Advice on bus bars

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

boji

Well-known member
Joined
Jan 6, 2010
Messages
2,375
Location
Maryland, USA
What material would you use to make a bus for a 24 channel mixer?

My instinct is to go with solid core copper found in standard 110v electrical lines in the home.

Another option is to go with a backplane pcb and use very wide traces.

I guess my concern is capacitance you get from using thick wire.

Also, price is somewhat of an issue, I don't think I can afford pure silver wire.  :)

Any advice?
 
boji said:
What material would you use to make a bus for a 24 channel mixer?

A bus bar like for a ground point? The aluminum or copper bars with screws one sees in a mains panel should be perfect. check the local electrical supply or "home improvement warehouse."
 
Thanks guys, 14/2 NM cable it is.


A few years back ssltech chastised me for giving you grief about an old publication of yours.

He said, "Don't talk slick to a can of oil, son." 

From that day forward swore to never misspell it.  ;D
 
boji said:
What material would you use to make a bus for a 24 channel mixer?
Signal bus or ground bus? Depending on the value of bus-injection resistors, the typical impedance there would be about 200 ohms. So anything below 0.2 ohm guarantees less than 0.01% degradation of performance. For a ground bus, the lower the better; you really want to fight longitudinal noise created by all the individual channels' currents. Resistance of ground bus doesn't change noise created by magnetic induction, though. This noise is related to inductance and inductance of a line doesn't change much with section, depends mainly on length. 
My instinct is to go with solid core copper found in standard 110v electrical lines in the home.
That is a cost-effective and efficient solution.
Another option is to go with a backplane pcb and use very wide traces.
The result will be at least one order of magnitude far from a solid copper (or aluminium) bus-bar.
I guess my concern is capacitance you get from using thick wire.
That's where you lose me. Capacitance of the ground bus is irrelevant. It may be a concern for signal bus, where the capacitance of the bus is applied to the input of the summing-amp; in particular for VE summing, where the input capacitance reduces the stability margin, which then imposes increasing the NFB cap, resulting in reduced BW.
Also, price is somewhat of an issue, I don't think I can afford pure silver wire.  :)
That would not be worth it; 10x price for 10% reduction of resistance compared to copper. Anyway, as usual there's a law of diminishing returns. You may use a 600sqmm bus-bar for sub 10e-4 ohms resistance, you will be limited by the contact resistance of the connectors.
 
Abbey, have I told you lately that I love you? Thank you for the rock solid/star edification.

And yes, I was talking about returns, auxs, signal & ground. The whole shebang.
 
I offered a short answer before because the question is incomplete.

Wire resistance needs to be evaluated in the context of the circuit. All circuit connections have impedance so will experience voltage drops from current flow. Prudent design balances the management of that. Inside a multi-thousand watt power amp high current paths require low resistance for good performance. Audio signals are generally very low power so very low impedance wiring is often used as a band-aid or instead of executing the design in such a way that makes wire losses smaller or insignificant.

Sorry for a non-answer answer... But this is one of the several difficult areas that console designers kill brain cells trying to master.

JR
 
Back
Top