The Objective2 (O2) Headphone Amp DIY Project - Page 378 - diyAudio
Go Back   Home > Forums > Amplifiers > Headphone Systems

Headphone Systems Everything to do with Headphones

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 30th January 2014, 11:46 PM   #3771
diyAudio Member
 
Join Date: Jan 2014
Hey guys, I have a problem.

I had thought I had finished my board, but then when I plugged in my wall adapter, I noticed my U5 was getting ridiculously hot, and I took out the adapter and batteries.

I looked under the board, and it seems there might have been a short between the pins for the U5. Then, while trying to remove some of the sodder, I seem to have melted/scratched part of the pcb between the pins.

Is my U5 fried if it just gets ridiculously hot everytime I plug in the adapter? Is there any way to check if my other components are safe? And is my PCB still usable?
  Reply With Quote
Old 31st January 2014, 09:41 AM   #3772
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Your PCB is almost certainly fine. Just make that there is continuity between the relevant connections in the damaged area and link any damaged traces with wire.

U5 should run pretty much cold normally. If it gets hot it is either because its inserted incorrectly, it is not the 7912 version or there is a short on the output. Just because its got hot doesn't automatically mean its been damaged but I would replace it anyway.

With the units switch set to OFF you should have plus and minus 12 volts relative to ground on D1 and D5.
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 4th February 2014, 08:22 PM   #3773
Tokarin is offline Tokarin  Malaysia
diyAudio Member
 
Join Date: Feb 2014
Hey, new to the o2 scene.

Anyways i've finished assembling my unit, unfortunately i've encountered a few issues.

First issue was that the output would pulse, similar to heartbeats. I resoldered most connections and it seemed to solve the issue.

Next thing i know after 5 minutes of use, the amp just goes "Buuumb" and goes silent...

This is the second time it's happening, the first time i removed R4 and resoldered it.

Also i realised one thing, i tried to measure the voltage between the 2 batteries, i'm getting 48V instead of the 24v stated on NwAvGuy's post. and most values i get on my tests are two times what it is on the post.

Also somehow when i measure the resistance of R1 and R2, it seems to give me different values.

PS: I bought the Head-n-Hifi DIY package.
  Reply With Quote
Old 5th February 2014, 06:44 AM   #3774
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
There should be enough information in the last couple of months worth of postings on here to fix pretty much any fault on this amp.

Check the basics. Is the -/+ 12 volts correct on the two regulator outputs. I can't see how you can measure 48 volts DC anywhere (unless the AC input is incorrect and if that were so then things would be going pop)
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 5th February 2014, 08:33 AM   #3775
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
As faults and fault finding issues seem to crop up a lot on this amp I have put together some notes.

Fixing the O2 Headphone amp.

This guide attempts to set out a definite fault finding procedure and should cover most eventualities of non functional units. So just work through the steps measuring and checking as you go.

Checking the supplies...

The unit must first be put into a state that allows all critical voltages to be measured.

Preparation.
1) Remove ALL opamps and the comparator. Thats U1 through to U4
2) Make sure S1 is OFF.
3) Remove any batteries.

Measurement.
1) With your meter set to DC volts and with the BLACK meter lead firmly connected to ground (that is the common junction of C2, C3, C4 and C5 etc) measure the voltage on the striped end of D3. It should be higher than PLUS 15 volts and lower than PLUS 28 volts.

2) Keeping the BLACK lead on ground measure the DC voltage on the NON striped end of D4. It should be higher than MINUS 15 volts and lower than MINUS 28 volts.

If those conditions are OK now check the output of the two regulators. If the readings are incorrect you have a problem with either the AC input, a problem with the two rectifier diodes or a problem with incorrect or faulty regulators causing a short or partial short. Make sure that a 7812 is fitted for U5 and a 7912 for U6. Also make sure any electroylitics are fitted correctly with respect to polarity.


Checking the output of the regulators.
The BLACK meter lead is kept on ground unless otherwise stated.

1) Measure the DC voltage on the striped end of D1. It should be 11.5 to 12 volts approximately.

2) Measure the DC voltage on the NON striped end of D5. It should be MINUS 11.5to 12 volts DC approximately.

If you have incorrect readings for the plus and minus 12 volts yet have correct input voltages to the regulators, then the problem can only be either the regulators themselves or incorrectly fitted D1 and D5.

Checking the voltage comparator and switched output rails.

1) Disconnect the AC supply and turn ON S1. Wait for 1 minute to allow the caps to discharge and then fit just U2 in its socket making sure it is the right way around.

2) Apply AC power and ensuring S1 is still ON measure the DC voltages at pins 8 and pins 4 of the remaining empty IC sockets. There should be PLUS 11.5 TO

12 volts DC on pin 8 and MINUS 11.5 to 12 volts on pin 4.

If the voltages are low or missing then there is a problem around U2 and the FET rail switches. If they are correct then you should now check the comparator operation (next step below)

Checking the comparator operation and the FET switches. For this test FIT U1 in its socket. This allows a small current to be drawn and allows accurate checking of the rail switching circuitry.

The comparator acts as a low battery cut-off (to protect the batteries from over discharge) and should be checked as follows.

1) Rough test of comparator... Apply a SHORT across R9. This will force the comparators to change state and the DC rails on pins 8 and pins 4 of the opamps (U1 only fitted) should fall to zero.

2) Accurate test of comparator. The comparators change state when the voltage on pin 2 of U2 falls BELOW the voltage across the LED. In other words if there is 2.00 volts on the LED, the rails will cut off when pin 2 falls below 2.00 volts. Replacing R9 with a 47k multiturn preset allows different LED's to used and the trip point to be adjusted accurately by monitoring the combined battery voltage and setting the preset to cut off when the combined battery voltage falls to say to 14 volts (two 8.2 volt batteries containing 7 cells each and discharging to 1 volt per cell).

Checking the audio circuitry.

1) As U1 is now fitted a basic check is to measure the voltage on pins 1 and 7, 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.


I hope that covers most aspects of working and testing this great little amp.
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 6th February 2014, 07:01 AM   #3776
Leolabs is offline Leolabs  Malaysia
diyAudio Member
 
Leolabs's Avatar
 
Join Date: Dec 2004
Location: Bukit Mertajam
Send a message via MSN to Leolabs
Quote:
Originally Posted by Tokarin View Post
Hey, new to the o2 scene.

Anyways i've finished assembling my unit, unfortunately i've encountered a few issues.

First issue was that the output would pulse, similar to heartbeats. I resoldered most connections and it seemed to solve the issue.

Next thing i know after 5 minutes of use, the amp just goes "Buuumb" and goes silent...

This is the second time it's happening, the first time i removed R4 and resoldered it.

Also i realised one thing, i tried to measure the voltage between the 2 batteries, i'm getting 48V instead of the 24v stated on NwAvGuy's post. and most values i get on my tests are two times what it is on the post.

Also somehow when i measure the resistance of R1 and R2, it seems to give me different values.

PS: I bought the Head-n-Hifi DIY package.
Hi,

I'm from Penang and have build more than a dozen of O2.You can reach me and work it out for this issue.

Seems to me it's related to regulator failure.
  Reply With Quote
Old 17th February 2014, 04:35 AM   #3777
diyAudio Member
 
Join Date: Oct 2011
Location: Maryland
Default starting to test

I just started/restarted
finishing populating the board (it has been sitting for a while).

I measured R20 - it measures 10K
R14 measures the correct 100-300

So I guess I have a "short?" or messed up U1


Thanks for any suggestions.
  Reply With Quote
Old 17th February 2014, 06:17 AM   #3778
diyAudio Member
 
Join Date: Oct 2011
Location: Maryland
just saw from Mooly - post #3652

About maybe measuring resistance "in circuit" - questionable anyway...

So I will continue for now... with voltage tests, etc.

Thanks
  Reply With Quote
Old 17th February 2014, 09:19 PM   #3779
diyAudio Member
 
Join Date: Oct 2011
Location: Maryland
Yeah - it works!

Sounds great!
(Listening to Dan Folgelberg... )

Will definitely try out several other source and content.

added the ODAC - still need to find a cable and try that.

Thank you NwAvGuy, JDSLabs, Mooly and all you guys here!
  Reply With Quote
Old 18th February 2014, 06:15 AM   #3780
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
That's great, thanks for the update
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Headphone amp project grahamfocal Headphone Systems 7 21st June 2011 05:28 PM
My latest project - DAC + headphone amp gmarsh Digital Line Level 105 13th December 2010 02:31 PM
My headphone amp project trifidmaster Headphone Systems 2 22nd December 2008 03:52 PM
Mini Ipod headphone amp DIY project Nordic Headphone Systems 14 11th March 2007 02:35 PM
Need help for a battery headphone amp project dismalonyx Headphone Systems 1 15th April 2004 11:22 PM


New To Site? Need Help?

All times are GMT. The time now is 04:03 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2