CA3080E

[smallbearelec]

I regret, I did not buy more of these when I heard the first rumors that it was going out of production. It was discontinued in January. I do still have about 1500 pieces, so they will be available for some time yet (retail only) at $2.50 each.

[mrsage]

Is that the Ross Compressor chip?

What else is it used in?

[puretube]

free information block:

[BlackFlag1313]

Is a CA3080 the same as a CA3080E?  Are the CA3080A and CA3080E basically the same IC?

[puretube]

basically all 3 are the same  

[Transmogrifox]

I was actually just contemplating building a tremolo + string swell effect based on that chip tonight.  I roasted my JFETS from doing stupid things trying to get my EA tremolo to work, and have just decided that it's about as easy to tinker with the CA3080 since I have a few laying around that I haven't used for anything yet, and the oscillator in the EA is very slick.  I like it.

EDIT:  Oh, and my whole point in saying that, is it is sad to see them go.  I hope some of the other classic OTAs hang on for a while.

[Paul Perry (Frostwave)]

The NE5517 dual OTA (identical to LM13700) looks safe, since ON Semiconductor has started making them for Philips after the Philips fabrication plant burnt down.
I can't believe nobody in China is making 3080s, they make so many other chips from this era like the 1496!

[Mark Hammer]

The CA3080 may be going the way of the dodo bird, but what about the LM3080?  Anyone have any info on that?

[R.G.]

I hate to mention this, but a working OTA can be made from ten transistors and no other parts. Only one matched pair is strictly needed, but a four pairs makes it all dandy.

There are no passive parts in an OTA except conductor metalization.

Shoot, maybe I should whip up an all-transistor OTA replacement board for the CA3080. I suspect that with surface mounts, it might be not much larger than the 3080.

But Mark's right - look for LM3080.

[Paul Perry (Frostwave)]

The CA3080 may be going the way of the dodo bird, but what about the LM3080?  Anyone have any info on that?

LM3080  Product Folder  
Operational Transconductance Amplifier [Discontinued]

...how to win friends & influence engineers :x  :x
actually it's been gone for years IIRC.

[KORGULL]

Has anybody tried the NTE equivalent of this chip?
I was also wondering about the NTE replacement for the MN3007.
Any luck/experiences with these?

[Paul Marossy]

I used an NTE equivalent of the CA3080 in my Anderton Volume Pedal De-Scratcher. It works just fine.  

[jimbob]

I been using the nte 996 and sounds great.

[vortex]

Discontinued! My God, the 3080 Mojo quotient just hit the ceiling!

Actually, I just bought a bunch of these for 75 cents ea. ! I just finished servicing my Micromoog and there were a handful of the buggers in there. ..

[Transmogrifox]

Speaking of the anderton volume pot descratching circuit, where is that?  I have been tinkering with a 3080 trying to get a good tremolo and volume swell circuit to work.  I have not been able to get a good signal extinction at 0 volts on the bias input, which intuitively makes no sense to me.  There's a parasitic leakage somewhere that's biasing the thing.  If I put the load small enough on it, I can certainly kill some gain like that, but there comes a point where the current drive is not enough, thus distortion results.

How do you harness the OTA to supply good clean gain from, say, -60 dB to 0 dB.  I think if I could get a 60dB change I could make a good string swell effect.  I have been trying feedback and the works--yadda yadda.  I was quite impressed at what a nice clean unity gain follower it makes.  Great slew rate, but again I have been having trouble getting the signal level to inaudible at a low setting--and I think I just figured it out as I'm typing this:  Feed-forward.  We assume this away in feedback theory because we're generally dealing with low impedance (voltage) output amplifiers where the feed forward signal is virtually nothing.  I need to get the input de-coupled from the feedback loop.  Everything simply looks like a very high impedance input (output impedance is many 10's of Megs).  So never mind.   I talked myself through it and found my answer.

The damn things are so high gain it's super touchy to get them biased at center if you use them open loop, no feedback, but feedback screws up the linear gain to bias current relationship, something about the X/(1+X) relationship gets in the way.  Open loop, though, you need to give them significant common mode input to prevent clipping.  It's good though, I'm learning about OTA's now.  I have been afraid of them and avoided them for some time now--and it's good to have tried a few different things to build some confidence that I can make something with an OTA work...and this also gave me a good idea of one way to adjust the Tremolo depth.

If you made it this far, thanks for persevering through my thought process.  I hope you learned something, or have more suggestions or links to helpful sites about OTAs.  
Regards,

[rubberlips]

Has anybody tried the NTE equivalent of this chip?
I was also wondering about the NTE replacement for the MN3007.
Any luck/experiences with these?

Haven't tried the NTe replacement but I've got an MN3007 in a conbination phaser/flanger/delay kit I made years back. Wasn't that impressed with the circuit - background switching noise from the MN3007 and not enough volume to get it to the right level. Might have to have a play with it again sometime....oh stuff it. There's more fun pedals to build

Pete

[Paul Marossy]

Transmogrifox:

If you want a little more info on the Anderton Volume Pedal De-Scratcher, check out this page: http://www.diyguitarist.com/DIYStompboxes/Vol-Pedal-Retro.htm

There's also a PCB layout at www.tonepad.com  

[mikeb]

http://www.midwest-analog.com/catbooks.html

"Making Music With The 3080 OTA" by Thomas Henry - US$ + shipping.

Just buy it.

Mike

[Transmogrifox]

Thanks Paul M and mikeb.  That's the stuff I would be looking for.

EDIT:  Does the volume pedal descratcher go to an inaudible level when the pedal is at minimum?  I would like to hook up an envelope generator where the volume pot is connected.  I came up with a trigger circuit yesterday using a dual LM358 and a pair of BJTs and some CMOS inverters that works relatively well.  I was actually surprised to find that the CMOS inverter would tolerate a diode on the input---sometimes the built-in voltage throws them loopy. I had a diode, cap and resistor on one of the inverters to make an envelope generator.  

Take care

[Paul Marossy]

Does the volume pedal descratcher go to an inaudible level when the pedal is at minimum?

Mine doesn't - there is still a faint guitar at that position. I asked about this in a post a little while ago asking about how to get it to have no volume at all and some suggestions were made, but I haven't tried any of them yet.

Here's that thread: http://www.diystompboxes.com/sboxforum/viewtopic.php?t=29825&highlight=descratcher