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It won't reduce the battery life at all if you disconnect the charger after about 24hrs. It's been awhile since I looked at the calcs in this thread, but I think - 250mah/12ma =~21hrs. That small of a current you can probably leave connected semi-continuously. Not that you would do that, but it's not going to hurt if you forget for a day or two.

About the walwart - it's gotta be DC, and the batteries can't be more than the 8.4V variety - a 24V walwart is somewhat close at that rating (with 2X batteries, of course). If you used the 9.6V batteries that are available places, it won't cut it. Of course, the paragraph above assumes 250mah batteries. Those are pretty easy to get by a number of e-bay sellers. (I think the Thomas and MAHA's are way too expensive.)

Jameco has a very nice 24VDC at 500ma linear, regulated walwart for about $13. It gives pretty good sound when connected to a PIMETA - the bass is a tad "squishy" compared to a full-blown TREAD or batteries alone. If you're using Grado's, you may not even notice that deficiency (no offense).

I can't predict for your amp, though - the 500ma is a typical size walwart for headphone amps. The charger itself, as noted above, only uses 12ma. Adding double buffers and biasing probably brings a PIMETA up to 150-200ma, but maybe not that much. Your A47 will be less than that.

Please let me recommend a PIMETA. Tangent's design is genius in its simplicity. If you are contemplating something more than a CMoy, but less than a PPA/M3, the PIMETA is it. It is far superior to an A47 and can be built very cheaply.

Thanks for your answer tomb!!!!!!


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I've found a pretty cheap wallwart at a local store that I think will do. Anyway I don't plan to listen to the amp while plugged, it's just to recharge batteries. And, yes, I will probably use it with a pair of sr-60, . But I'm making the amp for portable use, so it will be permanetly connected to my k81 (since I bought them my other cans look at them with jealousy from the bottom of my shelf )

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Don't worry!!!!! a PIMETA is on the list, and so a PPA and a SOHA and probably a Millet and.................
I'm just new to diy (just a couple of cmoys) but I'm enjoying it much and it's going to be a long lasting hobby, I just want to start from the basics and learn as much as I can.


Thanks again!!!!!!

I hate to ask this but can anyone give me a full picture of all of the wires spread out so I can tell exactly where they all go. I think I know what is going on but not positive.

I am sorry it's not clear to you right now. I guess I should've photographed the entire assembly with the wires connected. If you refer to this photo:

1. The battery connectors are wired together - red wire from one is soldered to the black wire of the other one (melt some heat shrink on the joint). This leaves you with two 9V connectors with {one black lead<->connector1<->redblackjoint<->connector2<->red lead}.

EDIT: See the photos post below. The above is not really true - I used all of Tangent's prepared pads. The middle "+" and "-" pads provide the series connection between the battery sockets. However, either method is equivalent.

2. The black wire on the DC plug socket is the walwart/Tread negative lead. It bypasses the trickle charger completely and connects to the PIMETA board in the (-) position with the black lead of the battery connector assembly.

3. The red lead of the battery connector assembly is connected to the bottom terminal of the trickle charger perf board.

4. A short purple wire is connected from the positive terminal of the DC socket to the input of the trickle perf board. A longer purple wire (almost the same length as the black DC socket wire) is connected to the amp power output of the trickle charger: the middle position. This wire becomes the (+) power connection to the PIMETA board.

If no voltage is flowing from the DC socket, the battery (+) is routed through the single diode into the purple wire at the middle of the trickle perf board, and into the PIMETA.

If the DC power is connected (must be at a higher voltage than the two batteries), then battery voltage is blocked, except for the small trickle current provided by the VREG (LM317 - TO-92).

Of course, the PIMETA switch must be thrown before the circuit is complete to the amp. The trickle charger, however, will continue to flow current to the batteries as long as the DC source is connected.

Somewhere along the way in the discussion of the trickle charger, a 3rd diode was deleted. This diode used to be where the wire jumper is on the bottom right of the perf board. What this means is that if you connect a TREAD or other such source that has its own LED, and you do not plug it into the wall source, the batteries will drain backward through the walwart/TREAD's LED. It's not much of a hassle, but there are some people who keep their power plugged into a power strip and flip the switch on the whole thing.

I hope that helps. I'm not in a position to take my PIMETA's apart, photograph, and post them right now - maybe later on.

Alright, so you will have 3 wires running into the Pimeta instead of the normal 2 right? you still hook it up as a single supply and not a dual? I am pretty sure I understand. I don't want you to take them apart cause I know that is a pain I was just wondering if anyone already had a picture. Thanks a lot.

Yes - the batteries are treated together as a single supply. Because of the charger, the only wire that is paralleled is the negative lead of the DC socket and the negative lead from the battery string. Even then, they are soldered together into the same position on the board: (-). The only other wire soldered to the board is the purple wire from the mid-position on the charger: (+). EDIT: I actually used the extra pads - see the photos post below.

Tangent has provided the intermediate battery connections (M's) for convenience. However, adding the trickle charger is a little bit confusing compared to the original design. Soldering the battery leads together in the middle lets you think of the assembly as one battery only, simplifying the rest of the issues with connections.

At least, that's the way I chose to do it.

EDIT: Reviewed my notes, extra length was not an issue.

Hello,

I'm new to DIY so please bear with me. I built a Pimeta powered with 2 Tenergy 9v rechargables. Info with them says they are rated at 9 v, 250 mAh
http://www.all-battery.com/index.asp...ROD&ProdID=523
I built the trickle charger as described by Tomb and bought the suggested Wall Wart (linear-regulated 24VDC @ 500mA). The amp runs fine using the Wall Wart and sounds great with the batteries. But, I only get about 2 hours on the batteries after charging for 24 hours or more (listening with Grado 60's at low volume). Is that normal for this amp or is the battery voltage too high for the 24V power supply such that I do not get a full charge? Or, did I wire something up incorrectly (Voltages at various points on the board are "correct", approx 9V). Thanks!

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The Tenergy's are exactly what I use and I get 4-5 hrs use. That's with double buf's and the Tangent transistor-option for biasing into Class A. With the trickle charge of about 12ma, the charge should take 20-21hrs. The walwart, as described, actually puts out about 23.9V.

If this is your result with the batteries brand new, they may need exercising. It takes 3 or 4 charge cycles for the batteries to attain full charge capability.

If that's not it, you might look at wiring, or any additional component that could be drawing much higher current out of the batteries. For instance, a high-powered LED could draw 20-30ma, which is significant at this level of power draw. Or, if for some reason you have an opamp or buffer oscillating, that could be drawing more power. My results are typically with KSC75's, and the Grado's will draw more current, perhaps, but the Class A biasing should negate this difference, I would think.

Anyway, those are the things I'd check - maybe someone else can think of other possibilities. I'm hopeful that perhaps your batteries are just not broken in, yet.

Thanks for your reply Tomb! I've got the double buffs, but not the Class A bias. The batteries are brand new. Also, right now the OP amps I am using are TI OPA2132P and OPA132U. I'll install the AD 8620/8610 combo as soon as I get another Brown Dog adaptor and see if that makes a difference. Thanks again.

A number of people have been asking me about the exact connections to the board from the batteries, trickle charger, and power jack. So, I did some research and took a closer look at how I did my PIMETAs. As it turns out, I didn't connect the two battery sockets in series, but used all of Tangent's pads, instead. That's the same thing, really - and it makes no difference which you do - either connect negative to positive between the two battery sockets, or use the second set of pads on the PIMETA board.

In either event, here are some prepared photos that completely document the connections. I trust that they will be self-explanatory. If not, please post and I'll try to elaborate further. Thank you for your interest!

I've been trying to figure this out for days, but I'm going to leave the head-scratching for later days and just ask.

In the equation R = 1.25/(Battery capacity in mAh/10), where is this 1.25V coming from? Is this across the LM317? The schematic suggests two 9V batteries and 250mAh capacity. I am running on one 9V (rated at 7.2V) and 150mAh.

I have within reach a few wallwarts: 19VDC, 3.42A; 12VDC, 2000mA; 14.4VDC, 1000mA. I'm not sure the 14.4V one works, but suppose I were to use the 12V one, what would the resistor value be? I tried it setting R = 47 ohm and using the 12V wallwart, but I got this huge humming noise which completely sapped the bass (the humming was annoying too ).

Would I use the same equation, R = 1.25V/0.015A = 83 ohm, for the charger? Or is 1.25V a different value?

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1.25V is the voltage that the LM317 regulator maintains between pin ADJUST and pin OUT. Place a resistor between those pins and it sets the leaving current from the regulator.

Quoting Tangent from another thread:
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His reference to charge current as 1/10 the battery's mah rating is a general rule-of-thumb recommendation for trickle-charging batteries (equates to 10hrs, actually). So for your 150mah, you'd probably want 15ma.

R=1.25/15 = 83.3 ohms. Anything from 75 to 100ohms is probably fine.

Quoting Tangent again from his PPA battery board article:
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In your case, 7.2V is 6 cells. So 6 * 1.55V = 9.3V. You have about 3V across the LM317 and the 1.25V across the charge current resistor, so 9.3V + 3V + 1.25V = 13.55VDC. Consequently, your 14.4VDC and 19VDC walwarts will work, no problem. This is a very conservative estimate, but your 12VDC walwart is probably not close enough to be useful.

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I suspect the humming heard is due to it being unregulated, and as such it may be unsuited to charging while simultaneously listening, but with it's 2A current rating may be floating high enough to charge the cells (something a multimeter could check).

Ha! I just thought of this. I have a couple of 270mAh batteries so I would need a charger above 540ma? I never think of this stuff when I go to buy things.

Assuming that the batteries are in series, the current won't be affected. However, you will need a higher voltage. I ended up using a 24V wall wart for 2x9V.