[sdiy] On-chip transistor pairs

[Terry Shultz]

Hi , The LM324 is a quad opamp. LM194/LM394 is a matched transistor  pair.

regards,

Terry

> On Nov 3, 2017, at 4:40 PM, ijfritz at comcast.net wrote:
> 
> Isn't the LM324 a quad opamp? 
> 
> 
> Sent from XFINITY Connect Mobile App
> 
> 
> ------ Original Message ------
> 
> From: Ben Bradley
> To: SYNTH
> Sent: November 3, 2017 at 1:45 PM
> Subject: [sdiy] On-chip transistor pairs
> 
> The talk of exponential converters on VCAs brings to mind the use of
> transistors for expo conversion, specifically on-chip transistor
> pairs. Was there any use of National's (and later TI until they
> stopped production) LM324 precision dual transistor in a synth expo
> converter? The only product I know of it being used in was the Jensen
> 990 discrete op-amp. This tells Jensen's story of going through
> replacements for the LM324:
> 
> http://www.technicalaudio.com/pdf/Jensen_Transformers/Jensen_OpAmps_990_and_related/Jensen_JE-990_opamp_JAES_reprint_1980.pdf
> 
> On the first couple pages of text here is Deane Jensen's descriotion
> of the LM324, how it's made with many on-chip transistors wired
> together as two:
> http://www.johnhardyco.com/pdf/990.pdf
> 
> I noticed our friends from Latvia are now making an LM324 replacement:
> http://www.alfarzpp.lv/eng/sc/transistors.php
> 
> There was also the ua726 self-heating temperature-regulated pair used
> in classic synths that is basically unobtainable now. It would be good
> to have that remade, or perhaps even an LM324 version with an on-chip
> heater/temp regulator.
> 
> The newly-remade module-on-a-chip designs are wonderful in having
> everything built in, but I still want to make some "discrete" designs,
> and having these transistor-pair-on-a-chip products available helps a
> lot.
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