A mini PPA v2,my first portable attempt. - Page 3

yes, problem is that i have 13mm to work with, shortest I can get the op-amp board is about 11mm, that leaves 2mm to work with. I did find some pin sockets on newark that look very prommising.

WOW, listening to it now

MacBook>grubDAC>miniPPA>M50 headphones, sounds very very nice, im a truly happy camper

This is how the batteries sit, the paper underneith it is a layout i am working on for a larger case.

close up of the battery, three of these will fit in the case, but with the protection PCB it is a very snug fit.

detail of the bottom of the board, component leads need to be trimmed flush, if not slightly recessed, in order clear the bottom of the case and prevent shorting. I reflowed all the joints several times (with plenty of flux) to ensure good joints, and to smooth them down as close to the board as possible.

A comparison of two cases, left case is the one i am using, case on the right offers  a bit more headroom if the PCB slot is used, but has actually slightly less usable width due to the screw slots. It is 10mm longer also. The main benefit of this case is it would allow stacking an extra cell with room to spare. With a re design of the whole board (see print out in first pic) it would allow use of 4 1250mah cells (larger cells in pic), this might be a good option for someone who would put up with the extra bulk to get more voltage and longer run time.

this is where this hobby gets me into trouble, It's 12:40 and i have to get up in 4 hours to work another 16 hour day (6th in a row) and i can't bring myself to turn it off.

of course i am biased, but damn this thing sounds great. it has everything i love about the PPAv2, amazing detail, separation and sound stage, tons of power (in fact i have decided i need to cut the gain down 40-50%), and very black(?) noise floor, not sure the proper audiophile term here, but it is soooo quiet in the background, little details in quiet sections of music really pop out. in short its a PPA

I tried it with my ultrasone pro 900's also, everything as above but even more detailed, too detailed on some tracks (poor recordings, low bit rate etc.)  so i went back to the M50's as I usually prefer them anyway, the 900s can sometimes sound too metalic in the highs for my taste.

woo-hoo

There are a couple other people who have expressed interest in some boards, I was going to make another order anyway, but if others want a board that will help keep the price down. I would love to have others try this out.

I have been slowly putting the final touches on the new board, nothing earth shattering, but as it sits the op-amp bypass caps have been moved to the back side of the op amp board. These will be large SMD film caps, however there seems to be a large selection of SMD film type caps, so people should have the option of using large uf polyesters and similar, or ~.1uf high quality polypropylene. Might have too get a little creative mounting smaller sized (1206) caps, but should still work fine.  Maybe some more experienced PPA user can weigh in on this, but I think the "standard" 1uf polyester film cap is probably perfectly fine for 99.99% of op-amps.

I have moved the charge connector so that it doesn't interfere with the volume knob, and I revised the op-amp power circuit layout to a much cleaner design, most of the traces are on the top side, thus giving a very nice un-interrupted ground plain on the bottom. I also changed the layout of the buffer daughter board, it is smaller and has a cleaner layout, and no longer requires power and ground internal planes.

All in all i think the new boards will work just fine, and hopefully will work better with more finicky op-amps.

I also think i may have found a way to make the op-amp board(s) removable.

The one thing I would like to do is get a bigger battery! I initially thought that with 20ma for each buffer, and say 8ma for each op-amp, i would have a quiescent current for the amp of 84ma, so round that up to 90 ma, a 900ma battery should last at least 8-9 hours.

what i am finding, is that with 20ma buffer bias, and even lower power op amps (less than 2ma draw each, so figure 3ma with 1ma bias) the amp draws close to 120ma at a dead idle. So battery life is down to 7 hours or so.

of course 20ma bias is not the minimum, but its what i wanted to have. this was never going to be a long battery life amp, but i was hoping for 10 hours.

So, with almost half of the board space reserved for premium quality caps, i am pondering building another layout (in addition to the current one) that would use smaller (but still very good) caps, or even some of the new Panasonic EEH series that were recommended. Doing this It may be possible to use the same case (i love this case) but get a 1250mah battery installed. another option is to go with the 120mm long Hammond case, its a good match for the new iphone, and would allow for a larger battery, i just need to find a battery!

So, there will be board available, hopefully early next month, I hate to put a time line on it, but i have a habit of getting a board 99% done in a few days, then spending weeks on the last 1%..... so maybe if i set a deadline i will focus a but more...

joe

No, neither of them are. My plan was to just use the plastic cap, or to use a small piece of heat shrink around the output connector if i put an aluminum faceplate on it. I could just get an insulated connector, but i like the heavy duty look of the metal ground ring.

I finally got around to fully charging the battery pack fully, seems to top out at around 12.9v. I am running a test on it now to see how long it will last with my M50's playing fairly loud, just lower than is too loud for me. Op amp bias is 1ma, buffer bias is 20ma.

I also took the opportunity to re-test the DC offset, with the bass boost all the way down, and then all the way turned up.

With the BB turned all the way down, the DC offset is 0.2 to 0.3mV per channel , with the BB all the way up it goes to 1.2-1.3mV,  I'm thinking that is pretty hard to beat.

As for the second board design to allow a larger battery, that is looking fairly promising also, I am looking for input on caps though. the current board design will allow for up to 1000uf for main power capacitance, and 100uf for the op amps using premium caps(silmicII), and 1800uf/~200uf using slightly less botique caps (nichicon FG for instance).

The large battery design gives up some of this space, there may still be room for 1000uf of the botique caps, but I had to remove 1/2 of the op amp caps.

If any of you out there have found a cap that shines in the PPA or simillar amp I would love to hear about it, I want to make the board(s) as versatile as possible.

Joe

Battery test results 11.1v, 900mah Tenergy battery. 1 year old.

1641 op amps, biased at 1ma

buffers biased to 20ma.

Amp draw at idle ~120ma

headphones: M50 for first 4 hours, ultrasone pro 900's for the remainder.

Total listening time was 6.5 hours.

Not terrible, and seems about on par with what the battery should do. 6.5 hours would indicate an average draw of 138ma, that is consistent with the readings i was getting on my meter.

So, by my calculations, if the op amp bias is reduced to 10ma per channel, that would equate to ~8.3 hours of run time.

Should get more work done on the boards tomorrow, I will most likely order two boards on the next run, a revised version of this one, and a modified board that will sacrafice a little capacitor space for

a larger battery.

I am working on getting some PCBs, there appears to be enough interest to do at least a small group buy.

I'm a little apprehensive about making a bunch of boards, i would like to let a small group of experienced builders put some together to sort out any potential issues.

This is definitely not a project for beginners, there are a lot of small SMD components on this board, and due to the small size, not all of them are labeled, or labeled well. The boards and component leads have to be very carefully put together in order for it all to fit in the case.

As I stated before, I have a new revision of this board ready to order that will hopefully make it more stable with finicky op amps, as well as allow op amp board(s) to be easily removed and replaced.  but I am putting the finishing touches on a completely re-designed board that will allow a 30% larger battery pack at the expense of board space for caps (see previous post).

 If I order both at the same time it will save on production costs.

I am looking for input from people on what they might want in the board, obviously there are huge space constraints, but I have already added pads for Panasonic EEH series caps due to several PM's from a helpful member.

Joe

Quote:

That sounds great! At least there are no dac chips(looks like mostly transistors and resisters). I think it'd be great if some main components( caps,transistors, or even case) are included in the package? It is just my 2cents.

No on-board DAC.........yet....

I'm not sure I would be able to devote enough time to putting together complete or even partial kits, not that it is out of the question, but that takes a lot of effort to do properly, and i would hate to disappoint anyone.

Most of the components are available at mouser, even the case. I have built a BOM that will help getting the parts from them.

Off the top of my head, the parts that will need to be sourced from other vendors are:

Op-amps(mouser doesn't carry a lot of the poplar ones) and SMD caps------ Digikey or Newark

Battery (3 cells and PCB) ------ All-battery.com

So it shouldn't be too hard to get everything that is needed.

joe