The Objective2 (O2) Headphone Amp DIY Project

[cce121]

Hi guys,
I have post this problem on nwavguy's blog and waiting for approval,but i think it can benefit more people here as well.
I tested my newly built O2 with 2 cheap non-rechargeable zinc carbon batt(cause my ac adapter is still on their way here). It passed all the tests and ran without any problem for around 2hours with my laptop HO until I heard a weird 'oscillating noise' after I turn it on after turning it off for a minute. It sounded something like mobile phone RF interference but without the random loud-and-soft sound,just a low hum with fast repetitive tickling and it increased in intensity slowly(after 10seconds it is as lous as my music). I tried to 'reboot' it again but it came back after few seconds.
I thought of the rapidly-on-and-off issue but my resistors(r25 and r9 i think) are the revised(lowered) ones. I check their voltages as well,9.5V not low enough to shut down i think. What do you guys think might be the problem?
Anyway,I change the cheap batteries to tenergy rechargeables(not even fully charged). The problem disappeared and it can run for 5-6 hours.

[LeGoLarz]

Originally Posted by cce121

Hi guys,
I have post this problem on nwavguy's blog and waiting for approval,but i think it can benefit more people here as well.
I tested my newly built O2 with 2 cheap non-rechargeable zinc carbon batt(cause my ac adapter is still on their way here). It passed all the tests and ran without any problem for around 2hours with my laptop HO until I heard a weird 'oscillating noise' after I turn it on after turning it off for a minute. It sounded something like mobile phone RF interference but without the random loud-and-soft sound,just a low hum with fast repetitive tickling and it increased in intensity slowly(after 10seconds it is as lous as my music). I tried to 'reboot' it again but it came back after few seconds.
I thought of the rapidly-on-and-off issue but my resistors(r25 and r9 i think) are the revised(lowered) ones. I check their voltages as well,9.5V not low enough to shut down i think. What do you guys think might be the problem?
Anyway,I change the cheap batteries to tenergy rechargeables(not even fully charged). The problem disappeared and it can run for 5-6 hours.

Have you ground the enclosure to Pin 1 of the input jack J2?

[Splatem]

I tested a known good set of opamps and comparator, and I had the same symptoms, it still produced DC on the output.

So I shorted the source and drain pins on Q2, and this eliminated the DC voltage on the output jack. With Q2 source-gain shorted out, I am seeing good voltages and no DC on the output - pin 7 on U2 sits at 8.4V (instead of going -ve), pin 4 on U3/U4 is -11.7 V like it should be (instead of going +ve) It seems that the Q2 mosfet is faulty on both of these kits? I was careful handling them, weird to fry Q2 on two separate kits. It seemed that Q2 was working when U1/U3/U4 weren't connected, but apparently it couldn't handle any current running through it. Now I just need a couple more mosfets.

[LuisMCP]

Originally Posted by cce121

...until I heard a weird 'oscillating noise' after I turn it on after turning it off for a minute. It sounded something like mobile phone RF interference but without the random loud-and-soft sound,just a low hum with fast repetitive tickling and it increased in intensity slowly(after 10seconds it is as lous as my music). I tried to 'reboot' it again but it came back after few seconds...

I've got the same problem.

Fist time I turn ON the O2, I get the same oscillations.
When I plug AC and batteries were full, oscillations was out.

I have no idea what's the matter, it seems to me that low batteries goes to crazy oscillations.

[chickwhite]

Originally Posted by cce121

Hi guys,
I have post this problem on nwavguy's blog and waiting for approval,but i think it can benefit more people here as well.
I tested my newly built O2 with 2 cheap non-rechargeable zinc carbon batt(cause my ac adapter is still on their way here). It passed all the tests and ran without any problem for around 2hours with my laptop HO until I heard a weird 'oscillating noise' after I turn it on after turning it off for a minute. It sounded something like mobile phone RF interference but without the random loud-and-soft sound,just a low hum with fast repetitive tickling and it increased in intensity slowly(after 10seconds it is as lous as my music). I tried to 'reboot' it again but it came back after few seconds.
I thought of the rapidly-on-and-off issue but my resistors(r25 and r9 i think) are the revised(lowered) ones. I check their voltages as well,9.5V not low enough to shut down i think. What do you guys think might be the problem?
Anyway,I change the cheap batteries to tenergy rechargeables(not even fully charged). The problem disappeared and it can run for 5-6 hours.

When the voltage gets too low, the O2 will shut off. when it does, many batteries will pop back up to a high enough voltage for the O2 to turn back on. If the recovery and drain times on the batteries are fast enough, you get the oscillations. This can be true even with the revised resistor values. I would think this would especially true with carbon-zinc batteries. Their no-load voltage is generally much higher than their voltage under load. Another clue is that they worked for a few seconds after "rebooting" the O2. This allowed the batteries to recover enough to work for a few seconds.

If the 9.5V was the value under load, then I am wrong and they should have worked. I suspect that was the no-load value for the batteries. An oscilloscope would show the true picture.

[everlong]

Just did my second DIY project, the first was Cmoy and now the O2, fun I've done the "Initial DIY Testing" but only having batteries I couldn't do(correct me if im wrong) them all, alot of the test was with a wall adapter, but everything looks OK after the testing I could do.

Connected an ipod and tried with some cheap headphones, and it gave me music. But when I power the O2 on there is a big pitch sound for a ms, like alot of voltage is pushed to the phones, i reckon it shouldn't be like that. Is there a way to find the problem?

EDIT:

Could it be this?:

LOUD TURN ON TRANSIENT: A few have reported this problem and it’s so far been Q1 and/or Q2 are damaged. Check the U2 pin 1 and pin 7 voltages outlined in steps 13 and 17 later in this section. And repeat the battery removal test in the DIY Testing section. It’s likely Q1 and/or Q2 are either stuck on or no longer working in sync with each because one is damaged. It’s also possible C16, C21 and/or C1 are missing, not soldered correctly, or the wrong value. Before replacing Q1 or Q2 see Circuit Board Construction regarding static precautions and be extra careful with the new parts.

How do you do the test without having wall adapter? Alot of the testing is when you use the wall adapter without the batteries.

[Xaurot]

Originally Posted by Splatem

I successfully built a couple of O2 amps previously, but I am having trouble with two new ones I've just built. Both of the new boards are sending +11.08V of DC output through the headphone jack on both L and R channels. I have checked and double checked the resistances, and looked for any solder shorts with a magnifier. I can't see what I've done wrong, and hope someone can provide some tips to narrow down the problem. I am seeing the same behaviour on both new boards, which makes it seem unlikely that the op amps are all faulty or damaged.

I followed the troubleshooting guide on the nwavguy o2 page, and both boards pass all the steps up until I add the op amps in step 21. When U2 is installed (U1/U3/U4 are not installed) it all looks good, the power rails are +/- 11.7V, U2 pin 7 is +8.4V, U3/U4 pin 4 is -11.7V, and U3/U4 pin 8 is +11.7V. As soon as I install any one or all of the three op amps (U1, U3 or U4), the voltage on U2 pin 7 becomes -11V, and U3/U4 pin 4 becomes +8.7V, with U3/U4 pin 8 remaining +11.7V. Thanks in advance for any suggestions.

Hi Splatem, it seems I have the same issue with my first O2 - incorrect V- rail. Just like in your case when only U2 is in place, I am getting correct V+ (+11.7V) and V- (-11.7V). In my case only when I install all three U1, U3, U4 (with any combination of two op amps V+ and V- are still OK) the voltage changes to V+ (+11.7V) and V- (+1.5V). Both P2 output pins then get +11.2V DC. U2 pin 1/6= -12.4V, pin 2= -11.4V, pin 3/5= -11.7, pin 4= -14.2, pin 7= -10.7V and pin 8= 11.7V.

The strange is, that I do not get the wrong behavior all the time. Sometimes O2 works correctly - in this case both P2 output pins get 3.1-3.2mV and it even plays well (using my disposable headphones :-). After some time of play (can be even tens of minutes) is makes a loud click sound and I am back at V-= +1.5V. Sometimes it "starts" in OK state, sometimes in a wrong state. When it starts with wrong V-= +1.5V it even "heals" itself after a while. Maybe it is a function of temperature, I still did not figure out how to induce exactly right or wrong state.

When my O2 works all resistance and voltage measurements are according to troubleshooting guide except two differences: U2 pin 2 is always -8.8V instead of -8.4V and U2 pin 7 (O2 gate) is +8.4V in my case.

Inspiring by your post I shortly shorted Source and Drain of Q2 when getting an incorrect V-. This probably opened Q2 and "switched" O2 to a correct state (for while ....).

I am also wondering whether this behavior means only Q2 is damaged or whether there may me other issue. I also checked many times the soldering, even measured it with ohmmeter for shorts, checked all components, never displaced any of them during assembly and been extremely careful with both MOSFETs.

Unfortunately I already find out that to find Q2 replacement in my country is nearly impossible.

[cce121]

Originally Posted by chickwhite

When the voltage gets too low, the O2 will shut off. when it does, many batteries will pop back up to a high enough voltage for the O2 to turn back on. If the recovery and drain times on the batteries are fast enough, you get the oscillations. This can be true even with the revised resistor values. I would think this would especially true with carbon-zinc batteries. Their no-load voltage is generally much higher than their voltage under load. Another clue is that they worked for a few seconds after "rebooting" the O2. This allowed the batteries to recover enough to work for a few seconds.


If the 9.5V was the value under load, then I am wrong and they should have worked. I suspect that was the no-load value for the batteries. An oscilloscope would show the true picture.

9.5V is no load voltage. With load(connected to the amp) is aroudn 8.4-8.5 if I'm not mistaken. Is it near to the shut-down voltage? And yup,no problem with rechargeables(probably they don't 'recover' when not connected).

Let's hope this is the problem,I don't like to have some unknown issue down the road.

[jayce996]

Hi everyone,

i've completed the assembly of the O2 and during the testing found that there was just 0,7V near the first battery connection instead of 12V, after double checking i finally found that i've inverted Q1 & U5.
i tried to remove them to replace them but not able o it properly and finally had to break the pins and remove them completely.
now i have to buy one new Q1 & U5, but on Mouser i will cost 20€ for shipping and 1€ for parts.
do you know where i can buy them cheaper? or does anyone has some spare parts to send me to France?
Thank you in advance
(hoping that this is the only issue preventing me to make it working fully)

[Stealth3si]

Awesome I finally assembled the O2 and soldered the ground wire. The gains are also perfect. Thanks again!