Hello everyone! I have a little question: I can’t get my hands on a LM4040AIZ 4.1 for a reasonable price, but could order a 5.0 with 5 Volts.
Is it possible to simply replace the 4.1 and if so, do i need to also replace the 220 resistor and/or trim potentiometer?
The 220R, yes, you have to replace it with a resistor between 1K and 4K7.
The 100K trim-pot is fine.
Great, thank you so much! Also for your suggestions, can’t wait to build these modules.
They’re not my suggestions, I just gathered all the stuff spread all over the posts in a single post for easy reference.
Credit goes to the authors of the posts linked in each suggestion.
I ordered some AS3340s from AI Synthesis, and what I got was marked AS3340A. The datasheet says:
AS3340A/AS3345A are improved versions of AS3340/AS3345. AS3340A/AS3345A and have much more output frequency stability against Vcc and VEE . Frequency stability can be improved If external reference voltage (with level approximately 1/3 Vcc) is connected to pin 9 (Soft Sync. Input). AS3340A/AS3345A benefits from improved symmetry of rising and falling edge of triangle signal (approx… 50%).
Synthcube sells the AS3340A for $3 more than the AS3340, so it was a pleasant surprise to get these from AI Synthesis at $2 less than Synthcube, plus lower shipping cost as well. Though it just says AS3340 on the AI Synthesis website, so maybe you don’t always get the upgrade.
I’ve got one on a breadboard right now and what I see regarding the PWM frequency shift is… none. I mean, at frequencies from 100 Hz to 8 kHz, I’m seeing < 0.05% change in frequency when I go from 0.3 V to 3.65 V on the PW CV… and not always in the same direction. The datasheet doesn’t specifically say the AS3340A has improved stability with PWM but I certainly am not seeing anything significant.
Anyone else worked with the AS3340A? Do you have the same impression?
I was about to finalize my pcb design conversion to Eurorack and then, i discovered this thread. Now i have to redo all. Anyone have a schematic with ALL improvements described in this thread? My electronic engineering skills are very limited…
I’m back to looking at this and not sure what I’m doing differently, but… I’m definitely seeing the PWM frequency shift with an AS3340A. At least if it’s powered as (or rather, like) in the datasheet, with -12 V via 680R to pin 3. If I connect a regulated -5 V to pin 3 then the frequency shift is maybe gone or maybe just very much reduced. (I also find the CV scaling changes, so if I just switch the power without adjusting the tracking trimmer I get very much different frequencies.) I need to look at this a little more carefully and maybe research some of the other remedies that have been mentioned, but Alfa recommends the regulated -5 V in any case.
I made a blog post about my AS3340 test results:
tl;dr: My tests with AS3340 chips appear to indicate: (1) Pulse width frequency shift is seen with both AS3340 and AS3340A chips; (2) Using a regulated -5V on pin 3 does a good job of suppressing the pulse width frequency shift; capacitor from pin 4 to ground does not work; large resistor between PW CV and pitch CV summing node does work but relies on cancellation and so requires fine tuning; (3) A 10M resistor between pins 4 and 5 suppresses ringing oscillations on the pulse wave falling edge without unacceptably constricting the pulse width range; (4) The value of the pulldown resistor on the pulse wave output is not critical, but should not be too large or too small, and 51k is probably a good value.
Thank you so much for doing this research. Guess this means i have a good reason to use that regulated 5v from my power supply after all. I’ll have to think about how we could get a -5v from there. Maybe a 555 Negative voltage generator?
What on earth for? You already have a negative voltage, you only need to regulate it.
Kassutronics VCO3340:
I dont think my stripboard circuit has an onboard 79L05.
Its also very possible im missing something.
I think, the point is that it‘s easier (and more elegant) to make -5V from the -12V you have in the eurorack header by using 7905 than using +12V and a 555 and more components. But if you only got a 555 around, go for it! 
nah, im just clueless sometimes and this is the best way for me to get answers like this 
Want to build the 1222 VCO from scratch, is there a 1222 PCB design for printing or just the PCB available for purchase?
There’s a schematic for download, and there’s the board and panel set for purchase. But no Gerbers or KiCad files.
Is the rotary switch part the octave selector? I’m thinking of integrating it on the simple 3340 VCO, plus SYNC and FM inputs. If it is, how could I implement it without the CV input and just the 1v/oct input?
Edit: I just remembered an old thread about the octave switch and I just found it. Oops.
Well crap. I’ve got a new version of my AS3340A setup on a breadboard and … the pulse width frequency shift is back, with -5 V regulator power. I don’t know why, I thought I’d pretty much ruled it out before but now I’m definitely seeing it. About 40 cents (almost half a semitone) across the full pulse width range. Also unlike before, I’m seeing a good pulse width range with only 3M or even 1M between pins 4-5… but they’re not suppressing the falling edge oscillations under all circumstances. Hello, consistency? Will you be coming around any time soon?
It may be time to give up and use an external comparator for the pulse wave.
Added 2 hours later: And now it’s down to about 3 or 4 cents, and the oscillations are under control down to 10 Hz using a 1M resistor. I haven’t knowingly changed anything, or I did but I changed it back. Sheesh.
1222 VCO - new build mods/updates
I’m trying to get my head around the suggested mods for a 1222 VCO new build without going too far. this will be my second 1222 VCO after rather a long delay.
Below is my understanding after checking through various posts on the forum and thought it may be useful to get all the suggested working/generally approved of mods all together, Eric kindly originally put together a list of most of these mods a while ago.
MANDATORY (already documented in the 1222 Tuner Module fixes/improvements post from Oct 20)
SUGGESTED SIMPLE MODS (already documented in the 1222 Tuner Module fixes/improvements post from Oct 20)
replace L7805 voltage regulator with a L7808 (more suitable for Arduino Vin)
add 10M resistor between pins 4&5 of the 3340 to reduce ringing on square output, although I have also seen 1M resistor suggested for this?
FURTHER SUGGESTED SIMPLE MODS (from the forum but a little scattered about)
replace R13 with 200K resistor
add 20M resistor between two points marked on board (near-side R26 to far-side R12 or that what it looks like from the image)
Does this seem a realistic/accurate summary of mods to include for a new build?
Apologies if this post isn’t formatted very well, still getting to grips with the posting editor
Richard
(reference links below)
https://lookmumnocomputer.discourse.group/t/1222-tuner-vco-module-fixes-improvements/2072?u=mtb
https://lookmumnocomputer.discourse.group/t/1222-tuner-vco-module/16/453?u=mtb
https://lookmumnocomputer.discourse.group/t/1222-tuner-vco-module/16/605?u=mtb
I did some breadboard tests a while back. Mostly I used an AS3340A although some of it I also checked with an AS3340. And I wasn’t specifically following the 1222 schematic although I doubt if it matters for most of these.
That has nothing to do with CEM vs AS, it’s the current limiting resistor for the voltage reference. Value isn’t critical but should be above about 1k so that 1k to 4.7 k range is good.
In my breadboard tests 1M worked, larger values didn’t suppress ringing at the lowest frequencies.
I found a value of 4.7M, not 20M, is what I needed to suppress the frequency shift and @stmllr needed 6.6M. But @ChristianBloch apparently finds 20M good. I’m not too surprised at needing different values, since what you’re trying to do is cancel out one behavior with another and I’d expect it to vary depending on the chip and other variables, but then why did Christian find 20M worked for all the modules he made? It’s weird. If building a 3340 oscillator from scratch I’d say it’s better to use a -5 V regulator on pin 3, but that’s not practical for a 1222, so try 20M but you might need something different.
Yes. Polypropylene is good.
Thank you, I’ll give those a try on the new build then.
Any tips on placing the resistor between pins 4&5, presumably on the back of the board?