audio line out voltage

[Ban]

Pooh Bear wrote:

Ban wrote:

Spehro Pefhany wrote:
Hi, all:-

What's the minimum *peak* voltage without clipping that I should
allow for in a general purpose audio input that accepts a signal
from an audio "line out"? I see numbers like +20dB, which would be
almost 8V RMS. Is this correct?

I'd like to reduce the voltage supplies as much as practical on a
crossbar switch to reduce the power dissipation...


Best regards,
Spehro Pefhany

Speff,
If it is a XLR input, the voltage is balanced. So the peak voltage
is only +/-4V. I use the INA2137 to convert it to single ended(-6dB)
and then DRV135 to amplify and balance it again.

Where did you get that idea Ban ?

Most pro-audio outputs are driven by an op-amps supplied from
somewhere between +/- 15V and 18V

The 8V that Spehro mentioned is a typical rms voltage from such an
output. The peak voltage in this case would be about 11V.

Where an output is true balanced both pins 2 and 3 of the XLR are
actively driven - providing a pk-pk output of say 25V.

The INA ( and other ) solutions are simply expensive playthings. You
can do the same with an op-amp and a few Rs.

Graham

If the max level is +20dBu as Speff mentioned, the balanced input is only
4Vrms on each line. 25Vpp is exactly +21.14dBu or 8.8Vrms, that is just 10%
higher.
So how much CMRR do you get from your opamp and a few Rs? And if 1.70$ is
expensive for a dual differential amp, I wonder what kind of opamps you use.
Already the precision resistors needed(0.01%) will cost more.
--
ciao Ban
Bordighera, Italy

 

[Pooh Bear]

Ban wrote:

Pooh Bear wrote:
Ban wrote:

Spehro Pefhany wrote:
Hi, all:-

What's the minimum *peak* voltage without clipping that I should
allow for in a general purpose audio input that accepts a signal
from an audio "line out"? I see numbers like +20dB, which would be
almost 8V RMS. Is this correct?

I'd like to reduce the voltage supplies as much as practical on a
crossbar switch to reduce the power dissipation...


Best regards,
Spehro Pefhany

Speff,
If it is a XLR input, the voltage is balanced. So the peak voltage
is only +/-4V. I use the INA2137 to convert it to single ended(-6dB)
and then DRV135 to amplify and balance it again.

Where did you get that idea Ban ?

Most pro-audio outputs are driven by an op-amps supplied from
somewhere between +/- 15V and 18V

The 8V that Spehro mentioned is a typical rms voltage from such an
output. The peak voltage in this case would be about 11V.

Where an output is true balanced both pins 2 and 3 of the XLR are
actively driven - providing a pk-pk output of say 25V.

The INA ( and other ) solutions are simply expensive playthings. You
can do the same with an op-amp and a few Rs.

Graham

If the max level is +20dBu as Speff mentioned, the balanced input is only
4Vrms on each line.

Except that +20dBu limited outputs are normally / invariably 'single ended' or
'unbalanced'. Hence there are *NO* volts on the 'other line' at all.

You need to consider that every output is driven by an op-amp supplied from a
+/- 15 ~ 18 V DC supply.

25Vpp is exactly +21.14dBu or 8.8Vrms, that is just 10% higher.
So how much CMRR do you get from your opamp and a few Rs?

Simple. It depends on the R match ! Just about *every* pro-audio manufacturer
finds 1% tolerance Rs acceptable in this application ( some actually find 5%
suitable ! ). Bear in minfd that 1% Rs are actually typically withinn 0.3% of
value and are often better matched withina batch !

And if 1.70$ is
expensive for a dual differential amp, I wonder what kind of opamps you use.
Already the precision resistors needed(0.01%) will cost more.

You're wasting money on unnecessary specs. Even Neve never used resistors that
accurate ! I was a project leader there for some years btw so I kinda know !

http://www.ams-neve.com

I pay about USD 0.2 for a pair of balanced inputs. That's 8.5 x less than you
suggest. I put the money into the areas where it actually *counts for something*
!

Graham

 

[Ban]

Pooh Bear wrote:

If the max level is +20dBu as Speff mentioned, the balanced input is
only 4Vrms on each line.

Except that +20dBu limited outputs are normally / invariably 'single
ended' or 'unbalanced'. Hence there are *NO* volts on the 'other
line' at all.

You need to consider that every output is driven by an op-amp
supplied from a +/- 15 ~ 18 V DC supply.

25Vpp is exactly +21.14dBu or 8.8Vrms, that is just 10% higher.
So how much CMRR do you get from your opamp and a few Rs?

Simple. It depends on the R match ! Just about *every* pro-audio
manufacturer finds 1% tolerance Rs acceptable in this application (
some actually find 5% suitable ! ). Bear in minfd that 1% Rs are
actually typically withinn 0.3% of value and are often better matched
withina batch !

And if 1.70$ is
expensive for a dual differential amp, I wonder what kind of opamps
you use. Already the precision resistors needed(0.01%) will cost
more.

You're wasting money on unnecessary specs. Even Neve never used
resistors that accurate ! I was a project leader there for some years
btw so I kinda know !

http://www.ams-neve.com

I pay about USD 0.2 for a pair of balanced inputs. That's 8.5 x less
than you suggest. I put the money into the areas where it actually
*counts for something* !

oops, I'm paying that for a single MKT input capacitor, and I use 4. Those
opamps you use must be really cheap. I have worked on Neve desks and they
had transformers. :-( hardly any cheaper. BTW you do not work for Behringer,
do you?

Graham

--
ciao Ban
Bordighera, Italy

 

[Pooh Bear]

Ban wrote:

Pooh Bear wrote:

If the max level is +20dBu as Speff mentioned, the balanced input is
only 4Vrms on each line.

Except that +20dBu limited outputs are normally / invariably 'single
ended' or 'unbalanced'. Hence there are *NO* volts on the 'other
line' at all.

You need to consider that every output is driven by an op-amp
supplied from a +/- 15 ~ 18 V DC supply.

25Vpp is exactly +21.14dBu or 8.8Vrms, that is just 10% higher.
So how much CMRR do you get from your opamp and a few Rs?

Simple. It depends on the R match ! Just about *every* pro-audio
manufacturer finds 1% tolerance Rs acceptable in this application (
some actually find 5% suitable ! ). Bear in minfd that 1% Rs are
actually typically withinn 0.3% of value and are often better matched
withina batch !

And if 1.70$ is
expensive for a dual differential amp, I wonder what kind of opamps
you use. Already the precision resistors needed(0.01%) will cost
more.

You're wasting money on unnecessary specs. Even Neve never used
resistors that accurate ! I was a project leader there for some years
btw so I kinda know !

http://www.ams-neve.com

I pay about USD 0.2 for a pair of balanced inputs. That's 8.5 x less
than you suggest. I put the money into the areas where it actually
*counts for something* !

oops, I'm paying that for a single MKT input capacitor, and I use 4. Those
opamps you use must be really cheap. I have worked on Neve desks and they
had transformers. :-( hardly any cheaper. BTW you do not work for Behringer,
do you?

No- I'm not one of Uli's guys but I have to work to the same constraints.

A couple of guides here. Don't use input coupling caps if they're not needed.
Normally they're not for a line level stage.

*never* use transformers unless you have an Arab (oil rich ) sheikh as your
customer !

Neve entirely dropped transformers on the legendary V Series version 3 on.....

Graham