MOTM

Your original question was something like 'do I need those big caps that
don't sound good...this other site seems to avoid them by using proper
resistors...' or something like that.

What I was telling you is there are no DC blocking caps shown on that site
because those circuits most likely have +/- power. The quiescent output is
nearly (should be) 0 volts.




> -----Original Message-----
> From: media.nai@... [mailto:media.nai@...]
> Sent: Friday, July 26, 2002 5:47 AM
> To: Tony Karavidas
> Cc: motm@yahoogroups.com
> Subject: RE: [motm] simple headphone amp??
>
>
> At 2:44 PM -0700 07/25/02, Tony Karavidas wrote:
> >
> >I quickly looked at that page and the reason they don't use DC blocking
> >>caps is because those are all bipolar supply circuits. They just don't
> >>happen to show the power...
>
> I'm not sure what you mean here.  I'm talking about a DC voltage offset at
> the output due to the input bias current and input offset current (my
> understanding is that the inputs must draw at least some current and that
> they are not perfectly symmetrical).  Afaik, whether or not the DC source
> resistance seen by the input terminals is the same is not dependent on the
> type of power supply used.  Then again, I'm not an EE and I could
> be wrong.
>
> >What they are talking about is adjusting for offset errors, not power DC
> >offsets.
>
> Right, although I don't think I know what a power DC offset is.  I was
> talking about adjusting the feedback and input resistors to minimize
> offsets at the inputs.  Yet, all the examples shown by AD and commercial
> manufactures using the chip; either single sided, bipolar, or
> using a third
> half of a 2135 to imitate a split supply; use large caps in
> series with the
> output when used to drive headphones or small speakers.  Paul
> also seems to
> agree with the need for such a design.  So perhaps the adjustments for
> offset errors discussed on the website are insufficient in practice.
>
> Btw, it looks like sdiy is back up.
>
>
>
>