Mystery opamp

[Mr. Brokenamp]

Hi all,

I have an old Telefunken V672 amp that uses an ITT MIC-709 opamp.

Is this possibley an LM709 variation?

 

[moamps]

Yes.

 

[Mr. Brokenamp]

Thank you!

 

[JMFahey]

WAY back then there was not much else 

I am old enough to remember using 709 until I visited my supplier (must have been in 1970) and he told me: " hey, whiz kid, try this novelty, it´s called the 741 and does not need compensation capacitors  "

 

[JohnRoberts]

WAY back then there was not much else 

I am old enough to remember using 709 until I visited my supplier (must have been in 1970) and he told me: " hey, whiz kid, try this novelty, it´s called the 741 and does not need compensation capacitors  "

The first 709s were something like $60 a piece and would blow up if you looked at them crosseyed.

The 741 was the first modern opamp and a remarkable achievement at the time.

JR

 

[PRR]

The '709 has more potential gain-bandwidth than any internal-comp chip made for another 20 years. It is still a fine choice if input hiss is optimized and output is protected. I would not normally "upgrade" one willy-nilly. If it died, it was usually the technician's probe.

 

[ruffrecords]

The '709 has more potential gain-bandwidth than any internal-comp chip made for another 20 years. It is still a fine choice if input hiss is optimized and output is protected. I would not normally "upgrade" one willy-nilly. If it died, it was usually the technician's probe.

An old trick was to add a couple of discrete BJTs at the input for better noise performance.

Cheers

Ian

 

[JohnRoberts]

An old trick was to add a couple of discrete BJTs at the input for better noise performance.

Cheers

Ian

Old tricks involve adding BJT in front of, in back of, or both. 

Dropping BJTs in front was often done to lower noise using more silicon area for lower Rbb. The classic "pre" app note was national LM394. Adding BJT post for more current output capability was very popular to buffer good op amp front ends with stronger outputs. Why stop there?  Adding voltage gain in front can extend gain bandwidth product, adding voltage gain behind can increase voltage swing beyond the nominal 36V op amp process limitation as well as increasing  gain bandwidth. 

I even did one design in the 80's  with BJT both in front and in back, to make a precision rectifier (used inside the TS-1 audio test set) that didn't suck.  Typical precision rectifiers wrapped around op amps run out of gain to slew reasonably well from minus one diode drop to plus one diode drop at every zero crossing for very low level 20kHz sine waves. This limited gain bandwidth causes an effective HF roll off at low level.  Not a problem for general purpose dynamics processors but when attempting to deliver bench level test equipment it needs to work over a wider range of frequency and amplitude levels.  Even my improved precision rectifier was -3dB @ 20kHz and -50dBu.  :'(

JR