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Very Simple 3BJT Headphone Amplifier
Very Simple 3BJT Headphone Amplifier
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Old 30th July 2019, 07:38 AM   #31
xrk971 is online now xrk971  United States
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Very Simple 3BJT Headphone Amplifier
Looks good, what’s the bias current? The THD seems a bit high, maybe increase bias current? Cool FFT viewer, where do you get that?
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Old 30th July 2019, 12:07 PM   #32
avtech23 is offline avtech23  Australia
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Very Simple 3BJT Headphone Amplifier
85mA through Q1 and Q2. 9mA through Q3

A kind member pointed me to this thread a little while ago:

LTSpice Fourier viewer ( graphically )
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Old 30th July 2019, 03:18 PM   #33
gasboss775 is offline gasboss775  United Kingdom
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Originally Posted by Mark Johnson View Post
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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Old 30th July 2019, 03:32 PM   #34
Mark Johnson is offline Mark Johnson  United States
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Very Simple 3BJT Headphone Amplifier
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?)

Click the image to open in full size.

Last edited by Mark Johnson; 30th July 2019 at 03:35 PM. Reason: add image
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Old 30th July 2019, 04:56 PM   #35
xrk971 is online now xrk971  United States
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Quote:
Originally Posted by gasboss775 View Post
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.
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Old 30th July 2019, 07:12 PM   #36
gasboss775 is offline gasboss775  United Kingdom
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Quote:
Originally Posted by Mark Johnson View Post
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?)

Click the image to open in full size.
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.
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Old 30th July 2019, 08:54 PM   #37
gasboss775 is offline gasboss775  United Kingdom
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Quote:
Originally Posted by avtech23 View Post
85mA through Q1 and Q2. 9mA through Q3

A kind member pointed me to this thread a little while ago:

LTSpice Fourier viewer ( graphically )
What value did you use for R bias in your simulation?

I used 6.8 ohms in my circuit, would like to try lower but think I'll need better heatsinking.
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Old 30th July 2019, 09:56 PM   #38
avtech23 is offline avtech23  Australia
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Very Simple 3BJT Headphone Amplifier
I used 3.9 which is R10 on the schematic in post 16.
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Old 4th August 2019, 04:17 PM   #39
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Originally Posted by xrk971 View Post
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.
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Old 13th August 2019, 06:14 PM   #40
widea is offline widea  Netherlands
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Originally Posted by gasboss775 View Post
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?

Last edited by widea; 13th August 2019 at 06:36 PM.
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