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Audio amp help

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Audioguru:
The Headbanger circuit above adds positive feedback to cancel most of the negative feedback for lots of gain at low frequencies, a loss of high frequencies and lots of distortion and hiss.

Zero999:

--- Quote from: jeffheath on February 13, 2019, 12:59:36 am ---
--- Quote from: Richard Crowley on February 12, 2019, 10:46:37 pm ---An LM386 will easily drive low-impedance headphones supplied from common consumer line-level.  The LM386 has a minimum gain of 20 (26dB) and you can set it for gains up to 200 (46dB) using simple capacitor and resistor.

Your aversion to modern digital amplifiers seems unfounded.  If you examine the data sheets, you will likely find that a modern digital amplifier chips have lower distortion than that decades-old LM386.

--- End quote ---
The funny thing is, I don't have any aversion to digital amplifiers, It's just that I'm new to audio and didn't even know that "linear" just means analog.  :palm: I looked at the data sheet for the MAX97220 and was wondering if I could just add a ganged potentiometer as shown, (for volume control) or if there's "more to it than that"

--- End quote ---
There's really no such thing as a digital amplifier. It's a marketing term. The output is analogue, because it's PWM and there's an infinite range of duty cycle. Some class D amplifier accept a digital input, but that makes them a type of digital to analogue converter, as the output is still a continuously variable duty cycle.

Anyway, a class D amplifier generally makes little sense for something so low powered as a headphone amplifier. Yes, the MAX97220 just needs a dual ganged potentiometer for a volume control and it should be taper, rather than linear. This is because the human ear has a logarithmic response. Doubling the power will not make it twice as loud. To double the volume we need something like 8 times the power, but it's dependant on the sound being plated.

jeffheath:
I looked up the tda1308, and it's actually eol'd by the manufacturer, which is weird. I found an equivalent, the ts482, and drew this based off of the datasheet. I don't want to wait for anything to come in from china, so I'll just buy a breakout board and the get the components on mouser. I'm thinking it's class AB, so I shouldn't have to worry about board layout. I think i'd have to tinker with the complete board to get the volume pots connected anyway. Would I have to worry about the feedback resistors conflicting with the volume pot values?

Richard Crowley:
You have left out a couple of important components:
Rin1 and Rin2 are critical to the proper operation of the op-amp circuit. 
For unity gain they should be the same value as Rfeed1 and Rfeed2

If you provide Rin1 and Rin2 properly, then there will be no significant interaction between the value of the pot and the rest of the circuit.

jeffheath:

--- Quote from: Richard Crowley on February 13, 2019, 10:32:38 pm ---You have left out a couple of important components:
Rin1 and Rin2 are critical to the proper operation of the op-amp circuit. 
For unity gain they should be the same value as Rfeed1 and Rfeed2

If you provide Rin1 and Rin2 properly, then there will be no significant interaction between the value of the pot and the rest of the circuit.

--- End quote ---
I'm not sure whether or not I should have the capacitors before or after the pots, but I can change that pretty quickly, so I'll go ahead and get everything and put it together.

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