Stereo balanced Line Driver / Booster ?

[2Low]

I´m looking for a clean sounding solution to boost the stereo signal ( Mixbus ) out of my MCI console to the AD inputs of the „ Mastering „ converters.



Stereo XLR In/out and a volume pot (or dual mono) with at least + 12db gain boost



Thanks !

 

[ruffrecords]

Most MCI consoles can clip the input of any modern convertors. Are you absolutely sure you need to boost the signal? Which convertors are you using?

Cheers

Ian

 

[2Low]

Hi Ian



a Mix with 24 channels and proper gain staging runs at approximately around -10 db on the inputs of my AD converters ( Avid Omni set to +4db ).

 

[Bo Deadly]

That doesn't make sense. Virtually all AD converters take a relatively small signal of a few volts RMS maybe. But to accept a pro-level signal they use an attenuator in front. The better converters have a way to switch the attenuation off. That's what you should do in this case.

 

[Bo Deadly]

a Mix with 24 channels and proper gain staging runs at approximately around -10 db on the inputs of my AD converters ( Avid Omni set to +4db ).

Turn off the attenuation / pad or whatever they call it on the converter. A -10dB signal is just fine for an AD converter.

If it's not it will be because it's still too hot. Realize that as long as the noise floor of the signal is above the converter, you can apply gain digitally with no impact on fidelity. You could probably run at -40dB before the noise floor reached the noise floor of the converter.

Watch carefully for clipping of the converter and turn down the master output as necessary.

You want to bring the level down, not up.

 

[2Low]

I can´t see any attenuation on the AD inputs ...

 

[Brian Roth]

Did you try using the -10 selection instead of the +4?

Bri

 

[zamproject]

a Mix with 24 channels and proper gain staging runs at approximately around -10 db on the inputs of my AD converters ( Avid Omni set to +4db ).

-10dB what ? FS? is that peak or RMS ?
If RMS it's hot enough I suppose, if peak you have nice headroom but I wouldn't say too low either.
You'll need to check your studio(console) line level alignment, as the dBu<=>dBfs relation of your converter

To me (but that's just my taste that may defer from other) the console/studio line level is set @ -10dBFS (which is also my 0 PPM, analog peak) and 0 VU is aligned 8 dB below that (-18dBFS), I have both meters at master out.
With "proper" mix, 0 VU and 0 PPM are more or less hitting the same spot around 0, theorically -10dBfs peak, but fast DAW digital peak meter can show/catch around -6dBfs, probably ISP meter will add 1 or 2dB to that.

If my -true peak- (digital) hit around -10dBfs at the 2TK back record on a particular song/production it's probably OK too, it's usually when things are already peak shaped...

All in one...I'm not sure you have an issue ?

Best
Zam

 

[2Low]

Thanks for the quick replies ! ... maybe there is something wrong with the outputs of the console
I´ll check the analog outs / levels tomorrow

cheers Thilo

 

[Bo Deadly]

I can´t see any attenuation on the AD inputs ...

You're staring at it. It's the "Reference level". If you switch the reference level from +4dBu to -10dBV that will remove 11.8dB attenuation. Meaning the signal should then be ~12dB hotter.

But then you need to figure out what 0dBFS is which is where the AD converter clips. Use a fn gen to just barely clip an input with the input gain set to max and with no low-cut. Then see where the console output levels need to be to result in a recording of say -6dBFS. Mark those levels with bits of tape cut to make a pointer. That's the level that you know you can't go above or you risk overloading your converter.

 

[ruffrecords]

Hi Ian



a Mix with 24 channels and proper gain staging runs at approximately around -10 db on the inputs of my AD converters ( Avid Omni set to +4db ).

I think we are running into the realms of the poor definition of absolute levels in digital convertors. Looking at later posts it seems the reference level of your convertors is +4dBu. When you says this means the mixer output runs at -10dB what does that mean? Do you mean the level indicated in your DAW is 10dB below FS in other words its -10dBFS? If it is then that is about right because it gives you 10dB of headroom.

Edit: I just checked the manual and spec sheet for the Avid and nowhere does it mention what reference level means in terms of dBFS.

Cheers

Ian

 

[2Low]

Thank you for your suggestions !

I´m still interested to build a kind of „ Line Level Booster “

Balanced Stereo XLR In/out
a volume pot (or dual mono) with at least + 12db gain boost ( even better + 20 db )

 

[ccaudle]

Most MCI consoles can clip the input of any modern convertors. Are you absolutely sure you need to boost the signal? Which convertors are you using?

The gain structure in your console is off somewhere, all MCI equipment was built in an era when 24 dBu levels were the norm, and most modern A/D converters max at 24 dBu if they have any broadcast business, and 20 dBu max seems more and more common. In other words your console should be able to output levels at least 4dB over the maximum clipping point for your Avid converter. Although there is a note in the Avid user guide that the outputs can be set to +24 dBu max output level, so maybe the inputs can handle that as well. Either way, should be reasonably matched to your MCI console, certainly not needing an extra 12dB of gain.

What levels are you calibrating to, and what is your lineup process?

 

[Gold]

You get 12dB free gain by switching the converters from +4dBu to -10dBv on the converter.

Like Brian said.

 

[tlm3ed]

Are you single ended or do you have both pin 2 and 3 connected to a balanced input? The stereo buss 2T outputs should be +4 at zero VU on the meters and should allow peaks to +24.
Unless you have a Greg Hanks converter (that will accept +37) it is highly unlikely you need more than the MCI will supply to send your converter well into overrange.

Use a scope and boost the mix until the 2T balanced output clips (you must use both scope inputs and subtract them) then measure with an RMS meter like a Fluke 8060a or better. It should be close to +24.

Tom Maguire
TMI Engineering

 

[dmp]

I´m looking for a clean sounding solution to boost the stereo signal ( Mixbus ) out of my MCI console to the AD inputs of the „ Mastering „ converters.
Stereo XLR In/out and a volume pot (or dual mono) with at least + 12db gain boost

There's many options - I guess to narrow it down, here's a couple ideas:
- transformerless IC: use a ina134 receiver -> 5532 opamp gain stage -> drv134 driver stage. This would give you adjustable gain and transparent sound.
- transformer discrete: look at the Neve 1073 in line amp mode. A line audio transformer -> BA283 gain / driver stage -> output transformer

 

[Script]

For fixed gain, THAT1246 can easily be configured for +6dB (see Figure 6 in 1240 series datasheet). THAT1646 also gives +6dB.

Or could use THAT receiver and THAT driver (or INAs) wrapped around a VCA for gain control (two linked for stereo), controlled via one CV pot (so like makeup gain pot on a comp).

 

[user 37518]

12 dB sounds like an excessive amount of boost for a console notorious for having tons of headroom (are you using a JH-500?)

 

[RSRecords]

There's many options - I guess to narrow it down, here's a couple ideas:
- transformerless IC: use a ina134 receiver -> 5532 opamp gain stage -> drv134 driver stage. This would give you adjustable gain and transparent sound.

I built this essentially for a mastering engineer but just 3dB extra gain to do analog fades. Would be easy to configure for more gain. Think I used a different opamp and that corp chips. Used a P&G fader but a blue velvet would probably track just as well.