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NE5532 Headphones Preamplifier/Amplifier with EQ
NE5532 Headphones Preamplifier/Amplifier with EQ
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Old 18th August 2011, 09:44 AM   #11
afternath is offline afternath  France
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120Gohms for input impedance
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Old 22nd August 2011, 04:43 PM   #12
afternath is offline afternath  France
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Originally Posted by Anteaus View Post
D8, D9 are the wrong way. They need to be in the conducting direction. The way you have it, smoke instead of sound as the output pair will conduct hard.

Also, You may need to select the diodes to give the required quiescent current, as there is a fair tolerance on diode characteristics. Too little and you will have distortion at low sound levels, too much and the output stage will run hot.

As for the supply. I'd be inclined to either use a single-rail design, or if you have AC available, a proper dual rail design. Having the signal lines at non-ground potential could lead to all sorts of issues. Not to say it won't work, but he who ventures onto untried ground... finds out whether it works or not, and maybe saves others the trouble!

Carbon resistors are quite OK unless you are working at millivolt levels such as on a mic input. Metal film are preferable for audio circuits, though.

Finally, the standard and most important advice in amp design, watch how you return your grounds to common. If the load returns its current to the PSU via a wire shared with a signal ground, you will have instability. Keep them separated and you are OK. This is one of the things that can't be determined from a schematic, but where actual physical wiring matters.

Yes, there is a mistake D8 & D9 are reversed.

What do you mean by single rail supply? I'm using 12VDC unregulated power outlet.

About OP07 I have several ones.

For the grounding, i see i'm disturbing some people with virtual ground, but i said i don't like manipulate main power, and IMO placing a transformer or using double 9V batteries for a little headphone amplifier is makes me sick.

I don't understand your advice when you say separate signal ground, can you show me an example?
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Old 22nd August 2011, 04:57 PM   #13
Mooly is offline Mooly  United Kingdom
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NE5532 Headphones Preamplifier/Amplifier with EQ
To me a single rail design implies an AC coupled amp... and there's nothing wrong in that

Virtual grounds are fine as any point or potential can be called "ground" and all signals etc referred to that one point. Where it gets interesting is whether the "virtual ground" has the ability to source and sink much current. In other words does the amp running from it behave as a DC coupled amp with the ability to supply and source DC into the load (which is a valid output from a DC coupled amp) or does the virtual ground rely on for example a couple of resistors with large electrolytics across them, in which case the DC coupled amp can not supply significant DC current to a load.
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