Can someone educate me about the MC144B (or MC1448) dual op-amp?

[Steve Conner]

I did some searching. I can't find any reference to the MC144B at all. The MC1448, somebody once came across in an Ibanez stompbox:
http://www.diystompboxes.com/smfforu...c=45811.0;wap2

unless they made a typo and meant 1458.

It wouldn't surprise me if there had been a whole family of MC14x8, but the 1458 was the only one that ever caught on and they discontinued the rest.

[J M Fahey]

The 1458 is a *somewhat* obscure Op Amp which nevertheless is specified in certain "close to the edge" designs, by big commercials manufacturers which seem to know something we don't.
Marshall Lead 12. They specify a 1458 and the second gain stage has feedback resistors 220K/220 ohms which hints at a gain of 1000.
Not an easy task for most Op amps.
.
In the 9004 Rack Preamp they use M5201 and TL072 everywhere but for the headphone outs they also specify 1458

Music Man hybrid amps use 1458 to drive the output transistors which drive the power tubes and LF353 (similar to TL082) for the rest..

They are used as reverb drivers in other amps.

[tedmich]

gotta read the chip, NOT the schematic IME!

unless "sanding" has been done...

[Mark Hammer]

1458s have the ability to swing wide. I know they are frequently used in the envelope-follower/rectifier stages of several autowahs. If you try and replace the 1458 in a Dr Q or a Bassballs or DOD FX25 with a "better" chip, you'll get the worst sounding autowah you've ever heard. But in the case of the SC24, that's not how they are used.

[Enzo]

I still have a 1982 "IC Master." Two volumes of like 1900 pages each on thin paper.

Base number 144 yields:
DG144 Intersil
LM144 National
DG144 Siliconix
K144 Siliconix

Base number 1448:
No entries

[Mark Hammer]

I'm envious. Wish I had one of those, though happy someone as helpful as yourself still has a copy. Wonderful books.

None of those leads takes me anywhere productive. I'm going to have to ask my studio friend to see if he can provide any clarifying information about the identity of the chip on the board. He makes several rather arcane products, including mic preamps, but one of the things he has done is produce all-discrete plug-in replacements for some chips found in older MCI boards that are no longer available.

Hmmmm, that gets me thinking. Looking more closely at the schem it certainly doesn't appear to be MCI44B (or MCI448), but could the MC be from something OTHER than Motorola?

[J M Fahey]

Hardly.
Like selling an "IphSung"
Or a "Les Strat"

[Enzo]

I'be never seen MC elsewhere, but that doesn;t mean McPhooey Electronics isn't out there somewhere.


But how about a different approach We have talked about how SOMETHING must be special about these ICs since they specify them in some spots and various others elsewhere. But just how special do they have to be? ICs might be selected for voltage - either high rail rating or how close to rails the outputs can swing. Or slew rate, or open loop gain. Or noise figure. Or something about impedance - input impedance or how low an impedance the output can drive. Output current capability. Or maybe stability, some stage may be driving a capacitive load while others are not, and that could be a difference. And I am sure the engineers here could add tons to that list.

SO looking at the circuit, what MIGHT be special about them, and in any event, how does a common type like 4580 or 5532 or TL072 or one of the OPA whatnots that are popular perform in it? What might have been a far out spec back then, might just be a ho hum "everybody does that nowdays" spec today. So something modern ought to work, or at the least, if we install something that does NOT work, it might reveal something about why those parts were chosen.

[Mark Hammer]

Absolutely. That was the reason for my inquiry. I wanted to be able to look at a datasheet, mutter "Ahhhh, now I see what they were trying to do", and apply that principle to selection of currently easy-access chips for similar applications. I doubt that there is anythng there with mojo, and thoroughly expect something I can order from Mouser or Digikey to do the same thing. I'd just like to know what it is the chip was selected to DO that was deemed to assist optimum performance of the circuit.

[J M Fahey]

Enzo hit the nail on the head.
Most commercially made products aim to adress some special needs of a certain Market, and must "do" or surpass certain things to be popular and generate sales $$$$.
But because of their particular construction (they are not photocopies but individually designed) there may be some "extra" things they do in different ways.
Some designer may use one of those features available in a specific variant of what's basically "the same" Op Amp and his project depend on a specific type or brand.
I have seen schematics specifying certain transistor or IC brands only.
One fairly known example: RAT pedals use an LM308 .
You can use other, seemingly equivalent ones, from a 741 to a TL071 or Nasa approved "exotics".
None sounds the same.
The reason is, part of the distortion comes from the clipping diodes, thet's the visible clipping stage, but another part comes from the particular slew rate limiting typical of that particular Op Amp.
It's an externally compensated one, and the compensation net is *wrong* by a designer mistake ... which happens to sound good.
In an interview he explained "I was protoboarding it, wanted to add some extra brightness and added a capacitor, with a series resistor to tame it, in parallel with the feedback resistor to ground"
So far, so good, he would have made "another 741 with clipping diodes" distortion.
Grabbed a resistor and misread its value, now I don't remember whether he took a 470r for a 4K7 or a 47r for a 470r ; fact is it was 1/10 the needed value and *tried* (unsuccessfully) to push the high frequency gain of that poor 308 up by a 10X factor.
He said "as soon as I tested it, I heard a killer sound I had never found before .... I realized the mistake but, of course, left it as-is".
So yes, probably there is a good reason for using it.
Anyway, they are cheap and widely available, so don't reinvent the wheel.
Things become more complex with say, the once very popular RC4739 , because it comes in an unusual pinout 14 pin package, and you find it everywhere, from TAPCO mixers to Kustom to Craig Anderton's projects.