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 Forum index » DIY Hardware and Software » The layout factory
+/- 10V reference for balanced modulator
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cslammy



Joined: Apr 27, 2018
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PostPosted: Sat Mar 30, 2019 9:20 am    Post subject: +/- 10V reference for balanced modulator
Subject description: Lower parts count way to do this?
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Hi there:
Finished a AD533 based Balanced modulator recently based on an old Electronotes design.

It needed a temp. stable +/- 10V reference for X Y and DC trim.

I came up with this, based on Elby designs work on the improved ASM VCO.

https://audiodiwhy.blogspot.com/2019/02/electronotes-balanced-modulator-part-i.html

But It's been bugging me...there must be a lower parts count/more elegant way to do this. What I used is big and clunky.

perhaps A 10V ref (EG: ADR01ARZ-ND) and then invert it with an op amp (must match the op amp resistors closely....). +V references chips are everywhere, but not +/- chips?

The B-Mod reference doesn't require sourcing a lot of current.


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PHOBoS



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PostPosted: Sat Mar 30, 2019 2:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

If it doesn't need much current than a voltage reference and an opamp doesn't sound like a bad idea. To get the negative voltage precise
you could use a (multiturn)trimpot.

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ixtern



Joined: Jun 25, 2018
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Location: Poland

PostPosted: Sun Mar 31, 2019 11:12 am    Post subject: Re: +/- 10V reference for balanced modulator
Subject description: Lower parts count way to do this?
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cslammy wrote:
Hi there:
Finished a AD533 based Balanced modulator recently based on an old Electronotes design.

It needed a temp. stable +/- 10V reference for X Y and DC trim.

I came up with this, based on Elby designs work on the improved ASM VCO.

https://audiodiwhy.blogspot.com/2019/02/electronotes-balanced-modulator-part-i.html

But It's been bugging me...there must be a lower parts count/more elegant way to do this. What I used is big and clunky.

perhaps A 10V ref (EG: ADR01ARZ-ND) and then invert it with an op amp (must match the op amp resistors closely....). +V references chips are everywhere, but not +/- chips?

The B-Mod reference doesn't require sourcing a lot of current.


I don't recommend using 317/337 voltage regulators as a source of reference voltage. They have big temp coefficient - about 6000 ppm.

You can use any positive voltage reference as a negative voltage reference. Below is the reference with TL431 I have used. TL431 has medium temp coeff - about 50 ppm. Resistors should be 1% with 50 ppm or better.

If you need very stable +-10V voltage reference you can use two REF01 (3-10ppm) or others. I have seen somewhere schematic for +-10V ref source using only two REF01 and nothing more but I cannot find it now.

And of course you can use any positive reference and inverting (-1) OpAmp (many schemes available) but there is always a problem with OpAmp temp drift (you should choose one with low drift - means costly) and precision resistors with low ppm.

As I can see in datasheet, AD533 has 100ppm temp drift so very stable ref voltage is not needed (50 ppm should be enough).


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