I have been looking for what i need to build this amp for days, but i always end up looping around in NwAvGuy's blog getting nowhere. I also suddenly found this forum but shimming through 402 pages to find a specific partlist or building schematic is just too much for me right now. So i'l try to ask here if someone could just give me what i need, please? :3
I need a place to buy the o2 amp PCB with oDAC.
I aslo need the BOM spreadsheet that i can add to mouser for the parts needed to build on the above PCB.
And the schematics to build it.
I would be really happy if someone could help me or direct me to some place where i actually do find what im looking for! Thanks in advance!
I need a place to buy the o2 amp PCB with oDAC.
I aslo need the BOM spreadsheet that i can add to mouser for the parts needed to build on the above PCB.
And the schematics to build it.
I would be really happy if someone could help me or direct me to some place where i actually do find what im looking for! Thanks in advance!
Great idea for testing the gain stage! For testing I only have a Fluke 87. Sorry but no oscilloscope.
First off, using the color bands on the resistors (and this site: Invalid Request) I have the following:
R7: 274 Ohm
R14: 10K Ohms
R16: 1.5K Ohms
R17: ? Looks like gold-black-black-brown-gold which isn't on the chart.
R21: Same as 17
Since I couldn't really tell what those colors were, I unsoldered one end of R21 from the board and measured it with only one end in the board at 1.004 K ohms. Looks like the resistors are correct.
It seems like the input jack connects the two channels to ground when nothing is plugged in so I plugged in a cable with no source connected to the other end.
Measurements are with everything plugged in except batteries and power switch on. I'm using the negative BT1 terminal for ground.
battery at pin 1 of P1: 1.603 volts
With gain switch out (2.5x gain)
U1 pin7: 3.908 volts (This is 0.1 volts lower than the expected 4.0 volts)
With gain switch in (6.5x gain)
U1 pin7: 10.15 volts (This is 0.27 volts lower than the expected 10.4 volts)
The slightly lower output voltages probably aren't the issue. Seems the op amp is working!
Off topic question on amp theory: If the op amp (U1 here) does the voltage increase, what does the second stage do? Just provide the current necessary to maintain that voltage when a load is applied?
Did you mean C14 in your last post? Before linking out anything I measured 3.9 volts on one side of C14 with the volume at max and nothing on either side of C13.
I linked the two pin of C14. With the gain at 2.5x and the volume at max I measured 3.9 volts on P2 pin 3. This quickly decreased as I turned the volume down. That seems to be expected result.
If we are seeing amplified voltage at the output then does that mean the gain is working but the voltage drops a lot as soon as a load (headphones) is applied? That's the only thing I can think of.
Just to make sure I wasn't crazy, I tried using the amp again. Same result. At max amp volume, the amp is quieter than plugging straight into my cell phone.
First off, using the color bands on the resistors (and this site: Invalid Request) I have the following:
R7: 274 Ohm
R14: 10K Ohms
R16: 1.5K Ohms
R17: ? Looks like gold-black-black-brown-gold which isn't on the chart.
R21: Same as 17
Since I couldn't really tell what those colors were, I unsoldered one end of R21 from the board and measured it with only one end in the board at 1.004 K ohms. Looks like the resistors are correct.
It seems like the input jack connects the two channels to ground when nothing is plugged in so I plugged in a cable with no source connected to the other end.
Measurements are with everything plugged in except batteries and power switch on. I'm using the negative BT1 terminal for ground.
battery at pin 1 of P1: 1.603 volts
With gain switch out (2.5x gain)
U1 pin7: 3.908 volts (This is 0.1 volts lower than the expected 4.0 volts)
With gain switch in (6.5x gain)
U1 pin7: 10.15 volts (This is 0.27 volts lower than the expected 10.4 volts)
The slightly lower output voltages probably aren't the issue. Seems the op amp is working!
Off topic question on amp theory: If the op amp (U1 here) does the voltage increase, what does the second stage do? Just provide the current necessary to maintain that voltage when a load is applied?
Did you mean C14 in your last post? Before linking out anything I measured 3.9 volts on one side of C14 with the volume at max and nothing on either side of C13.
I linked the two pin of C14. With the gain at 2.5x and the volume at max I measured 3.9 volts on P2 pin 3. This quickly decreased as I turned the volume down. That seems to be expected result.
If we are seeing amplified voltage at the output then does that mean the gain is working but the voltage drops a lot as soon as a load (headphones) is applied? That's the only thing I can think of.
Just to make sure I wasn't crazy, I tried using the amp again. Same result. At max amp volume, the amp is quieter than plugging straight into my cell phone.
Excellent stuff 
I tried to keep it as simple as possible when thinking out a way to test the gain stage but as you mention the output being fractionally lower than expected I'll explain why.
If you look at the circuit you will see that R7 and R14 actually form a divider although the effect is miniscule. We'll put the numbers in though. You have 1.603 volts being fed to the series chain of R7 and R14. If you calculate the current in that chain (ohms law) you will see it is I= 1.603/(10,000 + 274) which is 0.156 milliamps. The voltage across the 10k (which is the true opamp input voltage) is therefore 0.000156 * 10,000 giving 1.56 volts. That is the actual figure the opamp sees to amplify. Multiply that by 2.5 and you have your 3.9 volts. Same for the 6.5 gain setting.
I did mean C14 Yes, the output opamp is configured as a buffer (voltage gain of 1) and so whatever is at the wiper of the pot is what appears at the headphone output. C14 provides both safety from any DC appearing at the input (stops it passing to the output) and also makes the volume control quieter as it is turned (less prone to crackle) as any DC current flowing in the wiper is blocked. The final opamp stages are just in parallel to boost the current output. With that arrangement you shouldn't have any problems driving all normal headphones. If the opamps started to limit current wise then you would hear that as severe distortion... that won't be happening.
So that all proves beyond doubt that the gain stages are correct.
When you say the cell phone is louder, do you mean the 02 isn't loud enough when used with the cell phone as an input source ? You can get more gain from the 02 by reducing the value of R19. You could probably go as low as 82 ohms if you really wanted to. The 02 is really designed for line level inputs from audio components such as CD players and so on, phones with there somewhat "unknown" output arrangements can be a bit hit and miss depending how the line out signal is derived.
I tried to keep it as simple as possible when thinking out a way to test the gain stage but as you mention the output being fractionally lower than expected I'll explain why.
If you look at the circuit you will see that R7 and R14 actually form a divider although the effect is miniscule. We'll put the numbers in though. You have 1.603 volts being fed to the series chain of R7 and R14. If you calculate the current in that chain (ohms law) you will see it is I= 1.603/(10,000 + 274) which is 0.156 milliamps. The voltage across the 10k (which is the true opamp input voltage) is therefore 0.000156 * 10,000 giving 1.56 volts. That is the actual figure the opamp sees to amplify. Multiply that by 2.5 and you have your 3.9 volts. Same for the 6.5 gain setting.
I did mean C14
Yes, the output opamp is configured as a buffer (voltage gain of 1) and so whatever is at the wiper of the pot is what appears at the headphone output. C14 provides both safety from any DC appearing at the input (stops it passing to the output) and also makes the volume control quieter as it is turned (less prone to crackle) as any DC current flowing in the wiper is blocked. The final opamp stages are just in parallel to boost the current output. With that arrangement you shouldn't have any problems driving all normal headphones. If the opamps started to limit current wise then you would hear that as severe distortion... that won't be happening.So that all proves beyond doubt that the gain stages are correct.
When you say the cell phone is louder, do you mean the 02 isn't loud enough when used with the cell phone as an input source ? You can get more gain from the 02 by reducing the value of R19. You could probably go as low as 82 ohms if you really wanted to. The 02 is really designed for line level inputs from audio components such as CD players and so on, phones with there somewhat "unknown" output arrangements can be a bit hit and miss depending how the line out signal is derived.
You could buy a full kit at HeadnHifi, it includes everything you need to build the amp: (parts, PCB, enclosure, panels, AC adapter, 9v rechargeables, etc.) and he also sells the odac board. Afaik the kit was also significantly cheaper than from JDS.
Like it's already been said, you find tge documentation PDF at NwAvGuy's blog.
When I saw the phone is louder I mean that with the cell phone's volume at 50% and the headphones plugged into the cell phone, music is louder than if I keep the cell phone at 50% volume, connect the cell phone to the O2, plug headphones into O2, and turn the O2's volume all the way up. Basically the O2 at max volume is reducing the source's output voltage instead of amplifying it. This doesn't change if I use my laptop as a source instead of the cell phone. I was just using the cell phone to make 100% sure I wasn't somehow overpowering the gain stage. I just tried hooking the amp up to the pre-amp outputs on my receiver and had to go to 6.5x gain and max volume to reach a normal listening level and I listen at a lower volume than most.
So the gain stages seem to be working for DC power but not for music. The only thing I can think of is that something prevents it from increasing AC voltage. You mentioned that if the amp was current limited that I would hear really bad distortion which isn't the case.
So the gain stages seem to be working for DC power but not for music. The only thing I can think of is that something prevents it from increasing AC voltage. You mentioned that if the amp was current limited that I would hear really bad distortion which isn't the case.
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Well we have proved the gain stages are OK and that proof will hold for AC as well as DC... but I can tell you will take some convincing
Do you have an ordinary CD player with standard RCA outputs ? If so, is the 02 providing decent levels when used with this player ?
One other thought... are your headphones the more normal low impedance type or are they specified as 600 ohm ?
We can test the AC gain (it will spot on though) as long as your meter is capable of resolving low level AC signals reasonably accurately. We do that by playing a test tone (that you would burn to a CDRW) and measuring the levels going in and coming out of the O2.
Do you have an ordinary CD player with standard RCA outputs ? If so, is the 02 providing decent levels when used with this player ?
One other thought... are your headphones the more normal low impedance type or are they specified as 600 ohm ?
We can test the AC gain (it will spot on though) as long as your meter is capable of resolving low level AC signals reasonably accurately. We do that by playing a test tone (that you would burn to a CDRW) and measuring the levels going in and coming out of the O2.
o2 amp troubleshooting(one side much louder...)
Hey!
I just finished building my o2, but I have a little problem. It sounds really good, but one side of my headphones is much louder than the other side ...
I did some research, but I found nothing.
I REALLY need help
and THANK YOU for your help
Isaac
Hey!
I just finished building my o2, but I have a little problem. It sounds really good, but one side of my headphones is much louder than the other side ...
I did some research, but I found nothing.
I REALLY need help
and THANK YOU for your help
Isaac
I believe there is some problem with close proximity of components around the gain selector ? and the possibility of one part shorting to another. Have a look back from here at the posts in this thread.
I've seen it mentioned but never having built or seen an 02 I can't say for sure exactly what that specific issue is.
Circuit wise, the obvious area is around SW2 and the feedback return resistors R17/19 and R21/23. Make sure that only the appropriate resistor is actually in circuit and that they are not touching the switch or each other.
I've seen it mentioned but never having built or seen an 02 I can't say for sure exactly what that specific issue is.
Circuit wise, the obvious area is around SW2 and the feedback return resistors R17/19 and R21/23. Make sure that only the appropriate resistor is actually in circuit and that they are not touching the switch or each other.
For headphones I'm using Denon AH-D1001. They are 32 ohms and have a sensitivity of 103 dB/mW. They are normally very easy to drive and I can't image a normal operating amp needing max volume to reach normal listening levels with these headphones.
To measure the problem I'm seeing with AC I connected the RCA pre amp outputs of my receiver to the O2's input jack, plugged in my headphones, set the gain to 2.5x, turn the amp on, and set the O2's volume to max. I then used foobar to play a 800 Hz test tone very loud.
I set the Fluke to measure AC volts and connected the negative cable to BT1's negative side.
I measure the following:
P1 pin1: 359.9 mV
U1 pin 5: 350.0 mV Small drop expected as you mentioned before
U1 pin 7: 882 mV This falls in the 875 to 900 range I would expect. Seems U1 is okay with AC
U4 pin 5: 873 mV Small drop here but seems normal. Drop from R13?
U4 pin 7: 873 mV U4 seems to be outputting okay. AC isn't dropping under load.
P2 pin 3: 64.9 mV This is clearly a problem. What happened to about 800 mVs?
I measured the low output on both channels. So measuring further I found 873 mV on one side of R10, R11, R15, and R18 but only 65 mV on the other side of those three resistors. How a resistor could reduce AC voltage that much is the question here.
According the spreadsheet I have, these resistors are supposed to be 1 ohm. Pulling one end of R15 out of the board and measuring the resistance gets me 818 ohms! That explains the grey-red-black-back-brown color bands.
Looks like Mouser put the wrong parts in the bag. I didn't measure each resistor before soldering it but I did match the manufacturer part number on each bag with the BOM.
Looks like I now have four new resistors to order!
To measure the problem I'm seeing with AC I connected the RCA pre amp outputs of my receiver to the O2's input jack, plugged in my headphones, set the gain to 2.5x, turn the amp on, and set the O2's volume to max. I then used foobar to play a 800 Hz test tone very loud.
I set the Fluke to measure AC volts and connected the negative cable to BT1's negative side.
I measure the following:
P1 pin1: 359.9 mV
U1 pin 5: 350.0 mV Small drop expected as you mentioned before
U1 pin 7: 882 mV This falls in the 875 to 900 range I would expect. Seems U1 is okay with AC
U4 pin 5: 873 mV Small drop here but seems normal. Drop from R13?
U4 pin 7: 873 mV U4 seems to be outputting okay. AC isn't dropping under load.
P2 pin 3: 64.9 mV This is clearly a problem. What happened to about 800 mVs?
I measured the low output on both channels. So measuring further I found 873 mV on one side of R10, R11, R15, and R18 but only 65 mV on the other side of those three resistors. How a resistor could reduce AC voltage that much is the question here.
According the spreadsheet I have, these resistors are supposed to be 1 ohm. Pulling one end of R15 out of the board and measuring the resistance gets me 818 ohms! That explains the grey-red-black-back-brown color bands.
Looks like Mouser put the wrong parts in the bag. I didn't measure each resistor before soldering it but I did match the manufacturer part number on each bag with the BOM.
Looks like I now have four new resistors to order!
At least you found the problem If you want and while waiting for the parts, you can link out one resistor in each pair and see how it all sounds. It will be vastly different because 800ohms (400 with the pair) in series with the 'phones would be altering the damping and altering the response too.
The new 1 Ohm resisters came in yesterday and I got them installed. What a huge difference! Amp is now working great. It gets plenty loud with no need for max volume or 6.5x gain.
I figured out why I didn't notice the 820 ohm resisters when I followed the initial resistance testing steps on the blog. My ohm meter was reporting the resistance as 0.819 k ohms. I didn't have the best lighting and failed to notice the 'k'. Since "0.819 ohms" was within .2 of 1 ohms I thought that I was good and moved on. Lesson learned!
I figured out why I didn't notice the 820 ohm resisters when I followed the initial resistance testing steps on the blog. My ohm meter was reporting the resistance as 0.819 k ohms. I didn't have the best lighting and failed to notice the 'k'. Since "0.819 ohms" was within .2 of 1 ohms I thought that I was good and moved on. Lesson learned!
Ok so, I purchased the diy kit from jdslabs about a week ago. I constructed the objective o2 and once I got ready to test the amp there was no sound initially. So, after a friend took a look and told me I had some cold solder joints I went back and reworked those. I was then able to get sound from only one channel and that being the right. Now, I no longer have control over the volume with the potentiometer. Then, I though well let me touch up on some of the solder joint again. Upon doing so, I was able to get sound from the left channel and not the right and I was also able to have control of the volume via potentiometer. However, these issues still occur, I no longer have control over the volume and I can get no sound out of wither channel. Help and/or suggestions would be much appreciated.
Jayb21 have you gone through the checkout process? Are your DC voltages correct?
It sounds like you had no sound, then got sound in one channel, then the other channel, then no sound again, all by redoing your solder joints. If that is right, then one would have to assume that the problem is still with your solder joints, but until you can give some concrete measured results from the preliminary checkout process (measuring resistance and DC voltages) nobody can really help you.
Did the kit not come with the checkout procedures?
It sounds like you had no sound, then got sound in one channel, then the other channel, then no sound again, all by redoing your solder joints. If that is right, then one would have to assume that the problem is still with your solder joints, but until you can give some concrete measured results from the preliminary checkout process (measuring resistance and DC voltages) nobody can really help you.
Did the kit not come with the checkout procedures?
JDS labs in the US JDS Labs - Objective2 Printed Circuit Board / O2 PCB
Head'n'HiFi in Switzerland O2 Headphone Amplifier PCB
Note that both have a problem corrected. After NwAvGuy designed the O2 headamp Mouser stopped carrying the power jack that fit properly. Both these companies have boards that are adjusted to fit the available power jacks.