[sdiy] Differential amps and noise cancellation in dsPIC 33FJ128GP802 uP's DAC

[Tom Bugs]

There's also a full chapter on a FET compressor design in another of his 
books 'Self on Audio' (Chapter 10, if I remember right)

I didn't realise there was a 3rd edition of Small Signal Audio.. Great book!

On 05/05/2021 13:24, ulfur hansson via Synth-diy wrote:
> slightly OT, has anyone successfully built the FET compressor douglas 
> describes?
>
> sent from outer space
>
>> On 5 May 2021, at 11:32, Neil Johnson via Synth-diy 
>> <synth-diy at synth-diy.org> wrote:
>>
>> 
>> It's still chapter 26 in the third edition.  Also read through the 
>> first half of chapter 18 on line inputs.
>>
>> Neil
>>
>>
>> On Wed, 5 May 2021 at 11:34, Mike Bryant <mbryant at futurehorizons.com 
>> <mailto:mbryant at futurehorizons.com>> wrote:
>>
>>     Small Signal Audio Design (I have Second Edition so it may have
>>     moved chapter)
>>
>>     *From:*Tom Wiltshire [mailto:tom at electricdruid.net
>>     <mailto:tom at electricdruid.net>]
>>     *Sent:* 05 May 2021 11:17
>>     *To:* Mike Bryant
>>     *Cc:* synth-diy francesco mulassano via
>>     *Subject:* Re: [sdiy] Differential amps and noise cancellation in
>>     dsPIC 33FJ128GP802 uP's DAC
>>
>>     The circuit is straight out of Microchip’s datasheet and is what
>>     they recommend. But that’s not to say that it can’t be improved!
>>
>>     Which Douglas Self book did you mean? He’s written a few.
>>
>>
>>
>>     On 5 May 2021, at 11:11, Mike Bryant <mbryant at futurehorizons.com
>>     <mailto:mbryant at futurehorizons.com>> wrote:
>>
>>     You probably want to use something a little more complicated for
>>     the best performance.  Douglas Self covers this well in Chapter
>>     26 of his book.
>>
>>     *From:*Synth-diy [mailto:synth-diy-bounces at synth-diy.org
>>     <mailto:synth-diy-bounces at synth-diy.org>]*On Behalf Of*Tom Wiltshire
>>     *Sent:*05 May 2021 10:17
>>     *To:*synth-diy francesco mulassano via
>>     *Subject:*[sdiy] Differential amps and noise cancellation in
>>     dsPIC 33FJ128GP802 uP's DAC
>>
>>     Hi all,
>>
>>     The dsPIC 33FJ128GP802 uP (and others in the family) includes a
>>     16-bit DAC on the chip. The outputs from the DAC are provided as
>>     a differential output to help cancel any noise generated by the
>>     uP internally. NOt a bad idea, seeing as that is probably
>>     inevitable. Despite this precaution, the DAC is reasonably noisy
>>     and not suitable for all applications.
>>
>>     The example circuit for combining the differential outputs is
>>     shown attached - a simple diff amp with 10K resistors everywhere.
>>
>>     Now, my question is this:
>>
>>     If I change the gain of the differential amp by increasing R6/R8
>>     (to 47K, say) does this affect the noise cancellation properties
>>     of the diff amp?
>>
>>     It seems to me that it might, because the positive input now has
>>     a different proportion of signal going to it than the negative input.
>>
>>     Thanks,
>>
>>     Tom
>>
>>     ==================
>>            Electric Druid
>>     Synth & Stompbox DIY
>>     ==================
>>
>>     <image002.png>
>>
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