Just buy the JDS Labs version, its build quality is great.
https://www.jdslabs.com/products/35/objective2-headphone-amplifier/
It should output higher with no load since it's an unregulated power supply(transformer), the specified 12V rating is with the load drawing the rated current.The power adaptor is not a properly rated one. Even though it says 12V AC, it is actually around 14V.
You beat me to it. I'd add that it's one example of where bigger isn't necessarily better. Many people make the mistake of buying grossly over-rated (current-wise) unregulated wall warts and then end up with too high a voltage.It should output higher with no load since it's an unregulated power supply(transformer), the specified 12V rating is with the load drawing the rated current.
I have addressed this point before. My measurements usually show somewhat higher impedances than published or what others report. I use the same dummy load setup I use for THD+N vs power and such more cables and connectors are involved than someone just sticking a resistor right at the headphone socket. Since we are measuring such small values, these add up to to higher impedances as reported. I can switch to what others do but I think my test is more realistic as headphones also have thin and long cables that contribute the same increase.As it has already been requested, can you please double-check your output impedance measurements?
Other measurements show the O2 output impedance to be much lower.
0.54
http://nwavguy.blogspot.com/2011/07/o2-headphone-amp.html
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https://www.innerfidelity.com/images/JDSLabsO2ACPowered.pdf
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https://www.seeko.kr/zboard4/zboard...word=o2&select_arrange=headnum&desc=asc&no=13
<1
https://docs.google.com/spreadsheet...9VnTpkpjapOXt-4nFZ5YkGFIYs/edit#gid=292276897
reddit user slowsound
According to NWAVGUY's website:FYI I measured the output of the transformer supplied with the MD O2+SDAC (240V 60Hz, 12VAC 220mA)
Unloaded: 15.21 VAC
loaded: 12.85 VAC
Mains voltage during measurement: 230 VAC 50Hz
NWAVGUY's blog said:AC Wall Transformer - There has been some confusion over the wall transformer and it’s a critical component. Most wall transformers put out DC but the O2’s power supply requires at least 13.5 volts AC. The ideal transformer would be rated at 14 - 16 VAC and 400 mA or higher. In North America the Triad WAU12-200 from Mouser is rated at 12 volts but is really about 13.5 VAC with no load, and on normal 120 volt line voltage works fine for anything but full power sine wave testing or driving rare low impedance power hungry cans. If your line voltage is below 117 VAC or 235 VAC, and/or you plan to drive difficult low impedance headpones (i.e. HiFiMan planars), I would suggest a 14+ VAC transformer at 400+ mA.
Hi. I found someone tore massdrop version down. So, can it make some differences from original nwavguy version
https://www.massdrop.com/buy/massdrop-o2-amplifier/talk/241801
https://www.massdrop.com/buy/massdrop-o2-amplifier/talk/242344MD Will said:"That said, letting our contract manufacturer sub in some alternative parts to get us a prototype for pictures was definitely a poor choice we won't be making again. Think of how much pain and suffering could have been avoided if we'd waited the additional couple weeks it would have taken for sample quantities of all the proper parts to reach the manufacturer. Lesson learned there for sure.
Do you think it would be best to remove the PCB photos up right now to avoid confusion? Obviously it'd be best to post pictures of a PCB from our contract manufacturer with all the parts according to spec, but there's probably not enough time in this drop to make that happen... Actually, probably easier to add some notes on the pictures to avoid confusion instead. Let me know your thoughts on this."
FYI I measured the output of the transformer supplied with the MD O2+SDAC (240V 60Hz, 12VAC 220mA)
Unloaded: 15.21 VAC
loaded: 12.85 VAC
Mains voltage during measurement: 230 VAC 50Hz
Oh sorry, I didn't specified the load. I used a 60 ohms resistor during testing so It will be lower than what they tested with the O2 itself.Someone else on MD measured 13.8 no-load and 13.2 loaded. One MD operations guy posted pics with 14.9 no-load and 14.2 loaded. So these adaptor units seems to vary a lot by unit.
NwAvGuy: O2 Details said:AC WALL TRANSFORMER: The power supply, with a 13.5 VAC (no load) wall transformer, is right on the edge of letting some ripple though under worst case conditions. If the O2 is used with low line voltage, and for sine wave testing, or using very power hungry low impedance headphones, a higher voltage transformer is recommended (14 – 20 VAC). Some 12 VAC transformers and/or a lower AC line voltage may cause the amp to exhibit higher distortion during low impedance sine wave bench testing as the power supply will fall out of regulation and let AC ripple through the regulators. A 14 - 20 VAC transformer solves the problem (like the WAU16-400 in the parts list). In real world use, the WAU12-200 is the least expensive option and works fine at normal line voltages playing music (not sine waves) into 99% of headphones. The On Semi regulators reach their drop out voltage at about 11.5 VAC loaded. If the amp is driving a low impedance load at high current levels, you need at least 12 VAC loaded (200 ma or about a 60 ohm 5 watt resistor if you want to test a transformer). This doesn’t leave much room for using a 12 VAC transformer if the line voltage is low (below about 117 VAC) hence the primary 14 – 20 VAC recommendation
It seems like that he changed his answer. Anyway, I see now Mayflower, MD have QC problem. I considered O2 + D50. But it seems better to wait topping's new amplifier( A50?).I couldn't find the Reddit thread that had the pictures of the O2 internals from MD's product description with those "substitute" components but here's the response from MD in that thread.
https://www.massdrop.com/buy/massdrop-o2-amplifier/talk/242344
…and a peek on the MD O2 with a missing solder joint from a user that received a defective unit.
View attachment 14537
https://www.massdrop.com/buy/massdrop-o2-amplifier/talk/2155941
Someone else on MD measured 13.8 no-load and 13.2 loaded. One MD operations guy posted pics with 14.9 no-load and 14.2 loaded. So these adaptor units seems to vary a lot by unit.
OK, I was wondering who had gotten that alias!Hi. I found someone tore massdrop version down. And he found changing parts. So, can it make some differences from original nwavguy version
https://www.massdrop.com/buy/massdrop-o2-amplifier/talk/241801
I can recommend JDS too though. Workmanship is OK, customer service is stellar: if you end up with a problem they will help you however they canIt seems like that he changed his answer. Anyway, I see now Mayflower, MD have QC problem. I considered O2 + D50. But it seems better to wait topping's new amplifier( A50?).
OK, I was wondering who had gotten that alias!
Yes!Did you mean 'oliveoilthansnakeoil'?