Hi,
I am trying to add switchable phantom power on each input channel of a Yamaha PM-1000 mixing console.
In looking for a suitable switch, like for example a toggle switch to be mounted on each input channel, I've noticed that switches are typically rated for something like:
5A 120VAC/28VDC (or 2A 250VAC)
and this is sometimes qualified in manufacturers' datasheets as:
Maximum DC Voltage: 28VDC, etc.
My question is: if the switch manufacturer does not state a maximum DC voltage, or if the maximum DC voltage is expressed in terms of the maximum allowable current (5A 28VDC, as above for instance), is it safe to assume that incrementally higher DC voltages (like 48VDC) are allowable - given a proportional decrease in the amount of current (48VDC 2A max, for instance), or are any higher-than-rated-for voltages, even with much lower total current (25mA for a couple of condenser mics) not a good idea?
In other words, for a switch (like a toggle switch) -
does a 28VDC, 5A rating imply a 48VDC, 2A rating? or even a 48VDC, 100mA rating?
Thanks for the help everyone!
I am trying to add switchable phantom power on each input channel of a Yamaha PM-1000 mixing console.
In looking for a suitable switch, like for example a toggle switch to be mounted on each input channel, I've noticed that switches are typically rated for something like:
5A 120VAC/28VDC (or 2A 250VAC)
and this is sometimes qualified in manufacturers' datasheets as:
Maximum DC Voltage: 28VDC, etc.
My question is: if the switch manufacturer does not state a maximum DC voltage, or if the maximum DC voltage is expressed in terms of the maximum allowable current (5A 28VDC, as above for instance), is it safe to assume that incrementally higher DC voltages (like 48VDC) are allowable - given a proportional decrease in the amount of current (48VDC 2A max, for instance), or are any higher-than-rated-for voltages, even with much lower total current (25mA for a couple of condenser mics) not a good idea?
In other words, for a switch (like a toggle switch) -
does a 28VDC, 5A rating imply a 48VDC, 2A rating? or even a 48VDC, 100mA rating?
Thanks for the help everyone!
Just FYI....
Switch's are de-rated for DC.... An AC switch rating: The switch can switch at any point along the wave (might be zero, might be wide-open). DC is always switching at maximum voltage, maximum current. (I made a ton of $$ replacing switch's in Makita grinders.... the welders would run them on the 120vDC off the welder exiciter..... the switch's would work until JUST out of warranty).
So... even IF you really overmaxed the switch, As long as it was ON when the power came on, there would be no strain on the contacts.
Switch's are de-rated for DC.... An AC switch rating: The switch can switch at any point along the wave (might be zero, might be wide-open). DC is always switching at maximum voltage, maximum current. (I made a ton of $$ replacing switch's in Makita grinders.... the welders would run them on the 120vDC off the welder exiciter..... the switch's would work until JUST out of warranty).
So... even IF you really overmaxed the switch, As long as it was ON when the power came on, there would be no strain on the contacts.
Ok, here is my next newbie question:
In this circuit,
which can be found at this website,
would C9 introduce any possible distortion into the balanced mic signal when the phantom switch is open - in the absence of 48VDC biasing the + side of C9, or is this nothing to worry about?
Would making C9 a non-polar cap (like a film cap) reduce the possibility of distortion (if any)?
In this circuit,
An externally hosted image should be here but it was not working when we last tested it.
which can be found at this website,
would C9 introduce any possible distortion into the balanced mic signal when the phantom switch is open - in the absence of 48VDC biasing the + side of C9, or is this nothing to worry about?
Would making C9 a non-polar cap (like a film cap) reduce the possibility of distortion (if any)?
Suggest you go to the THAT Corp website
and look at the application documents for their preamp chips. There is about as thorough description of phantom powering that you will find anywhere, including the protection circuits necessary, should, say an input be grounded with no mike connected.
Charles
and look at the application documents for their preamp chips. There is about as thorough description of phantom powering that you will find anywhere, including the protection circuits necessary, should, say an input be grounded with no mike connected.
Charles
After reading your thread I have difficulty in understanding exactly why you want to turn off the Phantom at each channel. The phantom will work just fine with a microphone not requiring phantom power.
I'll give that one🙂
There are some good ribbons available nowdays that use phantom too. I'd look toward a different mixer if it were me.
There are some good ribbons available nowdays that use phantom too. I'd look toward a different mixer if it were me.
Partly because I have some line-level gear (balanced) that I want to run through the board, and partly because I'm of the sort that would rather eliminate something from a signal path if it is not necessary.
Pin #1 of the output XLR connector is not part of the Phantom Power supply, so it should only be connected to the chassis.
C9 will have no effect for audio input. 6k8 resistors render C9 'out-of-the-way' at audio freq's.
In that case I guess I'll use a larger electrolytic for C9 to lessen the steepness of the DC on/off transient and probably a 100 ohm resistor in series with the 48VDC before the cap.
One more question - would it make any difference to put the 100 ohm resistor before or after the switch? Or would it not matter?
My intuition tells me that any DC arcing across the switch as it is closed could be dampened a little with the resistor before rather than after, but I'm not sure.
Thanks again for your help, I really appreciate it.
Honestly, I would move the 10uf cap to the right of the switch, so its charged up at all times. I would then use a 100nf cap in the place of the 10uf's current position. this will hopefully help with transients caused by switch. I don't foresee major arcing, as there isn't much current draw.
Hope this helps.
Hope this helps.
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