Shielded cable for inputs?

Hello everybody,

I have a few ft of mogami w2549, i wonder if i should use shielded cable from the back inputs to the front pot? Or 20awg twisted wire should be enough?

I read somewhere in the forum, that the w2549 has low capacitance between the 2 conductors inside, but on capacitance from conductor to the shield. And i was thinking to use 2 cables, one for each channel. Use only one conductor for signal and the shield as gnd.

Is there a better way? Thanks.

I only use Mogami shielded cables for the phono preamp input. For all other signal wiring I use pre twisted 24gauge multi-strand copper wire.
Never found the need to use 'exotic' hookup wires. If the design and layout of pretty much any given preamp etc is neat and tidy and keeping it away from any AC wiring, then using such standard copper hookup wire is all that is required.

It has been my experience that shielded internal wiring is largely unnecessary except for very specific applications, such as:

a) Magnetic or MC Phono inputs - Recommended but not always necessary.
b) Internal runs of antenna wire - such as with tuners or receivers.
c) Equalizers and other external processors will sometimes use shielded internal wiring.

But, as a rule, line-level inputs and outputs do not require anything special.

ureche wrote:Hello everybody,

I have a few ft of mogami w2549, i wonder if i should use shielded cable from the back inputs to the front pot? Or 20awg twisted wire should be enough?

I read somewhere in the forum, that the w2549 has low capacitance between the 2 conductors inside, but on capacitance from conductor to the shield. And i was thinking to use 2 cables, one for each channel. Use only one conductor for signal and the shield as gnd.

Is there a better way? Thanks.

I think it is a good idea to use shielded cable from the phono inputs to the phono preamp board because these are by far the lowest voltage signals and therefore more susceptible to noise. Otherwise twisted pair should be fine. That said, I do see a lot of higher end stuff using shielded cables for all the inputs. I think even Roys latest pics show this. Either is probably fine. As mentioned above, the most important thing is cable routing and a proper grounding plan.

In my reading while prepping to build my SP13/PH12 I noticed that many builders recommend thinner wire for twisted pair input connections. Typically 24 gauge max. For some reason it is supposed to be superior to heavier gauge wire in terms of noise. I am a little skeptical of the science here, but I went with 24 anyway. I prefer solid, which I realize is not popular, but it makes the job look much neater and the wires hold their twist tightly.

Roy pics here: http://tubes4hifi.com/SP14-2018.htm

Did some pretty long runs on my custom cabinet using the twisted wire. No problems.

Little trick ... cut two pieces of wire longer than what you need, chuck one end into a vise and the other into a variable speed drill, and let er rip. Twists em pretty and evenly. I use a hand drill here for better control.

Thanks, i will use twisted wires (i'll try twisting them with the drill) and if there is any need, then, i'll try the mogami.

I only have 20awg solid wires. Why the max 24awg ? I wonder if this as something to do with skin effect i read somewhere.

Skin effect has no effect on audio frequencies, especially at the lengths we use.

The concept relates to long line, high frequency transmissions.

An idea adopted by cable manufacturers to sell expensive interconnects.

ureche wrote:Thanks, i will use twisted wires (i'll try twisting them with the drill) and if there is any need, then, i'll try the mogami.

I only have 20awg solid wires. Why the max 24awg ? I wonder if this as something to do with skin effect i read somewhere.

there is no max or minimum, other than practicalities and of course current and voltage, the latter two not really an issue with audio hookup wiring. I have never been a fan of solid core. For me, it is a pita to use and I also find it easier to neatly route etc. flexible multi strand wire. For all audio interconnect I use the pre twisted 24gauge which can be purchased in different color combinations, such as white/green, white/red and so on and for all B+ and filament wiring I use 18gauge flexible multi strand wire. As mentioned, the only time I use Mogami style shielded cable is for the phono inputs.
I buy all my wires from Jameco.

I agree the skin effect can be ignored, but for those who are interested here is a table showing the skin effect as a function of frequency and wire gauge. I don't know how accurate it is or its pedigree. I found it here:  https://www.powerstream.com/Wire_Size.htm

The skin depth indicates how much of the wire's diameter is actually used for current flow. The higher the frequency, the more the current wants to stay near the surface. If the skin depth is not 100% it doesn't mean the signal will not flow through the wire, just that the center of the wire is not used as much, so the resistance is a little higher.

No worries though at audio frequencies. As you can see, even an 18 gauge wire will have 100% penetration below 17KHz. And really, what's the big deal if above that there is a little more resistance? I know I wouldn't be able to hear it.

For those who are concerned, any wire 20 gauge or thinner should have no skin effect in the range of the best of human hearing.

Also, consider that we will eventually send these same frequencies through 12 gauge speaker cables, right?    

Anybody know of an "oxy free" solid 20ga wire? That can make a big difference on long runs and maybe not a problem with the short distances inside an amp, but every little bit helps.

There's always the old debate about 600v cable as opposed to what's generally available. Surprised that hasn't come up here, or I just missed it?