N
Neil Bernard
Guest
Hi I want a balanced output using two opamps (for audio) using a single rail
power supply +9v any ideas?
power supply +9v any ideas?
J
John Popelish
Guest
Neil Bernard wrote:
9 volts with a pair of .1 uf caps paralleling each of those parts to
produce an elevated zero signal reference. Then invert the out put of
the first signal to produce the second one.
If you can spare a third opamp, you can use high values for the
divider resistors and use that opamp as a follower to produce a
stiffer zero signal reference voltage.
If you want to keep output loading on the first output from altering
the second one, build an inverting and noninverting pair pf stages to
amplify the signal in parallel to produce the two outputs.
Keep in mind that many rail to rail opamps do not handle load
capacitance (cables) without going unstable. You may need to increase
their stability with either series resistance (say, 100 to 620 ohms)
between the opamp and the cable, or an RC series load between the
outputs and the supply rails (a pair of small caps, say, 100 to
1000pf, in series across the supply rails, with a resistor. say. 1k to
2k, from the center point to the output).
--
John Popelish
Use two resistors (or a pair of 5.1 volt zeners) in series across the
9 volts with a pair of .1 uf caps paralleling each of those parts to
produce an elevated zero signal reference. Then invert the out put of
the first signal to produce the second one.
If you can spare a third opamp, you can use high values for the
divider resistors and use that opamp as a follower to produce a
stiffer zero signal reference voltage.
If you want to keep output loading on the first output from altering
the second one, build an inverting and noninverting pair pf stages to
amplify the signal in parallel to produce the two outputs.
Keep in mind that many rail to rail opamps do not handle load
capacitance (cables) without going unstable. You may need to increase
their stability with either series resistance (say, 100 to 620 ohms)
between the opamp and the cable, or an RC series load between the
outputs and the supply rails (a pair of small caps, say, 100 to
1000pf, in series across the supply rails, with a resistor. say. 1k to
2k, from the center point to the output).
--
John Popelish
B
Bob Masta
Guest
On Sat, 15 Nov 2003 19:58:23 -0000, "Neil Bernard"
<nbernard@nbernard.co.uk> wrote:
and don't mind a big common mode voltage (4.5 V in your case)
then this should be pretty straightforward. Just use a normal
balanced output design, with a pseudo-ground at half the
supply. The problem with this approach is that in the real world
of audio, it's not unusual to try to use one side of a balanced
output relative to ground. If you build this for a special purpose,
don't use a 3-wire connector or someone may think they can
do that here.
Bob Masta
dqatechATdaqartaDOTcom
D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
<nbernard@nbernard.co.uk> wrote:
If you are *only* going to use the outputs as a balanced pair,
and don't mind a big common mode voltage (4.5 V in your case)
then this should be pretty straightforward. Just use a normal
balanced output design, with a pseudo-ground at half the
supply. The problem with this approach is that in the real world
of audio, it's not unusual to try to use one side of a balanced
output relative to ground. If you build this for a special purpose,
don't use a 3-wire connector or someone may think they can
do that here.
Bob Masta
dqatechATdaqartaDOTcom
D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
D
dB
Guest
"Neil Bernard" wrote
If your required gain is modest enough to be achieved with just one
opamp, drive one side of the output from this and invert it in another
to drive the other side, capacitively coupling both to get rid of the
d.c. offset.
If your required gain is modest enough to be achieved with just one
opamp, drive one side of the output from this and invert it in another
to drive the other side, capacitively coupling both to get rid of the
d.c. offset.
L
Luhan Monat
Guest
John Popelish wrote:
That pair of zeners in series is a "no-no" (at least with out some
resistor in there somewhere).
--
Luhan Monat, "LuhanKnows" At 'Yahoo' dot 'Com'
http://members.cox.net/berniekm
"The future is not what it used to be."
John,
That pair of zeners in series is a "no-no" (at least with out some
resistor in there somewhere).
--
Luhan Monat, "LuhanKnows" At 'Yahoo' dot 'Com'
http://members.cox.net/berniekm
"The future is not what it used to be."
J
John Popelish
Guest
Luhan Monat wrote:
current, while limiting the reference voltage to within a volt of the
center of the battery rails. 4.7 volt zeners would hold the reference
even closer to the center but would leak a bit more, especially if
they were both at the low voltage side of their tolerance.
--
John Popelish
A pair of 5.1 volt zeners across a 9 volt battery conducts almost no
current, while limiting the reference voltage to within a volt of the
center of the battery rails. 4.7 volt zeners would hold the reference
even closer to the center but would leak a bit more, especially if
they were both at the low voltage side of their tolerance.
--
John Popelish
L
Luhan Monat
Guest
John Popelish wrote:
'limiting the reference voltage' is insufficient. All of the stages
using this for center line voltage would have an extra 'signal' injected
into them. It would be better to use just one zener with an appropriate
resistor on the other leg.
--
Luhan Monat, "LuhanKnows" At 'Yahoo' dot 'Com'
http://members.cox.net/berniekm
"The future is not what it used to be."
Yo,
'limiting the reference voltage' is insufficient. All of the stages
using this for center line voltage would have an extra 'signal' injected
into them. It would be better to use just one zener with an appropriate
resistor on the other leg.
--
Luhan Monat, "LuhanKnows" At 'Yahoo' dot 'Com'
http://members.cox.net/berniekm
"The future is not what it used to be."
J
John Popelish
Guest
Luhan Monat wrote:
across the zeners keep the voltage swing at the reference from
happening fast enough to effect the amplified signals much.
I suggest you try it... both ways. The two zener approach also makes
lots less high frequency noise, which does get through the opamps.
--
John Popelish
Not better from a battery life viewpoint. The capacitors connected
across the zeners keep the voltage swing at the reference from
happening fast enough to effect the amplified signals much.
I suggest you try it... both ways. The two zener approach also makes
lots less high frequency noise, which does get through the opamps.
--
John Popelish
C
Costas Vlachos
Guest
"John Popelish" <jpopelish@rica.net> wrote in message
news:3FB7DA9D.FECB7B8@rica.net...
But what if the supply rises to 10+ Volts? Often people use cheap
unregulated wall supplies as battery substitutes, and these can supply a few
volts above the rated voltage. The Zeners will then conduct hard and the
result won't be pretty... I think the Zener idea can be a hidden danger in
this case, unless you are sure the supply will never exceed 10V. Still a
good idea for maximisisng battery life though...
Costas
news:3FB7DA9D.FECB7B8@rica.net...
But what if the supply rises to 10+ Volts? Often people use cheap
unregulated wall supplies as battery substitutes, and these can supply a few
volts above the rated voltage. The Zeners will then conduct hard and the
result won't be pretty... I think the Zener idea can be a hidden danger in
this case, unless you are sure the supply will never exceed 10V. Still a
good idea for maximisisng battery life though...
Costas
J
John Popelish
Guest
Costas Vlachos wrote:
--
John Popelish
It will keep a load on such a supply.
--
John Popelish
N
Neil Bernard
Guest
Great thanks for your help guys
"John Popelish" <jpopelish@rica.net> wrote in message
news:3FB68A7F.D3FFE11B@rica.net...
"John Popelish" <jpopelish@rica.net> wrote in message
news:3FB68A7F.D3FFE11B@rica.net...