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I have a TDA2030A based amplifier that should make a decent headphone amp except that its gain, at about 32 dB, is way too high.

It would be easy to change the gain setting resistor or even put in a switch to change the gain from say 10 to 15 to 20 dB for proper Headphone use. But there is a problem.

The TDA2030A data sheet says the chip needs to run at a gain in excess of 24 dB to maintain stability.

A resistor could be placed in series with the output. But that destroys damping factor and sound quality. That is not an acceptable solution.

Meier Audio uses the TDA2030A in their Corda Brick. It has switchable gain of -1 to +14 dB. So how do they do that with the TDA2030A?

Anybody got a working circuit they will share that gets the TDA2030A down to a stable switchable gain of 10-15-20 dB?

Suggestions?

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This question came from our discussion, support, and feature requests site for electronic hardware hacking enthusiasts.

  • \$\begingroup\$ Regardless which way you do it, attenuating signal so much just so you won't destabilize that unsuitable (for headphones) amp will have audible consequences from a SNR perspective. The TDA2030 will not make a "decent headphone amp" no matter what you do. You also didn't say what headphones you intend[ed] to use. \$\endgroup\$ – Fizz Oct 18 '14 at 23:40
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Lower the signal going in with an attenuator - just a couple of resistors should do the job.

A lot of headphone outputs on hi-fi amplifiers do have resistor attenuators despite what you said about destroying damping factor and reducing quality.

The dynamic impedance of speakers (headphone or otherwise) are mainly resistive but if you have some article or other that explains why this should be a problem I'd love to read it.

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  • \$\begingroup\$ It took me a while to understand that you don't normally do volume control by adjusting gain. Instead, attenuate the /input/ (OP rejects the incorrect solution of a series resistor on the output). \$\endgroup\$ – joeforker Nov 7 '13 at 17:42
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Easy. Add high current opamp after the TDA in the inverting configuration with adjustable gain/attenuation. The non-inverting input is grounded.

This schematic will shed some light on how to do it. Of course you don't need the tone controls. I would use a trimpot to find the desired divider by experimentation.

enter image description here

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