GR MP-500NV: tranny resonating?

[andychamp]

Hi there!
Something weird just happened: I'm feeding the output from a drum machine into the MP500's hi-Z input, my monitors' volume is down, and I start cranking the gain on the preamp.
Now I can hear the beat from inside my lunchbox!
I sh*t you not!

The sound is metallic and tinny, but it's unmistakeably that beat. I plugged in a bass to double-check and I can hear the attacks when I hit the strings hard and give a lot of gain.
The input, impedance and loading switches have no influence, and it seems the output pot has more of an effect.
The effect is noticeable pretty early on beats (2nd/3rd green output LED) and a bit later with the bass (orange and red output LED)
My best guess is that the output transformer's coils are resonating and are especially sensitive to transients. And the metal casing probably amplifies this.

I've seen (heard, actually) similar behaviour from tubes in cranked guitar heads, but this is a first from a mic preamp.

Has anyone else noticed such a phenomenon on a GR preamp (or any other brand)?

Am I breaking anything (frying tranny coils)?
Does this come with this kind of design?
Or did I get a lemon?

Besides that, I have no complaints about the unit and really would hate to send it back.
But this has me seriously worried.

I'll PM Dan Kennedy with a link to this thread, but I'm open to any serious input.


EDIT: I just did the same test with a Voxbox, a Germanium pre and an API 512c and they all react the same, although in varying degrees.(On the VB, it was almost drowned out by the noise of the meter needle)
But the GR definitely has the strongest reaction.

[jchas]

A couple years ago a similar thread was started regarding the ME-1NV. If I remember right a bunch of guys went to try it out for themselves. Dan responded that it is perfectly normal and won't hurt anything.

[heyman]

I noticed that on a Great River Mp2Nv when I was experimenting with using the pre as makeup gain on the backside of a Rolls Fulcrom.

Same thing, I cranked the gain and the word that described it was Metallic type feedback.

[Dan Kennedy]

Perfectly normal. Your hearing the windings and laminations of the output transformer move around a little bit with the magnetism generated by the signal.

In some designs the transformers are vacuum impregnated with a lacquer to stabilize them, but since the unit sounds the way I want it too, I'm not going to f*^k with the formula.

[andychamp]

Originally Posted by Dan Kennedy

Perfectly normal. Your hearing the windings and laminations of the output transformer move around a little bit with the magnetism generated by the signal..

Thank you very much for pitching in and reassuring me.

(...)but since the unit sounds the way I want it too, I'm not going to f*^k with the formula.

I totally understand & agree. I wouldn't want it sounding any different, either. Cool box!

[Wes Kuhnley]

Some units sing more than others do. The 500's and 1NV tend to sing more than 2NV's because the transformer is mounted directly the the chassis via the 4 corners, rather than a bracket fitted to the chassis. Like Dan said, perfectly normal.

[mds]

Lemme add one more...this happened to me with the MP2-NV and freaked my sh!t out...turns out its not abnormal or anything to worry about...I mix by listening to the GRs now. hahaha!

Mike