John Curl's Blowtorch preamplifier

[john curl]

It is the topology that is interesting and its place in history.

 

[dimitri]

Dimitri has it as well, but he has not put it up either.

I couldn't post it due to forum limitations, I need to convert it from grayscale to BW.

 

[scott wurcer]

Dimitri - The schematics I posted were grayscale. If you scan just the schematic and set the res to 150dpi and the longest side to 1000 pixels the .jpg is pretty readable even at worst quality.

 

[dimitri]

2nd try

 

[SY]

Beat me to it.

If anyone wants a larger version, click here.

 

[scott wurcer]

Raytheon also had a military fab that was the source for another audio "secret". Their 5534 was considered the best by some.

 

[john curl]

Now, let us simplify this design to its essential elements, and analyze that.

 

[chascode]

Raytheon also had a military fab that was the source for another audio "secret". Their 5534 was considered the best by some.

This information is from the July 21, 1980 issue of EE Times "Outstanding Op Amps" list, in the "High Audio Gain Op-Amp ICs" category:

Analog Devices AD544

Analog Systems MA-332

Fairchild µA771, µA772, µA774

Harris HA-2700, HA-2900, HA-4602, HA-5130

Intersil ICL157, ICL2600, ICL8017

Motorola MC-3400

National LM318, LM351, LM357

Precision Monolithics OP-06, OP-07, OP-15, OP-16, OP-215

Raytheon RC-725, RC-4559

Signetics NE5532, NE5533, NE5534

No audio op amps were listed by Advanced Micro Devices, Burr-Brown, Datel-Intersil, Micro Power Systems, Plessey, Silicon General or Texas Instruments at that time. I thought the TL07x series had been around since 1976.

Best, Chuck Hansen

 

[scott wurcer]

Chuck, you left out the punch line. MA-332 = Raytheon 5534 (selected for distortion due to large variation in standing current).

EDIT- Hmmm, on finding an old data sheet the MA-332 appears to not have external comp. Was there an internally comped single 5534 style op-amp?

 

[syn08]

It is the 'timing' that is important. Who were these designers?

My guess is Jerry Coutreau.

 

[john curl]

Who ever he was, he (she) was ahead of his time.

 

[Nelson Pass]

Perhaps you will tell us why.

 

[scott wurcer]

The only thing new I notice is the folded cascode, there are too many hits to search for an earlier occurance. John, do you believe this is the first?

BTW I once got a call from James B., "Are you telling me the AD823 was designed by a girl?"

 

[scott wurcer]

My guess is Jerry Coutreau.

I just talked to an old Harris guy, that's a good bet.

 

[zinsula]

The only thing new I notice is the folded cascode, there are too many hits to search for an earlier occurance. John, do you believe this is the first?

Jonathan Carr thinks it was Masao Noro who invented the folded cascode:
http://www.diyaudio.com/forums/showthread.php?postid=135373#post135373

Tino

 

[john curl]

Nelson, it was an IC, not discrete.

 

[Nelson Pass]

Nelson, it was an IC, not discrete.

All the JFETs are P channel?

 

[john curl]

So?

 

[scott wurcer]

Noro's application is dated 1981, I guessed they missed this prior art. John, my knee-jerk reaction is to look for topological innovation. Much here is a translation of known stuff to a new sandbox. If he invented the differential folded cascode, that's different. The flavor of FETs is related to the process, our JI complimentary process has N-channel. The FETs are fairly area inefficient and the 10pF feedforward capacitors are too. People migrated to just FETs on the input soon after this.

 

[john curl]

Forget the fets, look at the topology in an IC in 1978.