boji
Well-known member
In your standard, non-broadcast studio environment, would lining a backplane/power encasement with thin (due to costs) mu shielding be of any help, or would the 'returns' (pun) on such an investment be negligible?
Generally aluminum and/or steel on 4 sides is enough.
...thin mu metal isn't necessarily better shielding than thicker steel
Shielding is very uneffective when it comes to protect a mixer (or any kind of electronic equipment that extznds over several meters. Sensitivity to external magnetic fields depends directly on the inductance, which is also a direct function of length.boji said:Ok thanks 'yall. If rolling the desk around the control room has an effect on noise levels, I'll make extra shielding a concern.
I have never seen a bus several meters long. My last big un console was close to 2 meters wide, but a split with center master section meant signal buses were not that total length.abbey road d enfer said:Shielding is very uneffective when it comes to protect a mixer (or any kind of electronic equipment that extznds over several meters.
I thought loop area was important for magnetic pickup. Longer bus length also increases capacitance. Bus resistance is generally insignificant.Sensitivity to external magnetic fields depends directly on the inductance, which is also a direct function of length.
The differential bus can accurately transfer signals from a channel trip to master section feet away. Signal ground is a concept not a reference voltage, so there will always be tiny voltage potentials between all the sundry local grounds spread around inside a console. Differential buses allow us to subtract out those "ground" potential differences maintaining signal integrity.The best bus protection resides in the mixing scheme, in particular in balanced or ground-sensing bus, that actually cancelled noise differentially.
Should I have written feet long?JohnRoberts said:I have never seen a bus several meters long.
If only loop area counted, a straight wire would have no inductance. There is nothing like a half-turn in a coil. That's how current sense transformers work.I thought loop area was important for magnetic pickup.
Definitely part of the plan. I imagine the length of the PSU cable matters as well. Every OEM cable I've come across is meters in length, and usually not shielded. I'd like to make this cable as short as possible, and mount the linear power supply with its gigantic AC transformer directly under the console.Fairly standard practice is to put console PS (and transformer) in a separate steel chassis
Thank you Abby and JR. Squarewave posted a section of a mack1e mixer that used this technique. I added another three distribution rails to try this out on the summing PCB's at a later time--when I learn how to properly implement it!Differential buses allow us to subtract out those "ground" potential differences maintaining signal integrity.
I wouldn't recommand that. Having a huge magnetic field generator close to the sensitive bus is a receipe for disaster.boji said:I'd like to make this cable as short as possible, and mount the linear power supply with its gigantic AC transformer directly under the console.
A well designed mixer circuitry should not be dependant on stiff incoming rails. It's the internal rails that want to be stiff enough. Most mixers have resistors in their rails. Stiffness is provided by local decoupling or local regulators*. You certainly don't want to transfer current spikes to a remote PSU via meters of cable. Current spikes must remain in the shortest possible loop.Is a ~30ft, unshielded power interconnecting cable worse to have than a short interconnect, with the non-switching rack PSU very close to desk?
Ok thanks Abby for helping me avert disaster. Guess that's why console PSU's always come with a crazy long cable... : :Having a huge magnetic field generator close to the sensitive bus is a recipe for disaster
often a couple feet under the console...boji said:Definitely part of the plan. I imagine the length of the PSU cable matters as well. Every OEM cable I've come across is meters in length, and usually not shielded. I'd like to make this cable as short as possible, and mount the linear power supply with its gigantic AC transformer directly under the console.
long console power cords can experience IxR voltage drops. Designers can compensate for this in original design with extra rail voltage.Is a ~30ft, unshielded power interconnecting cable worse to have than a short interconnect, with the non-switching rack PSU very close to desk? Edit: Going to guess if the psu's emf is low, is mechanically quiet, and doesn't get crazy hot, a shorter, under-console mount is better.
Thank you Abby and JR. Squarewave posted a section of a mack1e mixer that used this technique. I added another three distribution rails to try this out on the summing PCB's at a later time--when I learn how to properly implement it!
Can you explain the aim? Any length added to bus makes me shiver. The potential for picking magnetically induced garbage is frightening.boji said:Off initial thread topic, but related: I'm about to run some 5ft interconnections from amphenol 10pin connector to bus bars with some shielded 18/3 wire, however I figured if bumping up to 14 or even 12ga would be better/safer (however slight), now'd be the time to ask.
Happy to, thanks for asking. Aim is to deliver PSU's power to long, previously discussed cable, then from the cable to back of console via an amphenol connector, which is a 10 pin screw-on type, solder cups at the back.Can you explain the aim? Any length added to bus makes me shiver.
You shouldn't have to worry too much about resistance in the power lines, within limits of course.boji said:Happy to, thanks for asking. Aim is to deliver PSU's power to long, previously discussed cable, then from the cable to back of console via an amphenol connector, which is a 10 pin screw-on type, solder cups at the back.
Need to get the power from that connector to the bus rails, somehow.
Should I instead consider bypassing the connector altogether where bipolar supply is concerned, and go straight to copper bars from the PSU's cable? I could still use the fancy connector to bring in power for relays, led's and digital stuff, is my guess.
fazer said:When I brought my api home years ago I put the power supplies under the board in a small rack case. I noticed when using a ribbon mic (lots of gain). Some 60 cycle noise . I moved it just 2 feet to the side and the noise was gone or at lease extremely quieter. The buses all run under with layers of aluminum for shield but the 4 powersuppies were inductive when under the console. Wire from the supplies are 16ga except for the ground wires that are 8ga. There are bypass caps on the modules but no regulators in the board , just the 605 supplies. I mostly use directs for routing. The 2mix bus of course is used all the time and is the important one.
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