the Pimeta-V2 thread - Page 18

double post. see previous post

Quote:

Originally Posted by i_djoel2000 

how to predict, or calculate the voltage of the battery after charging using the built in trickle charging circuit?

It's in the docs.

No. It will stay on after you unplug the charger, until the batteries die.

To do what you ask, you'd have to put the + end of the LED and current limiting resistor subcircuit between WALL and D1. The other end still runs to V-.

tangent, is it still recommended to use 22-33pF in C6 when i set the gain to 6? bigger capacitance makes the opamp more stable, right?
 

Quote:

Originally Posted by tangent 

 

It's in the docs.

 

 

 

No. It will stay on after you unplug the charger, until the batteries die.

 

To do what you ask, you'd have to put the + end of the LED and current limiting resistor subcircuit between WALL and D1. The other end still runs to V-.

 

i see..

so i guess it will be like this

tangent, i'm still confused why the opamps choice in pimeta are able to run perfectly fine with 8.4V battery

after the supply passes through TLE2426 (voltage divider), the voltage on each rail would be roughly 4.2V/channel (correct me if i'm wrong), while the minimum supply voltage of your opamps and buffers choice (ad8620, ad8610, LMH6321) are all 5v. how could they still run perfectly fine with 4.2V voltage supply?

Quote:

Originally Posted by i_djoel2000 

is it still recommended to use 22-33pF in C6 when i set the gain to 6?

What does gain have to do with it?

The docs are clear, I thought: 4.7 to 10 pF if you don't want to test (or can't), 1 to 100 pF if you do a square wave test.

It isn't that simple. If the highest possible value gave the best performance, I'd just say "use X". The higher the cap value, the greater the impact on the amp's bandwidth, and thus its overall performance. That is why there is an upper 100 pF limit in the range given in the docs.

You're confusing split supply voltages with rail-to-rail voltages. When the datasheet says a buffer works down to 5V, it means the same thing as if it says it works down to +/2.5V.

Quote:

Originally Posted by tangent 

 

You're confusing split supply voltages with rail-to-rail voltages. When the datasheet says a buffer works down to 5V, it means the same thing as if it says it works down to +/2.5V.

in that case, using 4x AA batteries (1.7V each) we can get a total of 6.8V. so using ad8620/8610 configuration with those 4 AA batteries should be more than enough right? because i'm still under the impression that using nearly 5V power supply is not really recommended. i was referring to your comment in the doc here:

'Bottom line: you can design a good-sounding PIMETA v2 that runs on 5 V, but you’d best have a good reason to push things this hard. If not, you’re needlessly closing off options for better sound'

because i'm really concerned with the battery life of portable pimeta. based on rough calculation, using 9V 230mAh battery, you only can get 3.8 hours, 4 hours top! i cannot even consider that kind of battery life as portable

Where do you get 1.7 V per cell?

Even if you're looking at the still-on-the-charger voltage, it's going to drop quickly from that after you unplug the power supply.

Quote:

Originally Posted by tangent 

Where do you get 1.7 V per cell?

 

Even if you're looking at the still-on-the-charger voltage, it's going to drop quickly from that after you unplug the power supply.

oh sorry, it's 1.2V (got wrong info!). let say i'm able to stick 6 AAA batteries into my casing, i can get a total of 6.6-6.8V. is it more than enough for ad8620/8610 or opa627 configuration?

I'd characterize that as "barely enough". It's equivalent in voltage to a 7.2 V type of "9V" NiMH battery. It differs only in being able to provide more current, or run for longer on the same current.

Quote:

Originally Posted by tangent 

I'd characterize that as "barely enough". It's equivalent in voltage to a 7.2 V type of "9V" NiMH battery. It differs only in being able to provide more current, or run for longer on the same current.

i guess i will have to work really hard to stick those 4 AAA batteries to my small aluminium case then. haish...

report will follow, the board is not even arrived yet

i found this in other thread:

Quote:

Originally Posted by tangent 

Quote:

Originally Posted by headfone I'm experimenting with running two 9.6V 230mAh (ea.) cells in parallel.

Beware that while discharging NiMHs in parallel is mostly safe (best if both batteries are the same age and have the same wear pattern) charging is not. Don't use the PIMETA v2's built-in trickle charger for a parallel pair.

why can't i use the built in charger for charging paralleled 9v batteries?

i'm planning to use 2 x 8.4V batteries in my pimeta..i changed my plan of using 6 x AAA batteries after i saw this post:

Quote:

Originally Posted by amb 

9V = +/-4.5V rails, and this is when the battery is not near depletion. This is too low for AD8620. The recommended minimum supply voltage is +/-5V, and add the fact it is not a rail-to-rail opamp (it clips at 1V below each rail), results in a rather sub-optimal combination.

this is what i was trying to say earlier..amb put it together into the right sentence. i read your comment (tangent) regarding the above post as well, but i did not quite understand it (something about rail to rail supply)

Quote:

Originally Posted by i_djoel2000 

why can't i use the built in charger for charging paralleled 9v batteries?

It's not so much a "never do this" as a "not a good idea" matter. Batteries are very strange beasts when you start to really look into how they behave; they are far from ideal energy storage devices. When you put two in parallel, they interact, multiplying the number of strange behaviors.

In any case, I don't think you actually want to parallel them. I think you want a series connection and are confusing the terms.

Quote:

Originally Posted by amb 

9V = +/-4.5V rails, and this is when the battery is not near depletion. This is too low for AD8620. The recommended minimum supply voltage is +/-5V, and add the fact it is not a rail-to-rail opamp (it clips at 1V below each rail), results in a rather sub-optimal combination.

AMB is quoting the datasheet here, which isn't really on-point on this matter. The fact that the datasheet recommends a given running voltage and gives its test result graphs at that voltage doesn't actually tell you where the lower limit is. This test does, and in fact it's overly harsh for a PIMETA, since it will have buffers easing the load on the op-amps. Even if for some reason the buffers don't help at all, my worst-case 7.6 V number is close to the minimum useful voltage from an 8.4 V battery anyway.

Bottom line, I think you probably could effectively drain a single 8.4 V NiMH battery with an AD8620/10 combo before you made the amp clip.

That's not to say that the op-amps will perform their best at these low voltages. It is quite possible that they will sound better when run closer to the datasheet recommended voltage, or higher. To do that, you would need to put the two 8.4 V batteries in series, not parallel, to create a 16.8 V battery. The third paragraph here tells how to connect them.

Quote:

Originally Posted by tangent 

 

It's not so much a "never do this" as a "not a good idea" matter. Batteries are very strange beasts when you start to really look into how they behave; they are far from ideal energy storage devices. When you put two in parallel, they interact, multiplying the number of strange behaviors.

 

In any case, I don't think you actually want to parallel them. I think you want a series connection and are confusing the terms.

 

woww, so 7.2V really is barely enough..i think using 9v battery would be the best choice for portable, but i cannot get a long battery life with it

so just this afternoon, i came across this thing :

it's an ON-ON switch. implementation:

i'll use 2 x 9v battery in parallel, then put a switch between them. this way, i can get double battery life, by using single supply only. when the first battery runs out (after around 4 hours), just toggle the switch, then you get another 4 hours

charging would be easier too since the supply is actually single supply, not paralleled, i can use pimeta's built in charger

There are 3-position switches of that sort.  An on-off-on switch would let you center the switch to turn the amp off entirely, or you could use an on-on-on switch to have the "off" position be one of the two end positions.

Quote:

Originally Posted by tangent 

There are 3-position switches of that sort.  An on-off-on switch would let you center the switch to turn the amp off entirely, or you could use an on-on-on switch to have the "off" position be one of the two end positions.

i bought ALPS RK097 pot with built in switch from your shop. so i think an on-off-on switch should be unnecessary

i just finished my pimeta amp. now it is up and running :)

i got almost 0V dc offset using LM4562/LME49710 configuration. but i don't know why, the LED1 is not turned on when i turn on the amp, the amp itself is working and no problem whatsoever. any idea what's the problem?

and i want to ask about the trimmer pot. i used bourns 10k 25 steps. isn't the rotating knob should rotate in steps? because my trimmer rotates just like analog potentiometer, and i can't really hear any sound difference when i play with the trimmer pot except a little bit distorted bass when i set the knob to minimum. also the knob does not have maximum and minimum limit, i tried to turn it up to maximum impedance, but there is no maximum, the knob keeps rotating when i rotate them. is this normal?

nb: i did not install RLIM, i bypassed them with wire