Running SSM 2143 from single ended PSU.

Rob Flinn said:

Hi folks

I have a scenario where I am building a 4 channel amp using some class D amps that will be running on a single ended PSU that have unbalanced inputs.  They will be used in a potentially noisy broadcast type environment & the plan is to add some SSM 2143 that we have knocking around  to create balanced inputs.

I have knocked up a small pcb which is using a 5534 to split the power rail & provide a centre tap.  However the centre tap will not be the 0v rail of the single ended PSU.  Assuming I use an output cap on the chip my question is how comfortable will the chip be if the output is referencing to it's -ve power rail instead of the psuedo centre tap that I have created to run the chip ?

AM I overthinking this or have I got my idea wrong ?

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Rob Flinn said:

Yes, sorry Abbey.  I was somewhere that I couldn't easily post a diagram.  It is a single unipolar supply to derive the rails.  Please see rather crude attached diagram

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abbey road d enfer said:

You'll need to add DC blocking caps to the inputs.

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Rob Flinn said:

Hi.  I've been trying to determine what value input cap & what direction they need to be.  There do not seem to be any practical circuits on the net that I've come across.  Any ideas ?  I was think 100u, but not sure of the direction.

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Rob Flinn said:

Thanks Abbey.

The polarisation of the output cap is fairly obvious.  Should the i/p caps be + facing the preceding device ?

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Rob Flinn said:

Thanks again.

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Rob Flinn said:

Thanks for all your help with this.  Having played around with this on the bench we have decided we need a seperate PSU for the ssm2143, because they start clipping at too low a level to be useful at the voltage we are using off the single ended supply.

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abbey road d enfer said:

This is weird. I guess it drives the power amp and that it has significant gain, 20dB like, so the line receiver should not clip before the power amp. Have you done a level diagram?

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Rob Flinn said:

We were running it off a split 18v supply & it wouldn't do 1v pk>pk without clipping.

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abbey road d enfer said:

Did you actually decouple the V/2 point with a good cap to ground (at least 47uF)?

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Rob Flinn said:

I used a 100uF to  hold the point that was feeding the + i/p of my op amps splitter.    I didn't have a cap on the ouput of the op amp.

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moamps said:

I used once SSM2143 supplied with a single PSU without problems but there was an OPAMP for DC bias as noted in datasheet.

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