[sdiy] Re: About this LC filter formula questions

[John L Marshall]

What would a really long length of coaxial cable do for you? RG-174?

Take care,
John
------------------------------------------------------------------
Pacific Northwest Synthesizer Meeting
August 9, 2003
www.sound-photo.com
------------------------------------------------------------------

----- Original Message ----- 
From: "jhaible" <jhaible at debitel.net>
To: "John L Marshall" <john.l.marshall at gte.net>; "Magnus Danielson"
<cfmd at swipnet.se>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, May 31, 2003 3:22 AM
Subject: About this LC filter formula questions


> Thanks John, and list,
>
> I know this. Really, the effects on the individual component
> behaviour is quite clear. I'm after a formula for that specific
> case of one special circuit (delay line built from lumped
> elements, and then coupling added). Even the general
> behaviour of this circuit is clear, because I've tested it
> in Spice. What I need is a formula to describe this circuit.
>
> Increase of the individual inductance *alone* would not have
> the desired effect, as increasing L (with C untouched),
> while increasing tg, also decreases fc. So there's a tradeoff
> between your bandwidth and the number of stages needed
> for a certain delay time.
> *But* the coupled inductors apparently get around this dilemma,
> as the coupling increases _both_ fc and tg, so less stages
> are needed.
>
> BTW, I got most of what I needed by experiment, meanwhile.
> I needed to know how close I can put the inductors together
> on a PCB without getting too much coupling, and to get
> the remaining coupling with a positive sign at least.
> I got that now.
>
> (Not sure if I make a pcb for this, but it's tempting, because
> my veroboard version is _huge_ and can be much reduced in size.
> It *should* fit into a 19" enclosure. (;->)
>
> The other question, about a formula, is just out of curiousity.
> I don't plan to build a coupled 18-inductor line.
>
> JH.
>
>
>
> -----Ursprüngliche Nachricht-----
> Von: John L Marshall <john.l.marshall at gte.net>
> An: <jhaible at debitel.net>; Magnus Danielson <cfmd at swipnet.se>
> Cc: <synth-diy at dropmix.xs4all.nl>
> Gesendet: Samstag, 31. Mai 2003 07:38
> Betreff: Re: [sdiy] LC filter formula questions
>
>
> > The net inductance will increase. Consider the case of closest coupling,
> > inductance increases by the square of the turns. Double the turns equals
> > four times the inductance.
> >
> > Take care,
> > John
> > ------------------------------------------------------------------
> > Pacific Northwest Synthesizer Meeting
> > August 9, 2003
> > www.sound-photo.com
> > ------------------------------------------------------------------
> >
> > ----- Original Message -----
> > From: "Magnus Danielson" <cfmd at swipnet.se>
> > To: <jhaible at debitel.net>
> > Cc: <synth-diy at dropmix.xs4all.nl>
> > Sent: Friday, May 30, 2003 4:47 AM
> > Subject: Re: [sdiy] LC filter formula questions
> >
> >
> > > From: "jhaible" <jhaible at debitel.net>
> > > Subject: [sdiy] LC filter formula questions
> > > Date: Fri, 30 May 2003 11:16:24 +0200
> > >
> > > Hi Jürgen,
> > >
> > > > When I build a delay line from inductors and capacitors
> > > > (approximating a transmission line with lumped elements),
> > > > all inductors the same value, all capacitors the same value
> > > > except the last one, it's easy to calculate the parameters
> > > >
> > > > Z (line impedance)
> > > >
> > > > tg (group delay for N stages)
> > > >
> > > > fc (cutoff frequency for the LPF behaviour)
> > > >
> > > >
> > > > But what if the inductors are coupled ??
> > > >
> > > > I have made some Spice simulations with variable k (between
> > > > inductors (n) and (n+1) ), and I found that all three
> > > > parameters change.
> > > >
> > > > With increasing k (k positive), both fc and tg are increased -
> > > > no wonder that the later version Hammond Line Boxes
> > > > used coupled inductors!
> > > >
> > > > But Z apparently changes, too. At least I see a lot of ripple
> > > > in Spice, so I guess I need a different termination for the
> > > > line to get a more even response. (Or will a Delay Line
> > > > from coupled inductors always have more ripple than
> > > > a non-coupled Line ?)
> > > >
> > > >
> > > > Question:
> > > >
> > > > Does anybody have a formula for Z, tg and fc, depending on
> > > > k, L, C and N for a delay line with coupled inductors?
> > > >
> > > > Magnus? Anybody ?
> > >
> > > Well, I might have... but what I don't have is the time. I will keep
it
> in
> > the
> > > back of my head. You should look in classic filter books since they
care
> > about
> > > couplings. A fair assumption is that they probably didn't care an
awfull
> > lot
> > > about it, but you can.
> > >
> > > The coupling works both ways due to reciprocacy, so it provides some
> > > feedforward and some feedbackwards.
> > >
> > > Cheers,
> > > Magnus
> > >
> > >
> >
> >
>
>