Wiring for several different voltages

KennoMonkey

Member
2011-02-07 6:36 pm
I’ve been contemplating the best way to distribute multiple power voltages within a single enclosure. I’m building a subwoofer with power amp, bass controller, cross-over, soft start, signal detector, speaker protection, etc. Each board seems to need a different voltage and some are regulated, some not. They are all DC. So far, I’ve thought about:

1) A terminal strip with each voltage on a separate screw. Wire directly from each board to the appropriate screw on the terminal strip.

2) A wiring harness consisting of a bundle of wires each voltage carried separately. This would be daisy-chained from one board to the next, taking off the required voltages with a splice.

3) A hybrid approach, daisy-chaining only like voltage i.e. -15/0+15V, -12/0/+12, -50/0/+50, etc.

The 2nd seems more appealing to me because it would be neatest. Is there a common practice for this? Another alternative I haven't thought of? Are there any drawbacks? Is it bad to use the same +12V to power a preamp, for example, and the coil on a relay? Any suggestions as to how to make the splices if I go with daisy-chain?

TIA Ken
 

rayma

Member
2011-04-29 8:37 pm
I’ve been contemplating the best way to distribute multiple power voltages
within a single enclosure. Is it bad to use the same +12V to power a preamp,
for example, and the coil on a relay?

Use twisted pairs, one for each voltage (DC and ground). Daisy chain is not good,
since this can cause interactions between the circuits drawing heavy currents
and low level circuits. If you distribute the same voltage to multiple boards, each
of the twisted pair of wires should originate at the power supply board. Even then,
it may be best to have two different supplies of the same voltage, one clean and one dirty.
You can do a lot to minimize the wiring with thoughtful pcb placement.
 
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powerbob

Member
2010-08-22 12:39 pm
To power your relay make a simple filter.

12v power supply to a 5 to 10 ohm resistor then a low esr electrolitic or even a film capacitor then your relay.

I would not worry to much about +-12 and +-15 you can almost always use one or the other voltage interchangeably.
 
Use twisted pairs,
Yes ! reduces interference
one for each voltage (DC and ground). Daisy chain is not good,
Yes ! do not share common routes for different circuits
since this can cause interactions between the circuits drawing heavy currents
and low level circuits. If you distribute the same voltage to multiple boards, each
of the twisted pair of wires should originate at the power supply board. Even then,
it may be best to have two different supplies of the same voltage, one clean and one dirty.
You can do a lot to minimize the wiring with thoughtful pcb placement.
minimise interference. complete EACH circuit using a twisted pair for the flow and return.
This applies to ALL signals, power signals, line level signals, etc.....

This is important on a mono block assembly. Becomes more important in a stereo build and can be the downfall of complicated multichannel builds with many modules that require interconnections.
 

KennoMonkey

Member
2011-02-07 6:36 pm
All good info. A couple of questions, when you say twisted pairs, I'm familiar with the concept for signals, where you would twist Left with Common and Right with Common separately. So, do you mean twist +V with 0 and then separately -V and 0? Or, can I twist all three together?

In my mind i was putting all the power supplies together in one place--like a PC power supply--then all the circuit boards distributed about. You made me realize I can distribute the power supplies as well.
Thanks!
 

rayma

Member
2011-04-29 8:37 pm
do you mean twist +V with 0 and then separately -V and 0? Or, can I twist all three together?

Yes, if possible I would have a separate twisted pair (Vdc and ground) for each class A audio
circuit needing that single voltage, making a single complete loop for each supply going to it.

The only time you should twist more than one DC voltage in a bundle (along with ground)
is in the case of bipolar supplies in a class B (or AB) amplifier or buffer. In this case,
each rail carries only half the audio waveform, and twisting both the positive and negative
supplies together (along with ground) will lower distortion that is caused by coupling those
distorted waveforms to other parts of the circuitry. Similar practices apply to pcb layouts for
power trace/plane routing/placement.

Generally, dirty devices like large relays, digital circuitry, etc. should have their own supply,
or at least branch off before the regulator that is feeding the audio circuits.
 
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