http://edn.com/ContentEETimes/Documents ... future.pdfBob Dobkin, Linear Technology’s co-founder, vice president of engineering, and chief technology officer, spent his early design days at National Semiconductor, during which he moved op amps beyond the 1-MHz-bandwidth barrier with the LM318 (Figure 5). No fast PNP transistors then existed; there were only lateral NPNs (Editor - I think they meant PNP here) with 1-MHz bandwidth. Improvements in process technology helped, but the greatest speed gains often resulted from clever topological choices. Dobkin employed an architecture that split the input signal into a dc path through the lateral transistors and an ac path with feed forward capacitors that went around the PNP transistors for the 10- to 15-MHz bandwidth breakthrough.
This made me think: With only lateral PNPs available in the NE5532/NE5534 to the Mullard Designers (and perhaps Rupert Neve) how did they get the speed to make the 5534 suitable for audio?
I think they used Dobkin's LM318 split-path approach.
This may explain the 5534s internal workings.
Ignore the front-ends of the LM318 and 5534 which are completely different and look at the 2nd stage area around the PNPs.
This is the LM318 schematic:
LM318 Internal Schematic
NE5534 Schematic:
NE5534 Internal Schematic
It looks like C3? in the LM318 is providing the feed-forward path around the lateral PNPs.
Isn't that what the 40 pF capacitor is doing in the NE5534?
Both parts have the same "hook" in their open loop gain and phase response.
LM318 Open Loop Gain and Phase Response
NE5534 Open Loop Gain Response
Just a thought...
And one more thing. Am I the only one that has noticed the gorss error in the Philips and ON Semiconductor version of this part?
NE5534 Schematic with huge error:
NE5534 Internal Schematic
The inputs in an NE5534 ARE NOT PNP.