The Objective2 (O2) Headphone Amp DIY Project

D2 and D6 are working.
The batteries seem to be fine.
When running on battery power, all of the voltages at U2 are positive, so are the voltages at both + and - terminals.
I will try swapping the comparator just to be sure it's not Q1/Q2; as I have no idea how to diagnose a comparator unit.

Remove the AC supply.
Measure the battery terminal with reference to Ground. What is your voltage?
Pin 4 of U2 should be about -8.4V running on battery.
 
Last edited:
Remove the AC supply.
Measure the battery terminal with reference to Ground. What is your voltage?
With reference to ground: 9.88V; -8.83V
I have also checked the voltages with the switch in the ON position, the results were: 1.03V 9.82V (the negative voltage seems to be gone)
Pin 4 is at 1.12V
Edit: Come to think of it, it might be a battery problem. I will feel very stupid if it ends up being just that. I've checked the voltages and they check out, however on load the voltage on one of the batteries approaches 0. To make matters worse, everything was just fine 2 weeks ago, that is the sole reason as to why I've not considered any of the batteries to be the culprit.
 
Last edited:
With reference to ground: 9.88V; -8.83V
I have also checked the voltages with the switch in the ON position, the results were: 1.03V 9.82V (the negative voltage seems to be gone)
Pin 4 is at 1.12V
Edit: Come to think of it, it might be a battery problem.

9.88V seems very high for a battery. Not a typo?;)

Seems like pin 4 of U2 is not supply properly.
Next step is trace to your switch.
Pin 2 and pin 5 of S1.

If still no negative supply, check D6 and R2.
Both terminal of D6 should have negative supply.
 
Last edited:
9.88V seems very high for a battery. Not a typo?;)

Seems like pin 4 of U2 is not supply properly.
Next step is trace to your switch.
Pin 2 and pin 5 of S1.

If still no negative supply, check D6 and R2.
Both terminal of D6 should have negative supply.
Not a typo :). (when talking of batteries, I mean NIMH ;) )
As I've mentioned, one of the batteries might be corrupt. It's voltage drops to 2.4V under a load.
 
Not a typo :). (when talking of batteries, I mean NIMH ;) )
As I've mentioned, one of the batteries might be corrupt. It's voltage drops to 2.4V under a load.

Possible damage cell and you may need to replace or it did not charge properly via R2. :D

You may remove both batteries and use AC for power. Wait till the replacements then put both batt back.
 
Possible damage cell and you may need to replace or it did not charge properly via R2. :D

You may remove both batteries and use AC for power. Wait till the replacements then put both batt back.
Thank you very much Jason for leading me to the answer.
Just to sooth my mind, I will take it to my uni so that I can test it with a bench supply. I won't be getting new batteries as I've never used it without the AC plug anyway. :eek:
 
Hey guys I just finished building my O2 and I'm having a slight problem. There's a small amount of channel imbalance on the left side so it's a tiny bit too loud, but only at certain volume levels on the pot. In addition I get seemingly random crackling that's isolated the the left channel. Any ideas on what could be wrong? I admittedly might not be grounding it properly but I don't know why this would cause it to be only on the left side (this is based on my essentially nonexistent knowledge of anything electrical). Thanks!
 
Administrator
Joined 2007
Paid Member
The imbalance that varies with volume setting sounds like an imbalance of the two sections of the volume control. That is quite common on many controls and the only fix is to fit a different one.

This details how to check the gain but from your description is sounds just like the pot at fault. Post #4020

http://www.diyaudio.com/forums/head...o2-headphone-amp-diy-project.html#post3988791

Crackling could be something else. There is some known problem of the close physical proximity of parts ((around the gain switch ???) that can cause them to touch and short out.
 
I lent a friend my DMM, but I rechecked the resistors' placement and they're all fine. I'll assume for now I just need a new pot.

In relation to the crackling, I don't really know how I could fix it if it's just something shorting out... Everything appears to be in place and I don't see what could be shorting. I guess I could post pics or something if it's necessary.

Although when I first turn it on and plug something in, I get a weird crackling/static with a little clicking, but after around 30 seconds it goes away, and if I unplug my source it's not present. Maybe a non-issue but I'd like to at least know what's causing it.
 
Administrator
Joined 2007
Paid Member
Hard to say what the crackling could be as there are many possibles.

You need to run the O2 in isolation with the inputs shorted and see if it crackles then. Does the crackle respond to physical movement ?

Also does the level of crackle vary with the volume control setting ?
 
I've been using it now with my PC instead of my phone (OPO), and most of the crackling seems to be gone. I have a feeling the cable I was using with my phone may have been causing most of it (I use the phone regularly and haven't had any issues with it). Although now, if I tap on the pot/knob at high volumes it will put out some static, maybe that's normal since tapping (fairly lightly) on the pot isn't something you do everyday, but I just want to make sure everything is in working order. Thanks for all the help with newbie questions!
 
I took a few snapshots of my o2 and noticed that some of the solder didn't flow to the other side. I'm guessing I should add solder to the top side? There is a few that need it, here is an example of one circled in red.

attachment.php
 

Attachments

  • a.jpg
    a.jpg
    114.8 KB · Views: 259
Last edited:
So I've been using the amp virtually all day yesterday and today with no issues. Tapping the pot doesn't cause any issues and any static/crackling is gone. I want to put it all on the faulty cable but I wouldn't have thought it could cause those issues. Is it possible the cable caused all of them? And I'm using an AC power supply Jason.