[sdiy] decoupling on modulars power bus

[karl dalen]

Well, well,i have since long time used pre and post regulation.
First the manin power supply a LM317 and a Lm337, then on 
every module there are post regulation a Lm317L and a Lm337L.

These regulators are dirt cheap! buy a pack of 100 units
of each and you will be settled. You could up it a bit futher
by pre with a 723 regulator.

Reg
KD

--- James Patchell <patchell at cox.net> skrev::
> As an example of what Harry is talking about...take a look at a VCO I did:
> 
> http://www.oldcrows.net/~patchell/synthmodulesII/200-1007.pdf
> 
> I have three of these on a simple power backplane that connects power up to 
> all of the modules:
> 
> http://www.oldcrows.net/~patchell/synthmodulesII/back.jpg
> 
> You can...if you look carefully...see a PC board that connects all of the 
> modules together...this is the power distribution.
> 
> I use the LM4041-ADJ for the voltage reference on the VCO's...plus a lot of 
> bypassing (Harry can testify to this :-)....
> 
> I get no soft sync...no cross talk between modules...and the VCO's are rock 
> solid stable...
> 
> 
> At 01:13 PM 5/24/2005 -0700, Harry Bissell Jr wrote:
> >Sci-fi author Colin Capp wrote in his short story
> >"The Subways of Tazoo"  (excellent engineering read
> >btw)
> >
> >* A snowflake would not stand a chance in Hell unless
> >you had a ton of refrigeration equipment alongside it.
> >Now what exactly is the problem... is it that you are
> >in Hell... or that you are a snowflake ??? *
> >
> >Point.  The power busses are probably fine. More
> >likely the VCOs are defective of design.  Most VCOs
> >assume that the power bus will be perfect, and trust
> >the raw power rails for some mission-critical
> >voltages.
> >
> >These are (in the usual sawtooth core) -
> >
> >1) Ramp Reset level (voltage divider from pos. rail)
> >2) Expo converter reference (resistor to pos. rail)
> >3) Initial frequency pot (tied to pos. and neg. rails)
> >4) Any front panel controls (tied to pos. / neg.
> >rails)
> >
> >If you inject ANY noise on these rails... you are
> >hosed.
> >
> >These points should be connected to on-board precision
> >voltage references (LM4040 for example).  Any
> >variation
> >of supply voltage will not directly affect the
> >freqeuncy.  This is good engineering practice and is
> >almost always overlooked.
> >
> >The other solutions are
> >
> >1) separate power supplies
> >2) decoupling the power rails severely... you need an
> >RC time constant much longer that the interfering
> >noise... from an LFO that is DAMN low
> >3) on-board power supply regulators
> >
> >This just bit me in the @ss last night I might add.
> >I went with the on-board voltage references, but need
> >to include the front panel controls as well. It did
> >help a lot
> >
> >H^) harry
> >
> >
> >
> >--- Julian <julian at 22host24.com> wrote:
> > > I'm having a few problems with interference between
> > > modules on my modular.  Notably lfos affecting
> > > oscillators through the power bus.
> > >
> > > At the moment, the bus is just a simple passive
> > > stripboard affair (with a run of tinned wire along
> > > the back to increase the gauge of the ground strip)
> > > - basically a clone of the doefper distribution
> > > board.
> > >
> > > What are my options for decoupling?
> > >
> > > I have a few such busses in my modular, each serving
> > > one 19" row of modules.  What's the best way to
> > > connect these up to the psu?  In some sort of star
> > > configuration, no doubt, but should i try and
> > > decouple these from one another at this point also?
> > >
> > > In fact, is decoupling even the correct term?  Any
> > > suggestions, preferably with component values , )
> > > appreciated.
> > >
> > > Cheers, Julian
> > >
> > >
> > >
> 
>          -Jim
> ***************************************************************
> http://www.oldcrows.net/~patchell
> 
> ***************************************************************
> 
> 
>