OPAMP question regarding headphones

A

Anders N. Vinje

Guest
Hey.
I have this problem with my samick mixer. Well its no problem when you are
making music alone even then the output must be at a 75% setting.
But when i need to have two headsets connected to the headphoneoutput the
output is just to low.

So Since i got some Opamps laying around. I exchanged the TL074 that was in
the mixer with
Burr Brown OPA134 OPAMPS. Now the noiseratio got MUCH better. Well anyway,
since i had some
opamps left i got this idee.
First of all i can start with that electronics is just a hobby. I have no
education whatsoever but i am planning to. Ok here we go:

I want to have enough power to drive another headset. So if i take the
headphone output and run
it through the OPAMP witch is in a untiy gain configuration. I guess it will
works as a
buffer so it wont run down the orginal signal....
So the question is: What am i missing? Will this work?

I guess the headphone output voltage may be to much for the OPAMP.....?
Is this just stupid?


Rough schematic (dident bother to draw the opamp configuration)

in signal (One channel)
-------
|
|
| |
| |/ potentiometer
| |--------------------- To headphone A
| |\ |
| |
| | ----- To OPA134 (unity gain configuration) -- To
headphone B
|
-----
---
-
OPA134 datasheet.
http://www.elfa.se/pdf/73/731/07312010.pdf

Anders Vinje
 
Anders N. Vinje wrote:
Hey.
I have this problem with my samick mixer. Well its no
problem when you are making music alone even then the
output must be at a 75% setting.
But when i need to have two headsets connected to the
headphoneoutput the output is just to low.

So Since i got some Opamps laying around. I exchanged the
TL074 that was in the mixer with
Burr Brown OPA134 OPAMPS. Now the noiseratio got MUCH
better. Well anyway, since i had some
opamps left i got this idee.
First of all i can start with that electronics is just a
hobby. I have no education whatsoever but i am planning
to. Ok here we go:

I want to have enough power to drive another headset. So
if i take the headphone output and run
it through the OPAMP witch is in a untiy gain
configuration. I guess it will works as a
buffer so it wont run down the orginal signal....
So the question is: What am i missing? Will this work?

I guess the headphone output voltage may be to much for
the OPAMP.....?
Is this just stupid?


Rough schematic (dident bother to draw the opamp
configuration)

in signal (One channel)
-------
|
|
| |
| |/ potentiometer
| |--------------------- To headphone A
| |\ |
| |
| | ----- To OPA134 (unity gain
configuration) -- To headphone B
|
-----
---
-
OPA134 datasheet.
http://www.elfa.se/pdf/73/731/07312010.pdf

Anders Vinje
Click to expand...
There's a problem with this schematic - headphone A is fed by a
potentiometer. This means the output will have some significant impedance,
which will decrease the volume and increase distortion, depending on the
volume setting. Also, connecting/disconnecting headphone A will affect the
volume and sound quality at headphone B. Finally, wouldn't you rather have
two volume settings? If you use different types of phones at the same level
one might be intolerably loud while the other is too quiet.

It would be better to use two buffers, one for each pair of cans (actually
fit thay are stereo you need four buffers). Have the buffer outputs feed the
speaker elements directly - set the volume before the signal goes in to the
buffer and not after.

Do you know anything about the headphones you want to drive, such as
impedance or power handling capability? A 600ohm 3W load looks very
different from a 16ohm 100mW load..

Adam
 
Anders N. Vinje wrote:

snip

I guess the headphone output voltage may be to much for the OPAMP.....?
Is this just stupid?


Rough schematic (dident bother to draw the opamp configuration)

in signal (One channel)
-------
|
|
| |
| |/ potentiometer
| |--------------------- To headphone A
| |\ |
| |
| | ----- To OPA134 (unity gain configuration) -- To
headphone B
|
-----
---
-
Click to expand...
Unfortunately this will not work for several reasons. First the OPA134 is
not designed to drive headphones. Whilst it might work initialy, it will
almost certainly exceed the dissipation of the device. Second, as others
have noted, the potentiometer to headphone A needs to be low to drive
headphone but high so as not to waste power. Better feed headphone A
direct from the pones output and headphones B via a pot and a headphone
driver chip.

HTH

Ian
 
Anders N. Vinje wrote:
"Jacobe Hazzard" <spamsink@ATeudoramail.DOTcom> wrote in
message
news:XKZMb.10994$ZuL1.5773@twister01.bloor.is.net.cable.rogers.com...
Anders N. Vinje wrote:
Hey.
I have this problem with my samick mixer. Well its no
problem when you are making music alone even then the
output must be at a 75% setting.
But when i need to have two headsets connected to the
headphoneoutput the output is just to low.

So Since i got some Opamps laying around. I exchanged
the
TL074 that was in the mixer with
Burr Brown OPA134 OPAMPS. Now the noiseratio got MUCH
better. Well anyway, since i had some
opamps left i got this idee.
First of all i can start with that electronics is
just a
hobby. I have no education whatsoever but i am
planning
to. Ok here we go:

I want to have enough power to drive another headset.
So
if i take the headphone output and run
it through the OPAMP witch is in a untiy gain
configuration. I guess it will works as a
buffer so it wont run down the orginal signal....
So the question is: What am i missing? Will this work?

I guess the headphone output voltage may be to much
for
the OPAMP.....?
Is this just stupid?


Rough schematic (dident bother to draw the opamp
configuration)

in signal (One channel)
-------
|
|
| |
| |/ potentiometer
| |--------------------- To headphone A
| |\ |
| |
| | ----- To OPA134 (unity gain
configuration) -- To headphone B
|
-----
---
-
OPA134 datasheet.
http://www.elfa.se/pdf/73/731/07312010.pdf

Anders Vinje

There's a problem with this schematic - headphone A is
fed by a potentiometer. This means the output will have
some significant impedance, which will decrease the
volume and increase distortion, depending on the volume
setting. Also, connecting/disconnecting headphone A
will affect the volume and sound quality at headphone
B. Finally, wouldn't you rather have two volume
settings? If you use different types of phones at the
same level one might be intolerably loud while the
other is too quiet.

It would be better to use two buffers, one for each
pair of cans (actually fit thay are stereo you need
four buffers). Have the buffer outputs feed the speaker
elements directly - set the volume before the signal
goes in to the buffer and not after.

Do you know anything about the headphones you want to
drive, such as impedance or power handling capability?
A 600ohm 3W load looks very different from a 16ohm
100mW load..

Adam

Don´t really know about the power handling capability.
But i kinda rember the impedance was 32 Ohm.... Not sure..
So do you got any suggestion how the potentiometer(s)
should be connected in the circuit to overcome the
impedance problem?
I think i will go for the four buffer soulution since i
got the dual versions(OPA2134) of the the opamps.

This has been most helpfull.
Click to expand...
This is a fine opamp to drive headphones. One problem with adjusting the
volume of a stereo signal is that you need to attenuate both channels - this
means using a dual pot, or two separate pots for each channel. If your mixer
already has a volume control, it might be best to just leave it out
altogether, or use a binary level switch like in the link you posted
elsewhere.

And you can simplify things even more if you ignore my previous comments and
drive both pairs of headphones at the same level (this depends on your
intended use). In that case, you can probably get away with a single pair of
buffers driving both sets. Either way, the circuit from the project in your
link would be a good starting point, and will probably do exactly what you
want. Just build one or two pairs of that circuit, and include whatever
volume controls you want (suggestions are given there for the dual-pot
method as well as the switched method).
 
"Jacobe Hazzard" <spamsink@ATeudoramail.DOTcom> wrote in message
news:XKZMb.10994$ZuL1.5773@twister01.bloor.is.net.cable.rogers.com...
Anders N. Vinje wrote:
Hey.
I have this problem with my samick mixer. Well its no
problem when you are making music alone even then the
output must be at a 75% setting.
But when i need to have two headsets connected to the
headphoneoutput the output is just to low.

So Since i got some Opamps laying around. I exchanged the
TL074 that was in the mixer with
Burr Brown OPA134 OPAMPS. Now the noiseratio got MUCH
better. Well anyway, since i had some
opamps left i got this idee.
First of all i can start with that electronics is just a
hobby. I have no education whatsoever but i am planning
to. Ok here we go:

I want to have enough power to drive another headset. So
if i take the headphone output and run
it through the OPAMP witch is in a untiy gain
configuration. I guess it will works as a
buffer so it wont run down the orginal signal....
So the question is: What am i missing? Will this work?

I guess the headphone output voltage may be to much for
the OPAMP.....?
Is this just stupid?


Rough schematic (dident bother to draw the opamp
configuration)

in signal (One channel)
-------
|
|
| |
| |/ potentiometer
| |--------------------- To headphone A
| |\ |
| |
| | ----- To OPA134 (unity gain
configuration) -- To headphone B
|
-----
---
-
OPA134 datasheet.
http://www.elfa.se/pdf/73/731/07312010.pdf

Anders Vinje

There's a problem with this schematic - headphone A is fed by a
potentiometer. This means the output will have some significant impedance,
which will decrease the volume and increase distortion, depending on the
volume setting. Also, connecting/disconnecting headphone A will affect the
volume and sound quality at headphone B. Finally, wouldn't you rather have
two volume settings? If you use different types of phones at the same
level
one might be intolerably loud while the other is too quiet.

It would be better to use two buffers, one for each pair of cans (actually
fit thay are stereo you need four buffers). Have the buffer outputs feed
the
speaker elements directly - set the volume before the signal goes in to
the
buffer and not after.

Do you know anything about the headphones you want to drive, such as
impedance or power handling capability? A 600ohm 3W load looks very
different from a 16ohm 100mW load..

Adam

Don´t really know about the power handling capability. But i kinda rember
Click to expand...
the impedance was 32 Ohm.... Not sure..
So do you got any suggestion how the potentiometer(s) should be connected in
the circuit to overcome the impedance problem?
I think i will go for the four buffer soulution since i got the dual
versions(OPA2134) of the the opamps.

This has been most helpfull.
 
I want to have enough power to drive another headset. So
if i take the headphone output and run
it through the OPAMP witch is in a untiy gain
configuration. I guess it will works as a
buffer so it wont run down the orginal signal....
So the question is: What am i missing? Will this work?

I guess the headphone output voltage may be to much for
the OPAMP.....?
Is this just stupid?


Rough schematic (dident bother to draw the opamp
configuration)

in signal (One channel)
-------
|
|
| |
| |/ potentiometer
| |--------------------- To headphone A
| |\ |
| |
| | ----- To OPA134 (unity gain
configuration) -- To headphone B
|
-----
---
-
OPA134 datasheet.
http://www.elfa.se/pdf/73/731/07312010.pdf

Anders Vinje

There's a problem with this schematic - headphone A is fed by a
potentiometer. This means the output will have some significant
impedance,
which will decrease the volume and increase distortion, depending on the
volume setting. Also, connecting/disconnecting headphone A will affect
the
volume and sound quality at headphone B. Finally, wouldn't you rather
have
two volume settings? If you use different types of phones at the same
level
one might be intolerably loud while the other is too quiet.

It would be better to use two buffers, one for each pair of cans
(actually
fit thay are stereo you need four buffers). Have the buffer outputs feed
the
speaker elements directly - set the volume before the signal goes in to
the
buffer and not after.

Do you know anything about the headphones you want to drive, such as
impedance or power handling capability? A 600ohm 3W load looks very
different from a 16ohm 100mW load..

Adam

Don´t really know about the power handling capability. But i kinda rember
the impedance was 32 Ohm.... Not sure..
So do you got any suggestion how the potentiometer(s) should be connected
in
the circuit to overcome the impedance problem?
I think i will go for the four buffer soulution since i got the dual
versions(OPA2134) of the the opamps.

This has been most helpfull.

When i wrote unity gain confiiguration i meant voltage follower
configuration. .......
Click to expand...


>
 
I thought i could be possible because i saw this page where they used the
opa143 to make a headphoneamplifie.
http://headwize2.powerpill.org/projects/showproj.php?file=cmoy2b_add_prj.htm

Do you know what the headphone driver chip is called ?




"Ian Bell" <ian@nowhere.com> wrote in message
news:bu21uj$dpc$1@news.ukfsn.org...
Anders N. Vinje wrote:

snip


I guess the headphone output voltage may be to much for the OPAMP.....?
Is this just stupid?


Rough schematic (dident bother to draw the opamp configuration)

in signal (One channel)
-------
|
|
| |
| |/ potentiometer
| |--------------------- To headphone A
| |\ |
| |
| | ----- To OPA134 (unity gain configuration) -- To
headphone B
|
-----
---
-

Unfortunately this will not work for several reasons. First the OPA134 is
not designed to drive headphones. Whilst it might work initialy, it will
almost certainly exceed the dissipation of the device. Second, as others
have noted, the potentiometer to headphone A needs to be low to drive
headphone but high so as not to waste power. Better feed headphone A
direct from the pones output and headphones B via a pot and a headphone
driver chip.

HTH

Ian
Click to expand...
 
Jacobe Hazzard wrote:

major snippage

Don´t really know about the power handling capability.
But i kinda rember the impedance was 32 Ohm.... Not sure..
So do you got any suggestion how the potentiometer(s)
should be connected in the circuit to overcome the
impedance problem?
I think i will go for the four buffer soulution since i
got the dual versions(OPA2134) of the the opamps.

This has been most helpfull.

This is a fine opamp to drive headphones.
Click to expand...
Sorry, but I do not understand this. Are you saying the OPA134 *is*
suitable for driving headphones. If you are, how do explain the datasheet
shows it is characterised only down to loads of 2K?

Ian
 
Ian Bell wrote:
Jacobe Hazzard wrote:

major snippage

Don´t really know about the power handling capability.
But i kinda rember the impedance was 32 Ohm.... Not sure..
So do you got any suggestion how the potentiometer(s)
should be connected in the circuit to overcome the
impedance problem?
I think i will go for the four buffer soulution since i
got the dual versions(OPA2134) of the the opamps.

This has been most helpfull.

This is a fine opamp to drive headphones.

Sorry, but I do not understand this. Are you saying the OPA134 *is*
suitable for driving headphones. If you are, how do explain the datasheet
shows it is characterised only down to loads of 2K?

Ian
Click to expand...
I think 'fine' is too strong an adjective for this case. The data
sheet

http://aes.sdsu.edu/documents/sbos058.pdf

says the output current limit is about 40 ma, but the output swing
graph shown that about +- 5 volts of head room is needed to get to
that current. It current limits smoothly in both directions, so it
will not distort terribly if you get close to the limit, assuming you
have the supply voltage to burn, but it is not as good as some other
types that have a higher output current capability.

Take a look at a couple that do a lot better with low voltage supplies
and high output current:
http://cache.national.com/ds/LM/LM6171.pdf
http://cache.national.com/ds/LM/LM675.pdf
http://focus.ti.com/lit/ds/symlink/opa551.pdf
--
John Popelish
 
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