The Objective2 (O2) Headphone Amp DIY Project - Page 175 - diyAudio
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Headphone Systems Everything to do with Headphones

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Old 31st December 2011, 11:28 AM   #1741
MrSlim is offline MrSlim  Canada
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Quote:
Originally Posted by pancakeplease View Post
Sweet, I might give this a shot! I have a multimeter back when I was testing my motorcycle battery's alternator. Gotta dig it out of the garage somewhere.


I read through RocketScientist's articles and the Resource page but he doesn't go too much into detail. It's written for people who know what a schematic translates to on the PCB board lol. All I know so far is put wire through board, solder the back. Do it where the holes are. Nothing else.

I'm willing to give it a shot at least and if it doesn't work out or I get stuck, I'm sure I can post some pics and get some help.

Thanks for the feedback.
Here are a few tips to get you started:

Print out the Documents package from NwAVGuy's site. The board layout with the parts labelled on it helps a lot.

Use the BOM (Bill of Materials) spreadsheet to upload the parts list to Mouser directly. (or PM ,me for my copy of a Mouser Project that is already input and ready to order).

Print out the "Testing Procedure page".

When you get the parts order, Mark the part # (R1 D1, etc) on the part bag label. Then stuffing the board is like paint by number.. (Part by number?.. )

Start with the smallest/lowest profile parts first and work up to the larger ones.

Some parts need to be oriented the correct way, some don't care:

Resistors can go in either way. Any capacitors (the C# parts) without + or - markings on them can go in either way as well.

The big "can" capacitors need to go in the right way. The negative wire is marked on the cans. Pictures of Completed boards can also help to figure out orientation.

Diodes(D#) are marked with a thick line on one end. Match that end up with the thick line on the D locations.

The Q and U parts (MOSfets and Regulators) backs are marked with a thick line on the board. This is the heatsink or Flat side on them(look for exposed metal, although one of the MOSFets is all plastic, if you compare it to one of the Regulators(7812), you can tell which side is the "heatsink" side.

Orient the IC sockets (U1-U4) according to the little cutout on the board layout. Pin 1 on the board is marked by a white dot, and a square printed circuit pad. Match this with the pin with the dot beside it on the actual IC itself..

It is mentioned in NwAVGuy's build document, but it's worth mentioning here too: There is a "via" (a hole that is used to connect the circuit between sides of the board but not connected to anything else) that is between S2 and R21 that is very close to one of the "standoff legs" of S2. Put S2 in temporarily before soldering anything else and you will see that the via can touch(or is very close) one of these legs. Bend or remove that leg on S2 itself. It has caused a few people some grief.

Also, cut the little Tab off the front of VR1 before you install it.. (also mentioned in the Blog).
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Old 31st December 2011, 12:00 PM   #1742
regal is offline regal  United States
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edit: wrong thread sorry

Last edited by regal; 31st December 2011 at 12:11 PM.
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Old 1st January 2012, 02:02 AM   #1743
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I built my O2 and I have to say it sounds decent but I was not blown away. There's nothing about this amp's design that would significantly modify long held opinions of price vs performance. Subjectively I think it may push the envelope in a small way.
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Old 1st January 2012, 07:32 PM   #1744
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Originally Posted by imminentdomain View Post
I built my O2 and I have to say it sounds decent but I was not blown away. There's nothing about this amp's design that would significantly modify long held opinions of price vs performance. Subjectively I think it may push the envelope in a small way.
Could you expand on that? For example what do you mean by 'not blown away"? Was the audio quality no better than a mini3? Did you hear noise? Distortion at higher volume levels? What are you comparing it to, particularly in reference to price/performance?

What amps would you say are superiour and why? What do they do that the O2 doesn't?
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Old 2nd January 2012, 01:04 AM   #1745
pby is offline pby  United Kingdom
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Quote:
Originally Posted by imminentdomain View Post
I built my O2 and I have to say it sounds decent but I was not blown away. There's nothing about this amp's design that would significantly modify long held opinions of price vs performance. Subjectively I think it may push the envelope in a small way.
What did you find decent about the amp?
I also have to question if one should be "blown away" by an amp. In essence an amp should be as transparent as possible. We've all heard the saying "garbage in garbage out". Perhaps you were just hearing the source as it really is when nothing is added or taken away by the amp.
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Old 2nd January 2012, 02:02 AM   #1746
agdr is offline agdr  United States
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Originally Posted by pby View Post
We've all heard the saying "garbage in garbage out". Perhaps you were just hearing the source as it really is when nothing is added or taken away by the amp.
How true! When I built my first O2 amp I fed it initially with the headphone output on my Sony laptop. Yuk, no bass. Then I fed it via an optical link DAC from the same laptop and wonderful sounds ensued with plenty of bass. Nothing changed with the amp of course. Just two different sources doing their thing.
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Old 2nd January 2012, 04:04 AM   #1747
regal is offline regal  United States
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I built this amp all stock except MKT181 mouser caps (semi audiophile approved, I listen to Grados and frankly stock Grados weren't sounding very good, probably because to much damping, Joe tuned Grados to a hybrid with huge ugly distorion pattern (melos). Probably the drivers cancel some of the amps distortion in much the way the O2 uses heavy NFB to distort the incoming signal in order to cancel out the distortion on the output.

However, I tried this amp with a pair of Magnums which are Grados with a driver designed in 2011 instead of 2001. And the results were stunning, detail like I never imagined possible with these style phones.

I hate to say this but NwAV guy is simply adding huge amounts of distortion to cancel the non-linearity of the opamps, the NFB works and the output is low distortion. But because headphones are non-linear themselves headphone amp builders have been doing a similiar thing just including the headphone in the loop.

Its an interesting thing and certainly a very good amp, but purists should look at the distortion at pin 6 and 2 of each audio opamp and look at all the color being added to the input in order to get a low distortion output.

There is a whole lot of color added to the input of this amplifier, a whole lot.

And I am glad, it sounds good with fairly linear headphones.
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Old 2nd January 2012, 04:49 AM   #1748
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@regal, that's how it works. Why would you hate to say it? It's simple wave theory at work. It's why opamps, when most effectively implemented, provide the cleanest output you can get... generally speaking.
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Old 2nd January 2012, 05:07 AM   #1749
regal is offline regal  United States
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Originally Posted by ethanolson View Post
@regal, that's how it works. Why would you hate to say it? It's simple wave theory at work. It's why opamps, when most effectively implemented, provide the cleanest output you can get... generally speaking.
I know its just that NFB has had bad wrap, the implementation here works wonderful.

But those that say the O2 doesn't add distortion, have it backwards, it works by adding a ton of distortion to the input so it is cancelled by the output. An argument can be made that this cancelling is best left to the headphones or the ears starting with a more linear amplification.

But I like to hear all methods, and this O2 is a very very good one with the right headphones IMHO..
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Old 2nd January 2012, 02:13 PM   #1750
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When judging a headamp, I'm like the rest and speak in terms of net effect. From that perspective it's acceptable to claim vanishingly low distortion from the O2. I'm also quite surprised at how well the O2 works with low impedance loads. Many headphone amps have much more residual distortion into low impedance loads (<=32 Ohms).

Last edited by ethanolson; 2nd January 2012 at 02:17 PM.
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