The MOSFETs (and the rest of the power management circuitry) aren't necessary to the audio operation of the O2. There isn't really a trickle charger - only a series resistance to limit current to the batteries.
I'm not sure what your intentions are for 18v batteries.
Not really, as the O2 requires a +9V/GND/-9V power supply, requiring 2 batteries.
The schematic.
If you still intend to use batteries, I don't understand why the pwr mgmt circuit can't stay.
O2 uses bipolar DC supply & "real" gnd using 2 X 9V batteries and/or AC supply. What you are trying to build is single battery based "virtual ground" supply(remember there are no rail splitter resistors, transistors or opamps in O2). You can use 2 Lipos (+/-18V )to supply power to regulators & no need to mod rest of the ckt, especially O2's power management ckt. People have accidentally connected DC supply instead of AC with disastrous results as the O2 power socket matches with majority of wall-warts, router/laptop/spk adapters.
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Checking the Li-ion issue... My understanding is that the danger using such with the O2 is the recharging feature which starts when a dc source is plugged in?
Let's say that is sufficiently solved by for example a simple mechanical block of the dc socket when batteries are inserted. How is the amp performing with 2x2 cells of Li-ion which would discharge at about 7V? Please refrain from vague guessings like it isn't designed for it or whatnot. Are there any detectable/significant sonical differences? I'm using 32 Ohm IEMs.
About at what voltage does the amp turn off? It should be quite a good margin under 7V yes?
Thanks
Let's say that is sufficiently solved by for example a simple mechanical block of the dc socket when batteries are inserted. How is the amp performing with 2x2 cells of Li-ion which would discharge at about 7V? Please refrain from vague guessings like it isn't designed for it or whatnot. Are there any detectable/significant sonical differences? I'm using 32 Ohm IEMs.
About at what voltage does the amp turn off? It should be quite a good margin under 7V yes?
Thanks
The problem is that the O2 has a simple trickle charge circuit inside, which works fine for NiMH chemistry but is a no-no for Lithium Ion. Here is a link:
How to charge Lithium ion Batteries, lithium polymer batteries, and lithium iron phosphate cells.
And 5th paragraph down, "It is important to note that trickle charging is not acceptable for lithium batteries". One way around that is what I posted a few posts back in #4121 about disconnecting the trickle charge circuit (removing the 2 220 ohm 1W resistors) and instead wiring in two panel mounted fully insulated (none of the contacts can make contact with the panel) DC jacks to cable out to the actual manufacturer-recommended charger for the particular lithium batteries, which most likely will use a dV/dt shutoff signal.
The O2 only takes AC on the power input jack, 12Vac is the recommended. The power supply in the O2 creates +/-12Vdc from the 12Vac input.
The O2 should perform just fine with 2x 4.2v = 8.4V max lithium cells on each channel. Like you say the minimum discharge is usually recommended to be around 3.6V, so 7.2V or so per channel which is just fine. Like Richard Marsh noted a few posts above the internal impedance of the lithium batteries over the audio band may be lower, which is always a good thing.
The discharged-battery trip voltage points for the O2's power management circuit are in this post I did a while back, and they would most likely have to be adjusted for a lithium battery. I have all the math to do it in that post #106 in the thread. From that post, with the current O2 BOM values, the low battery turn-off trip point is 7.07V. His original values, before he discovered the (lack of) hysteresis problem and changed the BOM was 6.33V.
As for sonics, even with the potentially lower internal battery impedance I wouldn't expect to hear any noticeable difference between the lithium and NiMH. Keep in mind the batteries (and AC supply when that is plugged in) are bypassed inside the O2 by 220uF caps on each power rail. The major reason to go with lithium over NiMH is increased runtime, probably around 3x for the same physical size of lithium batteries.
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Thanks a bunch agdr! Useful posts are a bit tricky to find in massive threads, even when searching.
Oops, had overlooked that it used ac for input.
So to eliminate the danger of improperly recharging lithium cells the best/easiest way seems to remove R1 and R2 then.
About the on/off voltages I've seen different discharge charts for Li-ion (at room temperature I believe) which differ slightly regarding the lowest useful voltage before the V-drop when it's getting empty. (The difference might be due to temperature still. Btw are all cells on the market really virtually identical concerning discharge voltages?)
Anyway, the original values for O2 (from a post of yours): R25 = 2.74M, R9 = 40.2K : turn on = 6.95Vdc, turn off = 6.33Vdc. I seem to remember plots where Li-ion cells could crawl a tad below 3.5V (3.4V or so), so it seems useful to increase R25 and R9 a bit more. Would that cause any problems? Do you have any suggestions for good values? Also, Li-ion should handle lower turn off voltage just fine yes?
Thanks
Oops, had overlooked that it used ac for input.
So to eliminate the danger of improperly recharging lithium cells the best/easiest way seems to remove R1 and R2 then.
About the on/off voltages I've seen different discharge charts for Li-ion (at room temperature I believe) which differ slightly regarding the lowest useful voltage before the V-drop when it's getting empty. (The difference might be due to temperature still. Btw are all cells on the market really virtually identical concerning discharge voltages?)
Anyway, the original values for O2 (from a post of yours): R25 = 2.74M, R9 = 40.2K : turn on = 6.95Vdc, turn off = 6.33Vdc. I seem to remember plots where Li-ion cells could crawl a tad below 3.5V (3.4V or so), so it seems useful to increase R25 and R9 a bit more. Would that cause any problems? Do you have any suggestions for good values? Also, Li-ion should handle lower turn off voltage just fine yes?
Thanks
I'm no expert on Li-ion batteries but from what I understand, avoiding deep discharge and also not fully charging to 100% of its theoretical capacity are key to getting the best life from such batteries. Again, from my limited knowledge but I think cell voltages that make the packs up can vary and its important you know which you have when it comes to charging. You may see 3.6 or 3.7 volt cells and its vital you charge them correctly according to what you have.
Its very important that the charge cycle is terminated when the correct charge point vs current drawn is reached. Never trickle charge a Li-ion as that will destroy it rapidly.
Its very important that the charge cycle is terminated when the correct charge point vs current drawn is reached. Never trickle charge a Li-ion as that will destroy it rapidly.