Studio gear electrical characteristics/ratings

[ampgeek]

Toying with the idea of mating a pre-amp like the attached with a line driver stage also attached.

I am trying to make sense out of the guidance provided here regarding what voltage I should be shooting for at the XLR balanced line out.

http://www.sengpielaudio.com/calculator-db-volt.htm

Would that be 1.2vrms (+4 dBu) minimum with a 12.2 vrms (+24dBu) maximum?

Could anyone make a SWAG at what voltage will be coming off of the master volume pot with everything set, say for now, at high-noon on the dials?

I assume that the PI gives a 30X gain (60X total) across each triode. That would make ~ 1vrms at the master volume pot just about enough to drive the power tube grids positive.

Is it really that low?

I measured the PI grid signal voltage from a Marshall 2204 plan and saw ~ 9 vrms with everything dimed but failed to measure again at lower volume pot settings. So..in the ball park with the need for ~ 1vrms thought above I guess.

Any thoughts/input greatly appreciated! Especially from the studio mavens who could provide a signal level target range at the XLR output.

TIA,
Dave O.

[JazzGuitarGimp]

Most pro studios employ an "elevated" operating level scheme where +4dB is equal to 0 VU. At least that's the way it was before the advent of digital recording. So I'd say +4dB is as hot as it needs to be.

[Stevem]

Yup, pro gear runs +4, home gear/ non pro - 10 db.
Zero db is equal to .775 Vrms balanced, whenever you unbalance a signal thats running balanced you cut the voltage in half.

[ampgeek]

Thanks guys. The info is much appreciated!

Doing the math from the level pot in the pre-amp, through the WCF + balancing transformer and out to the XLR jack, I would need to fall below ~5.5 vrms at the level pot signal input before falling below +4 dBu at the XLR jack.

Does that sound like enough margin regarding pot input voltage level?

The WCF (White cathode follower) can take WAY more than that before even beginning to tax the power supply. ~64 vrms IIRC.

That led me to believe another (very low) gain stage and voltage divider before the WCF grid might be required to have some margin.

I guess it still comes back to the question of what signal level is to be expected at the pre-amp's level pot input with "normal" preamp volume settings.

Any thoughts/experience on that one?

Thanks again!
Dave O.