circuit boards/wiring etc

I have been reading alot about circuit board layouts and different wiring techniques. I would like to post some questions on this subject

1) What are the pros/cons of point to point wiring?

2) What effect does the circuit board layout have on the sound of an amp circuit? Are their any web sites that discuss this?

3) Is it Ok to mount transistors to heatsinks and then run wire from the board connections to their legs? What would be a good choice of wire for this?

4) I see a lot of people using silver wire. Does anyone know of a supplier for this in Australia?

Thanks for your time

Dan
 
Dan,
1) Some people say it sounds better to use point to point wiring. I have no opinion, as I've never done a side by side comparison between a PC board and an equivalent point to point circuit. There may be something to it, though, as a point to point circuit reduces the number of junctions between parts: resistor-solder-resistor, for example, as opposed to resistor-solder-copper trace-solder-resistor. It would be easy to get off on a tangent on the 'sound' of boards (i.e. FR4 vs. Teflon, etc.), but again, I've never done equivalent circuits.
Note that doing a *clean* point to point layout is an artform in itself. I'd recommend tracing some ideas on paper before beginning, so as not to end up with a mass of spaghetti.
2) This one I'm more skeptical of. I've known lots of people who would say that layout made a 'big difference' but on questioning, they would always admit that there were always parts changes or minor differences in the circuit that could just as easily be the cause of observed differences. I may be in a position to say more about this shortly, as I may alter the circuit board layout for the second pair of Alephs that I intend to build.
The disclaimer here being that I have seen PCB changes cure oscillation due to stray capacitance or whatever. If layout can cure that, perhaps it can make a sonic difference, but until I hear a clear cut case, I remain to be convinced.
3) I've seen lots of designs do so for TO-3 case output devices. For that matter, I do it on my tube amps--everything's on boards but the sockets for the tubes, which are wired with pigtails.
What kind of wire? Although everyone will have an opinion on this, I'd think 18ga. OFC would do just fine, perhaps even 20ga.

Grey
 

1) What are the pros/cons of point to point wiring?

Well, basically interconnections are kept as short as possible, so interferences, parasitic capacitance and other nastinesses are minimized. It can also be VERY sturdy if well done. Yet, the time and work involved in a PTP wiring is much higher than a PCB or even a Veroboard.

Having said that, i beleive that nowadays, except for some very specific circuits (dunno, very high power circuits, for example) is a waste of time and money. A well designed PCB will have low parasitics (even more, you can actually KNOW how much, most PCB design programs can do that) and will be relaiable and sturdy. That's my .02$


2) What effect does the circuit board layout have on the sound of an amp circuit? Are their any web sites that discuss this?

Same history here; it can have a measurable (and noticeable) difference, basically because tracks running closely toghether have a parasitic capacitance between them and magnetic field interactions too.

http://www.geofex.com is a site dedicated to guitar amps and pedals, but it discusses the pros and cons of PCB and PTP in a very interesting article they have. Well worth the read.


3) Is it Ok to mount transistors to heatsinks and then run wire from the board connections to their legs? What would be a good choice of wire for this?

I've seen a few amps doing that, and as long as it's not an extremely long wire, i beleive that should be ok. I beleive any decent cable will do, just get a gauge suited for the current.


4) I see a lot of people using silver wire. Does anyone know of a supplier for this in Australia?

I'm in Argentina... so beats me :D

Thanks for your time
 

rol1

Member
2001-05-12 12:28 pm
One of the power supplies I'm looking at is called a "Super Symmetric Power Supply". Would using PTP for such work against the design?

"Great care was taken with the circuit board layout to maintain symmetry between the rails. This helps keep the noise as a common mode signal the CMC can work on."

http://www.galstar.com/~ntracy/ACG/SSPS/SSPS.htm

This reads to be a good ps, but 5.1 seperate channels +5volts or 2 is a quick $240 of circuitboards and setting up to make my own boards are deeper than I want to go.

Besides, a few oz.'s of gold would increase the value of my equipment in a tangible way.
 
i've looked at the Super Symmetric Power Supply myself, seems interesting... anyway, you can easily implement that point-to-point, just try to keep it as symmetric as possible as the article mentions. as long as your wires are within +/- 20% or so of each other in length the differences in resistance should be negligible. as long as you keep everything nice and short and clean it should work just fine...

[Edited by dorkus on 06-20-2001 at 08:19 PM]
 

grataku

Member
2000-12-31 9:31 am
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Ding,
I may be off but not by much, tonite I will double check my figures just in case 20g=0.75mm2 18g=1mm2 16g=1.5mm2
14g=2.5mm2, 12g=4mm2, 10g=6mm2.
I usually never go higher than 3amps/mm2 but that's just me, and this is audio we are talking about! I try to keep things gauges to a max of 20 to 18 for general wiring and 14-16g for grounds and supply rails.
If you look at the electrical wiring tables the figure is more like 8 to 10amps/mm2. At those levels though I think you get what's called a fire.
Anyways, don't try to connect a 10g to any PCB or to a 100uF 35V electrolytic cap it will just rip things apart. What I am saying is use common sense and don't overdo it.
 
Lisandro_P said:

1) What are the pros/cons of point to point wiring?

Well, basically interconnections are kept as short as possible, so interferences, parasitic capacitance and other nastinesses are minimized. It can also be VERY sturdy if well done. Yet, the time and work involved in a PTP wiring is much higher than a PCB or even a Veroboard.



Point to Point wiring using eyelets is not reliable in any equipment subject to vibration. The problem is that when you solder a component lead to an eyelet there is almost no mechanical connection between the wire and the eyelet. What you end up with is basically a wire embedded in a blob of solder. If the component held up by those wires starts to shake or vibrate then the solder joint is going to fatigue and fail very quickly. You will then end up with a poor quality, intermittant connection.

I have seen this happen many time in older tube guitar amps (Fender amps are famous for this). It is one of the more common failure modes.

Phil