Can you blow a preamp input?

[multidose]

I'm just curious about a few things as safety measures. More to do with electronics than anything but here it goes...

i'm running a tube preamp on each input of a USB recording interface that has a gain control for a preamp on each one of its inputs. I adjust everything such that nothing is peaking out and i can get a good sound.

my equipment is the Studio Projects VTB-1 preamp, Art Tube MP preamp, and the Lexicon Omega USB interface.

So i'm wondering can I blow the inputs on the Lexicon Omega by running too much gain from the other preamps? Also, when shutting everything down should the gains be turned down on the Tube Pres? I just wonder if its harmful to my equipment when I want to leave the settings where they are at and unplug power

Any advice would be much appreciated, thanks!!

[mshilarious]

Originally Posted by multidose

So i'm wondering can I blow the inputs on the Lexicon Omega by running too much gain from the other preamps?

Unless the Lexicon was designed by incompetent EEs, no.

Also, when shutting everything down should the gains be turned down on the Tube Pres? I just wonder if its harmful to my equipment when I want to leave the settings where they are at and unplug power

It doesn't matter.

[dementedchord]

rarely do i disagree with #1 but i may need to this time... especialy if you're running the outputs of those pre's to the xlr inputs of that lexicon.... then it's a deffinate possibility... the concept you're wanting to check out is called gain staging....

[multidose]

I just thought it was a possibility and worth some consideration. but I guess i don't need to be too concerned about it from the sounds. I will check into gain staging... funny you mention it. I was thinking of searching for audio staging or something like that to see what I find.

I will probably be upgrading to the presonus firestudio project in a year or so. I assume it would be no different. I do use XLR inputs with the mic/line inputs yes... but why does this make any difference?

[mshilarious]

Originally Posted by dementedchord

rarely do i disagree with #1 but i may need to this time... especialy if you're running the outputs of those pre's to the xlr inputs of that lexicon.... then it's a deffinate possibility... the concept you're wanting to check out is called gain staging....

The input of any preamp needs to be protected against excess voltage, whether from an external source or its own phantom power. This is normally done with clamping diodes. This will limit incoming voltage (after the phantom coupling caps) to the power rails. Thus, the only way to destroy the input is to exceed the power rating of the diodes. That's more like hooking the preamp input to a power amp on full blast, or perhaps a wall socket.

It's possible the output device could be harmed by the phantom power of the second device, but again one would hope that contingency was considered. I do think that's a much more likely problem, since I don't see too many designs with diodes on the outputs.

[multidose]

i've heard of the phantom power issue, and so i've avoided that by running the phantom power on the 1st stage of preamps. Then i don't need to use the phantom power on the 2nd stage devices and i'm not affecting the 1st stage that way.

Good advice though, thanks!

[dementedchord]

Originally Posted by mshilarious

The input of any preamp needs to be protected against excess voltage, whether from an external source or its own phantom power. This is normally done with clamping diodes. .

granted a zener limiter is a good idea for protection... IME they aren't used that often...

[COOLCAT]

Originally Posted by multidose

I'm just curious about a few things as safety measures. More to do with electronics than anything but here it goes...

i'm running a tube preamp on each input of a USB recording interface that has a gain control for a preamp on each one of its inputs. I adjust everything such that nothing is peaking out and i can get a good sound.

my equipment is the Studio Projects VTB-1 preamp, Art Tube MP preamp, and the Lexicon Omega USB interface.

So i'm wondering can I blow the inputs on the Lexicon Omega by running too much gain from the other preamps? Also, when shutting everything down should the gains be turned down on the Tube Pres? I just wonder if its harmful to my equipment when I want to leave the settings where they are at and unplug power

Any advice would be much appreciated, thanks!!

isn't it better to run the pre-amp outs into the Lexicon Line In on the back?
or did I miss something again?

and I always mute before power down....I don't like the sound of that "popping click" going through the tweeter.


Lexi-Four servo-balanced TRS line inputs with up to +22dBu input levels let you hook up everything from keyboards to guitar preamps, including high-output professional gear. Stereo digital inputs are available via SPDIF jacks, and an additional high-impedance instrument input is included on the front panel for easy access to guitars and basses.

[mshilarious]

Originally Posted by dementedchord

granted a zener limiter is a good idea for protection... IME they aren't used that often...

It wouldn't have to be a zener, it would be an ordinary diode in reversed bias configuration. Such that the diode wouldn't conduct unless the input voltage exceeded the supply voltage (15V, whatever). Then the diode will conduct, and the spike will dump into the power supply. The negative rail is analogous.

You might not see them in some designs because the IC may have been designed with internal protection. For example, I can breadboard sloppily all day with OPA2134 and not toast one, but if I don't use diodes with OPA2277, it's gone in 60 seconds Even so, external diodes can typically handle bigger currents, so their use is warranted.

OP, Coolcat is right, use the line in. I am generally too lazy to look at every piece of gear people use, but Coolcat was not!

Also, even though you didn't say you were doing this, it's not possible to pass phantom from one device through an upstream device like that. Without getting technical, that just ain't the way it works.

[StevenT]

Originally Posted by multidose

I'm just curious about a few things as safety measures. More to do with electronics than anything but here it goes...

i'm running a tube preamp on each input of a USB recording interface that has a gain control for a preamp on each one of its inputs. I adjust everything such that nothing is peaking out and i can get a good sound.

my equipment is the Studio Projects VTB-1 preamp, Art Tube MP preamp, and the Lexicon Omega USB interface.

So i'm wondering can I blow the inputs on the Lexicon Omega by running too much gain from the other preamps? Also, when shutting everything down should the gains be turned down on the Tube Pres? I just wonder if its harmful to my equipment when I want to leave the settings where they are at and unplug power

Any advice would be much appreciated, thanks!!

Leaving the gains and levels on is not an issue. What DOES matter is the order you power on/off your equipment.

Example from my studio:
Art Pre-amp output to Mackie Mixer. Mackie Mixer to Korg D888 recorder.

Power on: Art Pre-amp, then Mixer, then recorder - any power spike output or "pops" would be going to a unit that is still powered off!

Power off: Korg recorder, then mixer, then pre-amp - that way ay power fluctuations again hit a unit that is powered off.

It is NEVER wise to power up a device that is plugged in to a unit that has its power on.

As to the Original Post Title "Can you blow a pre-amp?" - the simple answer is: it depends on how big the pre-amp is and the size of the mouth?