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...
What they are talking about is adjusting for offset errors, not power DC
offsets.
> -----Original Message-----
> From: media.nai@... [mailto:media.nai@...]
> Sent: Thursday, July 25, 2002 3:26 PM
> To: motm@yahoogroups.com
> Subject: Re: [motm] simple headphone amp??
>
>
> At 2:31 PM -0500 07/25/02, Paul Schreiber wrote:
> >
> >You need the output caps. Just bypass the electrolytics
> > with a 0.1uf film cap.
>
> Thanks, I've seen that trick used for crossovers, but I guess I forgot.
>
> If I use a non-inverting amp, should I still AC-couple the inputs?? Or am
> I better off using a DC-coupled inverting amp?? I've read an inverting
> headphone amp made from the same op-amp will be noisier, but it will use
> much fewer parts.
>
> >Use a dual gang, 25K or 50K log pot on the ∗input∗.
>
> OK :) Mouser sells 50K dual ganged log pots.
>
> At 12:36 PM -0700 07/25/02, Tony Karavidas wrote:
> >
> >Yes, those caps are there to keep DC from frying your headphones or
> >>anything else downstream. You cannot simply AC couple the input and
> >expect there to be no DC on the output. Look at the data sheet functional
> >>diagram and you'll see regardless of what comes in, the output is still
> >at >some DC level.
>
> That makes perfect sense, but you know what is odd?? I found this site:
> http://headwize.com/projects/opamp_prj.htm
> and _none_ of the op-amp circuits have output caps. According to that
> site, offsets can be sufficiently minimized by using the right feedback
> resistors.
>
> Yet, all of the commercial applications of the 2135 that I found used
> output caps. So did all of the examples in the AD's application notes.
> Two out of two professional EE's on this list agree. So I guess, what is
> possible in theory isn't safe enough in practice.
>
> >This device can be powered bipolar, and that might allow you to
> circumvent
> >>the DC blocking caps.
>
> It can, but I chose it because it can be run single-sided. That, and
> because I already have a few.
>
>
>
>
>
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>