True bypass to phantom power

[joaquins]

Is there any way to make a true bypass to the phantom powering part of a preamp? I'm looking to take out the caps out and 6k8 resistors of the equation when not needed, so for dynamics mics and such I don't have them in the chain, I want to build a couple of preamps but with parts I can get locally and no nice caps around, so for condensers I should live with this, for any other source why?

I'm asking for a way to do that without the complexity in the better way to do that that would be to power off the phantom, add a delay to all discharge and then bypass the caps, and then in the other way, put the caps in the way and after a delay (shorter, nothing to charge but caps must be before) activate the phantom power.

Ideally it should be done with a 4PDT without relays (for my comfort) but if not other way to do it right and without pops I can live with relays.

JS

 

[jasonallenh]

Just don't build phantom into your pre, then use a remote battery supply when you need to power a condenser.  ;D

 

[joaquins]

I would like to do something like this but inside the box (of the pre) but good designed so no extra precautions to have wile using and be sure that nothing will blow in the air because accidental operation, two different input connectors would be other option but still a PIA. Ideally a switch, as I said earlier, but I' thought about that, or a box with just phantom powers for most my preamps, I'd still prefer a switch. I'm thinking in using a combo connector so TRS without phantom and XLR for phantom.

JS

 

[jasonallenh]

I'm thinking in using a combo connector so TRS without phantom and XLR for phantom.

I think this is the best idea... mainly because that's what most recording interfaces do instead of giving you individual phantom buttons. I'm pretty sure that even with the combo connector, the phantom caps/resistors aren't completely bypassed. At least not without bypassing the mic pre and heading straight to a line-amp. right? wrong? I don't know... just more of an assumption.

 

[ricardo]

This is most important when you are using Ribbons or other Low Output Dynamics.

For this, its better to make a dedicated Ribbon preamp like AEA or Millenia Audio.

I describe such a beast in the Yahoo MicBuilders Group modified from M-Audio DMP3 ($50-100 from eBay).  You have to join.

You can optimise loadsa stuff for this.

 

[ruairioflaherty]

For this, its better to make a dedicated Ribbon preamp like AEA or Millenia Audio.

As long as it doesn't sound like the Millennia, a very overrated mic pre IMO.  I say that as some one who owned 9 channels for many years.

 

[abbey road d enfer]

Is there any way to make a true bypass to the phantom powering part of a preamp? I'm looking to take out the caps out and 6k8 resistors of the equation when not needed, so for dynamics mics and such I don't have them in the chain, I want to build a couple of preamps but with parts I can get locally and no nice caps around, so for condensers I should live with this, for any other source why?

I'm asking for a way to do that without the complexity in the better way to do that that would be to power off the phantom, add a delay to all discharge and then bypass the caps, and then in the other way, put the caps in the way and after a delay (shorter, nothing to charge but caps must be before) activate the phantom power.

Ideally it should be done with a 4PDT without relays (for my comfort) but if not other way to do it right and without pops I can live with relays.

JS

  Vactrols for phantom switching. Relays for shorting the caps because you need timing. You may use two dpdt switches then you'd do the timing...
How important is it for you that the 6.81k res are disconnected?

 

[joaquins]

Is there any way to make a true bypass to the phantom powering part of a preamp? I'm looking to take out the caps out and 6k8 resistors of the equation when not needed, so for dynamics mics and such I don't have them in the chain, I want to build a couple of preamps but with parts I can get locally and no nice caps around, so for condensers I should live with this, for any other source why?

I'm asking for a way to do that without the complexity in the better way to do that that would be to power off the phantom, add a delay to all discharge and then bypass the caps, and then in the other way, put the caps in the way and after a delay (shorter, nothing to charge but caps must be before) activate the phantom power.

Ideally it should be done with a 4PDT without relays (for my comfort) but if not other way to do it right and without pops I can live with relays.

JS

  Vactrols for phantom switching. Relays for shorting the caps because you need timing. You may use two dpdt switches then you'd do the timing...
How important is it for you that the 6.81k res are disconnected?

They could remain connected to each other if there is nothing in the other end, because CMRR, it could get down by 10dB with a 10Ω unbalance and a well designed electronic input. I won't do the timing because I want it to be safe, so if I do the timing something can go wrong. Still, how do I discharge the caps if I leave 6k8 open, I don't know, I don't want to need a micro controller to do so, It should be simple or never will see the light of sun, still more complex than a simple switch, of course...

I understand the vactrol, I don't understand why. Here is a schem to start to understand better.


When I asked about true bypassing I was thinking something more like this (next post with PDF PH bypassing 2)

JS

 

[joaquins]

Here the two resistors after the caps could be as high as wanted but have to manage the parasitic current on the caps, 1M should be fine, and won't affect CMRR because when they are connected also are both 6k8. They would keep the caps charged when unconnected. In the mic front end still should be protection diodes. When a phantom powered ic is connected it will represent a load on the other end and voltage on the mic side will drop, then in the other side, but shouldn't be as critical as the other option.

JS