[tangent]

Both bran damages fixed.

 

[MisterX]

Pfew, you really had me going for a minute there.

 

[headfone]

Quote:

Originally Posted by tangent /img/forum/go_quote.gif I've updated the PIMETA v2 docs to distill some of what we've covered here. Better coverage of how NiMH batteries behave, with pretty graph Redrawn schematic, human-friendly

Thx for doing this. Currently, I'm experimenting with running two 9.6V 230mAh (ea.) cells in parallel. But no dedicated experiments, as above. I just need some "convenient" power for my music. I'll report on anything noteworthy.
BTW, the image below is a partial look inside a Maha 9.6V 230 mAh batt. (a unit from late 2006, anyway). One of the terminals broke not long after I purchased it so I had to perform a bit of surgery. This is one of three 9.6V batts I purchased in late 2006. Surprisingly, this broken unit is the only one of three Maha Powerex 9V batts that my Maha charger still accepts -- the other two fault out for, I assume, high resistance/impedance.

 

[tangent]

Quote:

Originally Posted by headfone /img/forum/go_quote.gif 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.

 

[headfone]

Quote:

Originally Posted by headfone /img/forum/go_quote.gif Currently, I'm experimenting with running two 9.6V 230mAh (ea.) cells in parallel.

I repeated this test twice. Conclusion: two parallel 9.6V Maha, that I own, run no longer than either by itself. And that is 35-45min.
As noted earlier, I've had issues with Maha products acorss the board: batts of all sizes as well as their chargers.

 

[KeeChoon]

I had used a 850mah 2 cell LiPo battery (8.4v fully charged, the size of a standard 9V) for my Cmoy with good results and is considering getting a 3 cell LiPo (11.1v, 12.6v charged) to power a v1.1b Pimeta.

As I have chargers from my R/C car hobby, I have no problems charging them. Alot of these LiPo compatible chargers are rather economically priced compared to the 9V chargers I can find. There are also tons of such battery packs used in the R/C hobbies (NiMhs are almost extinct in the hobby nowadays) now and those at lower discharge rates (10C to 15C) are cheap.

 

[Spacehead]

200 mAH last about 5 hours
 
I have AD8620+ 2x HA-5002 + one led (10K RLED) + AD8022  + TLE2426 = 32.6 mA 
 
6x1.2V (2500 mAh each) last 70 hours.
 
you shouldn't have any problems with 9V battery. If the voltage gets too low sound starts to distort and dc offset raises. So must not leave amplifier on for long time. 
 
Those op amps work with about 8 volts. 

 

[zarcondg]

Quote:

I've updated the PIMETA v2 docs to distill some of what we've covered here.

Redrawn schematic, human-friendly

"O" that figures... lol. I should have looked at the PIMETA within the past few years.
I recall that being a 1M ohm resistor, not a 499 kilohm & 4.7pF. O.K v2 vs V1
 
Akin to the ground channel in the PIMETA v1.0, [C1 on Figure 4 in the BUF634 datasheet]. 10pF or 4.7pF that is the question. 220pF is way to big for an 8 Megohm buffer input impedance vs feedback loop impedance. Would the larger cap (10pF vs 4.7pF) make a bad difference in the audio band?
 
10pF it may be, as the boards are in, and that is what the silk screen calls for. If it gets installed at all, the provisions are there if need be. There are other ways, to defeat RFI.
 
P.S. the LMH6321 has a 250 kilohm input impedance, vs the BUF634's 8 megohm impedance.
well till later, I need some sleep. The OPA2134's and BUF634T's arrive today.

 

[tangent]

Quote:

I recall that being a 1M ohm resistor, not a 499 kilohm & 4.7pF. O.K v2 vs V1

 
Yes, I lowered those resistors because there's no reason for them to be 1M if the largest likely pot value is 50K.  If it makes you happy to use 1M instead, you can.  It will just raise the noise floor a bit.
 
 
Quote:

10pF or 4.7pF that is the question.

 
Answered here in the docs.
 
 
Quote:

220pF is way to big for an 8 Megohm buffer input impedance

 
Where are you getting 220pF?

 

[zarcondg]

I was exhausted, and I needed sleep. I don't want to hijack this thread, so I'll try to keep this short. (that didn't work)
Quote:

Yes, I lowered those resistors because there's no reason for them to be 1M if the largest likely pot value is 50K.  If it makes you happy to use 1M instead, you can.  It will just raise the noise floor a bit.

That makes sense, I saw that part of the schematic [PIMETA v1], scratched my head over the rather high value (thinking you were using the capacitive by-product of the resistor end-caps in the resistor package), and went back to the BUF634 data sheet Headphone amp [Figure 5, on page 9]. I'm using (mid-ref) 1k ohm (neg op-amp in) 10k or 22k ohm (BUF634 out), instead of there suggested feed-back loop (250ohm, 5kilohm). I'll eventually finish the page, and post the design (nothing special).
Quote:

Answered here in the docs.

I wish I had seen that back in 2006 when I first drew up the op-amp and buffer schematic chicken scratch draft. design #17 of 23 (I think there was, excluding revisions to any particular topology). Lots of reading here, much appreciated.
Quote:

Where are you getting 220pF?

BUF634 datasheet, Page 9, FIGURE 4.  "Boosting Op Amp Current.", [on chart in Figure 4] with OPA627, OPA132.

The OPA134 is not listed, scratches head. To bypass or not? Then I came across your (Tangentsoft) page on op-amps, there almost the same. Bypass it is.
What value? (Answer above link provided by Tangentsoft). It depends... lol

Back on toppic.
With PIMETA v1 battery life, the  BUF634 [bandwidth pin] resistor value may be of importance?
Would battery life testing with "Pink noise" or "White noise" into a predetermined ohm dummy load, rather then just a single sine wave be more accurate or useful at all? can it be done easliy without a full fledged lab?
[? not .]
 

 

[tangent]

Quote:

I wish I had seen that back in 2006 when I first drew up the op-amp and buffer schematic

That section is new to the PIMETA v2 docs, which didn't exist in 2006.
 
Quote:

Quote:

Where are you getting 220pF?

BUF634 datasheet, Page 9, FIGURE 4.  "Boosting Op Amp Current.", [on chart in Figure 4] with OPA627, OPA132.

 
Realize that not everyone uses buffered op-amps for driving headphones.  Also, the BUF634 is a different beast.  As the PIMETA v2 docs say, you have to do tests to find out the best value for a given circuit configuration and load.
 
 
Quote:

With PIMETA v1 battery life, the  BUF634 [bandwidth pin] resistor value may be of importance?

 
Very much so.  It's covered here, and in the datasheet section referenced from that.
 
 
Quote:

Would battery life testing with "Pink noise" or "White noise" into a predetermined ohm dummy load, rather then just a single sine wave be more accurate or useful at all? 

 
Headphone amp designs of this sort are quite inefficient.  Most of the power that goes into the amp gets turned into heat, not into sound.  Testing the amp with a signal going through it won't usually give a huge difference in the measured value, and makes it difficult to compare results against quiescent current values, which are otherwise easy to estimate.  Signal testing has many other legitimate uses.
 
 
Quote:

can it be done easliy without a full fledged lab?

 
When you do signal testing, you should use signals that are as pure as possible.  If you don't have a pure source, it's often better to not bother with the test than try to make sense of the results you get from using a dirty source.