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Old 1st April 2013, 01:30 AM   #1
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Default TDA1308 - changing gain resistors

Is anyone able to ascertain how the gain stage of this chip functions?

http://www.nxp.com/documents/data_sheet/TDA1308.pdf

The circuit appears in the datasheet (page 6, entitled Typical Application) and is geared for 32 ohm headphones, however mine are 600 ohm beyerdynamic DT880 and the circuit as I've implemented it gets to listening levels around 90% on the pot.

R3/R4 and R5/R6 control the gain (via some kind of phase inversion). Can anyone suggest what a suitable change to these resistors would be, to drive the DT880 more efficiently?
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Old 1st April 2013, 07:28 AM   #2
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I don't think that's a good amp for 600 ohm cans. It runs off 6 volts typical. But you can double R4 and R6 for a gain of 2 and see if that works better.
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Old 1st April 2013, 08:12 AM   #3
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Ok I will try it, though presumably the higher R value would use less current?
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Old 1st April 2013, 02:53 PM   #4
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Do you mean it will make the chip use less current? No.

Do you understand the purpose of those resistors?
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Old 1st April 2013, 02:57 PM   #5
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Unless you're trying to build a compact, portable amplifier, that chip is a very poor choice. To drive 600 ohm cans, you'd get much better results just using a couple of 5532s running off a 20 volt split supply.
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Old 1st April 2013, 03:41 PM   #6
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Audio Designs With Opamps

Figure 4 is an inverting amplifier like your chosen circuit. Read it and you might understand what the resistors do.
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