trim plus multiple outputs
« on: January 09, 2021, 05:01:18 PM »
I have a task to trim balanced line level +4dBu  +-6dB and split it into 3 separate outputs.

My current design is using THAT1246 balanced line receiver (-6dB) followed by passive switched attenuator (-6dB at zero setting), OA with +6dB gain and 3 separate THAT1646 to drive the outputs.

First question is, Is there any benefits in adding the switched attenuator into NFB OA gain setting network versus having the gain fixed and switched attenuator at the output?

Above does the job, BUT I had another idea to keep things balanced all the way and just use dual opamp and have common variable resistor to ground for both the positive and negative parts of the balanced line. This would also give me +-6dB trim and very few parts involved, if I use for example OPA1642 powered from +-18V I will theoretically get even better distortion performance and I dont see nay issues with headroom either, the question is how to do the split to 3 outputs but again just a resitor network and output buffer using similar OA like OPA1642 will do the job and its lot less parts.

Both solutions work and have low enough distortion but which one is better? What do you see as pros and cons of each solution?



 


abbey road d enfer

Re: trim plus multiple outputs
« Reply #1 on: January 09, 2021, 05:19:16 PM »
I have a task to trim balanced line level +4dBu  +-6dB and split it into 3 separate outputs.

My current design is using THAT1246 balanced line receiver (-6dB) followed by passive switched attenuator (-6dB at zero setting), OA with +6dB gain and 3 separate THAT1646 to drive the outputs.

First question is, Is there any benefits in adding the switched attenuator into NFB OA gain setting network versus having the gain fixed and switched attenuator at the output?
  There could be a very minor improvement in terms of noise. This would probably imply an inverting stage, since the gain of a non-inverting stage cannot be less than unity. You would need to reverse polarity somewhere else.

Quote
  Above does the job, BUT I had another idea to keep things balanced all the way and just use dual opamp and have common variable resistor to ground for both the positive and negative parts of the balanced line. This would also give me +-6dB trim and very few parts involved, if I use for example OPA1642 powered from +-18V I will theoretically get even better distortion performance and I dont see nay issues with headroom either, the question is how to do the split to 3 outputs but again just a resitor network and output buffer using similar OA like OPA1642 will do the job and its lot less parts.

Both solutions work and have low enough distortion but which one is better? What do you see as pros and cons of each solution?
What do you think will happen if you connect one of the outputs to an unbalanced line?
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: trim plus multiple outputs
« Reply #2 on: January 09, 2021, 05:46:33 PM »
What do you think will happen if you connect one of the outputs to an unbalanced line?

very good point, I'm scratching the idea, it is the most obvious things one don't see when looking too much into detail!

dogears

Re: trim plus multiple outputs
« Reply #3 on: January 09, 2021, 11:43:03 PM »
You could use a quadrifilar transformer for distribution if you have enough umph to drive it.

abbey road d enfer

Re: trim plus multiple outputs
« Reply #4 on: January 10, 2021, 04:23:36 AM »
You could use a quadrifilar transformer for distribution if you have enough umph to drive it.
A quadfilar xfmr does not protect the outputs when one is shorted.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


 

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