| Electronics > Projects, Designs, and Technical Stuff |
| Inverting or non-inverting for audio applications? |
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| ricko_uk:
Thank you all. :) TimFox, with reference to your schematic, could the Vin be the ground and output pins of an external floating MP3 player, like the headphone jack of a mobile phone? Thank you |
| TimFox:
You could do it if the external box were truly floating on battery power, but any conductance or capacitance from the "low" terminal of the external box to the "ground" of the amplifier would change the feedback circuit. Also, the "ground" of the external box would make an antenna for local EMFs, such as 50/60 Hz or MF broadcast stations. The only place I saw that suggested this was for an RIAA phono preamplifier, where the cartridge could float and connect through a shielded twisted pair to the input terminals. Using very low values in the feedback divider, this trick improved the noise and eliminated common-mode input voltage, since the feedback forced the inverting input to zero, agreeing with the grounded non-inverting input. If you are building the amplifier from discrete devices, you can reduce the common-mode distortion and common-mode input current problems by design techniques such as a cascode input stage. Of course, some monolithic op amps use that trick for the same reasons. |
| ricko_uk:
Thank you Tim! :) |
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