Studio Series Headphone Amplifier construction thread

[jamesfeline]

Hello forum members hope all is well
I know there are numerous headphone amplifier designs (very nice ones in the DIY audio store) plus I am a big fan of the JLH single ended Class A design but I have become very fond of this design and the PCB layout (no surface mount and big solder pads for us oldies)
Also to my ears sounds very nice, I have decided to make a test bed for tweaks and document on this wonderful forum

I decided to make my 1st module with good quality budget components with a few notes below

1. The op amp is a OPA2134 ( I have used an OPA2134 audio op amp here for best budget performance) but will try other op amps once completed
2. Matched all the transistors 1st time I have done this
3. Used Jantzen output inductors ( from HiFi collective UK based online company ) 0.005mH Jantzen Air Core Wire Coil AWG20, 0.8mm diameter wire
4. Cardas`s quad eutectic solder in the build

I think this is a very good sounding headphone amplifier sure there are better designs but thought its worth a mention and would be fun to see once built how it compares with other designs

Spec Below

 

[jamesfeline]

Ok have completed the PCB, Just need to add the op amp / Earth Tag and PSU fuse
few pictures ..
will upload the test bench later as still work in progress

 

[jamesfeline]

The BDA 139/140 output transistors are matched pairs

 

[jamesfeline]

Schematic attached but one channel shown

 

[jamesfeline]

So this is a pic of my test bench (still not 100% finished) this comprises of the following?

1- mains inlet with power switch plus power indicator & fuse
2- 2 power transformers (one dedicated to the headphone amplifier and the other for remote control and muting relays) make Talema
3- remote control PCB
4- ground loop break PCB
5- Two independent muting relay boards
6- Aux control PSU (12v Audiowind SR-1 / A230 ver 1.2 PCB)
7- updated PSU with better components - P8042-1 PSU
8- 50k log volume pot

 

[jamesfeline]

remote control PCB

 

[jamesfeline]

2 Power transformers -

 

[jamesfeline]

Headphone power supply -

 

[jamesfeline]

Aux PSU -

 

[jamesfeline]

Mute relays -

 

[jamesfeline]

Earth ground loop breaker - PCB

 

[jamesfeline]

50k motorised volume pot -

 

[jamesfeline]

I currently have 4 head phone amplifiers to compare against each other

1 - This one in this thread (Studio series headphone amplifier)
2 - JLH Class A single ended Headphone amplifier (currently my favourite)
3 - The Whammy (DIY Audio store)
4 - High-Performance Stereo Headphone Amplifier (SC magazine sept 2011 vol24 number 9)

 

[mandu]

Is this HPA a Elecktor design? I recall building something like this 20 years before. Regards.

 

[jamesfeline]

hello Mandu

this design was published in the Australian electronics magazine (Silicon Chip)
Nov 2005 - for some reason years ago I purchased loads of PCB's at a good price and have always been pleased with the sound quality also the op amp can be replaced like the 627 as an example
regards

 

[lineup]

The circuit of this amplifier follows the circuits of many design.
There is nothing special. One opamp followed by a transistor output stage.
But the design is good and the sound should be nice.

 

[jamesfeline]

exactly sounds good with matched transistors and quality components
I believe the PCB was designed around noise cancelling layout rules ??
As I said I still believe my JLH class A singled design has the edge

 

[cowanaudio]

This is a good amp that can drive essentially all headphones. I built one when the design first came out.

 

[jamesfeline]

I have a blue shield after my user name now

 

[TNT]

How is it "Studio"? Whats special?

//