uA748/LM748 - Old Op Amp with frequency compensation pins

[Rob Strand]

I found stash of these in my parts recently.

FYI: as an opamp option for parts scroungers and experimenters.

The uA748 was Fairchild's response to the LM301A. 
- It is not a LM301A with a different part number.  It's a different design.
- It's an uncompensated LM741/uA741.
- If offers the ability add an external compensation cap to set the bandwidth and slew rate (like the LM301A, LM308)
- The offset pins are done different to the LM741.  See datasheet for two options. 
  (Perhaps some new ideas for chip hacks.)

Original Fairchild Datasheet (approx 1971), with internal schematic, shows both offset trim methods,
https://datasheetspdf.com/pdf-file/1305449/Fairchild/UA748/1

ST datasheet, with schematic,
https://www.st.com/resource/en/datasheet/ua748.pdf

TI datasheet, one of the few TI datasheet showing the connections to the comp pins and offset pins.
https://datasheetspdf.com/pdf-file/1398434/etcTI/LM748/1

[something to check: the ST datasheet internal schematic looks like an LM301A.]

[iainpunk]

very interesting internal schematic. i see a possible ''exploit'' with the comp. pin that doesn't double for the offset null. you can inject a signal there to use only the output amp in a weird way. i did a similar thing with a CA3160's comp/strobe pin.

cheers

[Rob Strand]

very interesting internal schematic. i see a possible ''exploit'' with the comp. pin that doesn't double for the offset null. you can inject a signal there to use only the output amp in a weird way. i did a similar thing with a CA3160's comp/strobe pin.

It has the right hooks.    The old LM318 diff-pair replacement trick might work except it needs PNPs (as per nat-semi AN222).

Doing nasty stuff like adding feedback resistors to the internal nodes hasn't been explored IMHO.  In many applications you wouldn't bother but for pedals it might change the sound in a good way.