Hello,
I starting to integrate an O2 amp output stage in a specific design for a desktop usage. As my design should have only digital input (one analog input should be handled by a DSP, far far away in the future...)
I was wondering as a very first thought if a PCM179x chip could have its I/V stage merged with the first stage of O2 amp and avoid usage of multipe op amp stages.
I will spend some times to study this possibility but if somebody have already put some time on it and conclude that is impossible and/or useless. Let me now
Regards!
I starting to integrate an O2 amp output stage in a specific design for a desktop usage. As my design should have only digital input (one analog input should be handled by a DSP, far far away in the future...)
I was wondering as a very first thought if a PCM179x chip could have its I/V stage merged with the first stage of O2 amp and avoid usage of multipe op amp stages.
I will spend some times to study this possibility but if somebody have already put some time on it and conclude that is impossible and/or useless. Let me now
Regards!
I don't see why that shouldn't work, given how DACs usually have an output buffer anyway that should have little trouble driving 10 kOhms. Leave out the NJM2068 (and feedback network) and connect the respective input to output pins, et voilà.
The amp will obviously only have unity gain then, but if your DAC outputs typical CD player level (~2 Vrms for 0 dBFS), that's a pretty decent amount of voltage to begin with. It might not drive an HE-6 or K240DF to ear-splitting levels, but most everything else should be fine. (Heck, even the 800 mV of a Clip+ only get tight with my least sensitive 600 ohm cans on very dynamic material.)
The amp will obviously only have unity gain then, but if your DAC outputs typical CD player level (~2 Vrms for 0 dBFS), that's a pretty decent amount of voltage to begin with. It might not drive an HE-6 or K240DF to ear-splitting levels, but most everything else should be fine. (Heck, even the 800 mV of a Clip+ only get tight with my least sensitive 600 ohm cans on very dynamic material.)
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If you are talking about LiPO (lithium polymer) battery, John from JDS Labs told me it wasn't compatible
That's why I modified my O²+OADC
Thanks. I knew Li-On would be no good but had never come across LiFePO4 before. No surprise it wouldn't be suitable though.
Swedish guy here so pardon my english spelling.
I have just builded my first o2 amb but i must miss something or i may be stupid.
i only got 4 pices for C6, C7, C10, C15, C17, C18.
Can someon please take a look at my board and see if there is some major wrong.
Robert
Had the same worries as my fellow swede and found this after a lot of pondering and searching:
"C6 & C7 – These have been the same 0.22 uF film caps used elsewhere in the O2 which have been working fine for hundreds of O2 builds so far. The 7812 regulator does not require any capacitor on the output and most datasheets for the 7912 also at least imply the capacitor is optional. But for the National LM7912, the data sheet says a 1 uF capacitor is required. I suspect this is just National being more conservative than their competitors, but just to be safe, you may want to use 1.0 uF ceramic MLC caps in this location such as the part used for C1 or, even better, the 5mm lead space version specified in the latest BOM spreadsheet."
Obviusly we both had found an old spreadsheet. The problem (for us not so skilled DIY:ers) with the newer spreadsheet, that I later found, is that it does not say where on the board the components go...
But on the other hand, a bit of fiddeling around is part of the fun!
//Ronny
One week with the o2 and i couldnt be more satisfied.
Using o2 with my hd600 and its so clear sound and also power when listning to music.
The feeling in the volume control feels so solid so fun just to start with very low volume and turn it up bit by bit.
Big thanks to headnhifi.com / Stefan.
Odac is my next order!
Using o2 with my hd600 and its so clear sound and also power when listning to music.
The feeling in the volume control feels so solid so fun just to start with very low volume and turn it up bit by bit.
Big thanks to headnhifi.com / Stefan.
Odac is my next order!
Hi all, I have just finished soldering my O2, and have passed all the initial tests until the first powered test with headphones. I have found the right channel works fine, however there is no sound through the left channel. Turning the volume creates some static in the left channel, but not the right. Also, removing the headphones and turning on the power makes a loud pop in the left channel but not the right.
I am about to go through the voltage checks under 'step by step dc voltages' (on nwavguys blog) but am worried that doing so may damage (or further damage) the components.
(I should mention here that I am a relative newcomer to diy stuff, but couldn't resist giving this a go)
Does anyone have any advice on what could be wrong? Is there somewhere I should start investigating first? Basically, it is just the left channel that is causing problems, whereas the right one is fine.
(I have already double checked that it is neither the headphones, audio source or any of the cables causing the issue)
Many thanks, hope people are having a Happy New Year.
I am about to go through the voltage checks under 'step by step dc voltages' (on nwavguys blog) but am worried that doing so may damage (or further damage) the components.
(I should mention here that I am a relative newcomer to diy stuff, but couldn't resist giving this a go)
Does anyone have any advice on what could be wrong? Is there somewhere I should start investigating first? Basically, it is just the left channel that is causing problems, whereas the right one is fine.
(I have already double checked that it is neither the headphones, audio source or any of the cables causing the issue)
Many thanks, hope people are having a Happy New Year.
Hi Mooly, thanks! Just tried that with power on, and power off with plug in.
In each case the reading was 0.0mv. Except U4, only with the power on, came to 0.1mv. (I tested a few times and got the same reading each time.)
Could this be what's causing the issue? I looked closely at the underside of the board and couldn't see any soldering issues...
I also measured the voltage from BT1 - to U4 and U3 pins 1 and 7. Would it help to know those values as well?
While off:
U3 1: -114mv
U3 7: -115.2mv
U4 1: -124.0mv
U4 7: -118.2mv
While on:
U3 1: 3.9mv
U3 7: 3.8mv
U4 1: 3.4mv
U4 7: 3.6mv
Hope I didn't manage to short anything out...
Those readings all seem OK. It's really only with power on that is of interest. With power off there will be stray and unequal residual charge giving unexpected readings.
OK... so lets check all the basic DC operating conditions (with the amp on).
1) Supplies first. Measuring from ground and on mains power you should have around plus 11.5 volts on pin 8 of all the opamps, and around minus 11.5 on pin 4.
2) Opamp U1 should also have zero volts on pins 1 and pin 7 (just like we measured on U4) The few millivolts you read are just a normal DC offset and nothing to worry over.
If it passes those tests then we have to trace the signal through the amp (I'm guessing you haven't a scope) but there are other ways and means. See what the checks around U1 show first.
Are the IC's in sockets ? If they are and if U1 measurements show nothing amiss then you can remove U1 and then link pin 1 to pin 3 and pin 5 to pin 7 to bypass that stage completely.
OK... so lets check all the basic DC operating conditions (with the amp on).
1) Supplies first. Measuring from ground and on mains power you should have around plus 11.5 volts on pin 8 of all the opamps, and around minus 11.5 on pin 4.
2) Opamp U1 should also have zero volts on pins 1 and pin 7 (just like we measured on U4) The few millivolts you read are just a normal DC offset and nothing to worry over.
If it passes those tests then we have to trace the signal through the amp (I'm guessing you haven't a scope) but there are other ways and means. See what the checks around U1 show first.
Are the IC's in sockets ? If they are and if U1 measurements show nothing amiss then you can remove U1 and then link pin 1 to pin 3 and pin 5 to pin 7 to bypass that stage completely.
Howdy! I've been reading the forums for a while. I mostly do software hacking so I'm a bit green at debugging hardware. =)
I have assembled the O2 kit and seeing a voltage that is too high on P2.
P2 pin 3 shows 30-45 mV [yuck]
P2 pin 4 shows 3.7 mV
I'm assuming 30-45mV for pin3 on P2 will damage IEMs?
Based on some of the posts here resoldered R12 and R13 which didn't help.
The measurements for those stayed:
R12 is 40.3k
R13 is 38-39k
When I unsoldering one of the legs of the R13 resistor I get a reading of 40.3k.
Reattaching the leg of R13 brings the impedance back to 38-39k.
Voltages on the op amps looks ok:
Pin 8 is 11.68V and Pin 4 is -11.68V on U1, U2, U3, U4
I removed U1, U3, and U4 and measured resistance and am seeing weird values for R25; R8, R4, R24
R25 is ~130k
R8 is ~140k (the value kept climbing slowly)
R4 155k
R24 160k
What should the next step be for troubleshooting?
Thanks in advance.
I have assembled the O2 kit and seeing a voltage that is too high on P2.
P2 pin 3 shows 30-45 mV [yuck]
P2 pin 4 shows 3.7 mV
I'm assuming 30-45mV for pin3 on P2 will damage IEMs?
Based on some of the posts here resoldered R12 and R13 which didn't help.
The measurements for those stayed:
R12 is 40.3k
R13 is 38-39k
When I unsoldering one of the legs of the R13 resistor I get a reading of 40.3k.
Reattaching the leg of R13 brings the impedance back to 38-39k.
Voltages on the op amps looks ok:
Pin 8 is 11.68V and Pin 4 is -11.68V on U1, U2, U3, U4
I removed U1, U3, and U4 and measured resistance and am seeing weird values for R25; R8, R4, R24
R25 is ~130k
R8 is ~140k (the value kept climbing slowly)
R4 155k
R24 160k
What should the next step be for troubleshooting?
Thanks in advance.
Firstly... you can not measure any resistors while they are in circuit... it doesn't work for several reasons.
The DC offset of 43 mv isn't that high in practice and is almost certainly caused by internal (and perfectly normal) imbalances within the IC's. Also the circuitry has no pretensions to DC accuracy. If you fitted suitable FET opamps for U3 and U4 that offset would drop to essentially zero... but then it wouldn't be an O2
If swap U3 and U4 the offset should follow the opamp i.e the offset will now be on the other channel.
The DC offset of 43 mv isn't that high in practice and is almost certainly caused by internal (and perfectly normal) imbalances within the IC's. Also the circuitry has no pretensions to DC accuracy. If you fitted suitable FET opamps for U3 and U4 that offset would drop to essentially zero... but then it wouldn't be an O2
If swap U3 and U4 the offset should follow the opamp i.e the offset will now be on the other channel.
I just looked at the data sheets for the NJM4556AD and the input bias offset current can be in the range of 50 to 500 nano amps (at 25C, higher temps will give higher offset). That means that this current flows out of the input pin and develops a volt drop across R12 (R13). Because the opamp is configured as a unity gain follower that voltage appears at the output.
Putting numbers in... and the worst case 500E-9 times 40.2K develops just over 20mv. But you have two in parallel and so that would give over 40mv offset (worst case). If the opamp were at the "typical" value then it would be 50E-9 * 40.2E3 which is 2mv. Again two in parallel so worst case just over 4mv.
Try swapping the opamps over first. Things such as contamination of the PCB/sockets/IC's could conceivably cause enough stray conduction to affect readings. You weren't eating a sticky bun while fitting the IC's were you
Putting numbers in... and the worst case 500E-9 times 40.2K develops just over 20mv. But you have two in parallel and so that would give over 40mv offset (worst case). If the opamp were at the "typical" value then it would be 50E-9 * 40.2E3 which is 2mv. Again two in parallel so worst case just over 4mv.
Try swapping the opamps over first. Things such as contamination of the PCB/sockets/IC's could conceivably cause enough stray conduction to affect readings. You weren't eating a sticky bun while fitting the IC's were you
Hello I am new here and new to generally doing diy audio/electronics projects, I just finished my O2 amp and went through the testing as shown in the o2 docs but it failed the "Low voltage shutdown" test as the voltage of either Pin 8 or 4 of U4 was over 1v (I can't remember which pin it was or the polarity of the voltage).
So I decided to leave it for a few weeks and and sort it out later as I was annoyed.
But here's the weird thing, when I did that test again a couple of months after this it passed according to the docs but the voltages on pins 4 and 8 of U4 are quite different and I am not sure if this is ok.
I have attached some images showing the measured voltages and where I measured from.
https://dl.dropboxusercontent.com/u/2000188/o2-amp-left-batt-removed.jpg
https://dl.dropboxusercontent.com/u/2000188/o2-amp-right-batt-removed.jpg
As you can see in the images I have used sockets for the gain resistors but have not socketed any resistors for them as I only need 1x gain for now.
I have also added sockets for the output resistors in case I ever wanted to alter the output impedance of the amp (unlikely).
Could not having any gain resistors socketed is messing up the readings on the testing?
For the testing I used this multimeter: http://www.amazon.co.uk/Compact-Digital-Multitester-With-Diode/dp/B000L0RINQ
So should I go ahead and replace Q1 and Q2 anyway considering the things mentioned above or is it ok? I haven't tried playing any music through it but I have a pair of cheap crappy headphones I can test it with but I am worried if it could blow up my player if something is wrong with the amp.
So I decided to leave it for a few weeks and and sort it out later as I was annoyed.
But here's the weird thing, when I did that test again a couple of months after this it passed according to the docs but the voltages on pins 4 and 8 of U4 are quite different and I am not sure if this is ok.
I have attached some images showing the measured voltages and where I measured from.
https://dl.dropboxusercontent.com/u/2000188/o2-amp-left-batt-removed.jpg
https://dl.dropboxusercontent.com/u/2000188/o2-amp-right-batt-removed.jpg
As you can see in the images I have used sockets for the gain resistors but have not socketed any resistors for them as I only need 1x gain for now.
I have also added sockets for the output resistors in case I ever wanted to alter the output impedance of the amp (unlikely).
Could not having any gain resistors socketed is messing up the readings on the testing?
For the testing I used this multimeter: http://www.amazon.co.uk/Compact-Digital-Multitester-With-Diode/dp/B000L0RINQ
So should I go ahead and replace Q1 and Q2 anyway considering the things mentioned above or is it ok? I haven't tried playing any music through it but I have a pair of cheap crappy headphones I can test it with but I am worried if it could blow up my player if something is wrong with the amp.
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Easy bit first. You won't blow anything up in the amp even if there is a problem somewhere. The basic check that all is OK is to make sure that the DC offset at the output for both channels is near zero. If that's OK then its a good sign all is well. If you have a high voltage present then there is a problem (so don't connect h/phones)
The power supply...
With the amp on you should have battery voltage (or 12 volts if on mains) on pins 4 and 8 of all the opamps. Positive on pin 8, negative on pin 4. When you switch off the voltage is removed but residual charge in caps will give small millivolt readings for hours after power off.
Assuming all is OK above then to test the transistors simply connect a link (shorting wire) from pin 2 of U2 to pin 4 of U2. In other words short out R9. That should shut the unit down and remove both the rails to all the other opamps apart from U2. If it does that then it should all be OK.
The power supply...
With the amp on you should have battery voltage (or 12 volts if on mains) on pins 4 and 8 of all the opamps. Positive on pin 8, negative on pin 4. When you switch off the voltage is removed but residual charge in caps will give small millivolt readings for hours after power off.
Assuming all is OK above then to test the transistors simply connect a link (shorting wire) from pin 2 of U2 to pin 4 of U2. In other words short out R9. That should shut the unit down and remove both the rails to all the other opamps apart from U2. If it does that then it should all be OK.
Ok with the amp powered up I get ~11.7v on pins 8 and 4 on U1 - U4
With pins 2 and 4 shorted on U2 I get 0.7v on pin 8 of U1, U3, U4 and 0.3v on pin 4 of U1, U3, U4.
Also the O2 docs specifically says to do that test I was talking about with one battery where it says "IMPORTANT! Low Voltage Shutdown" in the O2 details article.
With pins 2 and 4 shorted on U2 I get 0.7v on pin 8 of U1, U3, U4 and 0.3v on pin 4 of U1, U3, U4.
Also the O2 docs specifically says to do that test I was talking about with one battery where it says "IMPORTANT! Low Voltage Shutdown" in the O2 details article.
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That all sounds good. Shorting R9 changes the state of both comparators (U2) forcing pin 1 "high" and pin 7 "low". Removing batteries isn't the way I would test it tbh but its not my design so I won't argue on that
What you could do (and I would) is determine the trip works when the combined battery voltage drops below 14 volts. That's measured across both the batteries directly. 14 volts based on the fact that a 9 volt PP3 is typically 7 series connected 1.2 volt cells giving 8.4 volts per battery fully charged. Assuming 1 volt per cell as a lower limit then we get 14 volts for both in series. It is important not to discharge battery packs to far because the cells have slightly different capacities and the one that runs out first is then "reverse" charged by the remaining good ones... and that's damaging.
You can trim the cut off point by fitting a preset for R9 and then having set it correctly either leave it or replace with fixed resistors equal to the preset value setting.
Its the only way to do it
What you could do (and I would) is determine the trip works when the combined battery voltage drops below 14 volts. That's measured across both the batteries directly. 14 volts based on the fact that a 9 volt PP3 is typically 7 series connected 1.2 volt cells giving 8.4 volts per battery fully charged. Assuming 1 volt per cell as a lower limit then we get 14 volts for both in series. It is important not to discharge battery packs to far because the cells have slightly different capacities and the one that runs out first is then "reverse" charged by the remaining good ones... and that's damaging.
You can trim the cut off point by fitting a preset for R9 and then having set it correctly either leave it or replace with fixed resistors equal to the preset value setting.
Its the only way to do it