Hi, new guy here with a dead O2.
My few years old O2 (desktop edition with 6.3mm and RCA outputs) from Head 'n' Hifi kicked the bucket. It's just the vanilla O2 but with these modifications.
Problem description:
When using headphones the left channel has much lower volume compared to the right channel and there is a small amount of crackling noise that can be heard from the left channel.
Also, there is a moderately loud *THUMP* sound in the left channel whenever I switch ON the power.
The same issues are present even in the RCA outputs which are connected to Behringer B3031A speakers.
Right channel works perfectly with headphones and speakers.
I'm planning to fix this thing myself so any kind of advice is welcome. I already disassembled the O2 and I'm trying to find the faulty components at the moment.
I have low experience with soldering/etc. but I'm not afraid to try fix something that is already broken.
My few years old O2 (desktop edition with 6.3mm and RCA outputs) from Head 'n' Hifi kicked the bucket. It's just the vanilla O2 but with these modifications.
Problem description:
When using headphones the left channel has much lower volume compared to the right channel and there is a small amount of crackling noise that can be heard from the left channel.
Also, there is a moderately loud *THUMP* sound in the left channel whenever I switch ON the power.
The same issues are present even in the RCA outputs which are connected to Behringer B3031A speakers.
Right channel works perfectly with headphones and speakers.
I'm planning to fix this thing myself so any kind of advice is welcome. I already disassembled the O2 and I'm trying to find the faulty components at the moment.
I have low experience with soldering/etc. but I'm not afraid to try fix something that is already broken.
Your modifications link doesn't work.
Start by replacing the gain opamp.
Sent from my SCH-I545 using Tapatalk
@Tiihokatti
You will need basic tools like DMM, pliers to remove DIP8 ic, Soldering iron, elcheapo h/p.
Remove batteries & use only AC adapter.Perform all steps by unplugging AC adapter pin to O2. Do not remove/insert anything when its powered ON. Beware of accidental shorting by DMM probes.
1 Swap JRC 4556 opamps & see if the problem shifts to other ch. Hopefully they must be socket mounted.
2 If the problem doesn't shift you might need to change gain stage opamp by anything in hand like 5532, TL072, 4558, etc.
You will need basic tools like DMM, pliers to remove DIP8 ic, Soldering iron, elcheapo h/p.
Remove batteries & use only AC adapter.Perform all steps by unplugging AC adapter pin to O2. Do not remove/insert anything when its powered ON. Beware of accidental shorting by DMM probes.
1 Swap JRC 4556 opamps & see if the problem shifts to other ch. Hopefully they must be socket mounted.
2 If the problem doesn't shift you might need to change gain stage opamp by anything in hand like 5532, TL072, 4558, etc.
Last edited:
Is the desktop version using the same circuit as the 'standard' 02 ?
If its different then I would have to see the circuit to advise, if its the same then follow the guide linked to at the bottom of post #1 of this thread.
I can visit Partco next week so I'll stock up on opamps 'n' stuff.
5532, TL072, 4558, pliers, etc.
As for DMM and soldering iron, I'll go for the super-budget route: Wattnik ZD-99 and Biltema 15133
I'll first try switching the 4556 opamps to see if the problem is in there. I think there were some old steel pliers at my mothers place as she used to be a sewer.
5532, TL072, 4558, pliers, etc.
As for DMM and soldering iron, I'll go for the super-budget route: Wattnik ZD-99 and Biltema 15133
I'll first try switching the 4556 opamps to see if the problem is in there. I think there were some old steel pliers at my mothers place as she used to be a sewer.
Like I said, it's just the vanilla O2 with some extra wires (if the previous link didn't work: dropbox).
The link works, but is it the same circuit and component references as the standard battery model ? I've never built or seen an O2, I just work from the circuit diagram to advise... that's why I need to know in order to help 
I suspect your problem is more likely something shorting or touching rather than an opamp failure. A few voltage measurements would identify the problem.
I suspect your problem is more likely something shorting or touching rather than an opamp failure. A few voltage measurements would identify the problem.
It's the standard PCB and parts. Stamps on the PCB and all. The pics on the PDF has them tooThe link works, but is it the same circuit and component references as the standard battery model ? I've never built or seen an O2, I just work from the circuit diagram to advise... that's why I need to know in order to help
I suspect your problem is more likely something shorting or touching rather than an opamp failure. A few voltage measurements would identify the problem.
Just received all of my parts for the O2 build. It looks like a fun and rewarding project. Many thanks to RS (where ever he is) for the design and free implementation. I am quite familiar with power supply and amplifier circuits, but that comparator circuit has me stumped. I wonder if someone could explain how it works. My main question would be how does the voltage reference not fall in proportion to the total voltage, thus rendering a match impossible. I am missing something very simple, because obviously it works. Thanks.
Post #3775 explains a little on how it works (and how to test it).
http://www.diyaudio.com/forums/head...o2-headphone-amp-diy-project.html#post3806667
The voltage reference is an LED and the voltage across this diode is used as the reference for the comparators. The whole point is that the reference voltage doesn't change with supply voltage, and by not doing so it allows the variable battery supply to be compared to the always known and fixed reference point. Leds generate a fairly stable voltage even if the current through them varies, very much like a zener diode.
http://www.diyaudio.com/forums/head...o2-headphone-amp-diy-project.html#post3806667
The voltage reference is an LED and the voltage across this diode is used as the reference for the comparators. The whole point is that the reference voltage doesn't change with supply voltage, and by not doing so it allows the variable battery supply to be compared to the always known and fixed reference point. Leds generate a fairly stable voltage even if the current through them varies, very much like a zener diode.
I got mine from JLS Labs. They are in the US, but the price is only $5.99
I've read NwAvguy's section "The gain resistors", and some other stuff. I am still not sure I understand it correctly.
I think I want a 1x and 2.5x amp. What I want out of the amp is good sound out of my pc/laptop, on ~50 Ohms headphones (old Senn HD-455). Currently, I miss oomph, which cannot be attained by cranking the volume up. I think what is missing is the abilitly to repoduce low volume and high volume simultaneoulsy. I think that is called "dynamic sound".
I'd also like solderless installation the gain resistors for the 3.5 if possible, so I need these: 10-0518-10 Aries Electronics | Mouser
My questions:
1) When NwAvguy and other talks about "channels", they mean left and right channels, right?
2) So, R16, R17 and R19 affect left and R22, R21 and R23 affect right channel, (or the other way around)? This means R17 and R21 are a pair, should always have the same value, as do R19 and R23 (and R16 and R22)?
3) A 1x and 2.5x O2 would be:
R16 and R22 at 1.k Ohm
R17 and R21 empty
R19 and R23 at 1k Ohm ?
I think I want a 1x and 2.5x amp. What I want out of the amp is good sound out of my pc/laptop, on ~50 Ohms headphones (old Senn HD-455). Currently, I miss oomph, which cannot be attained by cranking the volume up. I think what is missing is the abilitly to repoduce low volume and high volume simultaneoulsy. I think that is called "dynamic sound".
I'd also like solderless installation the gain resistors for the 3.5 if possible, so I need these: 10-0518-10 Aries Electronics | Mouser
My questions:
1) When NwAvguy and other talks about "channels", they mean left and right channels, right?
2) So, R16, R17 and R19 affect left and R22, R21 and R23 affect right channel, (or the other way around)? This means R17 and R21 are a pair, should always have the same value, as do R19 and R23 (and R16 and R22)?
3) A 1x and 2.5x O2 would be:
R16 and R22 at 1.k Ohm
R17 and R21 empty
R19 and R23 at 1k Ohm ?
Last edited:
The O2 already has a gain of '2.5' with R16 and R17 at 1k5 and 1k respectively.
Gain = (R16/R17) + 1
Leaving R19 open gives a gain of 1 overall.
Yes, channels usually refer to left and right and yes, you are correct with the component references and how they relate to each channel. If you can get enough volume then you probably don't need more gain. If it sounds 'flat' and lifeless then its possible that what you were using before did not have a flat response like the O2... in other words you're missing tone controls or an equaliser.
Gain = (R16/R17) + 1
Leaving R19 open gives a gain of 1 overall.
Yes, channels usually refer to left and right and yes, you are correct with the component references and how they relate to each channel. If you can get enough volume then you probably don't need more gain. If it sounds 'flat' and lifeless then its possible that what you were using before did not have a flat response like the O2... in other words you're missing tone controls or an equaliser.
Thanks Mooly. I am looking to build a O2 from scratch, I am not currently using one, I'm just looking at the PCB .
I was used to a decent soundcard in a pc (the Terratec DMX Xfire 1024), and when paired with an amp sound was absolutely terrific to my ears. Regrettably, no more drivers for that card came out after XP, and the 70's amp that I had caught on fire one day. I have not been able to find satisfactory replacement for either, and I have tried quite a bit. So I thought I'd give the O2 a try, realizing this will only be a partial solution. I may get a DAC, but I'm hoping the O2 will breathe some life into a regular PC output too.
It is difficult to explain what I miss in sound in other setups, but I think it is the difference between loud and soft volume levels, especially if a lot is going on at the same time.
. I was used to a decent soundcard in a pc (the Terratec DMX Xfire 1024), and when paired with an amp sound was absolutely terrific to my ears. Regrettably, no more drivers for that card came out after XP, and the 70's amp that I had caught on fire one day. I have not been able to find satisfactory replacement for either, and I have tried quite a bit. So I thought I'd give the O2 a try, realizing this will only be a partial solution. I may get a DAC, but I'm hoping the O2 will breathe some life into a regular PC output too.
It is difficult to explain what I miss in sound in other setups, but I think it is the difference between loud and soft volume levels, especially if a lot is going on at the same time.
Last edited: