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AD843 - my new favorite opamp! - Page 2

post #16 of 29
Quote:
What annoys an AD843?
The only surefire way I know of to piss off an 843 is to power it up from a slowly rising power supply. You see this with bench supplies when you have the current limiter turned down too far, so that it stays in current limiting mode for several seconds while the rail caps on an amp charge up. Except that with an 843, current limiting stays on forever in this situation, because the chip drains a lot of power in this state.

There are other ways, but I've never gotten down to a science how to reproduce it.
post #17 of 29
Thread Starter 
So a wallwart PS with tons more amperage than the amp even comes close to drawing is unlikely to do this, I take it? It's an 18V 800mA wallwart.
post #18 of 29
aeriyn, what headphones were you listening to the AD843 on? Have any experience comparing it to OPA627s on Grados?
post #19 of 29
I have 2 AD843s sitting here. I tried them in my Pimeta with my MS2 and I prefered the OPA627. I was going to try them in my PPA, but I remembered I have the isolation JFETS at around 10ma. I don't feel like installing more just to test the chip. I doubt it, but will the AD843 run with only 10ma current?
post #20 of 29
Thread Starter 
As was stated previously, the AD843 draws 13mA of quiscient.

As for the headphones I'm using, they are my DT440s. I've never heard Grados on OPA627, but I've heard my headphones on OPA627 and it's not lively enough for me. Very detailed, very resolved, but slow. Too slow for me.
post #21 of 29
Quote:
Originally Posted by aeriyn
So a wallwart PS with tons more amperage than the amp even comes close to drawing is unlikely to do this, I take it? It's an 18V 800mA wallwart.
Yes your situation will not be effected by what tangent in describing, this is because in the case of the bench psu.

You can get it to maybe max current of 100mA.

While the AMPs rail caps are charging upto rail they might like 200mA, what this is doing is making their stored potential rise for some period of time.

You wallwart won't have any problems doing the initial charge.

I suspect this is why tangent and mouser go :S when not so experienced head-fiers like me say we are using 6000uF of rail cap in a PPA.

He knows that he can't tell the difference between a 2000uF rail and a 6000uF rail, and he also knows that the larger rail might bring out other problems that wouldn't be as apparent with the smaller rail.
post #22 of 29
Quote:
Originally Posted by @sia@home
... I suspect this is why tangent and mouser go :S when not so experienced head-fiers like me say we are using 6000uF of rail cap in a PPA.

He knows that he can't tell the difference between a 2000uF rail and a 6000uF rail, and he also knows that the larger rail might bring out other problems that wouldn't be as apparent with the smaller rail.
Funny thing is, I just pulled out all the C4 caps in a Pimeta and it still sounded pretty good with only 2 x 1 mfd film & NiMH battery pack. Had an OPA2107 in it though, this is only an initial impression not a comprehensive assessment. There "might've" been a small touch of distortion but it'd take a lot more listening to be sure.
post #23 of 29
Quote:
Originally Posted by @sia@home
I suspect this is why tangent and mouser go :S when not so experienced head-fiers like me say we are using 6000uF of rail cap in a PPA.
Hehehe, I almost put a 20,000 uF Sprague power cap in my first PPA clone. We just had it layin around the lab and I thought hmm....
post #24 of 29
I think there are some misconceptions about mfd though... these are ~ 100mA circuits, it is certainly not necessary to have thousands of mfd on the power rail BUT low impedance from these monster sized caps is a good thing (but mostly offset by sufficient film, ceramic and tantalums as per spec sheets for the chips).

It could actually be preferrible to have a 12.5mm x 30mm cap in a higher voltage & lower mfd value. That would keep very similar impedance, esr, but be gentler on supply components. So it's not that the voltage rating "needs" be higher, but that it can be a good thing to have low ESR without high mfd. Of course there are organic, tantalum and more exotic ways of achieving this but the staple electrolytic is often most cost-effective... just so darn B I G for a portable amp.
post #25 of 29
On a more related note, the 843s sound really interesting since I'm into more agressive music, so I'm grabbing two w/ my next order to newark on monday to throw in my new pimeta that I am almost done with. It's sporting 8xAA @ 2000mAh for power, so even w/ the high draw of those op-amps and 2-1-2 stacked buffers, it still has almost 20 hrs of life on a charge. Should be a perfect match for those Grado 125s I'm getting friday
post #26 of 29
I did a brief spot-pricing comparison of AD843JN (DIP-8), per 1, here are a few;

Newark $9.33

Digikey $8.56

Allied Electronics $11.09

Futurlec $6.90
post #27 of 29
Not bad, about half the price of the OPA627's.

-Ed
post #28 of 29
Went 'live' tonight, chance to hear the AD843 against the OPA627:



I prefer the AD843's, no contest. They brought tears to my eyes, on music I thought I knew.
post #29 of 29
Edit: Nevermind, found what I needed.
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