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The Objective2 (O2) Headphone Amp DIY Project
The Objective2 (O2) Headphone Amp DIY Project
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Old 13th December 2011, 11:47 PM   #1431
Limp is offline Limp  Norway
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Quote:
Originally Posted by RocketScientist View Post
If you don't have an oscilloscope I can only make "blind" suggestions. Make sure all the parts around U2 are the correct values and correctly soldered. Getting any of those wrong, especially C1, C16, C21, R4, R24, and R8, could make the turn on transient worse by "unbalancing" the circuit. I'm also assuming you didn't modify the amp in any way (use parts not on the BOM, etc.)?

This may sound weird, but try pushing the power switch in (with no front panel or just the bare board) at an angle from both the power jack side and from the volume control side and see if that makes a significant difference in the pop. Pushing it from the side will slightly rotate the sliding portion inside the switch. If one side of your switch is making contact much sooner than the other side that might make the transient worse. If so, you might have a marginal power switch.

You can also try making C1 smaller--say 0.1 uF or 0.22 uF but if it's too small, the amp may not turn on at all with partially discharged batteries and the transient associated with low battery shutdown might be worse. In my testing (see the scope photos in the O2 Details article) 1 uf was optimal.

With my amps, using "average sensitivity" headphones the turn on "tick" isn't very loud or objectionable. With my HD650's it's even softer. With my balanced armature IEMs, which are some 20+ dB more sensitive, the tick is more of a "pop" as it's 20+ dB louder.

What headphones have the loud pop?
Thank you very much for your effort, I'll be checking things out as soon as I get the opportunity.

The headphones are Sennheiser HD25-1, which are rather middle of the road regarding sensitivity. I'm not too worried about the headphones, they are some tough buggers, but the pop is truly physically painful.
I am pretty sure this is more than what there is supposed to be, I imagine it would be nearly ear damaging with IEMs, that is if the armatures don't snuff it.
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Old 14th December 2011, 12:32 AM   #1432
jschristian44 is offline jschristian44
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Oh okay, thanks nezbleu that clears some things up for me, I really appreciate that.
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Old 14th December 2011, 05:22 AM   #1433
Turbon is offline Turbon  Sweden
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Quote:
Originally Posted by jschristian44 View Post
Two guides would be awesome, the more pictures the better as well. From what I can tell it's basically just soldering the parts on the board, but I know some parts need to connect to some hookup wires, etc that I am a little confused on. Thanks again!
The only hookupwire I'm aware of is a groundwire for the enclosure.

Brgds
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Old 14th December 2011, 10:04 AM   #1434
greenalien is offline greenalien
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@Limp - I also use Sennheiser HD25-1 headphones, and there's only a soft thump at turn-on, nothing loud at all, which would add to your suspicion that you have a problem with the amp.
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Old 14th December 2011, 03:22 PM   #1435
dixter is offline dixter  United States
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I'm going to build an amp for my Beyer DT880 (600 ohms) and was curious as to what would be the best gain for them...

Presently I have built one of the amps for my other phones and it works very well with those but I want to optimize the gain for 600 ohms on a different amp.

any suggestions for the gain resistors... source will be Ipod LOD.

Thanks in advance..
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Old 14th December 2011, 04:26 PM   #1436
maverickronin is offline maverickronin  United States
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Regarding the O2's on/off thump/click, I don't find it objectionable even with my ~32ohm and 119dB/mW Shure SE530s.
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Old 14th December 2011, 06:22 PM   #1437
dewasiuk is offline dewasiuk  Canada
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Did some audio testing a few days ago and the amp works great! Using ath-m50s, I couldn't even tell there was an amp because it was so transparent. I'm excited to test it with some more revealing headphones in the future. At low gain setting and when the pot is at a very low volume, I do notice channel imbalance even though I trimmed the bottom leg of the gain switch so it's not touching the via.
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Old 14th December 2011, 06:25 PM   #1438
Byxxi is offline Byxxi
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Quote:
Originally Posted by Limp View Post
The headphones are Sennheiser HD25-1, which are rather middle of the road regarding sensitivity. I'm not too worried about the headphones, they are some tough buggers, but the pop is truly physically painful.
I am pretty sure this is more than what there is supposed to be, I imagine it would be nearly ear damaging with IEMs, that is if the armatures don't snuff it.
Do you turn down the volume before you turn the amp on/off. If I remember correctly, it was advised to do so.
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Old 14th December 2011, 06:46 PM   #1439
dixter is offline dixter  United States
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Quote:
Originally Posted by dewasiuk View Post
Did some audio testing a few days ago and the amp works great! Using ath-m50s, I couldn't even tell there was an amp because it was so transparent. I'm excited to test it with some more revealing headphones in the future. At low gain setting and when the pot is at a very low volume, I do notice channel imbalance even though I trimmed the bottom leg of the gain switch so it's not touching the via.
I had the same problem on one of my amps... it was so bad that with the volume dial all the way down I was still getting some signal in the left side.

I put an omh meter on the volume pot and measured both sides.. they were way off... so I thought I had a bad pot... started to remove the solder with solder wick and just before I was going to use the solder sucker I decided to measure it one more time.. to my suprise the readings were now matching.
I know for a fact there wasn't any bridging going on as I looked at the back side of the board very carefully.. only thing I can think of is that I may have had some solder between the pot and the board, when I wick'd it maybe the solder
flowed better and fixed the issue...

I'd measure the resistance of the volume control all the way down and all the way up and compare the left/right numbers to see if they match...

Last edited by dixter; 14th December 2011 at 07:09 PM.
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Old 14th December 2011, 06:50 PM   #1440
MrSlim is offline MrSlim  Canada
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Quote:
Originally Posted by dixter View Post
I'm going to build an amp for my Beyer DT880 (600 ohms) and was curious as to what would be the best gain for them...

Presently I have built one of the amps for my other phones and it works very well with those but I want to optimize the gain for 600 ohms on a different amp.

any suggestions for the gain resistors... source will be Ipod LOD.

Thanks in advance..
Buy the sockets for the gain resistors and buy a full set of gain resistors and then you can try them all out.. It'll cost you a whole $3.05 to do that, and if you want to change them later, you don't have to worry about desoldering them... (look under the "Gain Resistor" heading in the BOM spreadsheet)
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