The next step for me--PIMETA. Any advice?

[The Monkey]

After 3 cmoys and several cables, I am going to take the next step and build a PIMETA (thanks to n_maher for some advice on this decision). I don't want to break the bank, so I'll probably go easy on the tweaks (also because I'm still a DIY newb). Other than reading Tangent's wealth of information and reviewing this forum, does anyone have any advice before I get started? I haven't even ordered the parts yet. FWIW, I'll probably use 2 9V batteries and I won't be trying to fit it in a small enclosure. Just something I can take from the den to the bedroom.

Any and all advice is appreciated, as always.

 

[amb]

If you're going to power it with batteries, then make the amp draw as little current as possible to prolong battery life. This means use opamps with low quiescent current, no class A biasing on the opamps, no stacked buffers, and no wideband mode on the buffers. This actually helps you save money as well because you can skip some parts.

 

[mono]

IMO, since you need only limited portability and size isn't an issue, you might consider using ~ 12 AA cells instead of 2 x 9V.

This would give you roughly 10X the runtime between charges, OR not as much concern/compromise on the things AMB mentioned.

 

[The Monkey]

Quote:

Originally Posted by amb If you're going to power it with batteries, then make the amp draw as little current as possible to prolong battery life. This means use opamps with low quiescent current, no class A biasing on the opamps, no stacked buffers, and no wideband mode on the buffers. This actually helps you save money as well because you can skip some parts.

Am I making a potenially big sacrifice in SQ if I power it with batteries?

 

[Megaptera]

If you're looking at batteries to save money, you could get a cheap unregulated wallwart and put together a simple LM317 regulator (the kind the TREAD uses, if you like), and you'd be saving money by the time you'd have gone through your second pair of 9Vs. It would also let you do things like class A biasing, stacked buffers, etc. that improve the sound at the cost of more current draw.

 

[The Monkey]

Quote:

Originally Posted by Megaptera If you're looking at batteries to save money, you could get a cheap unregulated wallwart and put together a simple LM317 regulator (the kind the TREAD uses, if you like), and you'd be saving money by the time you'd have gone through your second pair of 9Vs. It would also let you do things like class A biasing, stacked buffers, etc. that improve the sound at the cost of more current draw.

Yeah, I'm on the fence right now about whether I should battery power it or get a wallwart. Is it possible to do both? I'm not necessarily looking to save money with the batteries (your point is a good one that over time they add up), but having to plug in the PIMETA in my bedroom could be inconvenient.

 

[n_maher]

Quote:

Originally Posted by The Monkey Yeah, I'm on the fence right now about whether I should battery power it or get a wallwart. Is it possible to do both?

Absolutely, look for a switching, isolated DC jack. If you want a Mouser part # shoot me a PM. Here's how I had the back panel of one of my PIMETAs set up.

Nate

 

[Sinbios]

How long could it be expected to run with class A, 2x stacked buffers, AD8620/AD8610, and one rechargeable 9V? I'm not worried about spending money on batteries, since it's rechargeable, I just need it to last longer than say, 14 hours.

 

[ROK3]

Quote:

Originally Posted by The Monkey Am I making a potenially big sacrifice in SQ if I power it with batteries?

Battery is generally considered a "cleaner" power source than AC. You would not be losing any sound quality with the batteries...

Hope This Helps,

ROK3

 

[mono]

Quote:

Originally Posted by Sinbios How long could it be expected to run with class A, 2x stacked buffers, AD8620/AD8610, and one rechargeable 9V? I'm not worried about spending money on batteries, since it's rechargeable, I just need it to last longer than say, 14 hours.

Random guess would be 60mA, about 3 hours give or take. AAA cells might get you 14 hours (ballpark) going on this 60mA guesstimation.

 

[Sinbios]

Quote:

Originally Posted by mono Random guess would be 60mA, about 3 hours give or take. AAA cells might get you 14 hours (ballpark) going on this 60mA guesstimation.

Ick, then I would need 8 AAA's, and my charger only does 4 at a time =_=

Is it possible to fit two 9V's into a serpac H65?

 

[mono]

Quote:

Originally Posted by Sinbios Ick, then I would need 8 AAA's, and my charger only does 4 at a time =_= Is it possible to fit two 9V's into a serpac H65?

Yes, two will fit- unless you want an amp in there too.

Even if you sawed-down the Pimeta board to be shorter, maybe even the case studs, in H65 you'd have at most 40mm clearance. It's at least 1, practically closer to 2 cm too little clearance for 2 9V batteries.

 

[Sinbios]

So, what are my choices? I don't think class A is a big deal, since it's 1.1mA... I guess the buffer stacking could be cut down. How much improvement in quality does 2x stacked really give? How much current draw does it cut down?

 

[Megaptera]

I found with my Pimeta there was a clear improvement going from one buffer per channel to two buffers on the left and right channels, and the ground channel unstacked. Current draw for the buffers depends on the bandwith control resistance (R11), and you can check the graphs in the datasheet to calculate that.

To figure out how long a given configuration would last, add up the total current draw of the opamps, buffers, LEDs, etc for a sum total. Then figure out the milliamp-hours that your battery configuration will provide -- somewhere in the forums there's a link to a webstore that lists mAh values for all different batteries -- and it's a matter of simple arithmetic from there.

 

[Sinbios]

Thankfully, I found this thread: http://www6.head-fi.org/forums/showt...v+battery+pack

Thanks to tangent's calculations, I think it'll last quite nicely with one 9V battery and one backup. Though, I'll still have to find out the operating current draw...