There has been a lot of fearmongering from the electronic music crowd for a long time about electronic music parts going out of production.  Usually it's just a case of some guys who are naturally kind'a jumpy.  However, this one looks serious; Intersil has recently set the status of the CA3280 Operational Transconductance Amplifier to "To Be Discontinued".

"What you talkin' bout Willis?"

An Operational Transconductance Amplifier ("OTA") is something like an opamp, but is really quite different.  It's an amplifier; and like an opamp it has a pair of differential inputs and a single output.  But the output is a current source instead of a voltage source.  The gain of the amplifier is expressed as a transconductance (current out / voltage in), and that gain is programmable because it is proportional to the current going into a gain programming pin.  While opamps are almost always implementing some function by the use of a specific feedback network, the OTA is very often used open loop (or partially open loop).

OTA's are perfect for a multitude of electronic music applications because they can control a parameter, such as amplifier gain or filter frequency, and control it very accurately over a range of at least three decades.

The first OTA chip was the RCA CA3080 introduced around 1969 or so.  The current OTA of choice is the CA3280 introduced roughly around 1971.  By a complex series of corporate megers and acquisitions, GE bought Intersil and formed GE Semiconductor, GE then bought the entire RCA Corp. and merged the two semiconductor groups, GE sold the combined semiconductor group to Harris, Harris sold all assets to a management buyout group, which reorganized things and chose the name "Intersil" for the new company.  Or something like that; I was napping at the time.

So here's my recent email conversation with Intersil support on the matter:

I received a response the next morning:

I tried for a few more details:

And received this the next morning:

Hokay, well...  I don't blame Intersil.  The process used to make those chips is very old and has been handed down through a number of corporate buyouts.  And I'm sure the CA3280 hasn't been their top seller.  Still, this sucks.

Also, this appears to affect the entire CA line which, besides the four OTA's, includes transistor arrays, opamps, video amps, amps with unusual circuit configurations and taps, special purpose radio and television circuits, and so forth.  Most of these are somewhat antiquated designs and have few practical uses today.  The transistor arrays are certainly nice, but given how easy it is to hand-match transistors, I don't see an array of less-than-great transistors on a chip as an especially compelling story.  But the OTA's are a serious loss.

What to do?  Well, several things:

And... this is a wonderful opportunity for another semiconductor manufacturer to build a 21st century version of the CA3280.  Are you listening Analog Devices National, On Semicondcuctor, THAT Corp., Linear Technology?  Or even Intersil.  I'll be happy to consult on such a project.

There is a replacement for CA3080 made by NTE,
the NTE996. See their cross reference:
http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/$$Search?OpenForm

Hey Dr. Sync,

Yeah, I know about that... the CA3080 isn't the interesting OTA though;
it's not a low noise device (it doesn't have a noise spec), it doesn't have
input linearization and the offset voltage isn't very good. What I really
want is a replacement for the high end CA3280.

Or better yet, an even higher quality OTA!

-- Don

I tried, too, to persuade Intersil to keep at least the CA3080, which I use often. (Note that you can achieve very respectable dynamic range with this part, and that it will operate on just a few volts and with very little current.) Too late; the plant somewhere in Ohio is gone, Intersil told me. Then I corresponded with NJR, a second-source manufacturer of the LM13700. (This is essentially a dual version of the CA3080 plus linearization diodes and output Darlingtons.) NJR wanted to know my annual usage of the '3080. Knowing full-well that anything less than 500,000 would not interest them, I didn't pursue my case. But NJR obviously has a fab line capable of this "archaic" linear process. So, my fellow analog enthusiasts, I suggest that you petition NJR for the '3080, '3280, and their like, if your quantity requirements are large enough to make it worth their while. Note that In desperate repair situations, some of the LM13700's pins can be wired into a '3080 PCB pattern and provide identical results. Also note that Phillips and second-source ON Semiconductor still (as of this writing) makes the NE5517, which is similar to the LM13600 that National discontinued. I am trying to recall if there is a Phillips part that emulates the '3280, but I can't think of the number. One other thought: If the demand for the NTE996 persists, maybe NTE will have enough influence to get an off-shore manufacturer to produce them regularly. I bought a few hundred NTE996s around April, 2005, when NTE's stock was about 1100 pieces, and Mouser is still showing availability. Perhaps NTE is ahead of the game, and indeed has a new source for these parts. NTE must know that Intersil ran out of CA3080s, though, because the price has gone up about three-fold since I bought them.

I wanted to mention the BA6110-types as for instance used in a previous Oakley-VCA but I just read these are discontinued as well... Hmm, it'll be unlikely, but perhaps other Japanes/Rohm-types exist ? (I didn't look yet)

CA3080' s for sale in batches of 50 on ebay, from Hong Kong
just snatched up a bunch myself
http://cgi.ebay.com/PACK-OF-50-PIECES-CA3080-CHIPS-ICS_W0QQitemZ7363262505QQcategoryZ41415QQssPageNameZWD1VQQrdZ1QQcmdZViewItem
-james

I have a question. I am designing a high order analog filter for the audio range.
Higher order Imitation of SSM 2040 OTA VCF used for analog synths.
What about using higher frequency BW OTA's like the Burr Brown OPA660.
It has an OTA and a buffer so seems perfect for filters. Used more for RF with a BW at 850MHz and a slew rate of 3000V/us.
Would this be equivalent or better then 3280AE for audio range?

Of course I see that Texas Instruments is discontinuing it (Is this a conspiracy). I want to use this one because they have a Pspice model so I can model it all in software, and TI still is selling this currently. (how long?)
(By the way does anyone know if there are pspice models for CA3280 or 3080??, I have searched)
Somebody should pick up the 3280. NTE seems the best hope.

Thanks for any input/comments
james@siliconbreakdown.com

James,

The OPA660 is very different approach to OTA's, and it's absolutely nothing like the CA3280, the SSM2040, or any of the other OTA's used for electronic music.  It's a very different internal design, with very different characteristics, and it is used in a different way.  Not that the OPA660 isn't an interesting chip...

If you really want an SSM2040 filter, check out Jürgen Haible's SSM2040 Style 4-pole Filter, or the Synthesis Technology MOTM-440 module.

A conspiracy?  Nah; more like a very weird chip that didn't sell.  And then after acquiring buying Burr Brown, Texas Instruments has to figure out what to do with all that stuff they got.

Somebody picking up the 3280?  No... somebody needs to introduce a chip that's even better than the CA3280.  Let's raise the bar a little, shall we?  It's been thirty years, man; surely we can make some improvements.

Maybe this is why the chip industry is going to china! What's next, the 741?

These chips are commonly used in audio compression / dynamic range systems. The stupidity of the IC industry is that they neglect to understand that the VCA is one function that does not work well in digital. You can't dynamically compress or expand in digital without generation of rounding noise....not to mention the fact that even 24 bit has a limited dynamic range.

The industry likes to PUSH its super-small surface mount multi-function digital ICs for cell phones....while neglecting the rest of the industry. They're shooting themselves in the foot! The US is the largest exporter of industrial controls - which use lots of linear ICs. Small and compact means unreliable and unserviceable. Surface mount does not belong on an airplane or in a car! Ceramic DIP does.

Ok, enough ranting and raving. I have had a problem with this chip for almost 11 years. in 1997, I designed an audio compressor based on the Motorola MC3340P, as part of a broadcast audio processor. The MC3340P is an inverse-coefficient voltage controlled attenuator, which made compression circuits real easy to build. (positive voltage reduces level!)

It was discontinued the year I designed the boards, and by the time I had made my first prototype built, I had to re-design again. This time I used the Matsushita AN829P, a dual direct-coefficient VCA. I think that the AN829P was originally designed for television sets, which needed volume to be remote-controlled. This time I had to use an LM324 and a resistor current circut to make the inversion for the compressor. This was not a big deal.

Then, they discontinued the AN829P. I almost went to using the CA3280, but had problems with its manufacturer, Harris, who was a "competitor" in the broadcast industry at the time. Out of frusteration, I designed my own fill-in replacement for the AN829P. My first prototype failed, because I negelected to cancel the DC offset from my 3 transistor VCA. Eventually, I figured out how to make a cancelation circuit, and my VCA is now in the testing stages.

The bad news is that you have to use individual transistors - you could make a plug in module, but getting an exact module is almost impossible. If you're making a 1970's based synthesizer, you can use many different VCA circuits. For audio applications, the SSM2164 works well. I'll stick to my own circuit, due to the costant discontinuation of fixed ICs.

PS. If you want, the MC3340P has a well drawn internal circuit. I am going to try to build it, and see if it works!

Hello Don,
Is the "Blackmer VCA Devices" from thatcorp (http://www.thatcorp.com/vcas.html) the much awaited replacements for the CA3280 likes??
see also: http://www.thatcorp.com/vcahist.html

Also Have you found any other replacements?
thanks

Hello Don,

We have problem to buy CA3080M96. As your suggestion above that NTE996 can be replaced but NTE996 has DIP-8 package according to the datasheet but we need SOIC-8 package. Have you ever buy NTE996 in SOIC-8 package?

Hi Don: Thanks for the GREAT blog about the OTAs. We are now reviving and old product that used the 3080, and have found some surplus supplies.

Do you know of any date codes to avoid with the Harris or Intersil parts?

Thanks - JON