[sdiy] Unity Gain Diff-in Diff-out driver

BrightBoy jdec at mindspring.com
Wed Mar 25 03:27:41 CET 2020


A balanced circuit does NOT require each leg to be equal and opposite
to reject noise.

Time to let Bill Whitlock of Jensen Transformers take you to school:

https://www.jhbrandt.net/wp-content/uploads/2014/11/Design_of_High-Performance_Balanced_Audio_Interfaces.pdf

There are many other papers that Bill has written (many published by the AES)
that you should research (they aren't hard to find with Google)

BB

-----Original Message-----
>From: Ben Riggs <benalog1977 at gmail.com>
>Sent: Mar 24, 2020 9:50 PM
>To: Neil Johnson <neil.johnson71 at gmail.com>
>Cc: SDIY List <Synth-diy at synth-diy.org>
>Subject: Re: [sdiy] Unity Gain Diff-in Diff-out driver
>
>Hi Neil,
>
>It is to act as a buffer, hiZ in low Z out and unity gain. Yeah, 2 basic voltage followers would do it, but I expect the preceding circuit won’t be outputting an equal amplitude signal with ref to 0V, but I expect the driver to output to be equal and opposite. If that makes sense.
>
>I apologise for the late response. With all the crazy shit going on in the world, I spent 3 days travelling to get out of India before they closed the airports (I got to Delhi in time for the last flight to Sydney on Saturday). I’m now in isolation in Perth, I didn’t quite get home though - I guess this is my new home for the next few months.
>
>Regards,
>Ben Riggs.
>
>Sent from my iPhone
>
>> On 22 Mar 2020, at 5:49 am, Neil Johnson <neil.johnson71 at gmail.com> wrote:
>> 
>> Hi Ben,
>> 
>>> I’ve been playing with differential driver circuits as part of a larger synth circuit I’m working on to seek a simple solution, what I’ve come up with just seems wrong but the sim has it working exactly as I need.
>> 
>>> https://drive.google.com/file/d/19rlz3_bgVclgZm5fZo7isq43QrmVGfst/view?usp=sharing
>> 
>> I'm still not understanding what exactly you are looking for?  That
>> circuit is a poor simulation setup so I am not at all surprised you're
>> getting some perfect answers.
>> 
>> If you just want to buffer a differential signal then just use two
>> opamps.  If you want to remove any common mode signal you need a
>> proper diff.amp and a test bench that will show you what the simulated
>> CMRR is (yours won't).
>> 
>> If you can specify what you want then you might get some more useful advice.
>> 
>> Cheers
>> Neil
>
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