The Objective2 (O2) Headphone Amp DIY Project

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fenderf4i

Member
Joined 2012
NiMH batteries lose a certain amount of charge when they sit unused for long periods of time. The low-discharge batteries are less susceptible to this.

I would say that if you're actually going to be using the amp, self-discharging won't be an issue and the extra battery life is more desirable in the 250mAH battery. If the amp is mostly going to sit in a drawer unused, then get the low-discharge ones.
 
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Xaurot

Member
Joined 2012
Splatem said:
@xaurot
I will be testing a replacement MOSFET for Q2 in about two weeks, and will let you know if it fixes the problem I am seeing.
Click to expand...

I replaced the Q2 MOSFET today (thank you for spare parts, @swalter :) ) and it did resolve the problem in my case. In addition to that, my O2 started to pass the low voltage battery shutdown test as well.

Finally listening to ODAC+O2 ... ... wow :D :D
 
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VJK

Member
Joined 2012
@Fender4i, thanks very much. After re-check I noticed that I had swapped U5 & U6 :( my bad. After correcting that the R5 still measures 245K but the amp works fine :) . I got stuck on another issue though, when connected to ODAC (without cutting the traces and keeping the functionality of the input jack), there is a screeching noise on the headphone :( . The ODAC alone seems to be working fine. But the O2, now with the ODAC wires connected exibits this funny behaviour ! rechecked for shorts and bridges, but none exists. Note my ODAC has the output jack and J1 and J2 are bridged.
 
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VJK

Member
Joined 2012
Update : I cut the ODAC wires to check the O2 independently again and it fails. There is a sudden screech in the headphones (the screech increases in volume when I reduce the volume control!!) . Looks like I blew up something :( need to check voltages again. Although everything is cool to touch.
 
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VJK

Member
Joined 2012
Funny thing happening with Voltage testing. The resistance test checks out fine. The voltage test with just U2 checks out fine as well. Voltages with just U1 on the board, checks out fine as well. With just U3 out, Voltage at D1 shows is 11.7 and at D5 is -12. I did plough through and put the U3 in and rechecked the voltages at D1 and D5 the result is a pass! both show 11.7 !! I further checked pin 4 and 8 on U4 and pin 4 was showing 0.77v and pin 8 showed 11.7 !! I rechecked to confirm. Now the fun part, I was trying to figure out what could have gone wrong, keeping the amp still powered on, could have been 40 seconds or so, I rechecked pins 4 and 8 and this time they show the correct values!... I repeated the experiment and observed the same behaviour.. pin 4 on U4 starts off at +0.77 or so and then in a minute after the amp is on, climbs down to -11.7 !! any idea on next steps ? I am stuck. I don't have an Oscilloscope, but have a good DMM.
 
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