Hello everyone,
This is my first post, I really enjoy the site. I'm new to the world of audio electronics and I'd like to build a stereo XLR audio switcher for a studio application as a school project. It will be used to feed the powered audio monitors in a studio I'm building in a few months. I'm designing the box to be passive in the audio path using relays. I have much of the electronics worked out, but I'm unsure how to create silent switching when the audio source is selected. I need the audio signal to sort of ramp-up (quickly) so there's no speaker pop. Can I do this with a capacitor without filtering any of the signals? Does anyone have any suggestions of how I can accomplish this keeping a full range audio signal and passive components?
Thank you for your time,
Eric
This is my first post, I really enjoy the site. I'm new to the world of audio electronics and I'd like to build a stereo XLR audio switcher for a studio application as a school project. It will be used to feed the powered audio monitors in a studio I'm building in a few months. I'm designing the box to be passive in the audio path using relays. I have much of the electronics worked out, but I'm unsure how to create silent switching when the audio source is selected. I need the audio signal to sort of ramp-up (quickly) so there's no speaker pop. Can I do this with a capacitor without filtering any of the signals? Does anyone have any suggestions of how I can accomplish this keeping a full range audio signal and passive components?
Thank you for your time,
Eric
If you want to ramp up the audio you need some active circuitry to do that. Things like a VCA (voltage controlled amplifier) are used.
But it isn't required. What you want is switch on the moment the signal is zero, so called zero crossing switching. But in general that is only needed if there is DC on the signal line. That can be fixed with a series cap, which should have a charge/discharge path to ground on each side.
With only AC music, there may be a small 'tick' when switching, but certainly not a big bang in the speaker.
Try it first, you may not need anything.
Jan
But it isn't required. What you want is switch on the moment the signal is zero, so called zero crossing switching. But in general that is only needed if there is DC on the signal line. That can be fixed with a series cap, which should have a charge/discharge path to ground on each side.
With only AC music, there may be a small 'tick' when switching, but certainly not a big bang in the speaker.
Try it first, you may not need anything.
Jan
I think you can "soft-mute" the output by switching in and out a resistor, 10 ohm, 1w, across the Vout-p and Vout-n at the XLR, with a relay. Time the relay control so that it switches in/out a short moment before/after the channel switching relays operates. This 10 ohm resistor forms a voltage divider with the source impedance. Assuming the source impedance upstream is 100 ohm, you will have about 20db attenuation when the resistor engages. You need to make sure this resistor does not overload the feeding sources, and add series resistors to the feeding signals if needed.
You cannot use a parallel capacitor to filter off the relay pop without filtering off highs of an audio signal.
Silent switching in pro boards is not done with relays. Some use a hand switch to control the LDR optocoupler, as the Silonix nsl-32sr3 once stocked at newark. LDR (cds cells) turn on & off in dozens of milliseconds, which is too slow to cause a pop.
Others use the mixer instead of switching, with the input pots ramped up & down with the hand to turn on or off various inputs. Reason you see the board with lots of slider pots in shots of control rooms of studiios.
I tried relay switching of inputs on hydrophones to a input of a TI DFSII DAQ (data acquisition system) in my youth. With no batteries or power supplies in the inputs or cables, switching made a big pop. With a timer shorting the DAQ input with another relay contact while the switching was being done, it made 2 big pops. Relays were teledyne TO5 units with 12 v coils.
Silent switching in pro boards is not done with relays. Some use a hand switch to control the LDR optocoupler, as the Silonix nsl-32sr3 once stocked at newark. LDR (cds cells) turn on & off in dozens of milliseconds, which is too slow to cause a pop.
Others use the mixer instead of switching, with the input pots ramped up & down with the hand to turn on or off various inputs. Reason you see the board with lots of slider pots in shots of control rooms of studiios.
I tried relay switching of inputs on hydrophones to a input of a TI DFSII DAQ (data acquisition system) in my youth. With no batteries or power supplies in the inputs or cables, switching made a big pop. With a timer shorting the DAQ input with another relay contact while the switching was being done, it made 2 big pops. Relays were teledyne TO5 units with 12 v coils.
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