-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Somebody in the thread at some point said:
Hi Joerg - Thanks for finding this. |> With e.g. *typical* (->ds, p.12) 32R-headphones, RL = 65 Ohm! Could |> anybody |> check the Z for OM-headset? |> Please calculate f0 for this value!!!!!! They're ~32R apparently, with 33R in series (R4405 / R4407) so it is ~65R. |> If we can't resolve the issue, | The solution is plain simple: have bigger C (at least 47u). | Or completely redesign the audio circuit. :-( The caps shown in the typical application circuit is 100u, not 1u. But the datasheet says -- it is about Cin but the last part is true for Cout and the transducers -- ''Selecting Input and Output Capacitor Values Besides gain, one of the major considerations is the closed- loop bandwidth of the amplifier. To a large extent, the band- width is dictated by the choice of external components shown in Figure 1. The input coupling capacitor CI and resistor RI form a first order high pass filter that limits low frequency response. CI’s value should be based on the desired frequency response weighed against the following: Large value input and output capacitors are both expensive and space consuming for portable designs. Clearly a certain sized capacitor is needed to couple in low frequencies with- out severe attenuation. But in many cases the speakers <============ used in portable systems, whether internal or external, have little ability to reproduce signals below 150Hz. Thus, large value input and output capacitors may not increase system performance.'' So the impact is we lost some bass end... maybe not a noticeable amount to what we would have with 100u due to the transducer performance. If there's no room for adjusting the value of the caps on the A5 or A6 PCB then I would just accept this. Maybe in future we can improve bass performance but it seems we have to do it by premium headphones and lower frequency output filter at the same time. Still, it's good spotting :-)) - -Andy -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.8 (GNU/Linux) Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org iEYEARECAAYFAkfzexwACgkQOjLpvpq7dMpzugCeORdZF4/BiozzyRV4ph5A/x/a jyAAmwVDURyAka4hJ33NF3fUJOeb6xFb =m+3N -----END PGP SIGNATURE-----
