Something I should add about the 8-cell 9.6V NiMH batteries...
I would imagine RocketScientist's concern about changing R1 and R2 for the 9.6V cells would be that someone would later forget they have changed the resistors and stick in a 7-cell 8.4V NiMH. That would result in a charging current 50% higher than indended, although should still be in the safe range from what I can tell. So if anyone changes R1 and R2 it would be a good idea to put a sticker over the PCB under the batteries saying "9.6V NiMH only" as a reminder.
Also a note about endpoint voltage. The endpoint voltage should wind up somewhere around 1.45x per cell for NiMH, or 10V for the 8.4V cell and 11.5V for the 9.6V cell. That would put the endpoint voltage near the supply voltage, given the schottky diodes, for the 9.6V cell. That is OK. A good way to extend the life of the batteries is to very slightly undercharge them, at the slight expense of run time. My Sony laptop here has the option of only charging the (lithium) batteries to 80% to extend their life.
I would imagine RocketScientist's concern about changing R1 and R2 for the 9.6V cells would be that someone would later forget they have changed the resistors and stick in a 7-cell 8.4V NiMH. That would result in a charging current 50% higher than indended, although should still be in the safe range from what I can tell. So if anyone changes R1 and R2 it would be a good idea to put a sticker over the PCB under the batteries saying "9.6V NiMH only" as a reminder.
Also a note about endpoint voltage. The endpoint voltage should wind up somewhere around 1.45x per cell for NiMH, or 10V for the 8.4V cell and 11.5V for the 9.6V cell. That would put the endpoint voltage near the supply voltage, given the schottky diodes, for the 9.6V cell. That is OK. A good way to extend the life of the batteries is to very slightly undercharge them, at the slight expense of run time. My Sony laptop here has the option of only charging the (lithium) batteries to 80% to extend their life.
Endpoint voltage is also dependent on charge rate, if you allow sufficient time, the 8-cell NiMH will in time also become fully charged in the unmodified O2. Stand-by charging is often misinterpreted as being safe for the battery, but it is not. NiCd batteries have no problem with a continuous overcharge at C/20. In fact, in emergency lighting, this method of standby charging is often used, where batteries are required to last more than three years under continuous overcharge. The robustness of NiCd batteries is the reason why they are still allowed in this application.
NiMh batteries will also withstand such treatment, in a sense that the cell will not swell, vent or explode or become dangerous otherwise. But the cell will degrade faster than a NiCd cell, so when standby charging indefinitely, a very low current of C/100 or even lower (just enough to compensate for self discharge) is often advised. In this sense, the 9.6V batteries have an advantage, because it would be a typical usage situation to leave the O2 plugged in unless needed on the road. The higher endpoint voltage automatically gives you a very low trickle current. So having a 9.6 V battery would buy a bit of battery life at the expense of getting those very last coulombs in at a very slow pace.
NiMh batteries will also withstand such treatment, in a sense that the cell will not swell, vent or explode or become dangerous otherwise. But the cell will degrade faster than a NiCd cell, so when standby charging indefinitely, a very low current of C/100 or even lower (just enough to compensate for self discharge) is often advised. In this sense, the 9.6V batteries have an advantage, because it would be a typical usage situation to leave the O2 plugged in unless needed on the road. The higher endpoint voltage automatically gives you a very low trickle current. So having a 9.6 V battery would buy a bit of battery life at the expense of getting those very last coulombs in at a very slow pace.
Thank you all for the comments. Now I am swayed to get the 8-cell battery and use unmodified O2.
As for the comments on keeping the O2 on the shelf for a long time, that is quite possible. Initially I am sure I'll use it daily. In the long run, however, it will sit on the shelf longer as I personally prefer listening to speakers than headphones. When I am on the go and want to listen to headphones I do not want to find the batteries flat. If they are flat I probably won't bother to wait for them to charge.
I remember the time when I had a digital camera using normal NiMH batteries. I ended up not taking many photos because every time I wanted to take a picture, the batteries were flat. I charged them up but the opportunity to take the photo was gone.
As for the comments on keeping the O2 on the shelf for a long time, that is quite possible. Initially I am sure I'll use it daily. In the long run, however, it will sit on the shelf longer as I personally prefer listening to speakers than headphones. When I am on the go and want to listen to headphones I do not want to find the batteries flat. If they are flat I probably won't bother to wait for them to charge.
I remember the time when I had a digital camera using normal NiMH batteries. I ended up not taking many photos because every time I wanted to take a picture, the batteries were flat. I charged them up but the opportunity to take the photo was gone.
No one is selling complete kits..
You'll need to check the O2 board group buy and see if there are any spares left, order your own parts from the BOM, and if you want, get in on the Front Panel Group buy..
Here is my finished O2 amp.. and i must say its a solid piece of equipment.
Here is how it looks after i add a little of my own front panel design...
Hope to see more O2 front panel DIY works here..
Here is how it looks after i add a little of my own front panel design...
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Hope to see more O2 front panel DIY works here..
For that which the part is suited, so shall it be pulled out of the junk bin...Solid's good, if brief.
Is that front panel one piece or two? It does give a nice look.
And am I seeing that knob correctly? It looks like o-ring "grippers."
Solid's good, if brief.
Is that front panel one piece or two? It does give a nice look.
And am I seeing that knob correctly? It looks like o-ring "grippers."
The knob is from Kilo international. It comes with the rubber grip thingy..
Digi-Key - 226-3003-ND (Manufacturer - ML-50-3-6MM)
The front panel is a 2 piece design, aluminum plate on the back with the acrylic in front.
There are three factors contributing to this particular problem:
1. Accelerated self-discharge at capacities of >~2000 mAh / AA cell (and it isn't too low to begin with).
2. Reduced ruggedness and increased susceptibility to internal leaks under same conditions.
3. Internal resistance creeping up with cells sitting idle.
Thankfully we have LSD cells (Eneloop etc.) these days - my AA-operated camera has never given me trouble with these. Looks like they even make 9V blocks like that now (not Sanyo, but other manufacturers at least).
In case anyone is planning on doing a mini Desktop and either using the standard panels included with the B3 boxes or getting panels from the Group Buy that is ongoing, the 1/4" jack that RocketScientist(aka NwAvGuy) included in the BOM will not work due to its requirement for a 1.2 - 1.5 mm panel thickness..
An alternative I found with approximately the same physical dimensions and less specific requirements for the panel mounting is the Neutrik NRJ3HF-1 and NRJ-NUT-B combo (Mouser#s 568-NRJ3HF-1 and 550-1005)
An alternative I found with approximately the same physical dimensions and less specific requirements for the panel mounting is the Neutrik NRJ3HF-1 and NRJ-NUT-B combo (Mouser#s 568-NRJ3HF-1 and 550-1005)
Which DIY one would you recommend fitting in an equal sized box as the O2 or if it would fit in a slightly bigger box containing the both of them. Of course there has to be switches so one is able to use just one of them or both at your command
The Grub Dac from Beezar.com might fit the bill for you, although you'd have to figure out how to mount the board and connectors.. You could probably put it in the B3-080 desktop case along with the O2....
Thanks MrSlim, I'll check it out but tubes? what are they for? buffering?. I need no amplification since I'm going for the O2 but still, I'll look into them.
Hmmm, sorry - the grub dac looks intressting... But, the input is limited to 16/48 on usb. I am more in search for 24/96 as a minimum without amplifier.
Brgds
Hmmm, sorry - the grub dac looks intressting... But, the input is limited to 16/48 on usb. I am more in search for 24/96 as a minimum without amplifier.
Brgds
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I'm new here, and just wanted to drop a thank-you to NwAvGuy/RocketScientist for the great design and everyone organising the GB's to help materialize this amp. Very much appreciated!
I currently enjoy my music with a FiiO E7/E9 combo and a pair of HD650's. Can't wait to put together an O2.
I currently enjoy my music with a FiiO E7/E9 combo and a pair of HD650's. Can't wait to put together an O2.
The O2 probably won't sound any different than the E9 for you, since even the latter's 10 ohm output impedance is plenty low for HD650s, and about 160 mW of power should be ample, too.
Anyway, the O2 should be a fun project, and you'll be happy you got one the moment you acquire some multi-driver IEMs or other similarly fussy headgear.
Yeah, I realise that, and I'm not really expecting any change in SQ (and I'm very happy with the FiiO). Anyhow, the thoughtful design of the O2 is what really sold it for me, and the O2 will primarily serve as a semi-portable, easy-to-pull-out-and-put-away amp for home listening, as the E7/E9 is my office setup and a bit too much of a hassle to move around. I also have other much more sensitive headphones, which might benefit from the O2 as well.