The Objective2 (O2) Headphone Amp DIY Project

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Excellent :up:

We now do the last steps of testing:

Checking the audio circuitry.

1) As U1 is now fitted a basic check is to measure the voltage on pins 1 and 7, which are the opamp outputs. This should be near zero to within a few tens of millivolts.

2) Fit U3 and U4 and again measure the DC voltage on the output pins (1 and 7). Again this should be near zero.

That hopefully covers all the basic testing of your O2. If it passes these tests then its basically OK. Any audio only faults, distortion, hum, noise etc would need testing with an oscilloscope to track down. Built on the proper PCB there should be no such worries.
 
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All the DC conditions appear OK then. We would normally use other test equipment now to trace a fault but there are still ways of checking it.

And do you have no audio at all on either channel ?

To test it further you need to be happy in identifying and locating the chip pins because we would need to link things with a bit of wire.

Easy check first. With volume turned up a little, can you hear any clicks or buzzing if you touch this point with a metal screwdriver ? Be careful of your ears, don't put the headphones fully on your head.
 

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Hey guys, I recently have started making an o2 amp. While checking through all voltages on the board, using NwAvGuy's guide NwAvGuy: O2 Details I noticed that the DC offset at P2 measured 36 mV and 16 mV, which is a lot higher than it should be. According to NwAvGuy, it should be less than 8 mV. I measured the voltage at the op amps but again it was the same values and swapped around, they presented the same value, so I don't think it's the op amps.
I checked all the solder connections, reheated them, and the resistors R12 and R13 both measure 37k ohm.

I then checked pins 1 and 7 on U1 as according to this post http://www.diyaudio.com/forums/head...eadphone-amp-diy-project-378.html#post3806667 and the voltages came up fine.

I'm wondering what I should check at this point or fix, or whether 16 and 36 mV is fine?

I just plugged in some beater earphones and when turning on the amp, there is an immediate loud click. It seems to play music, but I got an odd issue where there would be repeated loud clicks. I haven't been able to reproduce it.
 
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Loud clicks when turning on/off are probably normal because the 02 lacks any kind of output muting to prevent this.

Repeated loud clicks in normal operation suggests a construction error, a dry somewhere or two component leads touching etc.

The DC offset at the output depends solely on the characteristics of the two 4556 opamps. The offset should always be low, but it will never be zero due to the small but finite bias current that flows out of the two inputs. The data sheet quotes 500nA worst case and so that would give 18.5mV worst case offset assuming R13/13 are 37k

Its more complicated though because two opamps share a common resistor and so the offset could conceivably be considerably higher as two 'lots' of bias current are flowing into each raising the voltage further.
 
Loud clicks when turning on/off are probably normal because the 02 lacks any kind of output muting to prevent this.

Repeated loud clicks in normal operation suggests a construction error, a dry somewhere or two component leads touching etc.

The DC offset at the output depends solely on the characteristics of the two 4556 opamps. The offset should always be low, but it will never be zero due to the small but finite bias current that flows out of the two inputs. The data sheet quotes 500nA worst case and so that would give 18.5mV worst case offset assuming R13/13 are 37k

Its more complicated though because two opamps share a common resistor and so the offset could conceivably be considerably higher as two 'lots' of bias current are flowing into each raising the voltage further.

I replaced every op amp, controller, and voltage regulator and I'm still getting the same problem, high DC offset and extremely loud pop when turning the O2 on.

Clearly, this isn't good because the pop is so loud I can hear it clearly when my earbuds are on the ground and I'm up here

What should I look at to fix it?
 
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First let me just say that I have never built or listened to an O2 and so I can't say what is normal or not with regard to how quiet it should be at switch on, however things that would affect this are:

The two rails not turning on at the same time. If the power switch S1 is connecting one rail before the other then its possible that the switched rails controlled by the FET's have a glitch at power on, and that would result in an audible noise.

You could try as an experiment setting switch S1 ON and then turning the O2 on via the wall switch to the AC adapter.

Do you still get the loud click ?

The DC offset you quoted earlier sounds with normal limits tbh. Nothing before the final opamps can cause offset because of the AC coupling provided by C13 and C14.

You can prove that by swapping the opamp for an FET type such as an OPA2134 (or even a cheap TL072 as a test). That would give a true zero volts offset and prove that the offset was a normal limitation of the design.

And if anyone who actually owns an O2 is reading all this then perhaps they could comment on how silent or otherwise the switch on/off behaviour actually is :) A comparison of switching on via the wall socker vs the O2's own power switch would be great.
 
First let me just say that I have never built or listened to an O2 and so I can't say what is normal or not with regard to how quiet it should be at switch on, however things that would affect this are:

The two rails not turning on at the same time. If the power switch S1 is connecting one rail before the other then its possible that the switched rails controlled by the FET's have a glitch at power on, and that would result in an audible noise.

You could try as an experiment setting switch S1 ON and then turning the O2 on via the wall switch to the AC adapter.

Do you still get the loud click ?

The DC offset you quoted earlier sounds with normal limits tbh. Nothing before the final opamps can cause offset because of the AC coupling provided by C13 and C14.

You can prove that by swapping the opamp for an FET type such as an OPA2134 (or even a cheap TL072 as a test). That would give a true zero volts offset and prove that the offset was a normal limitation of the design.

And if anyone who actually owns an O2 is reading all this then perhaps they could comment on how silent or otherwise the switch on/off behaviour actually is :) A comparison of switching on via the wall socker vs the O2's own power switch would be great.

FWIW, plugging in the AC adapter with no batteries in and the switch on also causes the same click. Also I shorted something with the multimeter probes and now it won't even turn on :mad:
 
Hi,

I am interested in building an O2 amp and have some questions, I read through the last 10 pages of the main thread and could not find answers, could you please help me?

1. are there any validated variation builds available?
2. for standard build, is the BOM list from NwAvGuy's website still current?
3. if i want to build a desktop AC version, do I still need to get the rechargeable batteries?
4. is it possible to build a desktop DC version? I have access to a lot of different DC switching power supplies, and this could save me some money
5. is JDS the best price to get PCB?
6. I have some ebay bucks that I need to use up, is this ebay listing a legitimate PCB? and is it the latest revision?
eBay

7. any update/mod by users that's popular?

thank you in advance!

M

Edit: updated eBay link
 
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Hi,

I am interested in building an O2 amp and have some questions, I read through the last 10 pages of the main thread and could not find answers, could you please help me?

1. are there any validated variation builds available?
2. for standard build, is the BOM list from NwAvGuy's website still current?
3. if i want to build a desktop AC version, do I still need to get the rechargeable batteries?
4. is it possible to build a desktop DC version? I have access to a lot of different DC switching power supplies, and this could save me some money
5. is JDS the best price to get PCB?
6. I have some ebay bucks that I need to use up, is this ebay listing a legitimate PCB? and is it the latest revision?
eBay

7. any update/mod by users that's popular?

thank you in advance!

M

Edit: updated eBay link

Hi, that looks like the latest PCB.

I had some of the bare boards made earlier in the year and I still have some available. A couple of amps have been build using my batch of boards and they are working fine.

I'm charging £6 GBP (approx $8 US) each which would include shipping to the US. If you're interested PM me.

Thanks
Chris
 
Hey all.

I have an O2 built from a PCB NwNavGuy sent me way back when, in the JDS enclosure. It's been working great for a few years. Recently, I built up a Raspberry Pi 3 with Allo Boss DAC running MoOde Audio. I just got an iFi iPower 5V for it too (nice improvement in sound quality from that!). Then I noticed that I have a problem... Ratty buzz or hum, like a ground loop.

Here's a funny thing -- That buzz only happens when no audio track is playing from the RPi. If I put MoOde Audio on pause or stop playback, no hum. (??)

To troubleshoot:

- I tried the RPi playing through my home stereo. No buzz/hum that way, so the problem seems to be in the O2 only.

- I tried the setup with the O2 running from battery power. Buzz still there with a file loaded up but MoOde Audio on pause.

- I tried the original Canakit 5VDC psu instead of the iPower. The hum/buzz is much reduced. It's still there, but barely noticeable. (??)

- Finally, I just noticed that if I put something under the line input plug to prop it up (puts leverage on the input jack) the hum/buzz goes away completely. This makes me suspect the input jack is not making good contact with the ground bus on the pcb. The thing is, I re-heated all the solder joints yesterday, to make sure of no cold joints. Nothing changed. Maybe I'll hit the solder joints again this evening, just to make sure.

Has anyone had problems with these Kycon STX-3120-5B jacks' contacts going bad, or something along those lines?

Can I replace the blue version originally specified in NwAvGuy's BOM with the black one linked above?

Thanks.
 
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1. are there any validated variation builds available?
2. for standard build, is the BOM list from NwAvGuy's website still current?
3. if i want to build a desktop AC version, do I still need to get the rechargeable batteries?
4. is it possible to build a desktop DC version? I have access to a lot of different DC switching power supplies, and this could save me some money
5. is JDS the best price to get PCB?
6. I have some ebay bucks that I need to use up, is this ebay listing a legitimate PCB? and is it the latest revision?
eBay

7. any update/mod by users that's popular?

Some answers:

1. In terms of a full set of dScope measurements like NwAvGuy did, I'm not aware of any.
2. Yep. The red LED is now obsolete. I sell them out on eBay and you can find equivalent LEDs at Mouser. The AC-to-AC transformer is no longer sold by Triad and Mouser, but Jameco has them. See #7 below..
3. No need for the batteries if you go all AC. You can leave off R1 and R2 also, the two battery charging resistors, and D2 & D6, the battery diode logic.
4. I would never recommend a switching supply in anything audio without a bunch of measurements to make sure they are not leaking switching noise. You are best off with the original type AC-to-AC transformer. The Jameco transformer is only something like $8 plus shipping.
5. JDS works. Mayflower probably also sells bare boards. Lol, and shameless plug, I sell them on eBay too from time to time. :p
6. There never were any revisions or versions of the O2 PC board. He released just the one set of Gerbers. Since then a problem cropped up where the original power jack was no longer made and all substitutes have leads that are too wide for one of the holes. So any O2 boards you find for sale commercially have the Gerbers modified to change the width of one power jack lead hole.
7. Mine. :D Out on my website I have a list of "modern O2 part upgrades":

O2 upgrades

Nothing radical in here, just some minor part improvements due to new parts that have become available since that O2 BOM was released back in 2011. The 9th item in there lists the part numbers at Jameco for the O2 AC-to-AC transformer (they have a couple of good choices).

And "O2 modifications" for special situations to solve certain problems.

O2 modifications

The modifications are more technical. Most folks won't need them or want to mess with them.

Also take a look at my list of "O2 build mistakes to avoid" for things to watch out for on your build:

O2 mistakes

Have fun DIYing!
 
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Scratching my head

I recently built my O2 and no sound came on but the light came on.
Eventually i ordered Q1 and Q2 again thinking i fried them.
So i soldered new ones on my board.
And I got stuck at the testing part with no batteries but with AC power and the O2 switched on. All the voltages are correct but
U2 Pin 7: 7V instead of 9.8
and at R24 I get -9.4 instead of -11.4 V.
Can Anyone help me out to find the problem and how to resolve it please?
Any advise is appreciated
 
I have an O2 built from a PCB NwNavGuy sent me way back when, in the JDS enclosure. It's been working great for a few years. Recently, I built up a Raspberry Pi 3 with Allo Boss DAC running MoOde Audio. I just got an iFi iPower 5V for it too (nice improvement in sound quality from that!). Then I noticed that I have a problem... Ratty buzz or hum, like a ground loop....

I think I've found the answer. From O2 Mistakes

"Don't forget the wire you have to solder onto the middle front (ground) terminal on the input jack and wrap around the nearest case cover screw. This single point ground puts the case at the same potential (voltage with respect to earth ground) as the PC board ground, which helps eliminate sources of noise and hum."

Ah ha! I don't think I have the case grounded to the pcb ground. I'll try that this evening, see if it makes a difference.

Thanks to agdr for compiling that O2 troubleshooting guide. Very helpful!
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