Substitute for CA3094/LM3080N OTA

[Tone Meister]

Need to replace a single OTA in a Peavey Mace preamp. Original Peavey part number is 70487478 and the industry equivalent is CA3904. Peavey replaced the original part with LM3080N but that is now obsolete also.

Anyone know of a suitable substitute? To be specific about its role in the circuit, it needs to replace U15 in a Peavey Mace preamp. Schematic attached.

[MarkusBass]

Is it the same as CA3080? I have two of them at home but it may be easier to buy it here:
OP AMP IC HARRIS CA3080E CA3080EZ CA3080 DIP-8 | eBay

Please note that several other opamps in the amp are also of the same type.

Mark

[Tone Meister]

I realize that, but they are in critical roles in the preamp. Peavey strongly suggests that not just any OTA chip will function in the LFO or summing amp role in these amps. They claim their original 70487478 and later on the LM3080N were "selected" for those roles. I just got off the phone with Grant Brown and he reiterated that same position but also added "the recipe we used to select those OTAs has been lost." The same chip is used in the DDT compressor circuit.

So, I don't know if those chips will work or not. I had already seen those in your eBay link, but I'm not confident enough to purchase until I can get some further expert advice based on personal experiences with subbing for these chips.

[MarkusBass]

I also heard such stories about "specially selected" golden chips from respected manufacturers and after that I found out that the chip is noting more than plain NE5532. So you may believe, or not - it's your choice .

Mark

[g1]

That ebay item is from China. I don't buy any obsolete components from there.
These may be legit, especially if they are used:
LM3080N Transconductance Amplifier - $2.99

[Tone Meister]

I also heard such stories about "specially selected" golden chips from respected manufacturers and after that I found out that the chip is noting more than plain NE5532. So you may believe, or not - it's your choice .

Mark

With all due respect, I am unable to see the parallel. Could you please elaborate?

https://www.onsemi.com/pub/Collateral/NE5532-D.PDF

CA3094 datasheet(1/14 Pages) INTERSIL | 30MHz, High Output Current Operational Transconductance Amplifier (OTA)

http://www.ti.com/lit/ds/symlink/lm3080.pdf

[nosaj]

That ebay item is from China. I don't buy any obsolete components from there.
These may be legit, especially if they are used:
LM3080N Transconductance Amplifier - $2.99

I'm pretty sure these are also Audio Labs of Georgia has 10
Audio lab of Ga

nosaj

[Tone Meister]

I'm pretty sure these are also Audio Labs of Georgia has 10
Audio lab of Ga

nosaj

Ordered a couple from each source, thanks guys. FWIW, Audio Labs has pretty exorbitant shipping prices for being just two states away. Anyway, here's hoping they work and that I now have some spares on hand.

[Enzo]

An OTA is not "just a 5532". Look at the data sheet, it is an op amp with an output transistor.

We have two threads on this amp now?

I suggested elsewhere that while it was more critical in the phasor, it wasn't elsewhere in the amp. You got the phasor working, now replace the les criticalone you stole.

And I remain on the record as thinking their $15 workaround is worth the price. They could just as easily left everyone hanging.

[Tone Meister]

An OTA is not "just a 5532". Look at the data sheet, it is an op amp with an output transistor.

We have two threads on this amp now?

I suggested elsewhere that while it was more critical in the phasor, it wasn't elsewhere in the amp. You got the phasor working, now replace the les criticalone you stole.

And I remain on the record as thinking their $15 workaround is worth the price. They could just as easily left everyone hanging.

Nope, made a separate thread for the OTA subtitute since it could easily get lost in the mix over on the amp repair thread.

The real kicker was that Peavey wouldn't be specific about where in the circuit the workaround part would actually work, at least Grant Brown wouldn't, and he is among the most knowledgeable there. He suggested harvesting an original part from a non-working donor amp.

[Enzo]

I actually researched that once. If you look at the data sheets for CA3080 and CA3094, they aere similar enough that one would work for the other unless a certain feature was used. And in that also where it mattered. I forget now. Grant is a good guy, but I suspect, like me, he'd have to do the same research again to come up with an answer.

[nosaj]

Ordered a couple from each source, thanks guys. FWIW, Audio Labs has pretty exorbitant shipping prices for being just two states away. Anyway, here's hoping they work and that I now have some spares on hand.

Yes but they usually have the hard to find stuff thats not knock off or counterfeit.

nosaj

[J M Fahey]

I think MarkusBass meant that often "mystery/magic" chips turn out to be quite plain vanilla ones, not that 5532 and 3080 are the same or equivalent.

We have seen such things elsewhare, specially in the Audiophoolery world, but Peavey is a solid feet on the ground type of company, when they say specially selected I believe them, in this case being equivalent to "matched power transistors", "selected for low noise Op Amps or transistors", etc. , not magic dust involved but some technical measurable characteristic.

Looking at the Peavey schematic, I see that:
* U15 is used as the last preamp stage before the Master volume
* I see a crude compressor there, U2B charges C58 to signal peak value, the attack time comes through R87, the discharge time through R90 which modulates U15 gain.

Since there are no trimmers or presets to adjust gain or threshold, I imagine this circuit needs selected 3080 , probably with transconductance within a certain range, to work "just right".

Lab Series amp L5 uses a similar OTA circuit, but they made it adjustable, as in "inject xxx mV audio at the input, adjust output trimmer to 1.2 (or 2) V RMS" just before the Master Volume.Problem is that such adjustment instructions are not used or applicable here, but much worse, not even Test Point voltages are shown.

So:
1) not sure a random 3094 or 3080 will work properly there.
We donŽt even know what it "should" do.

2) in any case, if you lack U15 and this channel does not work at all, IŽd plain pull U15 out of the board and connect U2b output (pin 7) straight to Master Volume / post gain R93 hot.
YouŽll lose the "tube emulation" which probably was not such a big deal anyway.
If needed, you can increase U2b gain (increasing R86 or decreasing R85) so it roughly matches the other channel, built around U14.

[MarkusBass]

I think MarkusBass meant that often "mystery/magic" chips turn out to be quite plain vanilla ones, not that 5532 and 3080 are the same or equivalent.
We have seen such things elsewhare, specially in the Audiophoolery world, but Peavey is a solid feet on the ground type of company, when they say specially selected I believe them, in this case being equivalent to "matched power transistors", "selected for low noise Op Amps or transistors", etc. , not magic dust involved but some technical measurable characteristic.

Thank you Juan - this is exactly what I meant. I'm not saying that there is some relation between 5532 and 3080. I'm just saying that some companies (including respected American companies) often say that they use some specially selected components but quite often this is just a marketing bulls**t (for musicians who do not have any clue about electronics). This is the case of so called "golden chip" which is nothing more than plain NE5532. Let's hope it's not the case with Peavey.

Mark

[Enzo]

Peavey publishes a master semiconductor reference with all their house numbers. They have very few selected parts, but the ones they do have usually matter.

Marketing BS usually only happens with parts consumers would buy, like tubes or speakers. There is no incentive for PV to BS one or two ICs out of a hundred other types. That wouldn't be their style anyway. They are the people who made the effort to create a small workaround for the TL604 when TI stopped making them.

An example is certain transistors of common type, but sorted on a curve tracer for a voltage characteristic needed in a particular circuit. The selected part is given a different part number from the common part.