Mixer External Power Supply - what is best practice for stability and low noise?
I may need to redo PS for my mixer, 24 channels, stereo out and monitor section, some basic switching, in order to maximize mixer stability. Supply current cca 2-3 A, voltage 17V.
PS has the following components:
- external power toroid transformer,
- rectifier and power smoothing caps,
- DC lines to regulators
- boards with 317/337 regulators
- connection from regualtor boards to channels. Each channel is decoupled at LF with 220UF caps rails-ground, and all IC's are decoupled at HF with 100nF directly at IC pins rail-rail.
- mixer grounds star point, for four grounds (0F, 0IN, 0P, 0A)
I'm including skecth of my current setup (sorry for lack of artistic ability, I hope it is clear enough), with which I have problem with oscillations in mixer.
What is BEST PRACTICE to implement PS for such mixer, mostly maximizing STABILITY, avoiding oscillations as much as possible?
1) Power transformer doesn't fit in the box, so it must go external.
Is it better to:
a. have it at distance from mixer(say 2-3 meters) or
b. as close as possible to mixer, just far enought to prevent hum induction to mixer frame
2) rectifier diodes with say 4x10000uF smoothing caps and 100nF bypass, pre-regulator.
Better to have it:
a. as close to mixer as possible, to have ground and DC lines from CAPS to 317/337 regulators as short as possible, but in this case connection to mains ground is longer?
b. as close as possible to external transformer, to bring 0V point (between smoothing caps) as close to mains ground as possible?
3) DC connection (2x rail plus grounds) from smoothing caps to regulator boards 317/337 @ 17V
-Q1. should it be as short as possible? Is it more stable if shorter?
4) boards with 317/337 regulators
-Q1. Do these need to be as close to mixer channels as possible?
-Q2. Is it better to have one higher power board (317/337 plus boost power transistors on large heat sink), or better to have several lower power boards (just 317/337 on smaller sinks) feeding parts of mixer?
5) regulated DC lines from 317/337 to channels
-Q1. can these be say 1m long? Does the length of regulated rails influence mixer stability and noise?
6) mixer grounds star point
-Q1. Is it better to have ground star point:
a. as close to mains rectifier smoothing caps as possible, meaning that I take four ground cables say 3meter long, and connect them far from mixer, directly in between remote power smoothing 10000uF caps?
b. as close to channels as possible, meaning that I connect grounds inside mixer box, and then go with just one say 3metre long cable to point between 10000uF smoothing caps?
...
I may need to redo PS for my mixer, 24 channels, stereo out and monitor section, some basic switching, in order to maximize mixer stability. Supply current cca 2-3 A, voltage 17V.
PS has the following components:
- external power toroid transformer,
- rectifier and power smoothing caps,
- DC lines to regulators
- boards with 317/337 regulators
- connection from regualtor boards to channels. Each channel is decoupled at LF with 220UF caps rails-ground, and all IC's are decoupled at HF with 100nF directly at IC pins rail-rail.
- mixer grounds star point, for four grounds (0F, 0IN, 0P, 0A)
I'm including skecth of my current setup (sorry for lack of artistic ability, I hope it is clear enough), with which I have problem with oscillations in mixer.
What is BEST PRACTICE to implement PS for such mixer, mostly maximizing STABILITY, avoiding oscillations as much as possible?
1) Power transformer doesn't fit in the box, so it must go external.
Is it better to:
a. have it at distance from mixer(say 2-3 meters) or
b. as close as possible to mixer, just far enought to prevent hum induction to mixer frame
2) rectifier diodes with say 4x10000uF smoothing caps and 100nF bypass, pre-regulator.
Better to have it:
a. as close to mixer as possible, to have ground and DC lines from CAPS to 317/337 regulators as short as possible, but in this case connection to mains ground is longer?
b. as close as possible to external transformer, to bring 0V point (between smoothing caps) as close to mains ground as possible?
3) DC connection (2x rail plus grounds) from smoothing caps to regulator boards 317/337 @ 17V
-Q1. should it be as short as possible? Is it more stable if shorter?
4) boards with 317/337 regulators
-Q1. Do these need to be as close to mixer channels as possible?
-Q2. Is it better to have one higher power board (317/337 plus boost power transistors on large heat sink), or better to have several lower power boards (just 317/337 on smaller sinks) feeding parts of mixer?
5) regulated DC lines from 317/337 to channels
-Q1. can these be say 1m long? Does the length of regulated rails influence mixer stability and noise?
6) mixer grounds star point
-Q1. Is it better to have ground star point:
a. as close to mains rectifier smoothing caps as possible, meaning that I take four ground cables say 3meter long, and connect them far from mixer, directly in between remote power smoothing 10000uF caps?
b. as close to channels as possible, meaning that I connect grounds inside mixer box, and then go with just one say 3metre long cable to point between 10000uF smoothing caps?
...