The Objective2 (O2) Headphone Amp DIY Project

[agdr]

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.

[Michel01]

Hi everybody,

I'm intersted in getting one complete O2 amp kit (everything included) if possible.

Could anyone explain me the procedure to get it?

I live in Spain.

Thanks in advance

Regards

[timpert]

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.

[musical]

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.

[MrSlim]

Originally Posted by Michel01

Hi everybody,

I'm intersted in getting one complete O2 amp kit (everything included) if possible.

Could anyone explain me the procedure to get it?

I live in Spain.

Thanks in advance

Regards

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..

[madcap386]

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..

[sofaspud]

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."

[454Casull]

Originally Posted by sofaspud

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."

For that which the part is suited, so shall it be pulled out of the junk bin...

[madcap386]

Originally Posted by sofaspud

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.

[sgrossklass]

Originally Posted by musical

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.

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).