best way to unbalance a DAV BG preamp

[studer58]

I need to 'unbalance' the balanced outputs of my DAV BG8 to feed it into the unbalanced line inputs of a Zoom R16. How would I best achieve this without risking damage to the output chips of the DAV ? Use an XLR > 1/4" TS cable that ties pins 1 and 3 of the XLR together and connects them to the 1/4" sleeve with pin 2 going to 1/4" tip ? Or leave the pin 3/'cold'/ring of an XLR > 1/4" TRS disconnected ?

Also, does it make for better practice to feed the onstage mics directly into the DAV via short XLR cables (having the DAV located near the stage area) and then feed the long multicores into the remotely located recorder at line level..or simply have long mic cables (via same multicore) going into the remotely located DAV/recorder and thus only have a short line level connection. In other words, which is better for signal integrity ? Total distances involved are around 30 metres from mic to recorder.

[tourtelot]

FWIW, I almost always leave the shield (pin 1) disconnected at the 1/4" end when I unbalance. The shield still runs the length of the cable from pin 1 is dropped inside the 1/4". Pin 2 and 3 are the signal leads in a balanced line and I connect pin 2 to tip and pin 3 to sleeve. I am not certain about you specific application but it has worked that way for me for years.

D.

[Jim Williams]

It partly depends on which version of DAV you have, I've seen 3 so far. Early models used OP275 optout opamps, those drive 600 ohm loads and run on + - 20 volts. They feed 100 ohm output resistors so shorting one leg should be ok.

Later models ver.2 and 3 switched to MC33078 output opamps, those have trouble driving 600 ohm loads and don't short out as well on a 100 ohm load.

You can swap out that opamp to a LME49860 or BB OPA1612 and solve those worries and increase slew rate and lower THD too. Dropping in a SSM2019 for the that1510 or BB INA217 really helps these.

Or, if in doubt, float pin 3, connect pin 2 to hot and pin 1 to ground.

[Rolo 46]

P3 +P1 Ground
P2 Hot gives more level

[tourtelot]

Originally Posted by Rolo 46

P3 +P1 Ground
P2 Hot gives more level

Yep. +3dB but it also opens up the possibility of a ground loop.

D.

[panatrope]

From the man himself ...

> If I have to connect the output of the BG1 to an unbalanced input,
> should I leave pin 3 floating, or connect it to ground?
>
> Is the output stage servo balanced (ground sensing) or straight bipolar
> (normal and inverted, with ground as a virtual centretap)? The latter is
> important if I perform sum and difference matrixing (for M-S decoding) by
> connecting outputs 1+ to L+ and R+, 2- to L-, 1- R- (L and R being
> differential inputs).

best to leave it floating.
the output is pin 2 +, pin 3 - with pin 1 ground, no servo balancing.
regards
Mick

[panatrope]

Originally Posted by Jim Williams

... You can swap out that opamp to a LME49860 or BB OPA1612 and solve those worries and increase slew rate and lower THD too. Dropping in a SSM2019 for the that1510 or BB INA217 really helps these.

Like many posts in this forum, this only re-inforces an observation made during my previous professional life (not audio) by a colleague (in Texas, as it happens) that an engineer's urge to redesign/improve another engineer's work is one that is even stronger than sex.

[Rolo 46]

Anyhow
No pro ventures forth unbalanced
Its Lunacy imho

[rcrowley]

How do we know the line inputs are unbalanced? I can't find any definitive information one way or the other. Many lower-end devices simply throw a pad in front of the mic input and call it "line level", I would be surprised if the Zoom were any different.

Has anybody seen schematics for this thing? The published "technical info" is typically nearly devoid of any useful technical information. Perhaps we can expect no more for a plastic toy?

[Jim Williams]

Originally Posted by panatrope

Like many posts in this forum, this only re-inforces an observation made during my previous professional life (not audio) by a colleague (in Texas, as it happens) that an engineer's urge to redesign/improve another engineer's work is one that is even stronger than sex.

And we can add that those efforts have yielded far greater societal results than random breeding ever has.

[panatrope]

Originally Posted by Jim Williams

And we can add that those efforts have yielded far greater societal results than random breeding ever has.

Now that is a conjecture that is outside the scope of this forum.

(Reference Ellen Therry's proposal to George Bernard Shaw.)

[mixedupsteve]

Originally Posted by studer58

I need to 'unbalance' the balanced outputs of my DAV BG8 to feed it into the unbalanced line inputs of a Zoom R16. How would I best achieve this without risking damage to the output chips of the DAV ? Use an XLR > 1/4" TS cable that ties pins 1 and 3 of the XLR together and connects them to the 1/4" sleeve with pin 2 going to 1/4" tip ? Or leave the pin 3/'cold'/ring of an XLR > 1/4" TRS disconnected ?

Also, does it make for better practice to feed the onstage mics directly into the DAV via short XLR cables (having the DAV located near the stage area) and then feed the long multicores into the remotely located recorder at line level..or simply have long mic cables (via same multicore) going into the remotely located DAV/recorder and thus only have a short line level connection. In other words, which is better for signal integrity ? Total distances involved are around 30 metres from mic to recorder.

The product sheet I found says that the combo inputs when set in the line in position are balanced:
R16

Several are able to be used as an instrument input if a switch is set for that and of course they are unbalanced hiz if that setting is selected.

[mixedupsteve]

Originally Posted by tourtelot

FWIW, I almost always leave the shield (pin 1) disconnected at the 1/4" end when I unbalance. The shield still runs the length of the cable from pin 1 is dropped inside the 1/4". Pin 2 and 3 are the signal leads in a balanced line and I connect pin 2 to tip and pin 3 to sleeve. I am not certain about you specific application but it has worked that way for me for years.

D.

I usually use this chart when in doubt and that's what they recommend also:Sound System Interconnection

[Nobilmente]

Originally Posted by Jim Williams

It partly depends on which version of DAV you have, I've seen 3 so far. Early models used OP275 optout opamps, those drive 600 ohm loads and run on + - 20 volts. They feed 100 ohm output resistors so shorting one leg should be ok.

Later models ver.2 and 3 switched to MC33078 output opamps, those have trouble driving 600 ohm loads and don't short out as well on a 100 ohm load.

You can swap out that opamp to a LME49860 or BB OPA1612 and solve those worries and increase slew rate and lower THD too. Dropping in a SSM2019 for the that1510 or BB INA217 really helps these.

Or, if in doubt, float pin 3, connect pin 2 to hot and pin 1 to ground.

From a previous entry from Mick Hinton - I've mentioned this several times before, but (in the words of President Reagan) - "There you go again". No Charge!

Hi Jim
i've never used an mc33078 op amp!
all signal i.c's are now in 8 pin bases for ease of replacement/modification.
regards
Mick @DAV

[Jim Williams]

I sent out a ver. 3 last month and it came with 33078 opamps. Someone is putting them in there. They are gone now though.

[studer58]

Thanks for your replies, and since the R16 indeed seems to have balanced line inputs on it's TRS combo sockets there's certainly no point in feeding it with an unbalanced line (particularly if I'm planning on a long cable run, which would be more susceptible to RF and hum pickup ?) So DAV XLRs out to TRS all the way it will be...perhaps with some pads inbuilt to tame the hot outputs from the DAV. Does anyone have thoughts, biases or recommendations on the long mic-level multicore vs long line- level multicore issue in the OP ?

[didier.brest]

Originally Posted by tourtelot

+3dB

Twice the voltage = + 6 dB.

[tourtelot]

Originally Posted by didier.brest

Twice the voltage = + 6 dB.

Yes. Right you are. I always get that wrong

D.