OTA questions/advice - Page 1
Forum section: electronics / beginners

author: Weez
author_rank: Contributor
timestamp: April 02, 2014, 02:23:34 am
content: Hey all,I'm building a clone of the classic MXR Dyna Comp pedal and it calls for a CA3080 OTA. These aren't readily available anymore, apparently. I've done a bit of googling, and there doesn't seem to be a recommended replacement, either. I did find a couple of supposed "substitute" chips (I didn't check the specs yet, just read it on a forum)- the NTE 902 and NTE 996, but they are expensive, compared to what the CA3080 used to cost. So, I'd like some advice/guidance...Order supposed real CA3080's from One Hung Low via the 'bay - not real keen on that option, due to the chips being possible fakes, as well as extended shipping timesOrder from a likely more reputable German store (Musikding.de)...around $3.30 US, but possibly not cost effective after shipping and other feesMaybe go the overkill route and use just half of another more common dual chip?Or, maybe just build the circuit from discrete components. I'm still a newbie, and this is way beyond me at this point...is it even possible or feasible (too much room required on the board, component cost, etc.)? If it is, how would I go about it (I don't expect to be led step by step, just pointed in the general direction)?So, whaddya guys/gals think...am I just screwed and forced to pay through the nose for what I need? Did I just not look around hard enough?

author: dentaku
author_rank: Frequent Contributor
timestamp: April 02, 2014, 02:43:47 am
content: I'm a beginner too so I can't answer your question but considering how easy it is to get the LM13700 you could always just experiment with that.This is a useful document.http://www.nutsvolts.com/uploads/magazine_downloads/11/May%202003%20Ray%20Marston%20-%20Understanding%20And%20Using%20OTA%20OP-Amps.pdf

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 02, 2014, 02:55:18 am
content: There's not much difference between them, any OTA that is. The main differences seem to be, LM13700 is dual and has input linearizing diodes and output buffers available, neither of which you have to use. The main specs (bias, offset, gain and bandwidth) are substantially equal or better.Tim

author: edavid
author_rank: Super Contributor
timestamp: April 02, 2014, 03:07:23 am
content: I agree with the LM13700 suggestion, but if you want CA3080s, here's a US source:http://www.smallbearelec.com/servlet/Detail?no=219Hmm, Jameco has them for $4:http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?search_type=jamecoall&catalogId=10001&freeText=ca3080&langId=-1&productId=12116&storeId=10001&ddkey=http:StoreCatalogDrillDownView(they also have LM13700Ns)

author: Weez
author_rank: Contributor
timestamp: April 02, 2014, 03:16:33 am
content: Yeah, I thought I might have to go the overkill route, but no biggie I guess.Mouser only has smd available in quantities of 1, but DigiKey has through hole for about 2 bucks.I did find CA3080's at Small Bear, but they want $5 each.I'll probably order a few from Hong Kong, as the shipping is only a couple of bucks...just to have them in the drawer for breadboarding and whatever.So it looks like the LM13700's from DigiKey is what I'm going with - thanks guys.

author: Weez
author_rank: Contributor
timestamp: April 02, 2014, 03:22:57 am
content: Thanks edavid, must've been typing when you posted. Yes, I saw those, but $5 is a bit much for what they are, I think, even if they are "reissues made from the Intersil masks".

author: kc9qvl
author_rank: Regular Contributor
timestamp: April 02, 2014, 12:41:31 pm
content: NE5517 LM13700 NJM13700 will work. These dual channel though