I ask for that, because I will have dac section on positive voltage which will be discharging positive cells faster than negative.
Hey, this sounds like a quite nice idea. I'm currently thinking about a SMD-O2 version powered by li-ion cells with an integrated dac (probably the odac). Because i only want to drive iems, the 2V rms from the odac would be totally fine so i can left out the gain part to same more room. Is there any easier way for the low voltage protection part than nwavguy's solution? None of the li-ion protection chips i found so far, are suited for a bipolar design. Greetings
Look for Nokia li-ion or li-ion for apple devices (all nokia cells have protection). Own protection will be problematic, I think.
P.S O2 is not nessesary for iem's, sabre will control iem's without any gain
The idea to use cell phone batteries is not bad, but i was thinking of another way for realizing the dual-rail undervoltage protection not the protection of the battery itself. And you're right, the dac could probably drive iems but as far as i know, it has a quite high output impedance. Greetings
I have built and tested 4 O2+ODACs so far, they all tested the same way: With the USB cable unplugged, 3.5mm analog source unplugged, the O2 is dead silent even at 6.5x max volume, using Monoprice 8320. With the USB cable plugged in, the O2 is dead silent at 2.5x. At 6.5x noise can be heard once the volume is turned past 2-3 o'clock. (If using HD650, it's totally silent in every scenario.) So it's either the ODAC, or the USB cable. My USB cable has ferrite bead on the O2 end.
I spent an hour today, playing with the ODAC in a variety of different configurations: internal vs external, shielded vs unshielded, pc power vs USB hub - all had the same results. The ODAC, as a source to the O2, generates noise on the input while powered up. I was not able to find any significant correlation between the amplitude of the noise and any combination of the above listed configurations. With my 27 ohm, 115db sens. IEM's, at 2.5X gain and 100% volume, the noise is a bit above my threshold of hearing - approx 20-25 db. At 6.5X it seems about 2-4 times louder (makes sense) so I would guess it to be about 30-35 db.
I finally signed up on this site, just to say thanks to the designer (if he's still watching) for an excellent design. I finished building and testing it last night and it works excellently- my non-scientific tests switching between ipod classic headphone socket and o2 output via the dock connector find the sound much clearer in the latter, with a noticeably wider soundstage. Not that nasty "warm" (harmonically distorted) sound you get with a lot of equipment. I'm driving some slightly knackered HD570s though, which have a few odd resonances due to the plastic coming apart (!), so when I get some new HD650s soon I hope the result will be significantly better! Thanks nwavguy!
Two things occurred when I was building/testing that you might be interested in. The first is that before installing batteries, I spent some time listening to the o2 with a 12VAC power supply attached. Everything worked fine- no voltages surprising. Then suddenly and unexpectedly, the LED blew (and of course the output stopped working). I have no idea why this happened (especially since it had worked fine, had normal brightness etc for 2hrs or so).
I spent last night carefully checking voltages etc, and again everything was in order EXCEPT the regulated output of the 7912- oddly, this measured at -12.55V - which seemed even outwith the quoted widest tolerances (the 7812 was outputting +11.85V at this point). I expected this would be still OK though, since I understand the opamps here can work without issues from slightly unbalanced supply rails.
I continued with voltage checks over the next 15 mins or so. To my surprise, on remeasuring the 7912 output, it had dropped to a consistent 12.05V. So my question is, is this a normal behaviour as it warms up, or something else?
Hopefully I can post some pictures as I finish the case design- I've managed to squeeze some RCA inputs into the back, along with the power input socket- but it was not easy! I just always prefer to have power through the rear when on my desktop. The RCA inputs will allow me to connect my M-Audio device easily.
Two things occurred when I was building/testing that you might be interested in. The first is that before installing batteries, I spent some time listening to the o2 with a 12VAC power supply attached. Everything worked fine- no voltages surprising. Then suddenly and unexpectedly, the LED blew (and of course the output stopped working). I have no idea why this happened (especially since it had worked fine, had normal brightness etc for 2hrs or so).
I spent last night carefully checking voltages etc, and again everything was in order EXCEPT the regulated output of the 7912- oddly, this measured at -12.55V - which seemed even outwith the quoted widest tolerances (the 7812 was outputting +11.85V at this point). I expected this would be still OK though, since I understand the opamps here can work without issues from slightly unbalanced supply rails.
I continued with voltage checks over the next 15 mins or so. To my surprise, on remeasuring the 7912 output, it had dropped to a consistent 12.05V. So my question is, is this a normal behaviour as it warms up, or something else?
Hopefully I can post some pictures as I finish the case design- I've managed to squeeze some RCA inputs into the back, along with the power input socket- but it was not easy! I just always prefer to have power through the rear when on my desktop. The RCA inputs will allow me to connect my M-Audio device easily.
Hey Guy's
I'm new here I have been reading a lot lately and I have a problem with my O2.
A couple of months back I build my O2, while voltage testing all looked good. but after connecting the headphone I came to a problem: I seem to have the following problem: LOUD TURN ON TRANSIENT as described in the FAQ of NwAvGuy. But then backwards: when I turn off the device I have a loud turn off transient and turning on is normal.
So what did I do already: I checked all the voltages again. Q1 and Q2 seemed to be a bit off so I have replaced them with new parts. After this I did the voltage check again, now all seems fine. But after connecting headphones the loud turn off transient is still there...
I can't find nobody in this thread who has the same problem and google isn't much help either. Is there somebody with a bit more experience that pleas can help me?
I'm new here I have been reading a lot lately and I have a problem with my O2.
A couple of months back I build my O2, while voltage testing all looked good. but after connecting the headphone I came to a problem: I seem to have the following problem: LOUD TURN ON TRANSIENT as described in the FAQ of NwAvGuy. But then backwards: when I turn off the device I have a loud turn off transient and turning on is normal.
So what did I do already: I checked all the voltages again. Q1 and Q2 seemed to be a bit off so I have replaced them with new parts. After this I did the voltage check again, now all seems fine. But after connecting headphones the loud turn off transient is still there...
I can't find nobody in this thread who has the same problem and google isn't much help either. Is there somebody with a bit more experience that pleas can help me?
A few people have posted about that happening over the last year or so, some saying the LED actually exploded like it was hit with a huge amount of current.
I think there is a small design error in RocketScientist / NwAvGuy's power managment circuit. Pin 6, the inverting input on the second half of U2, gets pulled all the way up to the positive rail when the mosfets are off, which they are for the first second or so when the O2 is turned on to prevent thumps. But the input common mode voltage range of the NJM2903D comparator that he is using only goes to 1.5V below the positive rail. When that parameter is exceeded strange things can happen, like the other (non inverting) input which connects to the LED (pin 5) start pulling a lot of current and burn out the LED.
I don't have a solution for this one - would need a comparator with rail-to-rail inputs, open collector, and works with 24V - other than try a different NJM2903D chip. People don't report the problem very often, so apparently most of the NJM2903D chips can take the abuse.
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...more info, looks like I exceeded the 30 minute edit time. From this discussion thread at TI
Comparator LM2901AV: Common-mode input-voltage range: How to calculate / define - /etc... Amplifiers & Other Linear Forum - /etc... Amplifiers & Other Linear - TI E2E Community
it sounds like the TI/National version of the part will allow one input to go all the way to the positive rail as long as the other input (LED in this case) stays within the common mode input voltage range.
So another thing to try would be the TI version of the part, LM2903P, Mouser #595-LM2903P.
Comparator LM2901AV: Common-mode input-voltage range: How to calculate / define - /etc... Amplifiers & Other Linear Forum - /etc... Amplifiers & Other Linear - TI E2E Community
it sounds like the TI/National version of the part will allow one input to go all the way to the positive rail as long as the other input (LED in this case) stays within the common mode input voltage range.
So another thing to try would be the TI version of the part, LM2903P, Mouser #595-LM2903P.
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Still looking into the white noise I've been hearing with the ODAC and I have some interesting findings: the ODAC generates noise, even when disconnected from power. With the ODAC out of the case, isolated mechanically and electrically (except via the LOD, obviously), I can hear white noise on the amplified output when the USB cable is plugged into the ODAC and not plugged into the computer. Furthermore, if I plug the usb cable into the ODAC while listening, I can detect a short delay and a small thump before the noise starts, indicating that some circuitry on the ODAC board is being activated via the voltage present on the unplugged USB cable.
I've heard that the circuit and pcb layout for the ODAC have been maed public - can anyone direct me to it? I'd like to see if I can figure out what's going on here.
thanks!
I've heard that the circuit and pcb layout for the ODAC have been maed public - can anyone direct me to it? I'd like to see if I can figure out what's going on here.
thanks!
Right here:
http://www.yoyodyneconsulting.ca/downloads/General/ODAC/ODAC-release.pdf (opens PDF)
from George's site here
Yoyodyne Consulting/Audio Hardware/ODAC
and more info on NwAvGuy's blog here
http://nwavguy.blogspot.com/2012/04/odac-released.html
You either have a defective ODAC and/or your testing scenario is flawed in some way. Or maybe an incorrect interface to your O2.
My ODAC is dead quiet (measurable and audibly) with (powered or un-powered) USB cable attached, or without USB cable attached. Only in the case where you powered the ODAC but did not have serial data present do the outputs show some noise. (That configuration is not easily possible to set up.)
Cheers,
Dave.
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O2 Batteries
Would 9V 500mAh batteries be suitable for the O2?
e.g. 2 PCS 9V 9 Voltage 500mAh NI MH Rechargeable Battery Batteries 3 Years Warranty | eBay
Would 9V 500mAh batteries be suitable for the O2?
e.g. 2 PCS 9V 9 Voltage 500mAh NI MH Rechargeable Battery Batteries 3 Years Warranty | eBay
Does anyone have a step-by-step guide for modding an O2+ODAC to run off just the 5V USB input? I saw that someone had done it but the process wasn't particularly clear for an electronics newcomer. I don't really run my headphones at a high volume anyway so it'd be useful not to have to lug around the charging brick.
RS reported unused "no name" Chinese batteries exploding on the workbench. If you want, Tenergy also offers 9V in 500mAh ver. http://www.amazon.com/Combo-Tenergy-500mAh-Rechargeable-Batteries/product-reviews/B009MA8SAI
To reduce the chg. time you can reduce R1,R2 to 100R or 120R (same wattage) from the original 220R for 9V 500mAh batt.
Don't want to discourage your DIY skills but if you are new to electronics stick with the original RS design as 5V from USB involves SMPS ckts using SMD components.
Hi all, I recently built an O2 and have been enjoying it greatly. However, since I bumped up the gain on my phono preamp it's been distorting the sound pretty badly and seems to be overloaded. It sounds fine connected to a CD player.
Is there a good way to attenuate the signal so I can keep my phono preamp at 65DB of gain?
Is there a good way to attenuate the signal so I can keep my phono preamp at 65DB of gain?