Will the 74ac16 be an acceptable substitute for the 40106? - Page 1
Forum section: electronics / beginners

author: guitchess
author_rank: Regular Contributor
timestamp: November 20, 2020, 05:58:11 am
content: Hello,I'm planning on making the ubiquitous oscillator/synth. I have the 74ac16 in my cart from Digikey, but didn't know if there was some reason it shouldn't be used instead of the 40106.Looking at the datasheet, the 74ac16 is better in almost every way, except for max supply voltage. The 40106 has an 18v Vmax. Considering most folks on the web building synths are using 9v, it didn't seem like the lower voltage would make that big of an issue. Plus, I would be setting my synth up to run into an amplifier/mixer. Is that extra voltage needed?Thanks.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 20, 2020, 06:03:03 am
content: Did you mean '14?I would recommend against using 74AC: it is a faster ("advanced") version of 74HC, which itself is much faster than CD4000 CMOS. You are likely to run into problems with bypassing, noise, oscillation or squegging, etc.It sounds like you don't have any immediate need for speed, so the CD4000 family's higher voltage rating may be preferable.Tim

author: Zero999
author_rank: Super Contributor
timestamp: November 20, 2020, 06:25:58 pm
content: The 74HC16 doesn't exist. It would be nice if it did, as having a low power equivalent to the 7416, which has a high voltage tolerant output, would be handy.Yes, it seems like you meant the 74AC14. I agree, with the above: faster isn't always better. Higher speed ICs need more care with regards to the layout and decoupling.How many channels do you need? I've toyed with the idea of building one myself, just a basic keyboard with 16 polyphonic notes, tapped off the capacitors and fed into a mixer to give a sawtooth wave output. The 74HC7540 has eight channels, which makes it ideal.https://assets.nexperia.com/documents/data-sheet/74HC_HCT7540.pdf

author: guitchess
author_rank: Regular Contributor
timestamp: November 20, 2020, 07:07:25 pm
content: Oops! I did in fact mean 74AC14.Ok on the possible noise/bypassing issues. Didn't know what squegging was, and learned a new term for an issue that I have experienced before.The only reason I want to make this substitution is to eliminate redundancy in my parts cabinet. Might as well get a couple 40106s. $.80 won't kill me, and they wont take up much room.Thanks

author: Benta
author_rank: Super Contributor
timestamp: November 20, 2020, 07:39:02 pm
content: Alternative p/n to 40106 is MC14106 from ON. There are several suppliers for this part.

author: wraper
author_rank: Unknown
timestamp: November 20, 2020, 07:42:31 pm
content: Quote from: guitchess on November 20, 2020, 05:58:11 amBut 74AC or 74HC which is more suitable substitute are rated for 6V maximum.

author: guitchess
author_rank: Regular Contributor
timestamp: November 20, 2020, 09:10:25 pm
content: Quote from: wraper on November 20, 2020, 07:42:31 pmThanks,I noticed that. I thought I could possibly get away with this considering my synth would be fed to an amp. So, if I could only get a Vpp of 2 - 2.5, it would be more than enough for line level input.After the last few posts, I'm also wondering if the low voltage output might also help with minimizing noise, etc. from using the faster inverter.Just a thought.Thanks.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 21, 2020, 03:01:32 am
content: Surely the bigger problem is you aren't going to get a very accurate oscillator from either kind. Are you planning on something, like, slide-controlled or whatever, so that doesn't matter?The voltages don't matter very much as the thresholds are relative to supply voltage, over the same relative ranges (typically 30-70% of VCC). 74HC is still fast enough that it can cause EMI noise problems sometimes, just not so fast that you have to worry about it every time. Like, it's most likely fine for breadboarding. (CD4000 is so slow, it's hard to have any such problems at all. Case in point: the original Nintendo NES Controller used a CD4000 logic chip on board, and almost nothing else, not even a bypass cap. It sits at the end of a 3 meter or so cable!)Another point to consider: CD4000 has relatively weak outputs (a part of why it's so slow). Drive strength varies with supply voltage, so it's acceptable at 10V+, but rather weak at 5V (indeed, it stops working at all, somewhere below 5V). This may be important if you want to light some LEDs brightly, say. Whereas 74HC is fine for such tasks at 3V+.Both are handy for their own reasons; and, I guess you haven't given enough information to make a pick.A lot of analog circuits are made with higher supply voltages (classically +/-15V, but 9V and up is quite common too, yep), which can make interfacing with 74HC a pain (7V max, in practice you'll be using it at 3.3 or 5V). If you're using standard analog functions (ICs) it's quite likely you can find them in lower voltage flavors, and do just fine with +/-2.5V (5V total), which interfaces with 74HC just fine. If you're not, if you're exploring older circuits with VCOs and OTAs and discrete transistors and such, you will probably find the higher voltages useful.Tim