Where are you picking up the clock signal to look at it? At the op amp pin 1, or pin 3/5, or pin 6/7, or at CD4024 pin 1/74HC14 pin 3, or at the Sixteenth output? How does its shape and size compare in those five places? Does it still have the same strange shape and voltage limits you saw before?
Have you tried looking at it with the CD4024 and 74HC14 removed from their sockets?
You talked about installing a jack to connect to the scope, do you not have a scope probe? If not then maybe you can get away with connecting wires to a jack and using the wires as a probe.
The mix of CD4024 and 74HC14 strikes me as odd. I don’t know that much about logic chips, though, so maybe it’s OK to mix CD4000 and 74HC series that way.
I notice there are 100 nF bypass caps on the op amp but not on the other two chips. Probably not an issue but you could try adding those, one close to each chip from the power pin to ground. You can use little ceramic caps for that, if you have them or can get them, no need for those big green things.
I had the jack wired in off pin 7 of the opamp as that’s where the signal was going in to the 4024. I didn’t check anywhere else but wouldn’t hurt to check the outs of the 4024 and see if they are changing with the pot. The opamp oscillator was being affected by it, but somewhere after that it breaks down. I’ll check the 4024 outs and if they are being affected by the pot. I guess if they seems to be working then the breakdown can only be in the 74HC14. What that would mean I have no idea, but at least it would be an answer.
Something about I has to work though as the PP of the design has it running.
I tend to doubt it’s the 74HC14 but the simplest thing is to pull that and the CD4024 out and see if the clock is behaving with them removed. Check the clock at each of the points I mentioned. There’s probably no point in checking things downstream of the CD4024 if the clock is not behaving upstream.
Added: Belatedly a thought about the design came to me. There’s an oscillator that produces (or should) a ±5 V square wave. The output goes, through a resistor, to the clock input on the CD4024. Isn’t that bad? The CD4000 series spec sheets say input pin absolute maximum voltage is -0.5 V to VDD+0.5 V. Shouldn’t there be a diode on the op amp output, @Gwyniad?
Good point, hadn’t thought of that. To be honest, I’d just taken a square wave circuit that I used before and bolted it onto a binary counter with a few inverters to line things up, found it worked and called it good.
As you may be able to guess, I’m not much of an expert but I’m continuing to learn as I go thanks to the this forum!
So I’ve just run a probe around the opamp and gotten something to look at at least. I pulled the 4024 and 74HC14 and the clock still isnt responding to the pot.
If it’s not responding to the pot, how is it that there are different frequencies in the different pictures? For instance in the pin 1 picture it’s 12.5 Hz, in the pin 3/5 picture it’s 24.4 Hz. I don’t believe both can happen at the same time. At least not if the op amp is working right, and even if it isn’t it’s hard to imagine.
The rise and fall times in the pin 1 and pin 3/5 pictures appear to be quite slow. I don’t know if that might be due to the scope or not. If it’s real it’s not what it should be. Those edges should be near vertical on this time scale.
Also, in both pictures, the upper voltage level is about 12 V while the lower is about 15 V. That shouldn’t happen. They should be about the same.
The pin 6/7 picture looks very, very wrong. That op amp should just be buffering the pin 3/5 signal so should look just like it. Instead it’s a triangle wave, but again asymmetric around 0 V, and with smaller amplitude than the pin 3/5 square wave, and with funny glitches around where it crosses about -4 V.
Was the 4024 pin 1/74HC14 pin 3 picture taken with those ICs in or out? You mentioned pulling them out but if they’re not present it ought to look just like the pin 6/7 picture and it doesn’t.
Altogether this looks bad. Have you tried a different TL072? Just on the basis of comparing the pin 3/5 and pin 6/7 pictures I can’t imagine any explanation other than a malfunctioning op amp. But even if it’s malfunctioning it’s oscillating, and I can’t see any way for it to be oscillating and not responding to the pot. So there seem to be multiple strange things going on.
That was with the other ICs still place. I just took them out again and got the below, but as I continue to observe, the frequency was gradually dropping. After about a minute it was down to 20hz. I tried it with a different opamp and the same thing except it started at about 200hz and dropping. EDIT : popped the original IC in and it started at 200hz… This thing just gets stranger and stranger.
I still get the same waveforms on the opamp pins with the swapped out chip, but again at higher frequencies and still with a 12ish Hz discrepancy. Still no response from the pot in either opamp.
I do still have a slightly slow response in the square wave but not as bad as the first opamp.
It’s not to be a boring guy but given the construction with the transistors, which apparently works, unlike the stripboard layout which has a few omissions, this one was certainly not used to build the module and made afterwards, so maybe is it good to remember that a “verified stripboard” can only be after having built from this one. No ?
a copy error happened so quickly
And all the opamps light all the LEDs so either the circuit doesn’t work the way it’s supposed to (unlikely, but possible I guess) or the ICs are good. Either way, it was my first attempt at translating a schematic to stripboard and it works so far which I’m happy with if nothing else.
Your right too a out the missing power connections for the 74HC14. It’s missing in the schematic but shows +5v to pin 14 and ground to 7 on the layout which from memory checks out with the data sheet.
I’m going to try and build the oscillator on its own small stripboard and see if I can get it to run properly. I would use a breadboard but I don’t have one
Hey everyone, just checking back in to report that I got it working. Built the oscillator stage again on its own bit of stripboard and that worked straight away. Hooked it up to the rest of the circuit and it sprang to life. Still don’t know where I’ve gone wrong with the original oscillator as I’ve used the same IC but at any rate, my clock with divider is working. As such I guess that verifies @Gwyniad s layout (once the amended one is uploaded of course). Also solved the pot problem sort of. Plugged a different one in and it worked even though old one was displaying the right behaviour. Shrugged my shoulders and moved on lol.
Despite my curiosity to go back and figure out the error on the first one I’m going to call this a win and not spend any more time scratching my head haha.
Thanks everyone for your help. I’ll see you on the next stuff up
Here is a strip board layout for the AI Synthesis Harmonic Mixer. I made one just now using this layout and it seems to work fine, although I’m noticing my bias pot seems less dramatic than the one in the demo (but I had to substitute the pot value since I didn’t have a B1K laying around). I removed the output volume pot to save panel space, so the output is dimed at all times. Hope this helps somebody.
Edit: I’m seeing the transistors are kinda hard to identify, so from left to right, the transistors are 2N3904, 2N3906, 2N3906, 2N3904
Also it looks like the 3.3nF cap is supposted to be a box polyester, instead of creamic as I showed it there.
@BlackDeath - Yes, it does some sort of clipping/wave shaping when you play with the bias. I think it’s pretty transparent around noon on my unit. If you want a totally transparent mixer I’d probably go with one that uses an op amp instead. But this one sounds decent to my ear and is a very easy build.
@jessecakeindustries This portamento circuit looks great, I think I’d like to build a few. If I were to put both diodes going into the same potentiometer, would that pot control both the rise and fall?
