I recently finished my first 1222 VCO, and it is providing sound for all waves, and all knobs seem to be working as intended! I am in the tuning process, but that is where I ran into an issue I cannot figure out. According to Sam his videos, for tuning you need to hook up to the test hole at the back, and turn the REF potentiometer to 4V. However, no matter how much I turn it, I do not get a reading higher than 0.35V. Any ideas would be appreciated!!
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Whatās coming out of the precision regulator?
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sorry if this is obvious but may aswell check all stops!!! is the ground of the meter connected to a ground? ie a sleeve of a jack for instance?
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I hooked up the multimeter to ground of one of the jack sockets, as well as other ground sources. If I turn the REF potentiometer the minimal voltage I read slowly goes up, but it does not go higher than approx. 0.35V (never over 0.4V). And it is not a decimal problem, as I checked this 12V power supply, which reads the voltage as intended.
I find this issue really weird, as everything else seems to work as intended: PWM, sine, saw all work, all knobs work, CNTR and other tuning pot meters work. Only the voltage test output needed to tune the REF pot meter is giving a strange reading.
Any other thoughts? Could it be a bad potentiometer, or should that have resulted in an absence of sound coming out of the VCO? Maybe I should first test the resistance of the REF potentiometer in min/max position to check whether it is working properly?
Thanks in advance for the suggestions!
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And you defo have a LM4040AIZ ( The AIZ is Crucial ).
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I looked up the data sheet but it doesnāt say what AIZ means in this context. Any ideas?
(Up to nowā¦) I am under the impression that the LM4040AIZ is a precision voltage regulator valued for 4.096V. I have used this voltage regulator I bought at an electronics store here in the Netherlands:
https://www.okaphone.com/artikel.asp?id=481691, where this data sheet is found: http://ww1.microchip.com/downloads/en/DeviceDoc/21653C.pdf
I am curious to hear whether this swap could be the reason for the issue I am havingā¦
The precision doesnāt really matter, because itās just used with the trimmer pot to set a +4 V reference. So AIZ versus BIZ isnāt actually important, and presumably if your substitution is wired correctly (differently from the LM4040, itās not pin compatible) it should work.
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@analogoutput: Thanks for your reply! I assumed that the precision voltage regulator I linked had the same pins etc as the LM4040AIZ, and therefore I just soldered it to the PCB as intended for the LM4040AIZ. How should I have wired this replacement substitution?
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Take a look at the datasheets. From https://www.ti.com/lit/ds/symlink/lm4040-n.pdf the LM4040 is wired like this:
and the TO-92 pinout is
From http://ww1.microchip.com/downloads/en/DeviceDoc/21653C.pdf the 21653C is wired like this:
and the TO-92 pinout is
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yeah the 4040 is a two wire device in a three wire package.
The substitute is not suitable. ( it could be made to work but would need reconfig, couple of extra components, extra jumper wires, etc )
Rob
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Richard,
The AIZ a k a Ted Nugent?
-Fumu / Esopus
Itās clear from the data sheet that the Z in AIZ refers to the package. Z stands for TO-92, M3 for SOT-23, and M7 stands for SC70. The meaning of the other two letters is not so clear.
First letter is tolerance and can be any of A through E. Second letter is temperature grade and can be I or E. Though for 4.1 V the datasheet lists only tolerances A through D (0.1%, 0.2%, 0.5%, and 1%, respectively) and temperature grade I.
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@analogoutput and @twinturbo Thanks for this information! I am a total electronics noob, so I do not think I would have figured this out any time soon by myself. 
If I understand you and the schematics correctly, it is not simply hooking of the pins differently, but it would require additional components etc., which messes up the tidyness of the VCOs PCB. In that case, I think it would be better for me to continue looking for the original LM4040AIZ. Any tips on where to find this component are welcome!
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I ordered mine from a supplier on eBay, like a lot of my gear. Thereās a filter on the search gadget so you can select only items that are sourced locally (I get a choice of UK or EU) and of course you can sort them by ascending order of price+shipping. Make sure youāre happy with the cost and the estimated delivery date, and buy. Iāve used this service a lot and Iām very happy with the ease of use and reliability.
Edit: make sure you get the 4.1V reference. There are other voltage references and only 4.1 will work.
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Well, again, youāre using it with a trimmer to make a 4.0 V reference, so anything 4.1 V to 10 V would be okay.
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There was a thread on sourcing.
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By now, I have replaced the BIZ precision voltage regulator for a LM4040AIZ, and now everything seems to work as intended! Thanks for all the help!
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Super