Re: [kicad-users] Kicad project for Low TIM (Leach Amp)?

2007-10-13 Thread jeremy

With KiCad, and I suppose any design package, you need
to know the physical size of the components. So hopefully,
the following is not off-topic. Most component choice
results in a decision on component size, and that will
affect the layout and physical arrangement.

If I do a PCB design in KiCad for the Leach amp, and
post it, then would you like SMD or normal components?

KiCad is new to me, so I'd appreciate any pointers.

You will notice that there is a major load of doo doo
on the net (and in the shops) about speaker-lead quality,
oxygen free copper, audio-gade capacitors etc. The more
research I do on this, the more convinced I become that
we are being hoodwinked. For example, super-low loss
speaker cables can actually cause an amp to oscillate at
supersonic frequencies because the L/C characteristics
move the poles and basically mess with the amp design.
Some blind tests have revealed ordinary lamp-cord sounds
better! Similarly, snubber caps look like a waste of time.
None of the maths, physical measurements or simulations
show anything other than infinitesimal differences. Very high
bandwidth amps can be prone to oscillation. Speaker wires
are NOT transimission lines at ANY audio frequency. 
self inductance of caps is also insignificant especially with 
today's construction; 6nH of inductance per cm of lead
wire totally swamps the calculations. 

Unfortunately the list goes on.

So I am pleased to see you tell me of some of the
tweeks that actually make a difference. But I'd
like to know why. :)

Do you know why to use metal film resistors? Would
SMDs be better these days for any of the components?

In no particular order, what I think is important in component 
selection is:

1) Nominal value.
2) How its characteristics change with temperature?
3) What electrical / thermal stresses can it take?
4) Physical size.
5) How does it deviate from its ideal model?
6) Build quality and therefore reliability.
7) How the characteristics change over time.
8) Is it a very specialised component?

with 1) only some components need to be tight tolerance.
If you make everything 1%, then it just makes it expensive.
Although tight tolerance can sometimes imply better
quality and reliability.

with 2), if the value changes with temperature, and you go
for tight tolerance, then there had better be some temperature
compensation, or you may as well use a cheaper component.
Almost all practical calculations and component specifications
involve temperature. Hfe (Beta) of a bipolar transistor actually
goes up with T, some resistive devices fall with T, some increase,
Random noise increases with T. 

with 3) These are the parameters that stop your equipment
blowing up when voltages and currents and heating takes
place. The biggest characteristic that is effected is probably
physical size. 

with 4) See 3 ! Of course, this is also where component
construction technology comes in. The most notable being
capacitors. How big would a paper-oil 8000uF capacitor be?

with 5) It depends on the use as to the effect. As noted
above, at audio frequencies, self inductance of a cap
does not have a measureable effect in most (of all?)
circumstances. However, the characteristics of a mica
capacitor make it ideal for the Miller-Cap. 

6) and 7) are self explanatory except that sometimes
smaller is better, and sometimes not!

with 8) specialised components might not be in the
market for a long time. So your design could be
rapidly uneconomical to repair.

Point 8) is one reason that I like the Leach design.
It's simple. Simple can often lead to better results.

Some off-PCB notes:

I am interested to know more about the issues you had
with the transformer. I don't know what is a
constant voltage transformer. Why would the hum be
bad? Was this a physical hum? If so then this is because
of loose laminations, and unaccaptable eddy-current
losses in the iron. The iron could be poor quality for
a transformer. If so it was probably inefficient. Or it
might have been fixed by physical sheilding if the
hum was electromagnetic radiation from the transformer
picked up in the early stage of the amp.

I can't fathom how the transformer can affect base
response unless the losses were so great that the
supply voltage was affected. Any ideas on that?
Voltage is voltage, and current is current. If these
are available to the components upon demand
and at required levels, then how can one
supply sound better than another? I reckon an
amp driven by 15,000 mice in a wheel would sound
just the same as one supplied by electricity from
an oil-fired power station providing that the mice
were well fed, we have a few 'subs' and we don't run out of oil.

Toroids tend to be low-noise, compact but draw a large
surge current on turn on. They are very efficient. The 
radiate less because of small or insignificant air-gaps
which otherwise radiate flux, and the construction gives
good sheilding.

Maybe the high efficiency of the toroid reduces its
regulation. (No load 

[kicad-users] Which way around is the CP cap symbol?

2007-10-15 Thread jeremy
In Schematic, the Capacitor (Polarised) - known as CP is a symbol that I am 
not familiar with.

It's a dark box inside a sort of shield. Is the dark box +ve?

-
Thanks.


[kicad-users] +VCC and -VCC

2007-10-16 Thread jeremy
VCC is there in powers

I can't find -VCC in Powers.

Can I make one somehow?

Thank you!


Re: [kicad-users] Re: I need a footprint for a 5W wire-wound rectangular resistor...

2007-10-27 Thread jeremy
Thanks.

I've muddled through that. How do I make a 3D model and link it
to the footprint?

On Saturday 27 October 2007 17:40:18 yajeed2000 wrote:
 --- In kicad-users@yahoogroups.com, j3r3m3l33 [EMAIL PROTECTED] wrote:
  Can someone point me to a footprint to import into Kicad that
  is for a 10W wire wound ceramic resistor? It's for the resistors
  that you see in this photograph:
 
  http://users.ece.gatech.edu/~mleach/lowtim/graphics/cktboard.JPG
 
  Thank you.

 Hi,
 It is very easy to make the footprint yourself using Kicad.
 First find a datasheet for the resistor you are using.
 In your case download this from the YAGEO website at www.yageo.com.
 Using the dimensions contained in the datasheet you can then make the
 footprint.
 If you use another resistor because the yageo ones aren't available
 follow the same procedure.

 David.



Re: [kicad-users] Re: I need a footprint for a 5W wire-wound rectangular resistor...

2007-10-27 Thread jeremy

I found out the basic steps by trial end error. If anyone has
some tips - especially for getting proportions and scaling
correct, then that would be good.

Obtain wings3d from http://www.wings3d.com/
Learn how to use it from http://www.wings3d.com/doghouse.php
and see what else it can do by looking up wings3d in youtube.
When you are ready to create a 3d component, then make one
using wings and concentrate only on the relative proportions.
This is because Kicad's module editor links the 3D in and scales
and rotates according to your needs. Therefore, a basic axial R
component could be scaled differently for different wattage.
Hint: A toroid can by streached and cut in half to make leads,
while a cylinder or cubes make the basis of the component
itself.

Save the wings file. Then export it into VRML 2.0 format.
This is what Kicad can read.

Create your footprint in Kicad, use it in your PCB layout.
Double-click on the PCB footprint while in PCB layout 
and then click the tab to set up 3d. Browse to the
VRML 3d exported file. Find the right scaling
and orientation to make the leads fit into the pads in the
footprint. Update the library and your board. Test the
3D view.

Learning curve: About 4 hours or so.


On Saturday 27 October 2007 18:17:22 jeremy wrote:
 Thanks.

 I've muddled through that. How do I make a 3D model and link it
 to the footprint?





Re: [kicad-users] KiCad and Python - how to use scripts like TTConv?

2007-11-09 Thread jeremy

This will help you with Python:

http://www.diveintopython.org/



On Friday 09 November 2007 10:45:43 pixostat wrote:
 Hello everybody!

 I'm new user on kicad-users. I use KiCad from last few months, now its
 time to start using scripts wrotten in Python. I downloaded latest
 TTConv package, but I don't now how to play with those nice scripts.
 What should I do to start using Python scripts with KiCad? Somebody
 can help me and explain how to do that?

 I have little experience with Python and Scribus - but Scribus has got
 special tools in menu to start and test scripts - my KiCad hasn't
 those features...

 My platform is: WinXP SP2 Proffesional PL
 Installed KiCad 2007-07-09 Unicode
 Installed Python 2.5.1
 Installed PIL 1.1.6 for Python 2.5
 Downloaded TTConv02-020807 Sorgenti

 P.S.
 Sorry for my English :(