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Old 1st September 2011, 03:49 PM   #1
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Default Can someone help me make a parallel line level buffer/head phone driver circuit

Hello there. I have a guitar effects kit and I'd like to listen to its line out signal directly through headphones and at the same time send that signal towards an amplifier.

My plan is to split the signal into two. One part is to be amplified and will be used to drive earphones and the other will be buffered (to make up for splitting the original signal) and sent to the guitar amplifier. Before anything else, is this even a good idea?

If it is, I have a couple of questions:
(to warn you guys in advance, I'm a total noob on audio electronics )

For the headphones driver:
-I would be needing a power transistor for this right?

-How much gain would a line level signal need to drive headphones? (what exactly are the voltages involved here?)

-Would I need to use a push-pull amplifier configuration or would a class A amplifier (with biasing) be enough? (would the biasing harm the headphones?)

-I'm sure I'd be needing high input impedance since the signal came from line-out, but would I still need to consider the impedances at the headphone connection end?


For the line level buffer:
-What is the line level voltage range?

-A single op amp buffer would do right?

-I'm guessing you'd need an op amp with very good frequency response but would a 741 do?

-would I still need to adjust the input and output impedances provided by the op amp?

Thanks guys
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Old 3rd September 2011, 05:12 PM   #2
Mooly is offline Mooly  United Kingdom
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Something like this can be as simple or complex as you want to make it...

If the line output signal is fine as it is now then nothing need be done there.

An opamp will drive h/phones if you have a reasonable supply voltage... it's not the best way perhaps but it will work just fine. An opamp as a h/phone driver would present a very high impedance across the line level feed... so no problem there. You could buffer the line feed if you wanted but there is no real need. A 741 isn't the best choice but again it will work. And its easily substituted too if you wanted better later on. Stereo or mono ? Single opamps or duals ?

I mentioned supply voltage... that's important. Higher the supply the easier this is. Driving h/phones with a 741 on a low supply won't work as the output will be low. This is because the opamp needs its output "padding" with a series resistor and this causes a loss of available voltage across the load.

Line output levels vary, there is no standard. A CD player puts out a maximum of 2 volts RMS as a typical figure. A 1970/80 's cassette deck or tuner might be nearer 0.5 to 1 volt maximum... both are called line levels.

Post #2 here gives some actual measured voltages needed to drive h/phones. This is a discrete h/phone amp and designed to run on a low single supply rail which made the design a bit of a challenge.

GERMANIUM Single ended Class A Headphone Amp.
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