[Soymilk]

i'm finally getting serious about building a maxed out pimeta. i've been slowly taking inventory of what i have available at work, and i made a list of the parts i'll be using. please point out any errors / things i'm missing. i have a few questions at the bottom too, so if you dont want to bother looking at the parts list, please at least scroll to the bottom and answer what you can out of those. thanks

Resistors - all 1%, whatever the light blue w/ colored stripes material is

R1(4) - 4.32Kohm (added one more for R4G, which i'd originally left out)
R2(2) - 100Kohm
R3G(1)- no stuff
R3(2) - 1Kohm, socketed
R4(2) - 10Kohm, socketed
R5(2) - 3.32Kohm, socketed
R6(2) - 1Mohm, socketed
R8(0) - jumpered socket, socketed
R10(2)- 1Kohm
R11(0)- not needed for discrete buffers
RLED - socket, play w/ diff values

Capacitors

C1(1) - .22uF (?)
C2/3(2) - i'll check to see what i have at work. i know there are nichicon 35V (480?)uF caps, not sure exactly what line they were (they had pl(m) on the side of em). i also know we use panasonic fm caps in stuff too. is xircom or something like that a good brand? we have 35 or 50v, i forgot, 1000uF caps of that brand (although they are quite large).
C4(2) - Wima MKS 2 6.8uF from tangent's shop
C6G(1)- 10pF NP0 Ceramic

Diode - not sure, i'll check to see what i have access to

Rail Splitter - TLE2426CLP

JFET Cascode set - from tangents shop

pot/switch - ALPS RK097 10Kohm pot

I/O jacks - 1/8" jack x2 (recommendations?)
case - most likely the black hammond aluminum extrude series w/ plastic ends
power source - jameco 24VDC, 500mA linear, regulated wall wart
power jack - recommendations?
knob - looking for one i like
led - whatever i can find for now

OPALR - AD8620
OPAG - AD8610

Buffers - i plan on building three discrete diamond buffers. do the different ones have different sound characteristics? im currently looking at the QRV05. any tips/things to look out for?

sockets - AE7313 (x5)


and now for some questions...

is it bad for R2 to be 100x pot vs the at least 10x recommendation? it does say bigger = better, right? should i just go for 100Kohm?

do i really need C1?

what i/o mini jacks are good, and what power jack is good?

does anyone know of where i could find a nice fat darkish preferrably metal knob? i'm looking for a dark gray/chrome color, but not black.

is it recommended to build the crossfeed circuit? how much difference does it make? if i understand correctly, it helps generate more realistic 3d sound, right? is there any reason not to build it?

thanks for the help

 

[MisterX]

What headphones you using?
A gain of 11 is massive overkill for of the headphones you will ever run across and it can actually lead to problems with some highly sensitive headphones.
You already answered you own question about sockets for the buffers.
100k R2
Measure the DC offset of your source(s) and see if you need C1.
Tangent's parts list gives you solid suggestions for the DC jack and I/O jacks.

No, you don't need crossfeed, in fact I think it is a waste because the Pimeta already has a pretty airy presentation.

 

[MrMajestic2]

A gain of 11 is quite high. I know, built it using the exact same resistors. Could be wise to think about lowering it a bit.

I wouldnt worry about R2 being 1M. I used the values in the schematics and it worked out great.

If you are not using BUF634 buffers, I dont think you really need R11 because that for bandwidth modification. Its not valid for the QRV-05. But it can still be mounted, it just doesnt do anything.

Dont get C1 unless you need it. Measure DC offset just like MisterX said. If you need them, 0.22uf is fine I think.
I used Elna Cerafine 1000uf/35v for C2/C3 and they are way too big. I had to tilt them on the board to make them fit.

I have the QRV-05 boards at home waiting to be built. I think the biggest worry I have is how to mount them in a good way. Since I tilted the C2/C3 I think I can get away with putting DIP sockets underneath the QRV-05 boards and mount them on top of the Pimeta.

Get sockets for the buffers and op-amps. Its much easier to change them around if you want. Also, socket the middle row of resistors if you want to play around with gain.

I skipped the crossfeed board since I dont like the sound of it. Not the actual board, but the effect.

I put header pins on all in/outputs for easy wiring.

http://www.head-fi.org/forums/showth...99#post3077699

 

[NelsonVandal]

Not only does different buffers sound different. Different output transistors have their own sound signature. I've only tried BC327/337 and BD137/138 so far, but I got MJE243/253 today and will try them sometime - in the future I'm afraid. The BD's are smoother and have a more powerful bass, and I prefer them over the BC's. The buffers I have are Sijosae's "diamond buffers" with emitter resistors. I've also built a pair of LISA II buffers, and the sound is a bit more "forward" than the Sijosae buffers. They still have that smooth BD 137/138 sound though.

If you're planning on a "maxed" PIMETA, you should go for buffers with CCS, like the ones by Mono. I think he called them Monofied Sijosae buffers. I think there's room in the PIMETA for them. There are more sofisticated buffers out there, but it would probably be easier to build a PPA v2 instead of a PIMETA.

LMH6321 seems to be a very "hot" buffer. I've only listened to it briefly, but it was very powerful and detailed. One problem is power consumtion and another "problem" is it's 12 V max.

I'd recommend you put the buffers on sockets so you can try different ones.

IMO the opamps have the greatest impact on the sound signature. Do some reading here on Head-fi on how different opamps sound.

 

[user18]

Don't forget the Browndog adapters for the opamps.

 

[Soymilk]

thanks for the replies!

i forgot to put that i was going to socket that middle row of resistors, too (i think it was r3-r8? something like that), so that i could change them around in the future if i wanted to.

haha yes, i realized while at work today that i'd just put the given values for the gain loop without thinking too much about it, and that they had a pretty high gain. what should i aim for? i'll currently be using a modified ksc75, but in the future i plan on getting a dt770/80.

my pimeta isn't going to be a portable one; i'm not planning on sticking batteries in at all. this should give me more flexibility with how to case it, since i can use a larger enclosure. i'll probably not have the buffers directly mounted to the board since it may get clustered that way, unless there's a reason to mount them?

i'll try searching for some more info on the other db's. so far i know of the qrv05, sijosae db, and monofied sijosae db. are there others i should look at?

 

[Soymilk]

i forgot to add, i wrote down more specific info on the caps i have available that i could use for c2/3 instead of going off of memory.

330uF 50V - had NKL on the side of em
470uF 50V - had Meritek on the side
680uF 35V - nichicon PL(M)
470uF 50v - xicon

also i saw a bag of 330uF 50V panasonic FM caps a week ago, not sure where they went though.

which of these would be the best to use? should i go for the nichicons? we also have 1000uF xicon 50v caps, but those are huge. but since i'm not trying to go portable or compact, should i just use those and mount them tilted?

 

[Soymilk]

oh yeah, so i need two of the so-8 to dip-8 adapters for my opamps, right?

 

[MisterX]

Unless of course you solder the op-amps directly to the circuit board.

I think I would go with the Panasonic caps....

 

[Soymilk]

alright, i'll see if i can find em. and yes, i want to keep things modular so that if the mood strikes me, i can do some opamp rolling in the future.

 

[MisterX]

I always considered the Pimeta to be one of the better platforms to get your feet wet with SMD soldering (assuming you have not already done so) because those pads are expendable.

But I certianly understand why you would want to use browndoggies.

 

[Soymilk]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif I always considered the Pimeta to be one of the better platforms to get your feet wet with SMD soldering (assuming you have not already done so) because those pads are expendable. But I certianly understand why you would want to use browndoggies.

well i have plenty of experience with SMD soldering, that's 90% of what i'm doing at my summer job right now. lots of (i forget the abbreviation) IC's that don't have pins sticking out, those are annoying, and when i see 0805's i think woah, big

. it just seems like it'd be annoying to remove / solder on another one if the board's already populated.

what value would you recommend for rled? i'm not too sure what kind of numbers i'm looking for, i was thinking something like 10K?

edit - and what value should i be looking for for R4? the gain calculator on tangent's site isn't loading for me

 

[AudioCats]

if you don't have to use batteries, why not build a regulated +/- power supply and skip the ground channel? Better sound and cheaper too.

 

[Soymilk]

Quote:

Originally Posted by AudioCats /img/forum/go_quote.gif if you don't have to use batteries, why not build a regulated +/- power supply and skip the ground channel? Better sound and cheaper too.

because then i have to build it. maybe in the future, but for now i want to focus on building the amp, not other stuff.

 

[Soymilk]

so i'm back from work today, i left early cuz i got bored and it's july 4th. wanted to check to see if the resistor values i found were fine, since many of them aren't quite what the schematic called for (but pretty close).

R1(4) - 4.25Kohm - i forgot that since i'm changing the gain loop values i needed to change this too, right? so now i should get 3.38Kohm resistors for R1 and R4G?
R2(2) - 100Kohm
R3G(1)- no stuff
R3(2) - 1Kohm, socketed
R4(2) - socketed - 4.25k
R5(2) - socketed - 2.38k
R6(2) - .99Mohm, socketed
R8(0) - jumpered socket, socketed
R10(2)- 1Kohm
R11(0)- not needed for discrete buffers
RLED - socket, play w/ diff values

i played with the gain calculator, and with these values for r3-r6 it should give a gain of a little over 5. is that still too high?

also, i found the 330uF panasonic fm caps, so i have 4 of those for C2/3.

edit - i also picked up a 10pF and a .22uF for c1 and c6. are capacitors of these values normally the type of material called for in the parts list? (10pF = np0 ceramic, .22uF = film)

i also got a few diodes, but they werent labeled very well so im not sure if they meet the specs or not. one had "diode 1w5711" on the bag, another had "diode 914", and another had "diode 4148". is this enough information to figure out the general specs of any of these diodes?