Very nice! I just finished my first 3340 stripboard using the LMNC simple 1V/Oct layout, it’s up and running but the pitch wobble on the PWM is pretty severe. I know this is common for the 3340 but I was wondering if there’s a way to help control it? Does the capacitor/resistor combo on the pulse out on your layout help with this?
Also, I’ve noticed that a lot of PCB circuits I’ve built have a circuit around the power with a series of capacitors between the power rails and ground (I’m not sure what you call this?) I’ve noticed you’ve not done this either, but I’m wondering if it’s why my Frequency Central 3340 osc doesn’t wobble on PWM much but this layout does…
for the bypass cap on the power supply you have some info here
PWM it’s with an external signal in PWM input, and the PWM pot ajust the level of signal in to zero to max , there should be no problem with that, I think you are talking about the PW pot
for PW pot you can add a trimmer pot on the pot for adjust what you want
(to pin 1 or 3 or both of the pot)
Thanks for the info! Yeah apologies, I guess I mean the PW pot - it’s just the pitch change is most noticeable when you use the modulation. Sorry if I’ve misunderstood, but does the trim pot on the PW pot not just change the points where the duty cycle reaches 0%/100% to stop getting the total cut out at those points? Either way, I’ll stick that in tonight and have a go
Here’s a quick vid! I forgot to include that it does it on all outputs, not just the pulse. Now I think about it there was one thing I did different from the stripboard layout - I didn’t have a 620R resistor so used a 680R instead, but thought that might be close enough…
Also, note the dead zones after about 1 o’clock - deffo need that trimpot
Are we talking about the resistor to −12 V? That one limits the current through the internal zener on the negative supply rail. Sam uses 620 ohm in the stripboard layout, 680 in the performance synth and the fart box, so should be ok, unless perhaps you load the circuit more than usual. The datasheets recommend slightly lower values.
You could try measuring the voltage on pin 3; it should be around −7.2 V on the CEM and −7.4 V on the AS, if I remember correctly.
So, I kept playing with it and managed to make some headway - I’ve now limited the pitch drift to about the the last 10% of the duty cycle. Not perfect but certainly much better!
10uf electrolytic caps on the power rails
*100nf ceramic cap from pin 4 to ground
*changed the 10k resistor from pin 4 to ground to 56k (a la the datasheet)
*added a 100nf cap from pin 14 to ground - don’t ask me why
I also added a 1M resistor across legs 4 and 5 (something about hysteresis, means nothing to me) and it helped, but also reduced the pulse width pot to doing its full sweep in about 10 degrees of rotation. I cba to rectify that and it didn’t seem to make a huge difference, so away with it.
Thanks for the help everyone, I just want to rack this thing and play with it now, but alas it’s 2am on a Monday
This is a mistake in Sam’s original simple 1V/oct oscillator design. He knows of this. Caustic probably copied over the mistake.
I use 2 series resistors here, to both pull down and make a voltage divider, to get 10V into the op-amp buffer instead of 12V. I don’t remember what values I used, but I choose them to be in between the CEM and AS specs. Double function, pull down and drop down
I’m using Caustic’s design, direct from the stripboard diagram at the top of this post. my only alteration is using a polystyrene cap for pins 11 and 12 to follow the recommendations of other designs.
to tune it I set the coarse knob to 12 o’clock, took my 0 coast and compared the tuning of C up and down a few octaves, using the trimpot in the back* to match where middle C is.
*I used a regular 10k pot here instead of a trimpot cuz I don’t have any single turns. I do have a bunch of multi turn trimpots though if I can drop those in anywhere to improve tuning.
See the datasheet. There should be a connection from pin 7 to a trimmer (say 20k) wired as an attenuator, to a 1M resistor, to pin 15. That’s the high frequency trim.
Even without that 1.5 octaves sounds low, but you won’t get the full range without the HFT.
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