Can't understand why to use differrent gains for negative and positive rails ? What is purpose ?
This is a piece of schematic from one factory made device. "Balanced" in quotes because of input.
This is a piece of schematic from one factory made device. "Balanced" in quotes because of input.
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Not sure why they've made it so unnecessarily complicated, but if you work out the gains, they aren't that different:
- For the non-inverting stages: (2 / (2 + 1.5 + 2)) * (1.2 / 0.82 + 1) = 0.896
- For the inverting ones: 1.5 / (1 + 0.75) = 0.857
- For the non-inverting stages: (2 / (2 + 1.5 + 2)) * (1.2 / 0.82 + 1) = 0.896
- For the inverting ones: 1.5 / (1 + 0.75) = 0.857
^^ I’m not sure that is absolutely true for a balanced headphone amp. I think all the benefits of balanced drive will be conferred provided the drive levels are very similar.
You still get the benefit of the elimination of the shared ground connection that will minimize crosstalk.
The actual transducer won’t work any differently.
You still get the benefit of the elimination of the shared ground connection that will minimize crosstalk.
The actual transducer won’t work any differently.
Dear OP,
You seem to be obtaining a "balanced" output from an unbalanced one. To do this with a single set of gain setting resistors is tricky but possible. This could probably be the reason why the design uses inverting and non-inverting circuits and ends up having slightly mismatched gains.
A quick and dirty way to get "similar" output is as follows,
OR
You seem to be obtaining a "balanced" output from an unbalanced one. To do this with a single set of gain setting resistors is tricky but possible. This could probably be the reason why the design uses inverting and non-inverting circuits and ends up having slightly mismatched gains.
A quick and dirty way to get "similar" output is as follows,
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The standard way would be single gain stage (non-inverting for lower noise perhaps?), then an inverter stage. 4 resistors total, only two of which need matching for accurate balanced output:
That "clever" circuit in fig 37 uses 7 resistors, and I think 6 of them need to be matched for well-balanced output. Also amp2 sees 134 ohms to ground due to the low resistor values, and AD8056 is a poor choice due to its RF bandwidth being much harder to stabilize than standard audio opamps.
That "clever" circuit in fig 37 uses 7 resistors, and I think 6 of them need to be matched for well-balanced output. Also amp2 sees 134 ohms to ground due to the low resistor values, and AD8056 is a poor choice due to its RF bandwidth being much harder to stabilize than standard audio opamps.