DIY Factory

Headphone Amp Project Mk1
A project brought to you by Kev.
Updated 31 December 2005

General background

On the surface, a headphone amp may seem like a simple task and should be cheap and readily available. The trouble with headphones in general, is that that are all very different and the way in which they are use is also very different. The smallest may be the In-Ear personal monitoring as used with the typical Walkman and now the common MP3 player. Right in your ear and with an attention to battery life these things run very well with pre-matsered CD music and compressed MP3 files and so 5volts and lower does seem to do the trick. At the other end of the scale is large and very low impedance headphones that more resemble speakers. Added to this may be the need to parallel multiple headphones and run uncompressed drums during a recording session. The fact is that a single unit will never satisfy both situations so there is a world of choices and application that can be described as a headphone amp.

I run an amp
see my site for details of the simple distribution box

I also have a B unit
trouble with the B unit may arise if the Headphones are very low impedance and you try to drive two or more with one output.
B have released a new headphone amp with more current capability

Some of these comercial units do offer good value for money and will leave you time to do other more worthwhile DIY projects and Behringer have recently released a 4 channel Headphone amp with a beeffed up output capability.

 

This project

The project presented here is aimed at the new DAW user that has a basic two channel sound card or interface without headphone monitoring or with headphone monitoring but requires an extra slave module for more grunt and more outlets. The TDA1905 is a chip based amplifier, quoted at 5 watts so it can be used on small speakers and this can be useful as will be explained later. This chip amplifier could be a perfect is an add on to the
DAW monitor switcher MkI , MkII , MkIII or as a stand alone unit for any small power amp needs up to 5 watts, speaker or headphones.

TDA1905 - PDF

Headphones

A huge variety of headphone is available for the musician and can they draw from the Pro Audio world and the newer consumer world all the way through to the Hi Fi world and any thing inbetween. Some if us make do with whatever we can get our hands on.... blah blah

____
.. AKG K240 .......... Beyer 770Pro ........ Sony MDR7509 ........... Fostex T40 ......

A typical selection of headphones, of which any or all might be found in your studio. How different can they be ? The trouble we have is that the presentation of specifications is not as consistent for headphones as it is for speakers. Speakers have the standard and consistent 8 ohm rating although others are available, Also the a specification for wattage and efficiency. Looking to headphones it can be hard to find a consistent language. For the headphone above I have listed what I can find.

AKG - K 240 Studio
impedance : 55 ohms
power : unknown
sensitivity : unknown
Beyer - DT 770 PRO
impedance : 250 ohm
power : unknown
sensitivity : unknown
Sony - MDR 7509
impedance : 24 ohm
power : 3000mW
sensitivity : 107 dB
Fostex - T40RP
impedance : 50 ohm
power : unknown
sensitivity : 93dB/m
 

The range of impedance is great and I can only assume the sensitivity is consistently in dB/m . Even so the one that surprises is the Sony MDR7509 at 24 ohms. This is very low and if two units were paralleled the total load is approaching speaker levels and it is impossible for an opamp based headphone amp to achieve this. Even our 5 watt amp here could have trouble with two of these.

AKG - K 240 Studio
impedance : 55 ohms
power : unknown
sensitivity : unknown
Beyer - DT 770 PRO
impedance : 250 ohm
power : unknown
sensitivity : unknown
Sony - MDR 7509
impedance : 24 ohm
power : 3000mW
sensitivity : 107 dB
Fostex - T40RP
impedance : 50 ohm
power : unknown
sensitivity : 93dB/m

 

 

Parts List
if there is one

Downloads

TDA1905 - PDF
sboa031.pdf - Texas Instruments (Burr-Brown)
DOUBLE THE OUTPUT CURRENT TO A LOAD WITH THE DUAL OPA2604 AUDIO OP AMP

 

Pics

none yet

ERRATA

So far so good.  Check back for any updates in this area.

 

Other amp alternatives

see Headphone Amp 2

 

Another Kit amp from Jaycar

It is likely there is a kit amp near you that will provide a possible building block for your headphone amp. Jaycar is my local kit supplier and they have a possible unit. Be aware I have not assembled or test this kit but it is typical of the sorts of kits available all over the world.

JAYCAR KIT : KC5311 RRP: $75.00 Aust
12V Stereo Amplifier Kit
Refer: Silicon Chip magazine May 2001
Ideal for use in the car or for Busking. This amplifier can be powered from a 12VDC power supply or battery, and can achieve up to 18W into 4-Ohms. Includes Bass, Treble and Tone controls. Kit supplied with case, PCB, RCA input sockets, combined aluminium back panel and heatsink, and all electronic components.
Specifications:
* Frequency response: -3dB @ 10Hz and 100kHz.
* Sensitivity for full power output: 50mV RMS.

 

Another simple HP amp found at random on the net

A simple opamp based unit bult on some veroboard.
Grado A47 Headphone Amp
Assembly and Schematic by Benjamin Feist see the PDF for his email adress
Based on The Apheared 47 amplifier as seen at www.headwize.com
right click
Benjamin's PDF


Elliot Sound Products (ESP)
http://sound.westhost.com/project24.htm
http://sound.westhost.com/project70.htm
http://sound.westhost.com/project109.htm
http://sound.westhost.com/project113.htm

... and there are many, many more are out there that range from simple opamp based units to complex descrete ClassA and all Tube units.

 

Contact : Kev for more info

this page is still under development
and more will be added


brought to you by Kev and the DIY Team at :
www.diyfactory.com