Is it ok to twist the powersupply wires around each other?

I want to twist a few wires around each other to make a nice neat amplifier. Namely, the 240V AC wires from the switch/fuse to the transformer primary, and the secondary wires from the transformer to the bridge. Is this going to be ok?

Just thought I better check if the mutual inductance is likely to cause any problems that are not out-weighed by a tidy chassis.

Cheers,
joseph.
 
I suggest that you try to keep 240 volts wires apart from secondary wires.

1 Safety reasons

2 Interference from outside (transients, noise etc)

Your primary goal with a transformer is to get isolation in every respect (besides different voltage).

It's OK to twist the secondary windings, the inductance thing is so little at 50/60 Hz. I would though take it easy in twisting the primary windings too much, a little doesn't hurt.
 
CMRR rules here?

bm_mode said:
I want to twist a few wires around each other to make a nice neat amplifier. Namely, the 240V AC wires from the switch/fuse to the transformer primary, and the secondary wires from the transformer to the bridge. Is this going to be ok?

Just thought I better check if the mutual inductance is likely to cause any problems that are not out-weighed by a tidy chassis.


If CMRR rules apply here, and I think they do, as long as you twist together, separately, primary wires and secondary wires you should have ripple rejection.

If that principle applies on microphone transformers, I don't see why it shouldn't apply to AC lines. Even if in this case the ripple is part of the AC itself.

Carlos
 
Twisting of both high and low voltage ac wiring is a good idea, just keep the two (LV & HV) separate from each other. When the pair of wires are wound around a common centre in a helix i.e. twisted, the magnetic field at a distance around them tends to cancel out. High current (usually low votage) AC wiring has lots more magnetic radiation which can induce hum into low level signal wiring. Actually, if you can't shield it, twisting a signal wire along with an earth wire will help shield it.

GP.
 
Not nessecarily a ground wire shields everything. You should pay attention to this:
It is the trick to twist the feed and the return wire together. In the case of AC line voltage, that would be live and neutral. In the case of Balanced signal wires, that would be + and - (NOT + and GND, or - and GND). The goal is to reduce Common-Mode currents which are often flowing through the ground.

If you stick by the rule of Feed and Return, than Twisting pairs is always a good thing :)

Bouke
 
Thanks for your help, I'm going to twist the primaries and the secondaries (but not together) as you recomend.

(This is one of the great things about this forum and its enormous combined body of knowledge/experience - not knowing much at all about electronics it would have taken me weeks to find the answer to this question by trolling through books/articles)
 
Careful with signal wires

The rules stated above may need a caution. They need to be feed&return pairs, not just any wires that lie near each other. I would be dubious about twisting together signal carrying wires if they are definately a +/- pair. This means the three wires going to an output transistor probably should not be twisted as each is one is a power feed, one is the input (to the x-istor) and one is output. Interactions between these induced by twisting may be undesirable.

I'm sur I'll be straitened out promptly if I've got this wrong.
 
bm_mode, I suggest that you build your amp as compact as possible and with short wires. This is the best advice I can give you.

It's also good to have the big caps located very near the output transistors. You could even have a couple of pcb mounted caps close to the output transistors. Things get more important if your amp is fast, then the wiring will be critical. For "normal" performance, just keep it compact.