Are all mic preamps setup like this?

[nerol1st]

I can't remember what forum I posted this on so if this has already been brought up on HC sorry.

 

 

So very simply I wanted to have a feed to the XLR input on the preamp (and ended up just going with that since it was the source of the issue).

 

But I also wanted to have a patch cable to the patchbay from the instrument input.

 

So just to be clear I had an xlr cable in the preamp as well as a 1/4" instrument cable both going in.

 

The problem (and this has me wondering is all preamps are this way because the mbox had the same issue with the line in and the XLR having something in them simultaneously) is as soon as you have a jack plugged into the instrument in on this thing it kills the gain on anything. So basically what I found is that it's one of the other despite if the other end is plugged into something or not.

 

Do some have bypass switches to get over the problem? That was the first idea that came to mind.

[Phil O'Keefe]

Some preamps do have a mic / line switch, and a few allow you to connect both simultaneously, but in my experience, plugging into the line input kills the mic input on most outboard preamps.

[UstadKhanAli]

On the one mic preamp (Peavey VMP-2) I have that has both line and XLR inputs, inserting a cable on the line input automatically kills the XLR input.

[MikeRivers]

 

I wanted to have a feed to the XLR input on the preamp But I also wanted to have a patch cable to the patchbay from the instrument input. So just to be clear I had an xlr cable in the preamp as well as a 1/4" instrument cable both going in . as soon as you have a jack plugged into the instrument in on this thing it kills the gain on anything. So basically what I found is that it's one of the other

 

It depends, and if that's the way yours works, that's the way it is. Most instrument inputs actually use a separate input stage to get the required high impedance input (which doesn't require nearly as much gain as a microphone). So whether there's a manual switch or the mic preamp is disconnected automatically by a switch built into the instrument jack, it's usually an either/or situation.

 

A couple of replies here have really talked about a LINE input rather than an INSTRUMENT input. Typically that's just a pad ahead of the mic input with blocking capacitors to keep phantom power from getting to a line output if you forget to turn it off. For a setup like that (which is most common on low cost mixers) there's no mic/line switch but you still won't have much success if you have both plugged in at the same time. When you plug in a mic, that's like hanging a 150 ohm resistor across the output of the pad that has an output impedance of 5-10K ohms and it makes it much more of an attenuator than what was intended. Your line input gain goes down by close to 20 dB.

 

Of course on many mixers, this problem is circumvented by the use of combo XLR-TRS jacks so you can't have two cables plugged in even if you were smart eough to deal with them electrically.

[nerol1st]

Yep to be clear we are talking inst in. It kills the XLR.

[tremolounge]

but wait a sec... LINE inputs are almost always on the back, with the XLR mic inputs. INSTRUMENT inputs are usually on the front. So in the case of the line/mic situation, yeah, the either/or thing messes things up when you want to have your line in wired to a patchbay. But with the inst in, it's no big deal, since you can easily pull the plug out when you want to use the mic. Yes?