[fairx]

hi guys, 
 
I'm thinking of building O2 amp myself and I only need the essential PCB 
 
however ordering from JDS directly, the shipping (to Malaysia) itself pricier than the item
 
I'm not sure if this is the correct place to ask, is the PCB sold on ebay reputable? it's slightly expensive but lower than JDS shipped..
 
thank you

 

[naif1985]

Hi everyone. My o2/odac rev-b has fallen off the table and the USB connection (female) came off. I took it to a shop and he welled it in place. But wen I plug it in my computer the windows doesn't recognizes the ODAC . I tried contacting the O2 alone but there's some noise in the sound I couldn't bare.
Did anyone had this same issue?

 

[raoultrifan]

I'm pretty sure the USB female plug wasn't perfectly welded/soldered onto the PCB. You need to provide some pictures with the "affected" PCB, if possible, or at least find another shop to do again that soldering.
 
Also, if PCB is really broken where the mini-USB female plug was soldered, then might be easier to purchase a good quality USB cable, to cut it from one side and to directly solder it to the PCB. You can leave out the small mini-USB B-type female plus or whatever female-USB you want.
 
Good luck!

 

[customeauser]

I got the o2 amp a few days ago. My HD600´s sound very detailed and nice. But there could be a bit more bass in some music.
Sometimes I miss the fullness of sound especially in Rock Music.
 
I´m from Germany so my english is not the best. Sorry for that.

 

[turkayguner]

  ...Being that if I were to start thinking about the engraving, I'd drive myself crazy for weeks trying to think of what to engrave...

I am in the very same situation. Thinking about it for over a week already..

 

[Bloos]

Does anyone find that the volume doesn't increase from 3 o'clock to max? Why is this?

 

[raoultrifan]

Actually it does increase a little bit, but that's a normal behaviour for a logarithmic potentiometer. Around 12 o'clock you should have around 10-15% of the max volume and around 3 o'clock you should probably have about 90% of the volume or even more.
 
https://en.wikipedia.org/wiki/Potentiometer
http://www.learnabout-electronics.org/Resistors/resistors_09a.php

 

[439598]

I'm surprised at the low number of posts here for a such commonly recommended amp. If anyone is interested in some cheap but effective mods to improve the sound of the o2 this post can help but keep in mind this was done with the desktop version of the amp with mains powersupply not batteries. It would be recommended that you have some basic knowledge of electronics.

The o2 amp never sounded good to me and I do not believe that this is what 'transparency' sounds like, if you like the sound then more power to you but If you are disappointed and want an amp that sounds more vivid, more detailed and natural then I recommend these mods. Testing was done by ear only, objective blasphemy, I know, but I can guarantee that some of the greatest with the he560 which had perhaps some of the worst synergy with the o2 out of the headphones I used with it (hd600, hd650, he400i and ath-m50), If the he560 could sound good with o2 then I knew I was doing something right

Surprisingly the biggest problem with O2 lies in the power supply capacitors, it is lacking in some capacitance. I tried many different variations of caps and eventually found the perfect balance, beyond a certain point more caps either made no difference or actually made the amp sound too laidback and smooth in the bass and mids, all 'slam' and no 'punch'. very high capacitance can also put a strain on your power supply.

The caps I recommend are:
2x 100uF Electrolytic
2x 47uF Electrolytic
2x 10uf Electrolytic
4x 0.1uF (100nF) polypropylene Film capacitor
optional 2x 4.7uF Electrolytic
optional 2x 0.47uF (470nF) polypropylene film capacitor


Any caps will do as long as they are rated for at least 35V to match the stock 470uF caps.
Be sure to keep the dimensions of the caps you buy in mind, even with the same voltage rating and capacitance they can vary greatly in size

To connect caps you must solder 3 wires onto the existing caps on the underside of the PCB for positive, negative and ground. there are 2 solder pads for the positive side and negative side and 4 solder pads for ground marked by the black dots, you can solder each wire on any of these pads. the new caps are paired in series and wired in parallel with the current caps, here is a diagram for clarity:

Unfortunately there isnt enough room for the new caps inside the standard O2+ODAC enclosure.
I have the new caps on a small breadboard, the wires feed out from the back and are connected to the breadboard, not elegant but totally reversible and easy, well worth the cost of a few capacitors.
if you like the results and want something more robust my suggestion would be to solder the caps to some perfboard, drill 3 small holes on the top of enclosure, 2 for mounting the perfboard and 1 for the wires.


if you are using the standalone O2 then there is room for a piece of perfboard in place of the ODAC inside the enclosure, keep the height restriction in mind when choosing caps. secure the perfboard with a nut and bolt on the outer mounting hole and feed the wires up from the bottom of the pcb through the inner mouting hole: https://www.jdslabs.com/images/products/35/full/O2-pcb-assembled.png.

Op Amps

Changing the op amps is also a good idea regardless of what people say. The 4556 and 2068 might be technically good chips but they really are some of the worst sounding ones I listened to, any well regarded audio op amp will be a big upgrade. if you are skeptical you can pick up a couple of NE5532s for a few dollars and swap out the 4556s, it will sound smoother and fuller.

The LM4562 is the best price to performance chip Ive tried, one of the most clean and detailed chips and only around $5 each. It works very well in place of either the 4556 or 2068. if you prefer a less analytical sound the OPA2132 could be a better choice but I havent tried it, only the expensive OPA2107 which is a very good chip but not to my taste and shouldnt cost more than $10

most, if not all bipolar audio op amps such as the LM4562 and NE5532 will work perfectly fine in the o2, they are very stable and versatile. I tried many other chips including non-audio op amps and JFET op amps with zero problems, some sounded very good aswell.


After modding you will be left with an amp that begs for you turn it up, the exact opposite of the stock o2 for me.

 

[raoultrifan]

There's another subforum for this: https://www.head-fi.org/threads/o2-amp-odac.616331/.

I've did some mods myself couple of years ago:
- https://www.head-fi.org/threads/o2-amp-odac.616331/page-328#post-12282731
- https://www.head-fi.org/threads/o2-amp-odac.616331/page-332#post-12382477
- https://www.head-fi.org/threads/o2-amp-odac.616331/page-343#post-12800989

I've also added 2 x Nichicon 4.700uF/50V in parallel with the original PSU caps, but AC ripple & noise was not changing much, so like AGDR said in one of his posts...just an RC filter could help here. So, you might want to cut the traces between the 470uF caps, add 1ohms resistors and also change the first 2 caps with others supporting a higher voltage (maybe you can try finding his post for a better understanding). However, I couldn't find O2's power supply as having flaws, after all...if the power supply would be really noisy, then O2 wouldn't be one of the least noisy headamp out there: https://www.innerfidelity.com/images/JDSLabsO2ACPowered.pdf (most of the inband noise is around -150dB).

BTW, are you 100% sure you want to swap +/-70mA output buffers for +/-38mA? This is will cut in half the output power, not mentioning the NE5532 may not like output impedances lower than 600 ohms. If you really hate O2's output buffer, maybe you can try pmillet's Butte that is using OPA551/552 as output buffers.

 

[439598]

searching headfi gets you buy and sell results, searching google gets this thread, thanks for putting me in the right direction.

I will try the resistor in combination with the current caps and yeah I prefer a different op amp, currently using the LM4562 which has even less current output. returning to the 4556 and 2068 still feels like a blatant downgrade everytime aside from extra the power

The LME49721 has a 100mA output current, nearly quadruple that of the LME49720 aka LM4562. It could be a very good choice if the sound quality is anything like the latter however its only available in a SOIC package so an adapter is needed

 

[raoultrifan]

Taken from the datasheet: "LME49721 has a high slew rate of ±8.5V/μs and an output current capability of • High-Fidelity Multimedia ±9.7mA". Let's not confuse this with the output short-current trigger.

AGDR and adydula@ tested with great success the OPA1688, so this might be a better output buffer.

 

[439598]

Taken from the datasheet: "LME49721 has a high slew rate of ±8.5V/μs and an output current capability of • High-Fidelity Multimedia ±9.7mA". Let's not confuse this with the output short-current trigger.

AGDR and adydula@ tested with great success the OPA1688, so this might be a better output buffer.

yeah I just noticed its only rated for max 5v supply! there is also the OPA1612 with 145mA but this only comes in a tiny VSON package, I guess the 1688 is only choice for a modern chip with decent current output

 

[raoultrifan]

Not sure where you're getting the numbers from, sorry.


OPA1612 @+/-15V has about +/-47mA


NJM4556 @+/-15V has about +80mA/-150mA

If you really-really want to get rid of the default NJM4556, then at least get an opamp able to match somehow the original. I was testing few years ago the MUSES 8920 and I've also test it extensively today.


MUSES 8920 @+/-15V has about +/-80mA (almost twice the OPA1612)

The main advantage of the MUSES 8920 is the lower input offset voltage, so the DC-voltage on outputs will be much lower than the NJM4556.
The main disadvantage would be the lower current, so output power will be a bit lower, especially for low-impedance headphones (32 ohms actually).

L.E.: For a 30-ohms resistive load I got 3.8V RMS (480mW) without visible distortions with NJM4556 in output buffer, instead with MUSES 8920 I only got 3V RMS (however, with some distortions around 20Hz frequency I was able to get almost 3.7V RMS). So for 30-ohms load the power will decrease from 480mW to a bit over 300mW. Be aware that O2 has no overload protection, so it's up to us to not overload it (some planars could kill the output buffer!).

 

[raoultrifan]

I did lots of tests today with the MUSES 8920 in output buffer and I said to myself that I could increase the performance of my beloved O2 headamp by modifying the R12 & R13 default values (read more about this on designer's blog).

Please note that modifying the critical default values of the R12 & R13 resistors will dramatically affect the DC-output voltage and might damage your headphones!

However, by using 2 x NJM4556 and default 42 kOhm R12 & R13 I got a DC-voltage of around +/-3mV on headphones-out plug. After increasing the values of R12 & R13 to 192 kOhm by adding 150 kOhm in series with existing 42 kOhm I got a DC-output to +/-12.5mV (quite high, so not recommended).

Wait, there's more...replacing the 2 x NJM4556 with 2 x MUSES 8920 and choosing 192 kOhm for R12 & R13 I got a DC-voltage of around +/-0.3mV for each channel! Now that's a DC-output that even 10 x times more expensive headamps will envy it.

Feel free to have a look on how a perfectly square signal looks like: original R12/R13 value vs. the increase value (blue is the signal generator and red is headphones output of the Objective2).


10 Hz square signal - O2 with R12 & R13 = 42 kOhm (default)


10 Hz square signal - O2 with R12 & R13 = 192 kOhm (almost perfect)


20 Hz square signal - O2 with R12 & R13 = 42 kOhm (default)


20 Hz square signal - O2 with R12 & R13 = 192 kOhm (about perfect)

Increasing the test frequency > 100 Hz makes impossible to see any difference.

Increasing R1 & R2 resistors is improving the very low-end transients for square signals. Not much of an audiophile test, I know, but O2 already measures perfectly on sinewaves, so only square signals could show some more things to dive deep into.

P.S.: Just realised today that OPA1652, when used in voltage-gain of O2, is having an even lower noise that NJM2068. Also, the transients when powering ON/OFF are a bit lower.

 

[439598]

Nice work, do you notice much sound improvements?