Dual Op Amps

[amz-fx]

One of these things is not like the other...

http://www.muzique.com/news/dual-op-amp/

regards, Jack

[DIY Bass]

Somewhere in the world somebody is already designing an op-amp board that uses unobtainium transistors and carbon resistors so they can make it a feature of a new boutique discreet distortion pedal.

[Mark Hammer]

Jeez, how do you "dead bug" install that? 

[paul.creedy]

How about a couple of these instead ?

[PRR]

> One of these things is not like the other...

So/but the other is like the one? Asymmetrical inequality?

Lots of folks stole my stolen idea to SMT/PCB a DIP-equivalent. Gives much work to writers of fiction. Over at DIYaudio there's always a thread someone got an evaluation sample and reports how much it improved his phono/CD/DAC/whatever.

I have real doubts about radical change of active gain in a well-designed system. Beware radio oscillation. However in pedal-world what is bad may be good and what is good may be baaaad.

Love the "741". Socket optional at extra cost??

[Fancy Lime]

Also: one opamp isn't really like another opamp, even if we are just talking about the conventional, non-discrete ones. Except in applications where the differences don't matter, in which case I would not expect the discrete ones to be different either, no? Interesting nonetheless, at least for circuits where it does make a difference. I've been meaning to have a crack at a discrete-opamp Rat, but who has the time...


Andy

[R.G.]

For a mental/layout exercise I used to try to figure out how to use SMT dual transistors to make an opamp that was all semiconductors, no resistors. Never got it completely there. But a DIY OTA with SMT duals is entirely achievable.

Just poorer performance than the integrated version.   

[amz-fx]

The one in the back might be difficult to fit into a pedal. The one-board version is a single op amp instead of a dual.

Samuel Groner's paper on op amps contains test results for many of the typical op amps used in pedals but also has data on a selection of discrete versions:

http://www.nanovolt.ch/resources/ic_opamps/index.html

Interesting reading for a cold weekend day when you have the time.

regards, Jack

[EBK]

The one in the back might be difficult to fit into a pedal.

How big is it?  It looks like it would quite comfortably fit in a 1590B with room for extra parts if you laid it down instead of positioning it as shown.

[Mark Hammer]

Buddy of mine makes replacement discrete op-amps for MCI mixing boards.  He uses one himself (Leon Russell's old remote recording mixer), and learned that the key components for it could simply not be purchased any more.  So, he makes them himself.

[PRR]

> opamp that was all semiconductors, no resistors. Never got it completely there. But a DIY OTA with SMT duals is entirely achievable.

A '3080-like OTA with a low-low Idss JFET bias is an opamp. Or a selected Germanium diode....

But designing without using resistors is like putting on your parka without using your right arm. I been doing that all week (fell on ice, bunged my shoulder). Not really something you "want".