I am exploring the possibilities of making a headphone amp based around an op amp. The amp only needs to have one set of analogue. I have a couple of Phillips NE5532's sat in my spares box which I would like to use if possible (salvaged from my NAD C520). The 5532 has an output impedance of 600ohms. I haven't settled on a decent pair of cans yet, so the amp should be capable of a wide range of loads. I quite fancy a pair of Grado GS1000's ;-) No, just kidding, SR60's are more in my league. Does anyone know of anywhere I can get my hands on a fairly simple circuit design, or a supplier of ready made PCB's for this purpose? I don't mind mains or battery supply either.
Regards,
Chris
Regards,
Chris
Rod Elliotts headphone amp projects
http://sound.westhost.com/projects-1a.htm
big website for headphone amplifiers projects articles & stuff
http://www.headwize.com/projects/
big DIY headphone discussion forum, with member projects
http://www.head-fi.org/forums/f6/
http://sound.westhost.com/projects-1a.htm
big website for headphone amplifiers projects articles & stuff
http://www.headwize.com/projects/
big DIY headphone discussion forum, with member projects
http://www.head-fi.org/forums/f6/
See: http://tangentsoft.net/audio/cmoy-tutorial/
Nice boards are available http://jseaber.com/cMoy/diy.htm and I don't know if he has any left, but joshatdot over at Head-Fi was selling some nice ones too. See http://www.head-fi.org/forums/f42/fs-custom-cmoy-boards-253920/
Nice boards are available http://jseaber.com/cMoy/diy.htm and I don't know if he has any left, but joshatdot over at Head-Fi was selling some nice ones too. See http://www.head-fi.org/forums/f42/fs-custom-cmoy-boards-253920/
He wants to use an opamp based topology with a relatively weak opamp. I agree, but that's what he wants...pikkujöpö said:
zebra: pikkujöpö is right. This design, especially with NE5532 probably won't satisfy into Grados. A simple design that would probably work well for you is the Szekeres driver, just a single MOSFET and some passives.
NE5532 dual op-apm
has got a pretty good level of output current.
As has the OPA2134, too.
In my opinion both these have current output enough
to drive Grados 32 ohm Hi-Fi phones.
This has also been told & confirmed by several members at this forum.
Now, NE5534 is even a better choice.
Besides having better data, this is a single op-amp.
Two NE5534 can dissipate like two times of one OPA2134/NE5532.
When 2-channels in same IC, the IC will have to handle power heat from left+right.
The usual limit of safe operation area ( SOA ) for 8-pin Plastic DIP chips is like 500-600 mW.
Because plastic melts down and destroys at some temperature.
About the same power level, 500 mW, is for one ordinary small signal transistor.
For example BC547, BC550 or 2N5551 and similiar 'audio transistors'.
TO-92.
Lineup
has got a pretty good level of output current.
As has the OPA2134, too.
In my opinion both these have current output enough
to drive Grados 32 ohm Hi-Fi phones.
This has also been told & confirmed by several members at this forum.
Now, NE5534 is even a better choice.
Besides having better data, this is a single op-amp.
Two NE5534 can dissipate like two times of one OPA2134/NE5532.
When 2-channels in same IC, the IC will have to handle power heat from left+right.
The usual limit of safe operation area ( SOA ) for 8-pin Plastic DIP chips is like 500-600 mW.
Because plastic melts down and destroys at some temperature.
About the same power level, 500 mW, is for one ordinary small signal transistor.
For example BC547, BC550 or 2N5551 and similiar 'audio transistors'.
TO-92.
Lineup
lineup said:
Well I'm listening to one with OPA2134(or was it opa2132).With 16 Ohm headplugs
.The sound quite hasn't got the bunch I'm used to, suprisingly good anyway.
P.S. I bet several members of this forum would confirm this as well,or am I mistaken ?
Edit: I will hopefully soon try it with a buffer and report back.
16 Ohms
earPhones
Yes, 16 Ohms takes even more current than 32 Ohm.
Now, 16 Ohms earPlugs have usually VERY high sensitivity.
( dB per milliWatt power)
So, the voltage needed across those 16 Ohm is extremely low.
From this follows that the current output will also be quite low.
I = U / R
Current (Ampere) = Volt / Ohm
Say: 0.1 Volt RMS / 16 Ohm = 6.25 mA average current.
These Op-Amps, OPA2134, have max output current like 30-40 milliAmpere.
So they should theoretically and probably even in reality be able to put out:
U = R x I
Volt = Ohm x Ampere
Volt = 16 (Ohm) x 0.035 (Ampere) same as 35 mA
Volt = 0.56
================
35 mA output means:
max 0.56 Volt average, for 16 Ohms earPlugs, Sony, Sharp, Yamaha, etc.
max 1.12 Volt average, for 32 Ohms hifi Grado
max 3.50 Volt average, 100 Ohms
max 10.50 Volt for 300 Ohms Sennhesiser hi-fi headphones
================
Now do not try to put out as much as those Voltages max output.
Because this can destroy your headPhones or earPhones
and if not,
it might DESTROY YOUR HEARING .. forever!
Lineup - has designed a number of transistor HeadPhone Amplifiers
... and so done some math & experiments with different headPhones, listening & measuring
earPhones
Yes, 16 Ohms takes even more current than 32 Ohm.
Now, 16 Ohms earPlugs have usually VERY high sensitivity.
( dB per milliWatt power)
So, the voltage needed across those 16 Ohm is extremely low.
From this follows that the current output will also be quite low.
I = U / R
Current (Ampere) = Volt / Ohm
Say: 0.1 Volt RMS / 16 Ohm = 6.25 mA average current.
These Op-Amps, OPA2134, have max output current like 30-40 milliAmpere.
So they should theoretically and probably even in reality be able to put out:
U = R x I
Volt = Ohm x Ampere
Volt = 16 (Ohm) x 0.035 (Ampere) same as 35 mA
Volt = 0.56
================
35 mA output means:
max 0.56 Volt average, for 16 Ohms earPlugs, Sony, Sharp, Yamaha, etc.
max 1.12 Volt average, for 32 Ohms hifi Grado
max 3.50 Volt average, 100 Ohms
max 10.50 Volt for 300 Ohms Sennhesiser hi-fi headphones
================
Now do not try to put out as much as those Voltages max output.
Because this can destroy your headPhones or earPhones
and if not,
it might DESTROY YOUR HEARING .. forever!
Lineup - has designed a number of transistor HeadPhone Amplifiers
... and so done some math & experiments with different headPhones, listening & measuring
use
LM317 + LM337
and one 0 Volt GROUND reference
I not long ago helped to advice one guy
that ordered one Velleman kit for such regulated supply
Topic with some information posts by Lineup
Symmetric supply or dual supply
for this Velleman power supply kit, you get LM317/LM337 and all components
+ instruction PDF
You have to buy some suitable transformer
that is all you need
I suggest, for Op-Amp supply
you need no more than one small
5-10 VA transformer (2x12, 2x15, 2x18 Volt)
LM317 + LM337
and one 0 Volt GROUND reference
I not long ago helped to advice one guy
that ordered one Velleman kit for such regulated supply
Topic with some information posts by Lineup
Symmetric supply or dual supply
for this Velleman power supply kit, you get LM317/LM337 and all components
+ instruction PDF
You have to buy some suitable transformer
that is all you need
I suggest, for Op-Amp supply
you need no more than one small
5-10 VA transformer (2x12, 2x15, 2x18 Volt)
Szekeres headphone Buffer (single mosfet follower)
is good.
Especially for HeadPhones 16-100 Ohm impedance.
For some HeadPhones, with Impedance 300-600 Ohm + lower sensitivity (SPL Decibel / millWatt)
you may need some Voltage gain.
Usuall Gv (gain voltage) like 5-8 wil be enough. (max + 9 dB).
All the above is for normal CD-player output level ( Max 2 Volt RMS standard ).
When comes to other soures to drive the input of your headphone amplifier you may need more voltage gain.
Or use one good Voltage preamplfier between Sound Source and one HeadPhone Buffer amplifier, Szekeres for example.
Szekeres original MOSFET Follower project is very popular & good.
His article can be found here:
http://www.headwize.com/projects/szeke1_prj.htm
is good.
Especially for HeadPhones 16-100 Ohm impedance.
For some HeadPhones, with Impedance 300-600 Ohm + lower sensitivity (SPL Decibel / millWatt)
you may need some Voltage gain.
Usuall Gv (gain voltage) like 5-8 wil be enough. (max + 9 dB).
All the above is for normal CD-player output level ( Max 2 Volt RMS standard ).
When comes to other soures to drive the input of your headphone amplifier you may need more voltage gain.
Or use one good Voltage preamplfier between Sound Source and one HeadPhone Buffer amplifier, Szekeres for example.
Szekeres original MOSFET Follower project is very popular & good.
His article can be found here:
http://www.headwize.com/projects/szeke1_prj.htm
An externally hosted image should be here but it was not working when we last tested it.
Here is one
later variation / modification to the Szekeres.
Using LM317 as one CCS, to bias MOSFET output into Class A.
later variation / modification to the Szekeres.
Using LM317 as one CCS, to bias MOSFET output into Class A.
An externally hosted image should be here but it was not working when we last tested it.
Well,
I managed to source the MOSFET's on e-bay, I just have to wait until I can get down to the local Maplin's (90 Mile round trip) for the rest of the bits.
Just a quick thought. Would strip board do this circuit justice, or would it benifit from using a PCB with a large ground plane?
Regards,
Chris.
I managed to source the MOSFET's on e-bay, I just have to wait until I can get down to the local Maplin's (90 Mile round trip) for the rest of the bits.
Just a quick thought. Would strip board do this circuit justice, or would it benifit from using a PCB with a large ground plane?
Regards,
Chris.
With regards to the power supply, could the amp be powered by a small regulated DC plug in type adaptor such as this,
http://www.maplin.co.uk/Module.aspx?ModuleNo=96964&DOY=28m8
Or would something like this be more appropriate?
http://www.maplin.co.uk/Module.aspx?TabID=1&ModuleNo=231&doy=28m8
http://www.maplin.co.uk/Module.aspx?ModuleNo=96964&DOY=28m8
Or would something like this be more appropriate?
http://www.maplin.co.uk/Module.aspx?TabID=1&ModuleNo=231&doy=28m8
forget thsecond one
it is for radio transmitters with high power output at 13.8 Volt
the first one link
the 1.5 A unit may suit,
but will only give you one positive voltage AC 24 Volt
and something like 35 Volt DC after rectification
I would not go for it.
What you would want, for most Op-Amp based headphone amplifiers
is a DUAL DC regulated voltage
for example
2 x 15 VDC = +15 Volt and -15 Volt ( total 30 Volt DC )
or
2 x 12 VDC
or
2 x 18 VDC
it is for radio transmitters with high power output at 13.8 Volt
the first one link
the 1.5 A unit may suit,
but will only give you one positive voltage AC 24 Volt
and something like 35 Volt DC after rectification
I would not go for it.
What you would want, for most Op-Amp based headphone amplifiers
is a DUAL DC regulated voltage
for example
2 x 15 VDC = +15 Volt and -15 Volt ( total 30 Volt DC )
or
2 x 12 VDC
or
2 x 18 VDC
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