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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Low distortion sinewave oscillator without big capacitor.
Date: Mon, 31 Mar 2025 23:09:03 -0400
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"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vsdi3h$3nagd$2@dont-email.me...
> On 31/03/2025 5:54 am, Edward Rawde wrote:
>> Not long ago JM posted a 1KHz sinewave oscillator with very low distortion.
>> It used a 470uF non polarized capacitor which in practice would probably be made from two 1000uF capacitors.
>> There's nothing wrong with that but I wanted to see whether I could make a working circuit without needing such a large 
>> capacitor.
>>
>> What I have so far is below.
>>
>> Any comments?
>
> It relies on the Analog Devices MAT-02 dual transistor, which is now obsolete
>
> https://www.analog.com/media/en/technical-documentation/obsolete-data-sheets/mat02.pdf
>
> The .asc file shows eight NPN transistors labelled MAT-02, presumably in four pairs of the part, but it isn't clear which of the 
> eight transistors should be paired up.

BCM61B is available and very reasonably priced.
https://www.digikey.ca/en/products/detail/nexperia-usa-inc/BCM61B-215/2119400
It can be used for Q1 Q2 and Q3 Q4 in the circuit below.

The remaining four transistors can use MAT14
https://www.digikey.be/en/products/detail/analog-devices-inc/MAT14ARZ-R7/2510588
which although a bit pricey has four independent matched transistors.
I can't find an LTSpice model for MAT14 so MAT02 is still shown in the circuit below.

>
>> What's the best way to control the output level?
>> Currently it's 5v pk-pk but I rather have half that.
>
> The rectified currents from the four phased shifted versions of of the output waveform flow through R13, R14, R15 and R16 into R11 
> and through it into the virtual earth set up at the inverting input of U3, where the summed current is compared with a fixed 
> current drawn from the +15V rail through D1 and R10.
>
> Doubling R10 from 330k to 680k would roughly halve the output amplitude.
> One could be more precise, but it wouudl be hard to justify the extra effort.

Ah yes, that takes care of the output level.
The revised circuit is below.
Line 459 will need to be unwrapped.

>
> -- 
> Bill Sloman, Sydney
>
>
>

Version 4.1
SHEET 1 3020 2792
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WIRE 800 -208 160 -208
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