Interest Check: PPAS redesign? - Page 2

I'd respectfully suggest that you rename the project given the rather large technical differences between whatever it is that you design and the PPA. Or at least ask Tangent if he minds you calling it that (not to mention the others that were involved in the original PPA).

I haven't followed or read the original PPAS discussion, but I'm surprised at the omission of the power supply isolation jfets for the voltage gain stage opamps. These seem to be a key feature of the PPA and ppl's LISA III as well.

I personally think that AA or AAA is the way to go, why is 9V a better idea?

mwofsi: It does have PS isolation jfets - one set for Main_V+ vs OpAmp_V+ though, not on each channel, that would take too much room.

Ah, I missed that FallenAngel. That's what those are before the TLE. Still, 4 jfets used, only two more would give isolation on each channel. Mind you I've not even heard a PPA let alone a PPAS. Are they close?

I know that your a big PPA fan .

I would agree with a name change as well.

If you're going with the booster, I would see if it's necessary to have an RLC network on it before the LDO to remove/reduce switching noise.

Yeah, absolutely love the PPAv2 and still use the PPAS because it's by far my favorite portable. I'm sure the Lisa III beats it but for bang/buck it's incredible.

Depending on opamps and buffers used they sound similar, but of course PPAS is lacking with driving high impedance headphones.

I would like to build one too. I would like higher performance then longer battery life!

If you boost the 2 AAs to 10v (~4x) you will only be able to draw 1/4 the current you could at the unboosted ~2.5V. This will probably mean the amp will be choking from a lack of power.
On top of that the whole booster thing is inherently low fi and noisy. I don't think it is suited for what should be a high quality portable amp

Current draw on 3x Sijosae Class-AB + 3 opamps is going to be only 30mA, if you use low-current opamps.

I don't know about 2x AA, I'd much rather use 4x AA or better yet, 8x AAA like my PPAS right now. It's a little tricky because you actually have to solder the battery pack yourself but it's well worth it, then no booster is needed.

Of course, now that the scope seems to have changed so much. Ideas anyone?

I don't think so. 9V have horrible power density and are about the same size as 2xAA. We can more than double the battery life going with AAs. The disadvantage being a few extra cheap parts. Plus the batteries are cheaper, a fast charger can be integrated instead of a trickle, and in a pinch you can find AA's cheap and everywhere.

Last night I thought that a LiIon cell may be a good idea. We can certainly integrate a charge controller for it, my problem with that idea is that it ties the project to a nonstandard part and mounting it will be less elegant. I just don't think the advantage is there. An iPod battery for example maxes out at 2200mAh/3.7V and is too large to fit the Hammond, so less power than the 2xAAs, larger, and more expensive. Harder to get too.

Yup, always the plan

I don't think this is a problem NiMH have very low internal resistance compared to other types, and the current draw limits will likely be higher than one 9V battery anyway, which are notorious for having horrible performance in this area. With 1C (ie. 2.7A) performance not usually being a problem with any battery technology, when we're drawing < 30mA (x4) we'll be fine.

Have you heard anything using it? As I said, the HPDAC sounds great to me and uses this topology. It's certainly not noisy. And I don't see why it would be with PSRR in the > -130dB range for the opamps and should be > -100dB for the buffer stage. The JFET isolation, LDO and lowpass filter should cut any noise at least another 60dB or more, and it's going to be in the low millivolt range to begin with.

More than 2 AA won't fit in the smallest hammond in any orientation. You might cram 3 in if you soldered them together, but no more. The available options are 2xAA, 3xAAA (larger and lower power) or 1x9V. I'm personally leaning toward 2xAA as it's the most practical and should offer the best battery life. As far as performance is concerned they should be similar.

I really don't see why you can't fit 8x AAA into smallest Hammond. I fit them in a case just a bit longer and that's with with the original board layout.

AAAs are 45mm long and 11mm diameter. The case offers 16mm vertical space and is 50mm x 80mm. You could fit 7 AAAs with 3mm to spare (ie. not enough) in the length and you'd have to solder the pack since the holder won't fit. Did the screw hole portion of the extrusion not block this, it looks to me like it'd get in the way. You could fit 4 across, again without a holder, but only one pack would fit (why you need the longer case ).

Should we abandon this idea and go back to emulating the original PPAS since nobody can agree on a powering strategy? I was excited

You can fit 8xAAA, that's a fact. I soldered them together, you can also do it like the Xin SuperMacro and have a "2-level" PCB with battery contact points which is actually VERY cool and doubles the available board space right away (which basically creates room for PCB-mounted jacks. This would be my best case scenario, but I can understand how hard this will be to design.

How did you arrange them? I'm pretty skeptical, Wiki lists the nominal diameter as 10.5mm, times 8 is 84mm, 4mm longer than the case. They obviously can't be stacked, and they're too long for two rows. How'd you do it?

Though I don't think this will work, it will take up all the space needed for jacks, pot and PSU caps.

They're not stacked on top of each other, they're set up like this:

x-x-x-x-
-x-x-x-x