Comparing The A47 and This Headphone Amp Spec'd in OPA2227 Datasheet

[joneeboi]

Having just built the A47 today, I have some questions on the differences between the A47 schematic and the one I spotted in the OPA2227 datasheet.

Apheared's 47 Amplifier

Similar OPA2227 Headphone Amp

I have two questions while my willingness to solder is still alive:

1) The first amplifiers in both schematics accept the signal in different places; one is inverting and the other is non-inverting. What difference does this ultimately make?

2) What does that 0.1uF cap on the power rails do?

 

[MisterX]

Quote:

1) The first amplifiers in both schematics accept the signal in different places; one is inverting and the other is non-inverting. What difference does this ultimately make?

One inverts the phase and the other one doesn't.

Quote:

2) What does that 0.1uF cap on the power rails do?

The bypass capacitors provide a low impedance path to ground for high frequency transients

 

[joneeboi]

I should have known. Then are they functionally the same circuit? Is there some sort of sound or measurement difference that makes one better than the other?

 

[Roee2807]

I think that the OPA2227 is very bad audio circuit,
The impedance of the HeadPhones are not constant so you have different
Gain to different frequency beacasue of voltage divider between the 200ohm
and the Headphone Impedance.
Which make that AMP Un transparent.
The published Headphone impedance is only at 1Khz but it is different elsewhere.
Audio Amp should have Very low output Impedance in order to be transparent

 

[majkel]

Quote:

Originally Posted by Roee2807 /img/forum/go_quote.gif I think that the OPA2227 is very bad audio circuit, The impedance of the HeadPhones are not constant so you have different Gain to different frequency beacasue of voltage divider between the 200ohm and the Headphone Impedance. Which make that AMP Un transparent. The published Headphone impedance is only at 1Khz but it is different elsewhere. Audio Amp should have Very low output Impedance in order to be transparent

x2, and that's why the A47 is better. And of course, the OPA2227 really sucks in terms of sound. OPA2228 is much better but still imperfect.