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The Objective2 (O2) Headphone Amp DIY Project
The Objective2 (O2) Headphone Amp DIY Project
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Old 31st December 2017, 07:07 AM   #5061
nenad88 is offline nenad88
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Tnx Mooly.
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Old 31st December 2017, 07:18 AM   #5062
Mooly is offline Mooly  United Kingdom
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The Objective2 (O2) Headphone Amp DIY Project
You're welcome
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Old 13th January 2018, 11:13 PM   #5063
Technical Petting is offline Technical Petting  United States
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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!
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Old 14th January 2018, 12:18 AM   #5064
adydula is offline adydula  United States
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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
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Old 14th January 2018, 01:17 AM   #5065
Technical Petting is offline Technical Petting  United States
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@Adydula That will work nicely, thank you! This is exactly what I was looking for, I guess I just never hit on the right keywords to search for! Thanks!
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Old 14th January 2018, 07:15 AM   #5066
raoultrifan is offline raoultrifan  Romania
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Quote:
Originally Posted by [...
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. [...]
Hello,

What planars are you using?

Thank you!
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Old 14th January 2018, 07:47 AM   #5067
Technical Petting is offline Technical Petting  United States
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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
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Old 14th January 2018, 01:28 PM   #5068
raoultrifan is offline raoultrifan  Romania
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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.

Last edited by raoultrifan; 14th January 2018 at 01:36 PM.
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Old 16th January 2018, 03:09 PM   #5069
sthcoaster is offline sthcoaster  New Zealand
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The Objective2 (O2) Headphone Amp DIY Project
Default 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
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Old 16th January 2018, 05:15 PM   #5070
Mooly is offline Mooly  United Kingdom
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The Objective2 (O2) Headphone Amp DIY Project
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.
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