Reading through a number of old threads on this board, I've just found this bit:
On the other hand, you might drop in OPA627 to a circuit that was designed with a 5534, and it might oscillate horribly . . .
Reminds me of when I built a set of playback amps for converting an old Telefunken M5 tape recorder to stereo. The circuit was designed for uA741 which had been state-of-the-art years ago when Goetz Corinth had developed it, but things like the NE 5534 were much fancier by the time my soldering iron hit the Veroboard.
Against all odds, the amps seemed to work nicely when I first connected the power supply, so I took out the AF millivoltmeter and the terribly expensive Agfa 15 ips playback calibration tape (300 USD was a lot of money in those days) to adjust the various level and EQ settings.
Everything looked good, right form the start, but strangely with each pass of the tape, I had to crank up the EQ pots for the higher frequencies further and further until I reached the mechanical stop of those pots. That's when I decided it might be a good idea to connect a scope and have a look at what was going on.
Things immediately became clear: my NE 5534's were oscillating like hell, to the extent that my playback amps were erasing the higher freqs on the calibration tape through the playback head. A little more with each pass of the tape which was totally ruined by that time.
Ralf
Topic: The joys of DIY (Read 1755 times)