Buffer headphone amp

percy

Member
2004-04-25 5:47 pm
CA
Are there any headphone amp designs that use only a buffer opamp ? Just a standalone buffer.
All I need is something to provide high impedance to the source and boost the output current high enough for a typical 32ohm heaphone, ofcourse low output impedance.
 
percy said:
Are there any headphone amp designs that use only a buffer opamp ?
Just a standalone buffer.
All I need is something to provide high impedance to the source
and boost the output current high enough for a typical 32ohm headphone,
of course low output impedance.

A good option is to use a dual Op-Amp, like for example OPA2134 (good quality/price)
and parallel the dual to give double current output.
Will power most every 32 Ohm headphones, more than enough.

At Raymond's DIY Audio Pages I found such a project.
Pictures and schematics, including power supply.
Very nice documentation indeed!
He has also two other headphone amplifiers and more good audio projects.

Opamp Headphone Amplifier

This is an headphone amplifier, based on the OPA2134 from Burr-Brown.
Two opamps are used, with one half of each buffering the output of the other half
for increased current capability.

A guy from Finland has built Raymond's project and documented this with images.
He uses PCB he made himself.
http://www.kolumbus.fi/antti.penttala/ele/headamp/


This is schematic:

[IMGDEAD]http://www.raymondaudio.nl/images/project7/2.gif[/IMGDEAD]
He uses 100k/10k gain=11.
This is changed easily.
Removing 10k resistor (R3) gives gain=1. (Unity gain buffer)
Making R3=100k gives gain=2.


Amplifier image:

[IMGDEAD]http://www.raymondaudio.nl/images/project7/7.jpg[/IMGDEAD]
The small heatsinks are for LM317 LM337 voltage regulator chips.
 
... and photo
 

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percy

Member
2004-04-25 5:47 pm
CA
Hi Chumi, great work. Its good to know that the LT1210 will not dissappoint.

I used LT1210 and it works like a best sounding chip headphone amp in my collection My Sony MDR-F1 headphones have only 12 Ohm and are driven perfectly - so deep bass I never heard form a small chip

Since you already have an opamp (OPA627) driving the buffer I'd imagine the buffer would be within the feedback loop of the opamp ?

I am trying to see if its possible, or if anyone has already made a buffer-only headphone amp. Although the LT1210 does seem well suited for the task.

Anyone willing to throw some ideas together to build such an amp ?
 
Unfortunately this time the PCB is not my design :( but works as great as my first project assembled on protoboard :) I ordered PCBs from www.unisonus.com - fully recommended source of PCBs - high quality at low price :)

Percy - DIL8 opamp (OPA627 - last time changed to MAX400) works as a DC servo to reduce DC voltage on output. It's quite important when driving low impedance headphones :) LT1210 works also great without DC servo (<40mV output DC) however only the best possible solutions are good enough :)

I still have 4 spare PCBs - 2 stereo amps could be made. So, if You (Percy, Karahara) want to have a pair I can share with You :) just send me a delivery address me via email :)

Now I'm testing +/-12V PSU units (4*MUR860, Rubycon ZL) with voltage regulators (LM2941/LM2991 as well as LT317/LT337) and without and ... unregulated is going to be my favorite! but final verdict is not jet announced :) What is yours experience in this area?
 

percy

Member
2004-04-25 5:47 pm
CA
in my quest to find a simple compact headphone amp solution, I have now also found the TPA6120 !
Now I am two minds whether to go with the TPA6120 or the LT1210 ? For the TPA I again see two options - the TPA6120 board from unisonus, or the EVM from TI direct. I like the simplicity of the unisonus TPA amp but I am gravitating to the TI EVM.
http://focus.ti.com/lit/ug/slou169/slou169.pdf

Help me decide!
 
I have experience with both. LT1210 were better to low extremely low impedance like my 12ohm. Specially better bass and dynamics. Bought are very detailed, high grade in high frequency and overall quality of bought is very good :) LT is already better from mechanical point of view – it is simple TO220 housing :) For TPA you need a special PCB with solderable PowerPad. My choice for the real best power headphone chip amp is LT :) but for a compact one … could be TPA :)
 
I do not have any experience with LT1010. But it is just a simple buffer and max. current is just 150mA :( In my opinion even BUF634 could be a better choice :) and TPA for sure. But nobody knows really without listening – this is the final test – always :) so try it and tell us how it sounds :)

If you are looking for really simple but high grade designs perander’s projects are not a best choice - are rather complicated and first impression is a little bit oversized. But Veteran www.unisonus.com seems to be good source – sometimes those projects looks like too universal but all the time keep high grade and are simple :)