Bus Assign switches, with 3dB attenuation

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
bjoneson said:
JohnRoberts said:
PS: Thank you for spelling bus correctly.

I've been reading Doug Self's and aside from a brief rant on the spelling of "bus", there's a whole section devoted to bus assignment schemes.
I haven't read his books but I like him better already.  ;D
In general he recommends keeping the bus resistors on the channel amp side of the switch, and shorting to ground when not in use. By switching the resistors off the bus when not in use, noise gain minimized by the ACN amps.  And it keeps a constant / consistent load on the channel amps.
Constant current but a bunch of that current.  In a large console with say 30+ inputs and 20+ assigns, and modest sized bus resistors, that adds up to significant signal current circulation in that quiet area of the input channel, and significant extra power consumption for a large console,  For a small DIY project probably OK.
By grounding the bus resistor at the channel when not in use, there's no signal to create capacitive coupling at the switch.  Though as was mentioned earlier, poor pcb layout can defeat the advantage, since you essential have a wide open bus wire running around the pcb when the busses are unassigned. Care needs to be taken to ensure it isn't run in close proximity to any "hot" channel traces.
True and true... but care must always be taken. Console design involves multiple trade-offs. For example all the extra signal current running into the 0V node down in the assignment section of the input strip could contaminate the 0V node integrity, degrading fader kill. So pick your specs to optimize.
In the design I think I've landed on (shorting 2k in series with 4.7k for attenuation), there is still a hot signal on the 2nd pole of the switch from the opposite divider, but I believe that signal would be attenuated  and therefore would not create significant crosstalk. It also likely depends on the physical construction of the  switch as to the proximity of the 2 poles.

Thanks again for all of the fantastic feedback and discussion. Little by little I feel like I'm learning and being able to have this type of dialog is really helping me understand the practical implementation of a lot of the theory.
Good luck... I usually learn what I did wrong after I build one.  :eek:

JR
 
JohnRoberts said:
Good luck... I usually learn what I did wrong after I build one.  :eek:

JR

Ha, I have no doubt I'll be dealing with my own instances of "learning the hard way", but this community has definitely gone a long way towards my ability to make "more educated" guesses. ;)

Thanks again for all that you do!
 

Latest posts

Back
Top