Headphone Buffer Amplifier

[EUVL]

> But the THD distortion is not nice - THD 0.287% is not acceptable.

I got 0.03% THD at 0.92V pk on 32R with 120mA bias.


Cheers,
Patrick

 

[PRR]

At that higher idle current, I get 0.04% with matchbook math.

It's mostly about the gain (NFB) and the current swing (as fraction of idle current).

 

[EUVL]

120mA is not high for 32 ohm.


Patrick

 

[edmortney]

Low-impedance (under 50 ohm) headphones will play well at home with your receiver and on-the-go with your smart phone, and that's why the vast majority of in-, on-, and over-the-ear headphones are low-impedance designs. High-impedance models are much better suited to home than on-the-go use. Sennheiser and Beyerdynamic are two companies that offer high-impedance consumer headphones with up to 600 ohm-rated designs.
Audioreputation.com

 

[miro1360]

I did this one, but I did not have time to test it in reality ...

https://ctrlv.cz/shots/2018/08/07/ETvB.png

https://ctrlv.cz/shots/2018/08/07/FGck.png

PCB 5x5cm:
https://ctrlv.cz/shots/2018/08/07/lTxw.png
https://ctrlv.cz/shots/2018/08/07/cPej.png

https://ctrlv.cz/shots/2018/08/07/MZqW.png
THD=0.002%/20k (250mW/32R)

IMD:
https://ctrlv.cz/shots/2018/08/07/Ase2.png
0.06%/19k+20k (50mW/32R)

OLG:
https://ctrlv.cz/shots/2018/08/07/4iVr.png

 

[EUVL]

It's a Scott Wurcer Phono without RIAA but with NFB. 🙂
A simplified universal differential or single ended phono preamp


Patrick

 

[lineup]

Here is a new version of this headphone buffer.
The distortion is low: THD 0.001%

 

[EUVL]

In practice if you want to have perfect thermal tracking (no DC drift), it is better to make top and bottom identical.
https://www.diyaudio.com/community/threads/mosfet-follower-headphone-amplifier.95841/post-1130743

My own experience is that CFP measures well, but sound a bit too bright.
I only use them for portables with very low bias.


Cheers
Patrick

 

[lineup]

In practice if you want to have perfect thermal tracking (no DC drift), it is better to make top and bottom identical.
https://www.diyaudio.com/community/threads/mosfet-follower-headphone-amplifier.95841/post-1130743

My own experience is that CFP measures well, but sound a bit too bright.
I only use them for portables with very low bias.


Cheers
Patrick

Thanks for your comment. I visited your link. To use LU1014 is an elegant solution. To use MOSFETs for cascode also benefit.

I have not built my circuit, so I can not tell about sound.
I take your word for that upper and lower should be the same.

Anyway I will post an upgrade with J113 transistors. With lower THD as well.

 

[lineup]

Headphone Buffer Amplifier upgrade Revision 2.
With J113 FETs.

Devices
3 x J113 FET
1 x BD139
1 x BD140

Power Supply
2x12VAC Transformer
Regulators LM7812/LM7912 or LM317T/LM337T

Adjustments
Adjust potentiometer for zero offset on the output.
Replace R6 if necessary for ~100mA in output stage.

As can be seen the THD is lower than my first version.
Like THD 0.045 is acceptable for a circuit without global feedback. Ask Nelson Pass!