[sdiy] Discrete Op Amps

[rsdio at audiobanshee.com]

The quote is hilariously the opposite of smart. Why would anyone who understands oscillator design describe transistors-on-a-chip as "dreaded?" The best way to match transistors is to have them made at the same time, on the same die.

The idea that it's somehow "better" to hand-match transistors is like saying you prefer rolling the dice and waiting for snake eyes instead of a sure thing. Even with the best hand-matching, nobody can force the manufacturer to deliver a set of transistors that were made under the same conditions. Discrete synthesizers can only match what's in stock, not make the best match possible.

Tons of great circuits call for a pair of transistors on a single die so that the temperature compensation and other aspects that require matching are ideal.

Brian

p.s. THAT Corporation have a great fab where they can design chips that actually isolate the substrate for different sections, even down to the individual transistor. The typical drawback of chips is that all of the transistors share the same substrate, which limits some design choices. THAT Corporation can design systems which isolation is possible so long as there are enough pins on the chip for each separate substrate. I recall that THAT bought a retired military fab, and this allows them to build chips using a different process from typical chip makers.


> Phil Cirocco's current modular offering is all about its discreteness...
> http://www.discretesynthesizers.com/dsc/dsc.htm
> 
> "What is true discrete? It means no chips whatsoever in the audio path. Many of our competitors say discrete - but the real truth is, their circuits are hybrid - meaning they use a combination of transistors, chips and some even use the dreaded "transistors-on-a-chip" devices, and try to claim discrete. The 9000 series circuits use only hand matched pairs, expertly selected from individual, ultra-linear transistors."