[tiagoncalves]

Thank you both for the explanation about the decoupling and bypass caps. So, if I understand, I'll put one ceramic cap (100 pF) between the V+ and V- of the both OPA2132 in the left and right channels.
I tried to draw a layout for this amp, assembled in a perf-board similar to the one I post above:
 

 
In the software I used, it didn't have a board template like the one I'll be using, so I had to draw the paths. I hope it's understandable.
I tried to make a ground circuit like what I think is a star grounding. Is it right? And I'll solder the small ceramic caps under the OPA2132, to have them right close to the chip.
If someone have some suggestions, I thank in advance!
 

 

[tiagoncalves]

One more question, about the trickle charger. If I make a trickle charger, the amp can be used while charging the batteries? can I leave it always plugged to the batteries in a continuous charging, or must I have a switch?

 

[Mullet]

Don't know if you've come across this yet... but it's what I used to build my A47. I used the same Radioshack perf board used for the CMOY.  I don't believe it puts the BUF634 in a feedback loop though. It basically achieves the same thing in a different way. Admittedly, I just assembled based on pictures rather than really understanding the circuit so I don't know which way is better... yours or this...
 

 

[tiagoncalves]

The case is almost ready, some photos of the work:
 

 

 
Yes, I had saw that layout, thanks. But then I made some changes to the schematics I was using, after have some replies here in the forum. I tried to improve the grounding, but don't know if it's that necessary, or if it's well made. And also, the BUF634 in a feedback loop, so the power supply capacitors are in a different place.

 

[tiagoncalves]

Ok, now I know what I want for a power supply! I just have a couple of power supplys from some old electric devices: computer, printer, etc. I think they are all switch regulated, and I learn somewhere that it's not the best way to power a amplifier. In the future, maybe I'll get, or build a linear power supply, but for now I'll use what I have... So, I just want to use it to charge the two 9 v NiMH battery that I'll use with the amp.
The idea is to have a switch to turn on an off the charger, but just charge when the amp is turned off (with another switch).
Can I use the schematics that Avro_Arrow gave me to charge the battery from drain to full charge, or is it just to maintain the battery charged?
I want to use the amp through the batterys and, when they are almost dead, use the charger (with the amp turned off) to charge them, without the need to remove the batterys from the amp.
This is the schematics from the Avro_Arrow trickle charger:
 

 
Later I'll post the schematics of what I think to do in my previous layout, the way to switch between battery-amp and trickle charger-battery.
Thanks.

 

[Avro_Arrow]

The charger above provides both voltage limit and current limit.
 
You do not have to use three 3R3 resistors...you can use any
combination as long as it is about 1R.
R1 (R2, R3) sets the current limit. With 1R, current is about 700mA
which is good for AAA and AA batteries. 9 volt rechargeable should
have a lower current limit.
 
R5 sets the voltage limit which for NiHM batteries should be 1.5 volts per cell.
 
The charger will charge batteries from dead as well as trickle charge them.

 

[AmarokCZ]

If I were you I would use some charger that is not so cruel to batteries. You can use some primitive temperature based charger like this (page 7 - "Fast charger for ...").

 

[tiagoncalves]

Thanks again Avro! Great, so I'll build this trickle charger and use it just to charge the batteries, and when I get the linear power supply, I'll just change the switch connections, so I can use it to power the amp also.
For the 9v batteries, does the current need to be set to around 180-200 mA? They should equal the mAh of the battery?

 

[Avro_Arrow]

Yes, thats called the 1C rate.
The great thing about this charger is that after
the voltage come up, the charge current drops off.
That way you don't overcharge the battery.
 
You have to know how many cell are in each 9 volt
battery, some have six and some have eight.
 
AmarokCZ's solution looks good too. Temperature rise
is the best way to terminate the charge for NiHM and NiCad batteries.

 

[tiagoncalves]

AmarokCZ, with that charger can I still use it when I get a better power supply (linear) and want just to maintain the batteries at full charge? Is this the trickle charge?
 
If I limit the current to 180 mA, does it mean that the batteries will charge at this rate, or it's just a maximum current protection? If they should charge at a lower rate, is that rate I need to change with the R1, R2, R3 resistors? I think I need a combinations of about 3R3 to achieve the 180 mA current. Hope it's right.

 

[Avro_Arrow]

Think of R1, R2 and R3 as being just one resistor. I drew it that way
to give my board the ability to mount up to three resistors in parallel.
 I just happened to have three 3R3 resistor and I wanted a 1R value.
 
The value for about 180mA is 3R99.
 
Here is a simulation that might help you understand how it works.
 
The schematic:
 

R1 sets the current limit. R2 sets the voltage limit. R3 does not change.
R4 represents the battery under charge. VM1 is battery voltage and AM1
is charge current. All resistors can be 1/4 watt. R2 is an adjustable resistor,
it's just easier to use a fixed value in the simulator. I added D1 as a safety
feature to keep the battery from discharging into the charger. 
 

 
The bottom scale represents the battery charging.
As the battery charges, the voltage rises and the current falls.
The voltage will never rise farther the the limit you set.
the current will continue to fall. Once the current is less
than 1/10 C, the charge is complete and the battery is trickle
charging.

 

[AmarokCZ]

tiagoncalves: it's not trickle charger, so it charges battery to full capacity and stops charging. Charging starts again only when you press start button. In this case it's good idea to add diode to protect battery from discharging into charger.

 

[tiagoncalves]

I think I understand the schematic, and how to limit the voltage and the current. I also learn about the formula V out = 1,25*(1+(R2/R3)), and it's meaning.
I just don't understand where I adjust the 1/10C charge rate. If my battery is 180mAh, should I use a R1 resistor of 35 ohm to have a maximum current of 20 mA? If I limit the current to 180 mA, does it mean that the charge rate is equal to 1C, instead of 1/10C?

 

[AmarokCZ]

Yes, 180mA = 1C (for 180mAh baterry). R1=35ohm sets current to ~20mA (C/10), because 0.65V/35ohm=0.019A.

 

[tiagoncalves]

Great,good to know the calculations are right. should i set the max current to 20mA in the case of the 180mAh battery?what happens if i leave it equal to 1C?it will charge much quicker,but can reduce the lifetime of the battery? thanks