The Objective2 (O2) Headphone Amp DIY Project

[kpsthakur]

That transformer should be fine, in fact its way over the current requirements needed by the O2

15V 250mA would work?

 

[Davey]

15V 250mA would work?

Sure. I use a standard 12VAC 200mA wall-wart transformer on my O2 and it's perfectly adequate.

Dave.

 

[Mooly]

15V 250mA would work?

Yes.

 

[TungstenC]

If C8, C9 is switched with C17, C18 in the O2 will this effect the O2 in anyway?

Since was done in Massdrop's O2s to make space for the 1/4 headphone jack

C17,C18 mounted in C8,C9 on the under side of the board

(photo:warrantyvoider)

 

[Mooly]

I can't see it making any difference at all tbh.

 

[sonichedgehog36]

For anyone in search of the ever elusive Booster Board and/or an Objective2 with AGDR's upgrades, you can get them here either via Head-Fi or eBay:

Objective2 (O2) Extreme Edition Amplifier: Preassembled with V3.1 Booster Board! | eBay

[FS] Objective2 (O2) Extreme Edition Amplifier: Preassembled with V3.1 Booster Board! | Headphone Reviews and Discussion - Head-Fi.org

 

[Bluess]

Hi guys, my o2 makes a loud distorted noise when I plug in the power adapter and it just killed my iem. Anyone knows what could possibly gone wrong?

 

[Mooly]

Difficult to say for sure. The lack of any form of output muting is (as I have mentioned before) is the O2's biggest design failing.

Have the IEM failed open circuit ?

 

[Bluess]

Difficult to say for sure. The lack of any form of output muting is (as I have mentioned before) is the O2's biggest design failing.

Have the IEM failed open circuit ?

Yes, I only plug in the adapter while S1 is OFF.
Probably opamp failure? All of other test Nwavguy posted to debug all passed except the p2 test.
I measure the voltage at p2 with adapter plugged in, S1 OFF and it went like 10V, the other is 7V.
It should be between 0 to 8mV while S1 is OFF with adapter plugged in? I'm a bit confused at this part

 

[Mooly]

The output stage of the O2 is capacitor coupled by means of C13 and C14. This means that any DC offset can only be caused locally around the output stage and the most common reason would be a loss of a supply rail.

The opamps would be the very last items to suspect tbh. First step, check the supplies to the opamp on pins 8 and 4.

 

[Bluess]

The output stage of the O2 is capacitor coupled by means of C13 and C14. This means that any DC offset can only be caused locally around the output stage and the most common reason would be a loss of a supply rail.

The opamps would be the very last items to suspect tbh. First step, check the supplies to the opamp on pins 8 and 4.

I got -11.6V on pin 4 and 11.6V on pin 8 on the U3, U1, U4

 

[Mooly]

That sounds OK, and so something odd is going on.

Measure and record the voltages on all eight pins and lets see what shows up. This has to be something basic like cracked print or a floating ground. Measure on the pins themselves, not on the PCB.

 

[Bluess]

That sounds OK, and so something odd is going on.

Measure and record the voltages on all eight pins and lets see what shows up. This has to be something basic like cracked print or a floating ground. Measure on the pins themselves, not on the PCB.

With the battery on, measuring the opamps at pin 4 and 8 gives below 1V.

 

[Mooly]

You should be seeing plus supply on pin 8 and minus supply on pin 4. These voltages vary depending whether on battery or mains.

On mains it should always be around -/+11.5 volts (which you mention you have) and on battery it will be between -/+9 volts and -/+6.5 volts at which point the low battery cut off should remove the supply.

ALL the other opamp pins should be approximately at zero volts DC.

If you only have 1 volt supply running on battery then first check that the battery voltage is OK at a point before the FET switches.

It might be best to make sure all is well on mains first.

 

[Bluess]

So I made a new board today, with everything on, voltage at pin 8 is 11.6V, pin 4 is 1.4V, could this be the negative ic problem?

 

[Bluess]

D1 and D5 still measures correctly, only when i plug in an opamp the voltage goes wrong on pin 4

 

[Mooly]

Pin 4 should be negative (supply voltage) but you mentioned in post #5251 that you did in fact have -11.6 on pin 4.

So your new board seems to have a different issue.

 

[Bluess]

Pin 4 should be negative (supply voltage) but you mentioned in post #5251 that you did in fact have -11.6 on pin 4.

So your new board seems to have a different issue.

Thanks so much for the help, but after struggling to find the problem. I gave up and just rebuild a new one, and some how this pops up

 

[Mooly]

So you need to trace the negative rail from the battery/power supply through the FET switches and from there to pin 4 of the opamp.

The FET's can be linked out for testing (Drain to Source) and that will eliminate any possible problems with the comparator.

 

[Bluess]

So you need to trace the negative rail from the battery/power supply through the FET switches and from there to pin 4 of the opamp.

The FET's can be linked out for testing (Drain to Source) and that will eliminate any possible problems with the comparator.

Just as you thought, the negative channel FET is dead. I replaced it with a new one and it sings okay now. Thanks again 😃