Very Simple 3BJT Headphone Amplifier

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PCBs came in :D
They look nice.
 

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Nice design. I love SE Class A headphone amps. Could a BD139 work here instead of 2SC3852? For circa 100mA bias it probably is not necessary to use a 3amp transistor. Rosina 2SC4795 could work well too?

I have built this using BD 139's and a bc549.

I do not have the means to measure distortion but looking at the output on an oscilloscope I can get about 6.7 V peak to peak prior to visible clipping.
 
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It appears to me that the schematic in post #11 is an inverting amplifier. Some commenters in this thread have gone to great lengths (e.g. input transformers) to un-do the effect of an inverting amp and force it to operate in non-inverting mode.

With a pair of 2-terminal loudspeakers this is easy to reverse: just flip each speaker's (+) and (-). It's harder to do with headphones, whose (-) terminals are shorted together at the TRS plug.
 
It appears to me that the schematic in post #11 is an inverting amplifier. Some commenters in this thread have gone to great lengths (e.g. input transformers) to un-do the effect of an inverting amp and force it to operate in non-inverting mode.

With a pair of 2-terminal loudspeakers this is easy to reverse: just flip each speaker's (+) and (-). It's harder to do with headphones, whose (-) terminals are shorted together at the TRS plug.

This might seem like a total noob question, but why does absolute phase really matter? Surely if both channels are 180° out of phase with their respective inputs the phase relationship between left and right is still correct?
 
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It's often discussed and often researched. Here are some links.

Consider a kick-drum. When struck, it produces a compression wave. If you invert it, you get a "rarefaction wave". Will the two sound identical?

Absolute Phase: Fact or Fallacy? | Stereophile.com

Absolute phase | PS Audio

Absolute phase - Wikipedia

Audibility of Absolute Phase

Or, consider that Nelson Pass's "Amp Camp Amp" is an inverting amplifier. He advises builders to reverse the terminals of their loudspeakers to get a noninverted result. Why do you suppose he does that? Is Nelson Pass crazy? (Does he think you are crazy?)

768075d1563048803-diyaudio-watt-m2x-sssssssssss-png
 
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This might seem like a total noob question, but why does absolute phase really matter? Surely if both channels are 180° out of phase with their respective inputs the phase relationship between left and right is still correct?

That’s why transient perfect speakers with first order XO’s sound more realistic with percussive instruments and drums. The rising edge of the tweeter matches the rising edge of the mid and woofer in phase rather than being opposite phase as required by the popular 2nd or 4th order LR crossovers. The Harsch XO is also close to being a transient perfect XO.
 
It's often discussed and often researched. Here are some links.

Consider a kick-drum. When struck, it produces a compression wave. If you invert it, you get a "rarefaction wave". Will the two sound identical?

Absolute Phase: Fact or Fallacy? | Stereophile.com

Absolute phase | PS Audio

Absolute phase - Wikipedia

Audibility of Absolute Phase

Or, consider that Nelson Pass's "Amp Camp Amp" is an inverting amplifier. He advises builders to reverse the terminals of their loudspeakers to get a noninverted result. Why do you suppose he does that? Is Nelson Pass crazy? (Does he think you are crazy?)

768075d1563048803-diyaudio-watt-m2x-sssssssssss-png

Thanks Mark, you have given me a lot to think about. I think I will try a phase reversal option using an NE5532 dual opamp and see if I can perceive a difference.
 

Thanks for the info unfortunately I don't have the necessary hardware.

As for my version, I didn't like it so much with 6.8 ohms in the R4 position ( post #2 ) and only around 65mA in the output transistor. I put 5.6 ohms in parallel with the 6R8 resistor and it sounds so much better. It runs with around 120 mA in the output transistors with the latter arrangement.
 
As for my version, I didn't like it so much with 6.8 ohms in the R4 position ( post #2 ) and only around 65mA in the output transistor. I put 5.6 ohms in parallel with the 6R8 resistor and it sounds so much better. It runs with around 120 mA in the output transistors with the latter arrangement.
Post #1 says:
"In order to achieve the best performance, the value of that resistor should be somehow dependent on the headphone impedance.
In/Around 1/7...1/8 times that, to be more precise."

I am curious, what is the impedance of your headphones, 32 ohm?
 
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