[sdiy] Dual Matched N JFET from Linear

[Mike Beauchamp]

In the triangle core of the solid-state Ondes Martenot, two JFETs are used:

https://ondes.net/schematics/JB1%20Circuit%201979.pdf

One is used to switch between positive and negative input voltages to 
the integrator. The other is used to change the trigger position of the 
comparator.

Mike



On 2025-06-21 12:53, René Schmitz wrote:
> On 20.06.2025 23:15, david walker via Synth-diy wrote:
>> hello taking about JFET,s can any point out any were on line that show 
>> you how to use JFET,s in oscillator circuits ?
> 
> 
> A prominent example is the SEM1a from Oberheim:
> 
> 
> JFET as high-Z buffer in the VCO
> 
> https://synthfool.com/docs/Oberheim/Oberheim_SEM1A/Oberheim_SEM_1A_Schematics.pdf
> 
> Two JFETs (Q2/Q3) are used in a source follower configuration to buffer 
> the main integration cap with high impedance.
> 
> Today we would probably find a jfet opamp instead.
> 
> (JFETs are also used in the SEM filter.)
> 
> 
> Another example:
> 
> JFETs as discharge switch
> 
> https://schmitzbits.de/vco3.html
> 
> This one used two FETs, but they don't need to be matched. And you can 
> do this with a single FET as well.
> 
> 
> I've only used once a dual JFET where good matching was required (in 
> fact this was a 2SK389), but this circuit was never published.
> 
> 
> FETs have large unit to unit variations, good for one-off hobbyist or 
> space mission work, but
> 
> annoying to show-stopper for mass production. So you'll not see them 
> that often in the wild.
> 
> 
> Cheers,
> 
>   René
> 
> 
> 
> 
>> On Friday 20 June 2025 at 21:58:12 BST, Mike Bryant 
>> <mbryant at futurehorizons.com> wrote:
>>
>>
>> LSK389 is hardly new.  Been around for a long time, although 
>> availability varies.
>> But the price never seems to vary.
>>
>> ------------------------------------------------------------------------
>> *From:* Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Tim 
>> Parkhurst via Synth-diy <synth-diy at synth-diy.org>
>> *Sent:* 20 June 2025 21:34
>> *To:* synth-diy at synth-diy.org DIY <synth-diy at synth-diy.org>
>> *Subject:* [sdiy] Dual Matched N JFET from Linear
>> Hey, Analog Hounds,
>>
>> Linear Systems is promoting a new Matched Dual JFET, and you might 
>> even be able to get a sample or two. Useful? Not?
>>
>> https://www.linearsystems.com/post/why-engineers-choose-the-lsk389-for-high-precision-analog-design?utm_campaign=d2b0395f-db24-487d-8e02-adcff714e7a8&utm_source=so&utm_medium=mail&cid=a05ef50a-a9c5-473d-950b-37f3f1a2d83d <https://www.linearsystems.com/post/why-engineers-choose-the-lsk389-for-high-precision-analog-design?utm_campaign=d2b0395f-db24-487d-8e02-adcff714e7a8&utm_source=so&utm_medium=mail&cid=a05ef50a-a9c5-473d-950b-37f3f1a2d83d>
>>
>> Tim (define "useful") Servo
>> ---
>> "Imagination is more important than knowledge." - Albert Einstein
>>
>>
>>
>>
>> ------------------------------------------------------------------------
>> *From:* Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Tim 
>> Parkhurst via Synth-diy <synth-diy at synth-diy.org>
>> *Sent:* 20 June 2025 21:34
>> *To:* synth-diy at synth-diy.org DIY <synth-diy at synth-diy.org>
>> *Subject:* [sdiy] Dual Matched N JFET from Linear
>> Hey, Analog Hounds,
>>
>> Linear Systems is promoting a new Matched Dual JFET, and you might 
>> even be able to get a sample or two. Useful? Not?
>>
>> https://www.linearsystems.com/post/why-engineers-choose-the-lsk389-for-high-precision-analog-design?utm_campaign=d2b0395f-db24-487d-8e02-adcff714e7a8&utm_source=so&utm_medium=mail&cid=a05ef50a-a9c5-473d-950b-37f3f1a2d83d <https://www.linearsystems.com/post/why-engineers-choose-the-lsk389-for-high-precision-analog-design?utm_campaign=d2b0395f-db24-487d-8e02-adcff714e7a8&utm_source=so&utm_medium=mail&cid=a05ef50a-a9c5-473d-950b-37f3f1a2d83d>
>>
>> Tim (define "useful") Servo
>> ---
>> "Imagination is more important than knowledge." - Albert Einstein
>>
>>
>>
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> 
> 
> -- 
> --
> synth at schmitzbits.de
> http://schmitzbits.de
> 
> 
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