the original CA3080 chips so it is a proper clone). If the stripboard was developed from that, someone may have copied things over. The little 78L05, most of them anyway, have reversed connections to the 7805 when you hold them side-by-side.

Not that I hate the LM13700, but it isn't specified to work on less than 10v supply, so it's just about getting away with it on 9v. Not sure if it works properly on 5v.
...but wouldn't be funny if the only reason any of those are working is that they've got miswired regulators and are really getting 9v?

[ElectricDruid]

It's funny about the LM13700. It's not specified to work at 9V, but it does. In fact, it'll go quite a lot lower. Someone on the SynthDIY list built a synth filter running at 3.3V with it. Perhaps some of the specs go a bit out at lower voltages, but it certainly seems to be fine.

[anotherjim]

But does anyone agree that that layout has the regulator shown wong way wound?

I don't understand why the spec of the 13700 has higher minimum volts. I think I've read that it was developed as a better CA3080 and if you ignore the extra output buffer and linearizing diodes, it pretty much is a pair of 3080's.

[ElectricDruid]

But does anyone agree that that layout has the regulator shown wrong way wound?

Yes, it looks like it's the wrong way around. I've never come across positive regulators that break the conventional pinout. But in a way, who cares?! Since the bits that are left all work at 9V, why not just leave it out? It'd make more sense that sticking a pointless regulator in there for no reason.

It looks like a Wasp-hangover to me. There probably was stuff in the Wasp that needed a 5V supply (since most of it was logic chips) so whoever copied the filter also copied the 5V power supply, without realising that it was unnecessary - or perhaps they thought that it would sound different at the higher voltage or something and wanted a really accurate clone. Seems pretty unlikely to me. More headroom is likely to help, I'd have thought.

[snk]

Interesting. Thank you all for your technical input.
(Most schematics or layouts i have found about the Wasp VCF featured the regulator, by the way...)

Any idea why the dry signal is always mixed with the processed (wet) signal ? Could it be a bad cut on the veroboard (but i didn't see any), or because i used a 2P4T (instead of a 1P4T) ? Or something else ?

[anotherjim]

Stripboard layouts are phenomenally difficult to assess without a schematic. The schematic is the bible of the circuit. PCB, stripboard or perfboard, the schematic is the reference from which the layouts are designed.
Now, I cannot find a link to a schematic with either the LM13700 or the input gain control.
The only ones out there are for true clones and Jurgens version for Eurorack modular synth, which is otherwise also a clone.
I'm thinking that none of the LM13700 versions actually had anything to do with Jurgen. However they probably just cross referenced the OTA chip pin numbers and used Jurgens schemes as a basis. Also let's be clear, Jurgen did not design the filter but he did help promote a long dead synthesiser product (the EDP Wasp) by publishing his cloning work.
Anyway, its a nightmare of dead links out there for this one and where someone claims they have it working, I'm not sure what circuit they built and some of the YT demo's offered are for Wasp filter original circuit clones anyway.

Here's yet another stripboard. Note the regulator is the right way around on this one. And no, the rotary switch having an extra pole is not an issue so long as the 1 pole used is wired right. The following calls for a 3P4T which just happens to be one of the more commonly stocked ones with suppliers.

[PRR]

> LM13700. It's not specified to work at 9V

Recommended to 9.5V.

There's no 9V cut-off in there.

The "Functional" circuit should quit at 2.4V. If it really has Darlingtons in it, 3.6V. We need some headroom over that. As the LM10 shows, it can be quite small. I've never doubted the '3080/'13700 can eat 5V and thrive.

[snk]

Thank you, Jim, for your insight.

I know that the schematic is the way to go, but unfortunately i am not skilled enough yet to read accurately a schematic  (It will come, one day, but at the moment i am struggling with simple schematics, ah ah !).
And indeed, i understand how difficult it is to troubleshoot a veroboard without the schematic reference...

Yes, i know that veroboard layout : i used to use a lot of tagboard effects veroboard, as most of the publishers know their stuff (and if a layout is published with errors, there is a discussion in the blog and the layouts got fixed quickly).
My only concern is that this layout never got published on tagboardeffects, so i am not sure that it is verified and working fine either  If i can't debug my build, I will try this one.
I had found this one too :https://billsabandija.blogspot.com/ (but it features individual outputs for each filter types, and i am more keen to using a rotary switch to select either one or the other).


After some more experiments, i have found some little things, but i am not techie enough to understand what it means :

- I tried to plug a LFO into the CV input : it works fine, the LFO modulating the filter cutoff, which is the expected behaviour. What wasn't expected is that plugging a wire into the CV plug made the "dry" signal disappear. Then, out of curiosity, i put the tip of the CV jack to the wire soldered to the CV input socket: i think that what i was hearing was what i was supposed to hear in normal conditions : the lowpass was acting as a lowpass, the distorsion had saturated the signal a bit, and no dry signal was present.
So i think there is something to investigate around that CV wire/jack socket...
I tried to put that wire on a on/off switch : it didn't cure the problem. I disconnected the ground of the CV jack socket : i heard some oscillaton/whining. So, for the moment, i replaced everything in its original configuration.

- The other thing is that on some filter types, the distorsion is waaay over the top, and making the filter self-oscillatiing (while by design the Wasp VCF shouldn't self-oscillate), while on some other filter types, the changes with/without dist are barely audible. So i guess something is wrong there, but i can't figure out what it is.

I successfully built an Anderton SuperTone Control this week, and both designs are roughly of the same level of complexity... But, as you wrote, with a veroboard it's hard to tell if the error is from the layout itself, from the wiring, or from a mistake on the veroboard...

[anotherjim]

Well, it helps to have some kind of schematic. Different parts but still the same job. Note the 1998 date, Jurgen did not need to consider replacing the CA3080 as it was still a widely stocked part then.
There no supply voltage noted but everything in the Wasp ran off 5v.

Looking at the rotary switch, only 3 positions are filtered. The fourth "NF" (misread as NP?) is No Filter. It is the filter bypass in the original synth. So there is meant to be a position with no filter effect.

To get a better "working" schematic, you could just annotate the things that are different on a printout of that. Because the 4069 chip contains 6 identical parts, the pin numbers could be different to make stripboard layout easy.

The next step is to find test voltages (to measure with your multimeter) that "ought" to be there without anything to tell us otherwise. First would be the supply voltage at places where + is annotated. This ought to be 5v if we have a working regulator. Mostly this is found on chip pins, but also see it goes to some other components. Every single one is worth measuring. Then there is the ground 0v shown as an inverted "T" on the scheme. It's easier for this to power off, put the meter on continuity/diode test (with a buzzer/beep sounder when the probes touch) and check for a beep between the supply 0v and every 0v point of the scheme.
The other voltages to find are any "bias" level that ought to be with no sound. Every part of the 4069 has an input and output. Each output that's used in the audio path will usually be at close to half of the supply voltage. So if the chip has 5V supply, the output will measure about 2.5v. For the 4069 schematic symbol, the output is the pointy end of the triangle. If the output voltage is greatly different from half supply, then something is probably wrong at the input side.

[snk]

Thank you for your help, Jim.

The next step is to find test voltages (to measure with your multimeter) that "ought" to be there

I will measure the voltages with my multimeter in a couple days, and let you know what i find.

Looking at the rotary switch, only 3 positions are filtered. The fourth "NF" (misread as NP?) is No Filter. It is the filter bypass in the original synth. So there is meant to be a position with no filter effect.

I thought it would be Notch Filter ("NF", or "Notch Pass" "NP") ? Some layouts i have found added this, despite a notch filter is not featured on the the original.

[ElectricDruid]

I don't agree about "NF" being "No filter". It *does* look like a notch filter to me.

The filter design is a standard 12dB state-variable filter. The only weird thing about it is using CMOS inverters in a linear mode instead of proper op-amps. On an SVF, you can create a notch response by mixing together the HP and LP outputs. That's exactly what the two 100K resistors are doing.

Rod Elliott mentions the trick here, for example:

http://sound.whsites.net/articles/state-variable.htm

[anotherjim]

Duh, you are right. I forgot the filter would still be working and missed the feedback from the LP output

[snk]

Hello,
A few months later, I went back on this faulty build, so i am giving some report.
I don't know what went wrong the previous time, but after trying again today, nearly everything works fine 
The gain, distorsion, frequency, resonance, lowpass & hipass as well as cv modulation : everything works as expected !

The only things not working as expected are the BandPass and the Notch filters. The Bandpass produce nearly no signal, and the notch doesn't sound like a notch (it sounds more like the dry signal only, with just a slight difference in the high freq range).
I am suspecting an issue in the wiring (if the bandpass is somewhat the sum of LP+HP, and the notch the difference of them, it would make sense, isn't it ?), but i have checked again and everything seems correct.

Anyway, I am already very happy with the filter working (and sounding !) fine, as i can enjoy a LP/HP with drive and CV modulation.
I will try a little bit to find why the BP and Notch do not work as expected (does anyone have a clue ?), but if i fail, i might end up boxing it into an enclosure with only a LP/HP switch instead of the rotary 1P4T.

In any case, thanks to everyone for the help !

[snk]

... With a little bit of thinking, i think i found the issue :
- as the resonance pot was layed out the wrong way, and as one pin of the resonance pot shared two connection (one going to the 1P4T as being "the bandpass position"), i just wired the "resonance wire to rotary switch" wire to 1st pin of the pot (instead of pin3, as told in the layout) : it works
- Also, the frequency pot is supposed to be a 10KA pot. But with a log pot, i found that the action of the filter was quite inaudible on the first half of the pot, which might have led to confusion. I will try with a linear pot, and report if it is better.

So, to sum up :
- I really don't know what initially was so wrong with my build...
- the layout from guitar-fx-layouts, made by sonusfluxa, can be tagged as verified for anyone who would like to build it...
- but please pay attention to the wiring of the resonance pot (which was either wrong on my build, or wrong on the layout, and have an influence on each filter types working or not) !

[John Lyons]

So is there any reason not to run this circuit as in the schematic at 9v?

[John Lyons]

Assumably the original was set at 5v because it ran on batteries right?
I guess I'll try 9v and we'll see.

[anotherjim]

I can't remember what I did in my build. I'd look but it's not here at the mo'. I think I would have run it at 5v, since it can be overdriven more easily and that's how it was in the synth, as it says here...
https://www.schmitzbits.de/wasp.html

[Strategy]

I ran my build at 9V and I don't notice anything weird about it. (No longer have the pedal, gave it to one of my collaborators - I miss it so maybe I'll build it again!)
Strategy