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PPAS Build Thread. - Page 9

post #121 of 254
Well, I'm convinced that I'm just going to need to find some funding and get more boards, because I want to try 8620/8610/buf634, 2107/something/buf634, and 2107/something/lmh6321 and I only have 1 board left.

Right now I'm thinking 2107/something/lmh6321 - you've said it was very detailed and had a nice slam, would you say it was less bright than the 8620?

Battery drain isn't a problem because I made a pack out of AAAs. I'm not sure if I wanna go with the lm6171.
post #122 of 254
Finally posted a full review found here:

http://www6.head-fi.org/forums/showthread.php?t=203099
post #123 of 254
Wow, yesterday I got the PCB for this little amp. I am so happy, because of I was never able to get a PINT PCB and I truly need a portable amp. Now I have a couple of questions. Could someone list multiple opamps combinations to be used on the PPAS? Also, it seems really impossible to find a SST310 online here in Italy; which else could be used?
post #124 of 254
The original thread lists many combos of opamps and buffers. The ones that say 2701 are actually opa2107, which I prefer with opa627 ground and buf634u buffers.


As for the SST310, you can use BSR57 just fine and is probably more available.
post #125 of 254
Quote:
Originally Posted by ozshadow
The original thread lists many combos of opamps and buffers. The ones that say 2701 are actually opa2107, which I prefer with opa627 ground and buf634u buffers.
Come on, just 2-3 items, like
x1, y1, z1 : laid back
x2, y2, z2 : details
x3, y3, z3 : fantastic!



Quote:
Originally Posted by ozshadow
As for the SST310, you can use BSR57 just fine and is probably more available.
Thanks, but it seems hard too.
post #126 of 254
Thread Starter 
http://www6.head-fi.org/forums/showp...75&postcount=1

Thats the first post of this thread, I tried to compile my impressions on working opamps.

NB that LM6171s are confirmed working, so the AD8066/LM6171 combo should work

By next week I should be able to get LM6172 working (i have an idea in my head, just havent had time to get to iron) so i'll give impressions on that and the AD8057

TBH, I reccomend the AD8066 for low draw, OPA2107 for high draw use, the AD8620 when compared to the others is too shrilly.

And the LMH6321s are better all around, but just has a higher draw.

As for the JFETs

http://www6.head-fi.org/forums/showp...37&postcount=4

is a list of alternatives
post #127 of 254
I think a key part of what setup you get depends on what headphones you use.

Like for Grados, I find the 2107/627/buf634 is a very nice combo
For darker Senns, I'd say 2107 or 8620/8610/buf634 or possibly 6321 if you can handle battery drain
For K701's and many IEMS, it basically depends on your personal tastes and what you listen to.
post #128 of 254
Quote:
Originally Posted by ozshadow
or darker Senns, I'd say 2107 or 8620/8610/buf634 or possibly 6321 if you can handle battery drain
My 8620/8610/6321 combo uses about 43mA, which will kill a 170mAh 9V in a little over 4 hours or a 250mAh in a little over 6. I use it with a 15xAAA 700mAh
battery pack and it lasts quite a while.

That being said, with Ety ER4 this combination is almost too harsh in the highs. Dunno how that compares to the headphones he has, but it is something to watch out for.

Based on your and ATAT's comments, I'm thinking about trying 2107/???/6321.
post #129 of 254
Thread Starter 
Opamp / buffer selection table--

---- Buffers ----

Purpose - Home mainly, occasional portable use
LMH6321, Class-A biasing, Trickle charging, larger hammond case.

Purpose - Mainly portable use.
BUF634, Small case.

----- Opamps ----

Sound wanted -

Bassy sound (good with IEMs, K501 .etc)
AD8066 / OPA132

Midrange / Dynamics / Detail (generally good all around, but esp with Grados, some IEMs)
OPA2107 / LM6171 (for highend detail)
OPA2107 / OPA627 (for more soundstage / midrange)
--- NOTE -- the OPA2107 requires 2x9v for low offset use.

Treblehead / "ER-4 type detail" (HD650? dont own any dark cans do dont know)
AD8620/AD8610 (too shrilly on cans with emphasized high ends, but could be good with HD650 types..)
-- Note -- AD8620 is extremely low draw, BUF634 + AD8620 can last an ungodly amount of time.



I'll refine this as time goes on.. anyone have anything to add?
post #130 of 254
Thread Starter 
Quote:
Originally Posted by pddjsteve
My 8620/8610/6321 combo uses about 43mA, which will kill a 170mAh 9V in a little over 4 hours or a 250mAh in a little over 6. I use it with a 15xAAA 700mAh
battery pack and it lasts quite a while.

That being said, with Ety ER4 this combination is almost too harsh in the highs. Dunno how that compares to the headphones he has, but it is something to watch out for.

Based on your and ATAT's comments, I'm thinking about trying 2107/???/6321.
my 270 mAH Accupowers go down pretty quick with this config (OPA2107/LM6171/LMH6321) I measured around 7 hours.

Also, 15x AAA? what case are you using and how do you recharge it?! dear lord.
post #131 of 254
Quote:
Originally Posted by ATAT
Also, 15x AAA? what case are you using and how do you recharge it?! dear lord.
It actually is 2 packs I made from AAA solder tab cells. I threw it into my hammond J1201 that had previously housed a cmoy and 2x9V. One pack is 12xAAA and it fits in behind the amp, in a 6x2 config. I ran it like that for a while, with 14.4V, then got the idea to add the other (3xAAA) which is just kind of crammed in around the jacks. I made a lm317 trickle charger but changed the resistor so it would charge the 700mAh instead of whatever the pint value would do. I charge it overnight off a 24V wallwart.
post #132 of 254
For non rechargeable people, a regular 9v is about 540 mah, so thats like 30 something hours typical.
post #133 of 254
Quote:
Originally Posted by ATAT
Opamp / buffer selection table
Thanks.
post #134 of 254
What the actual difference between an A47 and PPAS? As far as I recognize, the're both opamp + buffers designs, so where lies this big gap in soundquality?

edit: never mind, I found an answer:

Quote:
In the A47, you'll notice that the opamps aren't in series, they're actually in parallel. The output from the first half is driven in the input of the second half (this is how the gain is set), and then the two opamps are paralleled at the output. The resistors are there to stop large currents flowing between the opamps due to slight intrinsic differences.

In series, no benefit. In parallel, more current
So to rephrase my question, how does the PPAS compare to other opamp + buffer designs? What does it make so 'special'?
post #135 of 254
Thread Starter 
The PPAS is 3 channel buffered.

CMoy- Passive 2 channel
A47 - Parallel no-buffer 2 channel
PINT - 3 Channel no buffer
MINT - 2 Channel buffered

..

Also there is changes in the power supply
JFET isolation prevents ripples in the high current (buffer) supply from affecting the opamp supply.
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