dda -2dbu (-10/+4 ref levels)

Posted: Fri Feb 16, 2007 1:34 pm

Davedog wrote:

I LOVE all you 'real' engineer types. This is great stuff here. GAFF STICKY THIS!

Did I mention that I LOVE you engineer folks?

Now what fun would it be, being an [electrical] engineer, if we can't nitpick at little things like adding 449.7 nanoVolts of thermal noise (making the cumulative AWGN a whopping (-116) to (-122) below +4dBu.

Somebody has to worry about a few nanoVolts or microVolts of noise Cool

Posted: Sun Feb 18, 2007 6:18 pm

Thank God I became a mathematician. Dimensionless variables. All constants set to one. Life is good - at least in my day job.

Posted: Sun Feb 18, 2007 10:01 pm

Awwwwwwwww That's sweet Dave. I love engineers too, especially good ones. Console size does matter. After all, I've had the best.

Throw that Dog a Microbone or maybe a Dogphone?
The Demure Ms. Remy Ann David

Posted: Sat Mar 31, 2007 1:23 pm

[quote="Mises"]

rambelam wrote:

Good transformers cost upwards of $120 - $200+ apiece (just from what I've seen)... so you couldn't realistically be putting one of those babies on every single channel on your board... though I suppose you could put it on just a few select channels... depends how many -2dBu outoputs you have.

Holy Cow! You looking in the wrong spot. We get $90 Jensens or $ 75 Cinemags without even trying.

Posted: Sat Mar 31, 2007 2:10 pm

Sorry have to bring the geek out on this one.
Check out:
http://www.sengpielaudio.com/calculator-db-volt.htm

Heres some numbers:
-2dBu = 1.74Vpp
+4dBu = 3.47Vpp

-10dBV = 0.89Vpp

You need a gain of 2 to go from -2dBu to +4dBu
or you need a gain of 1/2 to go from -2dBu to -10dBV

Are these short unbalanced lines?
If yes a resitive divider will work just fine provide you pay attention to the input impedence of the -10dBV inputs.

Or use a simple class A fet amp with a gain of 2, If you would rather go up +4dBu.

I can send you circuits for either solution if you like.

The class A fet design is cheap compared to xfmrs. Although I do love cinemag! I use them in all my Apex 460 mods.

Best of luck.

Posted: Fri Jun 13, 2008 3:19 am

The actual reason why the operating level in many british mixers (and subsequently many japanese and US manufacturers) is -2dBu is that circuitry using commonly available IC's provides an actual clipping point of ca. +20dBu. Running the board at +4dBu internally would provide only 16dB of headroom, which was deemed insufficient, which is true in live applications, and that permeated to studio mixers. That's why they chose to run all internal signals at -2 dBu and interface with the external world via balancing/debalancing stages providing 6 dB gain/attenuation. The commonly used EBOS (Electronically Balanced Output Stage) take advantage of 6 dB increase of output capablity (typically + 26 dBu into a balanced load). Some high-end mixers used balanced inserts running at +4, but most of the products had unbalanced inserts at -2, in order to save circuitry.
Anyway, most of the outboard gear can make up for the difference. On a 1176, you just crank up the input and reduce output accordingly, on a 160, you just set the threshold 6 dB lower. For EQ, it shouldn't matter, except if it's very noisy.
In most cases, it will be transparent to the user; that was not the case when Tascam ran their mixers at -10 dBv (-7.8 dBu) from beginning to end.
You may have difficulties with a Fairchild 660 or 670, just as you would with a mixer that runs its inserts at +4, because the 660 was designed for 600 ohms input source AND 600 ohms output load (impeadance-matching), which no modern gear supports.
Most equipment nowadays is designed for impedance-bridging, i.e. low output impedance (10-100 ohms) and medium-high input impedance (5-50 kohms).

Posted: Fri Jun 13, 2008 4:35 am

Ummm, you really can't run a classic 1176 on the inserts of most modern-day mixer boards. The originals had 600 ohm terminated balanced bridging inputs. Now all the latter models which were silver faced utilized a 10,000 ohm, balanced integrated circuit chip, transformer less input. Those you can patch on inserts of most budget consoles.

And Teac/TASCAM referenced their -10 DB standard at .3 volts as it relates to a 1 volt 0 DB reference, as opposed to a .773 volts, 0 DBm into 600 ohms for a + 4 DB zero reference, which is 1.25 volts RMS. If that isn't enough to confuse you? I don't know what is? Yeah, most integrated circuit chip outputs can't deliver more than +18 DBu, into 10,000 ohm inputs. And so for most folks who don't have the pleasure of using a fully professional high-end console, you're stuck at much less headroom. Headroom is the difference between professional sound & beginner sound. But beginners can sound like professionals if you make your self some headroom.

Big mouth +28dbm broad, yeah baby.
Ms. Remy Ann David

Posted: Fri Jun 13, 2008 6:02 pm

RemyRAD wrote:

... Big mouth +28dbm broad, yeah baby...

yeah baby

an end of post quip this maybe
but
to understand it
is to understand the whole point

to use and interface old and retro gear with modern mixers and digital interfaces etc
and
to get them into the sweet spot

you need to understand why and how Remy is a
" big mouth +28dbm broad "

funny yes
but this is no joke

Posted: Mon Jun 16, 2008 4:02 pm

RemyRAD wrote:

Ummm, you really can't run a classic 1176 on the inserts of most modern-day mixer boards. The originals had 600 ohm terminated balanced bridging inputs. Now all the latter models which were silver faced utilized a 10,000 ohm, balanced integrated circuit chip, transformer less input. Those you can patch on inserts of most budget consoles.

I can only disagree with that. Most of these "budget consoles" have the capability to deliver +18dBu into 600 ohms, which is plenty even for a "classic" 1176, unless you want 30dB+ compression.

Posted: Mon Jun 16, 2008 4:16 pm

well I disagree

and it comes down to how much headroom you have chosen to have in those "budget consoles" OR the modern DAW

very difficult to get typical recorded program up into the sweet spot of things like transformered 1176 and LA2s

I have been asked a few times to mod these units to add just a little gain at the front end to suit the insert sends ... (or add a line driver to the send)
...
then PAD the output back a little to bring back into the insert return

I do think it is at the output that brings much of the sound people are looking for
so terminating and the PAD is probably the first thing to try.
The Gain Make Up Amp in these units often have enough to get you going but the risk is that you may get some noise with it. That's why finding 10db (or a little more) of signal at the front can help.

Posted: Mon Jun 16, 2008 5:23 pm

Kev wrote:

well I disagree and it comes down to how much headroom you have chosen to have in those "budget consoles" OR the modern DAW
very difficult to get typical recorded program up into the sweet spot of things like transformered 1176 and LA2s

It is your absolute right to disagree, but I know for sure that an 1176 is not expecting more than 0dBu to operate properly. When I installed the cutting room at Barclay Studios in 1976, we had a Neumann mixer, which ran on a single 24 V rail and used LF356's, hence offering only +16dBu output capability on the unbalanced insert points. The 1176's (with xformer inputs and 600 ohms constant-z attenuators) had enough gain to cope with that.

Quote:

I do think it is at the output that brings much of the sound people are looking for so terminating and the PAD is probably the first thing to try.

I agree with that; The output xformer in the 1176 wants to see a 600 ohm impedance because it has a relatively high leakage inductance that makes it ring if not properly damped.

Quote:

The Gain Make Up Amp in these units often have enough to get you going but the risk is that you may get some noise with it.

No, because the input attenuator is before the input preamp. Having less attenuation before the input preamp doesn't change noise.

Posted: Tue Jun 17, 2008 1:19 am

no no

I was referring to signals that might be for you, a very low signa,l with a great deal of headroom
and could be much lower than 0dbu

and I can see how a single 24v rail with around +16dbu unbal would also be quite low for a max signal

some people seem to want to see 20db+ of headroom

as for the gain noise / issue
to CRANK the gain make up amp can make noise for within the 1176

remember there are 1176's out there that were NOT the LN models
Low Noise

and I was referring to these things genericaly and including LA2's .... these things can be living being that have lived hard lives
and it is hard to find two the same

and for things like the Pendulum compressor +16dbu unbalanced would not get it into it's sweet spot and a PAD would be needed to bring it back into one of these desks

You seem to know enough about your gear to make your own choices and the comments here from Remy and I are not really directed at you.

IF all of this gets people thinking about how they interface there gear then this is a good thing.

While we are here on the 1176 ... the manual does give some good notes on how to interface it
.... read the manual

you can find PDF's on the net ... my site might even have one

This topic sponsored by: