hi everyone,
I've got an O2/ODAC that I've built from the JDS Labs kit. I'm very happy with it, except for one thing: it seems to be very susceptible to static. At times, it feels like I'm listening to vinyl because of all the pops and crackles.
I'm pretty sure the noise is static: a few weeks ago, I could hear someone approach from several meters away just because the static noise increased rapidly, until he discharged when he tapped me on the shoulder, causing a loud bang in my headphones.
I've ruled out the source material (MP3), that sounds clean on another playback chain.
I use the USB input of the ODAC, connected to a laptop. Headphones are Monster Jamz in-ears. Power supply for the O2 is the standard 2-prong wall wart.
Is this common for the O2/ODAC? Or should I go looking for a fault or soldering error?
While writing this I realized there's one fault-finding step I haven't taken yet: I can bypass the ODAC and use the line input, then I can see if the problem lies in the O2 or in the ODAC.
Other than that, I've no idea how to proceed diagnosing this...
I've got an O2/ODAC that I've built from the JDS Labs kit. I'm very happy with it, except for one thing: it seems to be very susceptible to static. At times, it feels like I'm listening to vinyl because of all the pops and crackles.
I'm pretty sure the noise is static: a few weeks ago, I could hear someone approach from several meters away just because the static noise increased rapidly, until he discharged when he tapped me on the shoulder, causing a loud bang in my headphones.
I've ruled out the source material (MP3), that sounds clean on another playback chain.
I use the USB input of the ODAC, connected to a laptop. Headphones are Monster Jamz in-ears. Power supply for the O2 is the standard 2-prong wall wart.
Is this common for the O2/ODAC? Or should I go looking for a fault or soldering error?
While writing this I realized there's one fault-finding step I haven't taken yet: I can bypass the ODAC and use the line input, then I can see if the problem lies in the O2 or in the ODAC.
Other than that, I've no idea how to proceed diagnosing this...
I've never come across or even heard of anything like that before. You need to be sure the crackling isn't coincidental to physical movement of the unit, that would be a more likely explanation.
Beyond that and I think you would have to try the set up at another location, just to try and get a handle on what may be going on.
Beyond that and I think you would have to try the set up at another location, just to try and get a handle on what may be going on.
The 02 needs a transformer with a single secondary of between 12 and 20 volts. 15 volts is ideal. The current rating needs to be around 200ma or higher which gives a 3VA minimum rating.
There should be dozens of suitable parts available. How you mount it depends on transformer and whether it is a PCB mount type or one with flying leads. You would run the two windings in parallel to get the full current rating.
44196 MYRRA, Isolation Transformer, EI 38 x 13.6, 3.2 VA, 1 x 230V, 15V, 213 mA, PCB MOUNTED 44xxx Series | Farnell element14
MCFM32/15 MULTICOMP, Toroidal Transformer, 24mm x 43mm, 3.2 VA, 2 x 15V, 107 mA, Panel | Farnell element14
If you meant a transformer already in an enclosure then you will have to search local suppliers for something suitable and that meets the above requirements.
There should be dozens of suitable parts available. How you mount it depends on transformer and whether it is a PCB mount type or one with flying leads. You would run the two windings in parallel to get the full current rating.
44196 MYRRA, Isolation Transformer, EI 38 x 13.6, 3.2 VA, 1 x 230V, 15V, 213 mA, PCB MOUNTED 44xxx Series | Farnell element14
MCFM32/15 MULTICOMP, Toroidal Transformer, 24mm x 43mm, 3.2 VA, 2 x 15V, 107 mA, Panel | Farnell element14
If you meant a transformer already in an enclosure then you will have to search local suppliers for something suitable and that meets the above requirements.
They were just examples really. For the USA you need to choose one with primaries suitable for your local mains voltage which I assume is 120 vac 60Hz. These examples were 230vac 50Hz so no, they would not be suitable. You need to look at your local supplier but they should all have similar suitable parts.
If you are in the US consider two wall transformers at Jameco (Jameco Electronics - Electronic Components Distributor) that would work great with the O2, now that Triad at Mouser doesn't make AC-AC transformers anymore.
There is the 14Vac 500mA, #171408 for $8.95
ACU140050C6951: Jameco Reliapro : AC to AC Wall Adapter Transformer 14 Volt @ 500mA Black Straight 2.1mm Female Plug : Power Supplies & Wall Adapters
and the 13.5Vac 1A, #2202765, for $3.95
240000000043: Arndt : 13.5 Volt AC-to-AC Wall Adapter Transformer : Power Supplies & Wall Adapters
I bought 5 of each of those a few weeks ago and tested them on the O2. Either one is better than the 12Vac in the O2 BOM since it gives an extra 1.5 to 2Vdc across the O2's vregs, which is badly needed. A very heavy load on the O2 - anymore more than 80mArms or so on both channels at once, can easily cause the vregs to go into dropout with just a 12Vac transformer.
And as I've written before, some history, NwAvGuy did know about that (PM chat at the time). His view was it wouldn't matter since the PSRR of the op-amps is good enough that ripple on the supply rails would be rejected. My view: don't go there.
Best to give it the extra couple of volts so the vregs don't drop out.The problem at the time was that Triad only made 12vac and 16vac, nothing in between. 16vac is too much, it can cause the un-heatsinked vregs to get hot as a firecracker under heavy loads. With these 2 Jameco transformers you have the best of both worlds. No dropout and (more) controlled vreg dissipation.
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I've made some progress toward identifying the problem.
- the noise is not static
- when I use the analogue jack input as the source, O2 output is clean
- when I use the ODAC as the source, ODAC output is dirty
- when I use the analogue jack input as the source and I leave the ODAC connected to my laptop, I get noise in the O2 output (though not as loud as when using the ODAC as the source).
- when I pause playback, the noise stops.
I'll have to check with another laptop...
Just curious, do you have the rev B (new version) of the ODAC? In the JDS photo here
Releasing ODAC RevB | JDS Labs Blog
The "rev B" text is just above that unpopulated 3.5mm jack in the lower left corner. The original ODAC had a design problem where certain PC's USB ports could cause the ODAC voltage regulator to go into oscillation (very low ESR ceramic caps used on the PC USB power line).
John should be shipping Rev B with everything by now, but maybe you had a kit sitting on your shelf for awhile.
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Interesting! First report I've heard so far about noise via the USB with ODAC rev B.
I think your input jack is not shorting to ground (on that channel) without the miniplug inserted.
If your amplifier is working correctly with the miniplug inserted, then I'm 99% sure that's the problem.
I wouldn't worry about this myself, but you could replace the input jack if you like.
Dave.
If your amplifier is working correctly with the miniplug inserted, then I'm 99% sure that's the problem.
I wouldn't worry about this myself, but you could replace the input jack if you like.
Dave.
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Hi,
I just built an O2 headphone amp (kit purchased from headnhifi), it works great!
I am a software guy with some very old electronics notions, and I would be grateful for a bit of help from someone more knowledgeable, about the following problem.
I have a small preamp box, mostly used to switch sources and adjust the volume. Its active component is a small ne5532-based board (bought on aliexpress around 10$), powered symetrically by a 2x15V toroid transformer, and I would like to combine the O2 and the preamp in the same box, which would then be a quite useful preamp with headphone output (duh).
However, when I power the O2 from one of the transformer's windings and connect the O2 input in parallel with the preamp's, I have a small hum in the O2 output.
It's very low (I can only really hear it at a volume level which would be very bad for my ears), but I know it's there, and this is very distressing psychologically
Both preamp and O2 are hum-free when alone.
The preamp board has a 47K Ohm pot on the output. I am thinking of just getting rid of the preamp board and connecting the 47K pot in parallel with the O2's 10K one to provide a preamp output with independant volume control.
So the O2 first stage would see something like 8k Ohm instead of 10k (assuming whatever is connected to the preamp output is high impedance). Would this be a significant change ?
Anything else I'm not seeing ?
Thanks a lot to anyone giving this a thought !
jf
I just built an O2 headphone amp (kit purchased from headnhifi), it works great!
I am a software guy with some very old electronics notions, and I would be grateful for a bit of help from someone more knowledgeable, about the following problem.
I have a small preamp box, mostly used to switch sources and adjust the volume. Its active component is a small ne5532-based board (bought on aliexpress around 10$), powered symetrically by a 2x15V toroid transformer, and I would like to combine the O2 and the preamp in the same box, which would then be a quite useful preamp with headphone output (duh).
However, when I power the O2 from one of the transformer's windings and connect the O2 input in parallel with the preamp's, I have a small hum in the O2 output.
It's very low (I can only really hear it at a volume level which would be very bad for my ears), but I know it's there, and this is very distressing psychologically
Both preamp and O2 are hum-free when alone.
The preamp board has a 47K Ohm pot on the output. I am thinking of just getting rid of the preamp board and connecting the 47K pot in parallel with the O2's 10K one to provide a preamp output with independant volume control.
So the O2 first stage would see something like 8k Ohm instead of 10k (assuming whatever is connected to the preamp output is high impedance). Would this be a significant change ?
Anything else I'm not seeing ?
Thanks a lot to anyone giving this a thought !
jf
Simplify. I think I would use the O2 as your preamp AND headphone amplifier, and set your other unit aside. If you need some sort of input selector, you could find a different unit or maybe utilize just that portion of your NE5532 unit.
Your "hybrid" powering scheme seems to have created a loop, or difference of potential, or some sort of asymmetry in the power supply circuitry. I suppose you could continue to investigate and possibly solve that issue, but it seems more straightforward (IMHO) to use the O2 for both applications.
Cheers,
Dave.
Your "hybrid" powering scheme seems to have created a loop, or difference of potential, or some sort of asymmetry in the power supply circuitry. I suppose you could continue to investigate and possibly solve that issue, but it seems more straightforward (IMHO) to use the O2 for both applications.
Cheers,
Dave.