Are there any better performing op amps for the o2 than the NJM4556? How would one go about researching this on his own?
In 2011, I'm sure the NJM4556 was the best op amp for the job. But that was going on seven years ago, and headphones have gained a ton of popularity since then, so there's reasonable motivation for chipmakers to design one.
By "better," I'm open to different definitions. My biggest problem with the o2 is that it can't power my planar magnetics very well, so better could mean more powerful without increasing distortion too much. Or better could mean longer battery life than the original low power design.
If someone can point me in the right direction I'd appreciate it!
In 2011, I'm sure the NJM4556 was the best op amp for the job. But that was going on seven years ago, and headphones have gained a ton of popularity since then, so there's reasonable motivation for chipmakers to design one.
By "better," I'm open to different definitions. My biggest problem with the o2 is that it can't power my planar magnetics very well, so better could mean more powerful without increasing distortion too much. Or better could mean longer battery life than the original low power design.
If someone can point me in the right direction I'd appreciate it!
Take a look at this thread by AGDR...his O2 Booster Board might just what your looking for...you can send him a PM to see if he still has boards.
ITs a pretty easy build.
LINK:
O2 headamp output booster PCB
ITs a pretty easy build.
LINK:
O2 headamp output booster PCB
Mr. Speakers Alpha Primes.
They do take a ton of power, I've been using the speaker taps on a 20 y/o Kenwood 50wpc (@ 8ohms) tuner. I estimate the tuner's amp is capable of 6 or 7 watts into 49ohms, and that the headphones need 2-3 of those watts to sound their best. I do not believe those numbers necessarily apply across different amplifiers, because the o2 seems only marginally underpowered, and it isn't anywhere near 3 watts. If the boost card doubles the power (like it doubles the current) I expect it to be money xD
They do take a ton of power, I've been using the speaker taps on a 20 y/o Kenwood 50wpc (@ 8ohms) tuner. I estimate the tuner's amp is capable of 6 or 7 watts into 49ohms, and that the headphones need 2-3 of those watts to sound their best. I do not believe those numbers necessarily apply across different amplifiers, because the o2 seems only marginally underpowered, and it isn't anywhere near 3 watts. If the boost card doubles the power (like it doubles the current) I expect it to be money xD
Hello,
I answered today to a similar question to a headfier: O2 AMP + ODAC | Page 369 | Head-Fi.org, hope that helps.
I've honestly no idea why would you need so much power to drive Fostex T50RP drivers, like Alpha Prime has inside; the scenario you speak about sounds more like HIFIMAN HE-5. Anyway, you could unplug the headphones and try playing a 0dB 1KHz wave file taken from Audiocheck website, then measure the headphone output with a multimeter to find out the exact voltage and gain your O2 is using. You'll need either to get O2's cover and measure directly on headphone's output plug, either to find a jack and wire it properly to get the output signal measured correctly (pay attention to any possible short-circuit you could cause).
Just listened now to Deep Purple - "Smoke on the water" with peaks getting at most to -3dB, with O2's gain set to 1X and volume potentiometer to the max. I felt that the volume was a bit too high for my ears. My O2 was feed by the ODAC that has a max. of 1.92V RMS on outputs. I was also testing the 3.5X gain, but after getting the pot. volume after 2 o'clock I wasn't feeling comfortable, so for feeding my Fostex T50RP MK3 from O2 amplifier even the low-gain of 1X can do the job for most music (depending on the dynamic range and volume of recording).
Best,
Raul.
I answered today to a similar question to a headfier: O2 AMP + ODAC | Page 369 | Head-Fi.org, hope that helps.
I've honestly no idea why would you need so much power to drive Fostex T50RP drivers, like Alpha Prime has inside; the scenario you speak about sounds more like HIFIMAN HE-5. Anyway, you could unplug the headphones and try playing a 0dB 1KHz wave file taken from Audiocheck website, then measure the headphone output with a multimeter to find out the exact voltage and gain your O2 is using. You'll need either to get O2's cover and measure directly on headphone's output plug, either to find a jack and wire it properly to get the output signal measured correctly (pay attention to any possible short-circuit you could cause).
Just listened now to Deep Purple - "Smoke on the water" with peaks getting at most to -3dB, with O2's gain set to 1X and volume potentiometer to the max. I felt that the volume was a bit too high for my ears. My O2 was feed by the ODAC that has a max. of 1.92V RMS on outputs. I was also testing the 3.5X gain, but after getting the pot. volume after 2 o'clock I wasn't feeling comfortable, so for feeding my Fostex T50RP MK3 from O2 amplifier even the low-gain of 1X can do the job for most music (depending on the dynamic range and volume of recording).
Best,
Raul.
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U3
Stumped...
Getting now V DC on one channel in my new DIY O2 using AGRD's upgrade/update BOM. Enough that I can feel one ear getting warm on my junk test old iPod HPs!!
Touched the solder iron to all joints etc. paying close attention to vol.pot R12/13 C13/14; run all the troubleshooting I could find on the www but no luck yet
R12/13 measures as it should at 40.2 ohm
On U3 I am getting the same rising V at pin 5 and pin 3 and at pin 1. On U4 they are all 0v as you would like to see. From the data sheet I see that pins 3&5 are the +input.
V measures correct as per construction notes on pin 8 & 4.
Swapped U3 & U4 IC but problem remains in U3 position
Tried swapping out U1 for new IC - no change
Any ideas??
Thanks
Stumped...
Getting now V DC on one channel in my new DIY O2 using AGRD's upgrade/update BOM. Enough that I can feel one ear getting warm on my junk test old iPod HPs!!
Touched the solder iron to all joints etc. paying close attention to vol.pot R12/13 C13/14; run all the troubleshooting I could find on the www but no luck yet
R12/13 measures as it should at 40.2 ohm
On U3 I am getting the same rising V at pin 5 and pin 3 and at pin 1. On U4 they are all 0v as you would like to see. From the data sheet I see that pins 3&5 are the +input.
V measures correct as per construction notes on pin 8 & 4.
Swapped U3 & U4 IC but problem remains in U3 position
Tried swapping out U1 for new IC - no change
Any ideas??
Thanks
Measure and post the voltages on ALL the pins of the opamp, as measured on the pins themselves, not on the board underneath.
Are you sure the supplies are correct ? + rail on pin 8 and - rail on pin 4
A missing (open) supply could still read as the same polarity voltage on pins 4 and 8.
If that reveals nothing then remove the opamp and repeat the voltage measurements on the empty socket. All should be zero apart from the supplies on 4 and 8.
Are you sure the supplies are correct ? + rail on pin 8 and - rail on pin 4
A missing (open) supply could still read as the same polarity voltage on pins 4 and 8.
If that reveals nothing then remove the opamp and repeat the voltage measurements on the empty socket. All should be zero apart from the supplies on 4 and 8.
Thanks Mooly
As per previous U4 returns perfect readings
U3 mounted
1 = rising to at least 10v (until I chicken out) over about 1 min
2 = same as 1
3 = same as 1
4 = -11.7
5 = same as 1
6 = same as 1
7 = same as 1
8 = 11.7
U3 unmounted
1 = oscillates lightly around +/-3mV
2 = oscillates lightly around +/-3mV
3 = see below
4 = -11.7
5 = see below
6 = oscillates lightly around +/-3mV
7 = oscillates lightly around +/-3mV
8 = 11.7
at first turn on immediately after U3 is taken out these pins measure around 400mV and then slowly over the course of a minute or more drop to 4or5mV
there is some capacitance collection and discharge happening?
something happening around U1 pin 1?
will have to come back to this later
As per previous U4 returns perfect readings
U3 mounted
1 = rising to at least 10v (until I chicken out) over about 1 min
2 = same as 1
3 = same as 1
4 = -11.7
5 = same as 1
6 = same as 1
7 = same as 1
8 = 11.7
U3 unmounted
1 = oscillates lightly around +/-3mV
2 = oscillates lightly around +/-3mV
3 = see below
4 = -11.7
5 = see below
6 = oscillates lightly around +/-3mV
7 = oscillates lightly around +/-3mV
8 = 11.7
at first turn on immediately after U3 is taken out these pins measure around 400mV and then slowly over the course of a minute or more drop to 4or5mV
there is some capacitance collection and discharge happening?
something happening around U1 pin 1?
will have to come back to this later
Interesting 
This has to be a physical issue around that chip. Something shorted or something open.
First thought is an open circuit between R12 and pins 5 and 3. The break could be the resistor itself or anywhere to and from the resistor.
If pins 5 and 6 were floating it would do just this as the opamp input bias current 'charges' up C13. In other words it is as if the resistor isn't present.
This has to be a physical issue around that chip. Something shorted or something open.First thought is an open circuit between R12 and pins 5 and 3. The break could be the resistor itself or anywhere to and from the resistor.
If pins 5 and 6 were floating it would do just this as the opamp input bias current 'charges' up C13. In other words it is as if the resistor isn't present.
Interesting
First thought is an open circuit between R12 and pins 5 and 3. The break could be the resistor itself or anywhere to and from the resistor.
If pins 5 and 6 were floating it would do just this as the opamp input bias current 'charges' up C13. In other words it is as if the resistor isn't present.
Yes there is not a lot to go wrong around those pins. I am in the process of lifting the socket out just to be sure there is nothing wrong under there - bit of something shorting or scratched trace? Who knows. When it is not obvious you go looking in the silly places.
R12 measures ok in circuit. I’ll Lift it and check - I have others so could just swap it out.
Ok - just been poking around R12 to see if there is conductivity to 3 or 5. Not get anything. I will get out the iron and have a play there. I’ll report back
Ok between C13 and U3 but no connection back from C13 to R12 -either my pcb is faulty, the trace is broken, or duff solder. Iron is heating up now
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Interesting
First thought is an open circuit between R12 and pins 5 and 3. The break could be the resistor itself or anywhere to and from the resistor.
If pins 5 and 6 were floating it would do just this as the opamp input bias current 'charges' up C13. In other words it is as if the resistor isn't present.
Got it!!!
Thanks Mooly. Might have got there eventually but having some direction and reassurance did not go amiss and has saved me time and hair pulling. What a great community.
Solder not quite right either at C or R end of trace - now fixed with a quick bit of reheating
Another O2 builder off to enjoy the music!
Excellent.