if im honest from what you describe I don’t think it would necessarily be a bad batch. I think there may just be an issue somewhere. does it only happen when something is plugged into the output jack? the output jack is wired through a capacitor to the output the lm13700 so I dont think it would effect the opamps. however it is directly wired to the LED at the top of the module. infact you can directly control that LED by plugging a control voltage into the output of the module.
if you look at the schematic you’ll see the output LED (top one) has its own opamp buffer as it was spare I figured to use that instead of a transistor or something. so if that is lit up. maybe the opamp is working. it could be something else.
but this may offer an answer. it could be what its being plugged into???
also see what happens when you take the lm13700 out. but plug something into the output of the module like an LFO to see if that changes anything with the LED. if it does that means the opamp works.
if its constantly on maybe check the soldering to the ground connection on the resonance pot??
I dunno im just spit balling, I think it might need another few stares to find a loose joint or something!!!
The signal flow is: Dixie VCO from my Eurorack > Input of the 1114 > Output to my audio interface
If I take out the LM13700 chips, and plug an LFO into the output of the 1114 module, both the LEDs flicker, which suggests the TL074 is working I guess? The interesting thing is that with the batch I suspect might be dodgy, only the top LED lights up when I use those TL074s. Odd.
I’ll have a bash at reflowing the solder on various points to see if there’s anything weird there. I’ve attached an image of the PCB anyway for keener eyes than mine. Please ignore the dodgy resistor soldering in places. I started this board ages ago before I got any better ha.
Schematics are one thing I have very little understanding of… something for me to work on!
well that’s a good thing only the top LED should do something when the output receives CV. the bottom one is not connected. however the bottom will light up when you put voltage into the CV input of the filter I think.
Interesting! Sounds like a short somewhere then. I’ll give it a good ol’ stare out and see what I can find. I’ve got another few LM13700 chips I will try too, juuuust incase.
what Caustic said would be a good place to start .something that was brought up the other day , solder the resistors and diodes from the top its easier to align the parts and the leads are straight on the bottom easier to trim off .
Thanks! This was something I started back as one of my first modules so there’s definitely a few suspect areas. I’ve re-flowed everything on the other side of the board and it hasn’t worked, but not necessarily these bits, so I’ll give that a try. If that doesn’t work, I’m crossing my fingers that it’s the LM13700, as everything seems okay (or at least, up to the standard of okay-ness as my other builds which all work fine haha).
No joy unfortunately The replacement LM13700s exhibit the same behaviour. I get a reaction when I plug in something to the output (with no input), and when I have something plugged into the input only the top LED comes on, with no signal.
I am going to try to resolder a bunch of the components and hopefully that’ll do the trick. If not, maybe double checking all the resistor values?
Hi, when you say top LED do you mean the output LED ?
I have built it but 100%DIY so I am not sure which one is the top one.
But if it is the case, then it means you do get voltage (signal) on the output…which is good sign. Maybe the DC offset of your input signal is too high ?
Keep trying, it is really worth it, that filter is really fun to use
I just built this, it was almost working. The signal was always quite distorted and resonance didn’t do anything, but filter and vca themselves seemed to work. I swapped the LM13700s around and it went completely silent, so I guess the other one of them is half-fried. So after double-checking all solderings I think I’ll just go and buy last LM13700 of my city next Monday and try it with that.
I built this on stripboard. I’ve been hunting bugs for couple of days already and I’m wondering if it’s functioning properly. The resonance oscillates on lfo rate even when resonance pot is set to zero. This happens with the high shelf on and off. The oscillation kills the input sound. Input sound starts to come through after the resonance oscillates on audio rates.
My reasoning is that the resonance VCA is not fully closing but I’m too noob to figure out what mods should be done make the VCA close properly. I’ve been able to tame the self-oscillation and then the filter behaves like normal filter but then I lose the screaming chracter.
The way it works now is already ok and playable. I just wish the resonance would be really off when set to zero. Video
Hi team, got my filter up and running and it is sounding great!
Noticing a significant drop in volume though when i patch the oscillator through it via going straight out of the oscillator, is this normal behaviour? Never used modular before so not sure
Signal levels in modular are all over the place. I think that this filter has slightly lower maximum volume than some oscillators output. And then there’s the subjective thing, that if sinewave and squarewave (or especially a hugely distorted chord) have same peak-to-peak -level, the sinewave sounds much quieter.
