hey guys, a friend of mine has an xbox360 and wants me to build him a small headphone amplifier for it, because the xbox only has a line out (which is just not loud enough)
the thing is most preamp circiuts run on 12 volts, which is a hell of a lot of batteries (my friend wants it to be portable for LAN'ing) and i know it can be done with a much lower voltage - a portable mp3 player uses just 1 aaa battery and that is loud enough.
what i really want to do is build it so it can get its power from one of the usb plugs on the xbox, so no batteries will be required.
i also want it to sound quite decent - as i am sure the usb has enough power to do (i think usb has 5v, 200mA output???)
i was thinking of using an opamp, but if you have a better idea please share.
thanks in advance
the thing is most preamp circiuts run on 12 volts, which is a hell of a lot of batteries (my friend wants it to be portable for LAN'ing) and i know it can be done with a much lower voltage - a portable mp3 player uses just 1 aaa battery and that is loud enough.
what i really want to do is build it so it can get its power from one of the usb plugs on the xbox, so no batteries will be required.
i also want it to sound quite decent - as i am sure the usb has enough power to do (i think usb has 5v, 200mA output???)
i was thinking of using an opamp, but if you have a better idea please share.
thanks in advance
Hi,
You need a small power amplifier not an op-amp. Basic difference
is the load impedance they are designed to drive, op-amps do not
do 8 to 32 ohm loads (typical earbud / headphone range).
http://www.national.com/mpf/LM/LM4863.html ?
/sreten.
You need a small power amplifier not an op-amp. Basic difference
is the load impedance they are designed to drive, op-amps do not
do 8 to 32 ohm loads (typical earbud / headphone range).
http://www.national.com/mpf/LM/LM4863.html ?
/sreten.Find out something on the specs of his headphones. Impedance and sensitivity as a minimum.
If they are 32ohm and 90dB/mW then 500mW into 8ohms will give 2.8Vpk into his phones producing 111dB peak but delivering just 125mW.
He doesn't need a lot of power. He does need current ability to suit his load.
Find out about the load.!!!!!!
BTW,
if the maximum average power output is 1.25mW (-20dBV ref 500mW into 8r0) then the phones are producing 91dB average, that is still too loud.
If they are 32ohm and 90dB/mW then 500mW into 8ohms will give 2.8Vpk into his phones producing 111dB peak but delivering just 125mW.
He doesn't need a lot of power. He does need current ability to suit his load.
Find out about the load.!!!!!!
BTW,
if the maximum average power output is 1.25mW (-20dBV ref 500mW into 8r0) then the phones are producing 91dB average, that is still too loud.
A USB port has enough "power" to blow your ears off. I see it was mentioned earlier that MP3's provide enough volume from a AAA cell. These almost certainly ( and I have not actually seen a circuit for one ) use a switching type output stage, and they may well also step up the 1.5 volts with a DC DC convertor.
Dan2 said:
One thing you may want to checkout, is how much 'PC-noise' is on USB power jacks.
Computer circuits generate a lot of noise. From high frequencies and also lower.
Any audio amplifier benefits from a CLEAN Supply.
For example those PC speakers we use, mostly use OWN Power supply adaptor.
You may have to filter the USB power a bit. Using some capacitor/resistor.
I am sure you can use USB, as you only need a few Volts to get enough power.
I guess we are talking 16 / 32 Ohm freestyle or light type of headphones.
The sensitivity of such can be very high: 100-105 dB per mW is not unusual.
And they can be powered good from only 2 x 1.5V batteries. = 3.0 Volt supply.
If you could find Specifications on headphones in question
it would be a good help for advice you.
As AndrewT has mentioned, there are 2 things we would want to know:
- 1. Impedance, in Ohm. Can be 16, 32
(Some modern hifi big headphones has got 150, 300, 600 Ohm impedance)
- 2. Sensitivity. In dB SPL = Sound Pressure Level
Usually how loud in dB at 1 mW input power.
Regards, Lineup
---------------------
fotenote:
There is new standard for sensitivity, used by e.g. Sennheiser.
SPL at 1 Volt RMS.
See my attachment:
Specifications for Sennheiser HD 650 ( Top of the line expensive HeadPhones)
Attachments
i didn't even think of noise on a usb power supply!! i will have to check that out.
as for the headphones - well - i want it to be able to run with any type as i may be building a couple for other guys. i seriosly doubt any of them will have top of the range type headphones. for example, the headphones i am building this circuit for are (almost) bottom of the range - the type that has vibration bass (little motors that shake with the bass) and although quality is ok, its not anywhere near the quality of expensive headphones.
as for the headphones - well - i want it to be able to run with any type as i may be building a couple for other guys. i seriosly doubt any of them will have top of the range type headphones. for example, the headphones i am building this circuit for are (almost) bottom of the range - the type that has vibration bass (little motors that shake with the bass) and although quality is ok, its not anywhere near the quality of expensive headphones.
If you care about sound quality, why not just steal others success? I think the very well renowned portable headphone amp Xin Reference use AD8615 as L/R amps and AD8531 as ground channel amp. They are specified for 2.7 - 6 V supply and are good for 150/250 mA output current. AD8397 is also a very popular opamp for headphones, 3 - 24 V supply, 310 mA peak output current.
For your convenience, use a board from Mini3, or why not the whole amp, it uses the AD8397 mentioned above for left/right and OPA690 for ground (specified for 4.5 - 12 V supply and can deliver plenty of current):
http://www.amb.org/audio/mini3/
This is a true hifi headphone amp. You can even buy complete kits from
http://www.glassjaraudio.com/main.sc
If you have "normal" = lowish impedance headphones, you don't have to worry about not having enough sound pressure. 1 V into phones like this is very loud, 5 V is crazy. It's simply not true that monolithic opamps can't drive headphones.
For your convenience, use a board from Mini3, or why not the whole amp, it uses the AD8397 mentioned above for left/right and OPA690 for ground (specified for 4.5 - 12 V supply and can deliver plenty of current):
http://www.amb.org/audio/mini3/
This is a true hifi headphone amp. You can even buy complete kits from
http://www.glassjaraudio.com/main.sc
If you have "normal" = lowish impedance headphones, you don't have to worry about not having enough sound pressure. 1 V into phones like this is very loud, 5 V is crazy. It's simply not true that monolithic opamps can't drive headphones.
Dan2 said:
Hard to find a datasheet.
Here is a Romanian schematic, with data on LA4570.
Max voltage is 4.5 Volt. And typically it is used with 3 Volt DC.
This means 2 x 1.5 Volt battery.
2 x 0.02 Watt = 20 mW is more than you probably ever need.
We can also see a bit about the PIN configuration and figure out howto use it:
From this page:
http://www.electronica.ro/audio/LA4570.shtml
Sanyo LA4571 may be a very similar headphone IC.
Here is one link to this PDF:
http://www.ddrservice.net/66c507f/Integrated-circuits/L/la/la4571.pdf
Regards, Lineup
thanks for finding that!!
just to double check - the odd looking symbol on pin 2 and 15 is the inputs??? and the 10k variable pots are the volume control (or gain?)??
if i use a usb and just run a diode in series that should give me the right voltage (or even a 3v regulator - that should help with the noise)
just to double check - the odd looking symbol on pin 2 and 15 is the inputs??? and the 10k variable pots are the volume control (or gain?)??
if i use a usb and just run a diode in series that should give me the right voltage (or even a 3v regulator - that should help with the noise)
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