Hi James,
I am also a long term hobbyist. I have an undergraduate degree in RE and an
MS in mechatronics/feedback control systems. I've been working in
industrial robotics for 12 years.
I see from your Sig that you are a filmmaker - does that have any
connection with your interest in electronics or totally separate?
Sean
On Aug 25, 2017 4:00 AM, "James Burkart" <***@burkartstudios.com> wrote:
> I've got so much to learn. Sean, what's your education and background? I'm
> a junior working on my EET and only have a hobbyist background.
>
> --
> Sincerely,
>
> James Burkart
> *Filmmaker & Documentarian*
>
> *Burkart Studios*
> 925.667.7175 | Personal
> 415.738.2071 | Office
>
> *Web:* burkartstudios.com
> *Facebook:* facebook.com/burkartstudios
>
> On Thu, Aug 24, 2017 at 9:28 PM, Sean Breheny <***@cornell.edu> wrote:
>
> > Hi Bob,
> >
> > My main suggestion is to characterize the behavior by providing various
> > input signals like impulses, steps, white noise, swept sine, etc. and
> > looking at the output on a scope. You might also vary the output load.
> This
> > gives you a good idea that you are not close to going unstable and you
> > aren't experiencing "peaking" around one frequency band or a null in one
> > band.
> >
> > I've had problems in the past with circuits like this where the output
> > stage has a nonlinearity about zero (like crossover distortion) which can
> > make the gain be reduced substantially near zero. This can result in
> > instability by causing integrator wind-up while the output is in the
> > low-gain region, followed by massive overshoot when it exits the low-gain
> > region, followed by a compensatory wind-up in the other direction due to
> > the overshoot, etc. This problem can be dealt with by making sure that
> the
> > transistors in the output are always biased with some minimum current so
> > their input-output gain never goes below a certain value.
> >
> > Note, too, that the op-amp can be treated as it's own finite gain stage,
> > where you close the loop locally around it and then close the loop again
> > around the whole system. This can make analysis of the entire loop easier
> > because once you guarantee that the op-amp gain stage is itself stable,
> you
> > can then treat it as a pure gain block or as a simple compensator (like
> an
> > integrator or integrator plus proportional gain or a lead compensator or
> > lead-lag compensator, etc.) You are sorta doing that already in that the
> > compensation cap is turning the op-amp into a fast integrator.
> >
> > I have developed a "theorem" of simple control design (which I am sure
> has
> > been stated before but I've never seen it put this way) - given any
> stable
> > system P, one can always close the loop around P with an integrator H
> such
> > that the closed-loop system will have zero DC error and be stable, for
> some
> > value of integrator gain K in H, and the system will continue to be
> stable
> > and exhibit zero DC error for any integrator gain Kprime < K. To put it
> > more simply, you can always control a stable plant using a slow
> integrator
> > and obtain at least the improvement of zero DC error, but also usually
> some
> > amount of improvement in servo tracking and regulation against
> > disturbances.
> >
> > Sean
> >
> >
> > On Thu, Aug 24, 2017 at 12:32 PM, Bob Blick <***@outlook.com>
> wrote:
> >
> > > Hi y'all,
> > >
> > > I'm trying to build some audio power amplifiers in order to use up some
> > > parts I have left over from a previous life.
> > >
> > > In the past I've always built the input stages from discrete parts but
> > > this one uses a conventional 4558-style opamp. Then I follow it with
> > > voltage and current boosting parts and finally enclose the whole mess
> in
> > > negative feedback.
> > >
> > > In this aforementioned past life I designed a lot of power amps so I
> know
> > > to design each stage to have as linear and balanced response as
> > reasonable,
> > > keep the gain low around the slowest components etc.
> > >
> > > Of course with the added gain and relatively low speed of the output
> > > stage, the internally compensated opamp is not able to keep things
> > stable,
> > > so I've added an external compensation capacitor. It does work fine,
> and
> > > I'm not looking for super high fidelity, but it's always nice to make
> > > simple changes that reap big benefits.
> > >
> > > So my question is, any ideas about compensation or changes I could
> make?
> > >
> > > I've attached a block diagram. Note that my output stage is the
> > right-hand
> > > amplifier block, it contains many discrete components, and most
> > > importantly, it is inverting. Therefore I am using the non-inverting
> > input
> > > of the opamp for the negative feedback.
> > >
> > > Thank you!
> > >
> > > Bob
> > > --
> > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > View/change your membership options at
> > > http://mailman.mit.edu/mailman/listinfo/piclist
> > >
> > >
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist