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Old 25th May 2008, 04:26 PM   #21
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Quote:
Originally posted by Mooly
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.
I believe 1 amp can be taken from a USB port.

I have used op-amps successfully to drive headphones.
I put a resistor in series with the output to reduce the impedance the amp sees. It obviously wont be really loud but I found it sufficient for monitoring purposes.
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Old 25th May 2008, 05:49 PM   #22
Mooly is offline Mooly  United Kingdom
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Hi,
One or two series diodes are fine perhaps with a 10 ohm series resistor and a 100mfd + a 0.1 for decoupling.
A couple of points, first the gain of the circuit is high -- is that a tape head symbol-- on pins 2 and 15. Notice also the grounding, the volume earthy end is returned to a cap in the second example with the wiper directly coupled to pin 6/11. The first example AC couples these.
This looks like an application for a Walkman (cassette) player and I think you will find the gains too high for your intended use.
You may just be able to use just the output stages and leave the OpAmp free ( inputs terminated correctly-- not floating ).
The data sheet reads as if the output alone has 29db gain.
Regards Karl
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Old 26th May 2008, 10:06 AM   #23
Dan2 is offline Dan2  South Africa
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Quote:
Originally posted by Mooly
This looks like an application for a Walkman (cassette) player and I think you will find the gains too high for your intended use.
You may just be able to use just the output stages and leave the OpAmp free ( inputs terminated correctly-- not floating ).
The data sheet reads as if the output alone has 29db gain.
Regards Karl

yes i think i will try just using the power amp stage, the line out of the xbox is about the same as a computer sound card (or maybe a little less).

just to make sure - i will ground both opamp inputs to terminate them?? and leave the output disconnected.
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Old 29th May 2008, 12:56 PM   #24
Dan2 is offline Dan2  South Africa
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i hooked the chip up to a small speaker - and got sound out of it with just an input coupling cap connected. it sounds horrible though, i hope when i get the right caps to connect up it will sound better (and a bit louder)
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Old 29th May 2008, 09:18 PM   #25
alex mm is offline alex mm  Romania
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Location: Baia Mare ,
Default headphone amplifier from reborn IC

...Hi to all , after two headphone amplifier buided , I have finished in short time an IC mini amplifier like in attached picture http://i31.tinypic.com/id64c4.jpg regards alex mm

B.T.W. sorry for my bad english
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Old 20th November 2008, 06:01 PM   #26
Dan2 is offline Dan2  South Africa
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hey guys - im finally startin on this project again, it's been on my "to do list" for way too long ;-)

just to refresh everyone's memory - i am building a headphone amp using a LA4570 chip. i have only connected up one channel (amp 2 in the pic)

pin 1 is NC

pin 2 and pin3 connected together, because i am only using the power amp.

pin 4 is NC

pin 5 i have connected to 100uF cap

pin6 connected to 4.7uF cap, which then goes to middle leg of 50k pot (pin1 of pot connected to input, pin 3 to gnd)

pin 7 connected to 220uF cap - then to headphone (only one channel)

pin 8 to gnd

pin 9 to vcc (4.3v), and 100uF cap to gnd

pin16 to gnd.

the amp is loud enough (has enough gain) but becomes very distorted quickly. it may be because of the caps i have used??

with the pot turned right down, there is a loud buzz, and when turned right up there is a pretty loud hiss. is ther any way i can make that better???

i connected a 1uF cap from pin6 to gnd, like shown is the pic, but that made things worse - everything except bass was attenuated, and it was softer (not as loud)
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Old 24th November 2008, 02:54 PM   #27
Dan2 is offline Dan2  South Africa
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ok i have been lookin at the way most guys hook up a pot to thier circuits, and i see there is a resistor in parallel with the input and gnd. i just dont know what value to use 'cos they aren't all the same value will this get rid of the buzz at low levels?
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Old 30th November 2008, 09:33 AM   #28
Dan2 is offline Dan2  South Africa
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anyone??
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Old 30th November 2008, 09:54 AM   #29
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Quote:
Originally posted by Dan2
ok i have been lookin at the way most guys hook up a pot to thier circuits, and i see there is a resistor in parallel with the input and gnd. i just dont know what value to use 'cos they aren't all the same value will this get rid of the buzz at low levels?
When using bipolar input opamps, we usually use something like 47k - 100k and when using JFET input opamps 470k - 1M. A rule of thumbs is to use a resistors with 10 x the pot resistance. I don't think it'll reduce the buzz.

If you want help with this amp you should show us a schematic of both the amp (including volume pot) and the power supply.
It'll be easier to understand what's wrong if you also show some pictures of it.

Maybe you should move the thread to "Chip amps", since this is a chipamp.
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Old 1st December 2008, 11:37 AM   #30
Dan2 is offline Dan2  South Africa
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ok i dunno how to move the thread, i will if someone shows me.....

ok so i have attached the datasheet i found for this chip....
Attached Images
File Type: gif la4570.gif (13.2 KB, 181 views)
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