CurtZHP
Well-known member
Been having a particular problem pop up on two (maybe three) separate preamp builds, and you know what the man said....
"Once is happenstance, twice is coincidence, three times is enemy action!"
Basically, the issue is the failure of the phantom power switch. It will work fine for a little while, then eventually just quit, leaving me with phantom all the time or not at all.
The first time was when I was working on my last tube preamp project. I had TWO switches fail. I didn't think too much of it because those two switches were dug from a box of junk parts, so who knows what shape they were in? So far so good on their replacement. The second instance involved a solid state build. Soon after using it a few times, the brand new switch failed. I have a possible third instance in that a two channel version of the solid state unit hasn't lost either phantom switch yet, but when I switch them on, I swear they make a slight popping sound instead of the usual click. I imagine what I'm hearing is arcing going on inside the switch.
So, naturally, I'm thinking that these toggle switches just aren't capable of switching 48VDC. I've read in a couple places that the typical off-the-shelf miniature toggle isn't designed to handle that, but can switch AC all day long. I've also read in a couple places that that's essentially bollocks. I'm inclined to believe that, since I have another preamp that I built from a kit every bit of twenty-five years ago, that uses the same type of switches for phantom power, but has never failed.
I've attached a schematic of the power supply I'm using for the solid state preamp. Could it be that the phantom stage is pushing too much current? Would simply adding a current limiting resistor to the 48V output solve the issue? I thought about putting the phantom switch on the AC side of the phantom supply circuit. That would likely work for a single channel unit, but not for a two channel unit.
"Once is happenstance, twice is coincidence, three times is enemy action!"
Basically, the issue is the failure of the phantom power switch. It will work fine for a little while, then eventually just quit, leaving me with phantom all the time or not at all.
The first time was when I was working on my last tube preamp project. I had TWO switches fail. I didn't think too much of it because those two switches were dug from a box of junk parts, so who knows what shape they were in? So far so good on their replacement. The second instance involved a solid state build. Soon after using it a few times, the brand new switch failed. I have a possible third instance in that a two channel version of the solid state unit hasn't lost either phantom switch yet, but when I switch them on, I swear they make a slight popping sound instead of the usual click. I imagine what I'm hearing is arcing going on inside the switch.
So, naturally, I'm thinking that these toggle switches just aren't capable of switching 48VDC. I've read in a couple places that the typical off-the-shelf miniature toggle isn't designed to handle that, but can switch AC all day long. I've also read in a couple places that that's essentially bollocks. I'm inclined to believe that, since I have another preamp that I built from a kit every bit of twenty-five years ago, that uses the same type of switches for phantom power, but has never failed.
I've attached a schematic of the power supply I'm using for the solid state preamp. Could it be that the phantom stage is pushing too much current? Would simply adding a current limiting resistor to the 48V output solve the issue? I thought about putting the phantom switch on the AC side of the phantom supply circuit. That would likely work for a single channel unit, but not for a two channel unit.
