[zhoufang]

I'm currently building a PPA clone with standard perfboard.
The powersource will be a series of AA NiMH cells.
Now I'm having a difficulty deciding whether to use 16 cells or 20 cells.

The reason for 20 cells is that:
the max (open circuit) voltage across a AA NiMH cell will be about 1.4v
1.4v X 20 = 28V
when we minus the voltage drop across a diode (in case I put my battery in reverse direction) and across the rail isolation Q3, the rail to rail voltage seen by the op-amp will be safely below 27v, the highest that AD8610 can take. (so that I can still use AD 8610 while getting the highest possible rail-to-rail voltage which I think the OPA627 may benifit from.

The reason for 16 cells is that:
the maxium rail-to-rail voltage will never exceed 25v and most of the time below 20v, so I can use more capacitance with lower voltage tolerance caps (my local shop only carry 25v and 50v silmic caps, 35v is not possible) and can start using some OS-con (they cannot take the voltage of 20 cells£©

at the current drawn by PPA circiut the voltage across each cell will be around 1.25v for most of the life for the NiMH cell of my choice, so my question is:
To the OPA627/637 will 23v rail-to-rail and 18V rail-to-rail cause any noticable differance?

http://www.tangentsoft.net/audio/opamps.html
Tangent said "whereas the 627's performance falls off a cliff below 9v"
So is the 9v refering to 9v rail-to-rail or +/- 9v?

Thanks for viewing!

 

[flecom]

ive run my pimeta from 18v on 2x 9v's and AC from a 24v regulated ac adapter and havent noticed much (if any) difference

running it off a 9v battery (aka 4.5+/-) it sounded quite terrible

 

[alfaudio]

quoted on his site:"That is, when I say "10V" I mean that V+ is 10V above V-, not that I'm using a +/-10V supply."
So I think when he says 9V, he might mean +/- 4.5V.

 

[zhoufang]

flecom:
your info is very applicable for my problem.
So your Pimeta is using OPA627/637 as well?

alfaudio:
Thanks for the info!

 

[tangent]

Quote:

he might mean +/- 4.5V

Yes.

 

[zhoufang]

Quote:

Originally Posted by tangent Yes.

Thanks for your clarification!