[sTaTIx]

After using the AD823 for the longest time, I just recently tested a BB OPA2227, and I was surprised at how artificially bright and glaring the AD823 was in comparison. The Burr-Browns made the AD823 sound harsh. I was wondering if I should have the same reservations if I were to decide between an OPA627 and an AD8620. Is the 8620 brighter than the OPA627 in the same way that the AD823 is compared to the 2227? I know that the 8610/8620 is a very highly regarded opamp around here, but if the harshness of the AD823 is any indication at all, it probably wouldn't match my tastes.

 

[puppyslugg]

The ad8610/20 are not 'bright'. They have great air and detail, and clarity, without being strident or harsh. The bass ain't too bad either. Not 'dark' sounding like the opa627.

 

[ppl]

When I Built the First version of my pocket amp it used an AD-823 and a stack of 4 EL-2001's I also found the AD-823 Glaring or as i would have called grain. since i had heard the AD-8610 in my larger portable Amp at that time and the quality was in no way like the AD-823 based amp. i could not wait untill the dual AD-8620 was introduced. When it was, i installed it replacing the AD-823 and was plesently surprised. I love the sound of the AD-8610/20. it is now ranking second as my all time faviorite Op Amps with the power hungry AD-843 being My fav still after all these years.

However the AD-843 is not for Amps with sloppy or not well bypassed PC layouts. it is also one of the most ineffecient Op amps i have used. With +/- 15 volt supplys you will only get about 6-7 Volts RMS output. most other opamps will Do 10 Volts On the same supply voltage. to make matters worse the AD-843 will lock-up to one of the supply rails if the max. input voltage is exceaded. this condition will put half of the powersupply voltage into your headphones if (1) you slowly power up the amp from a current limited power supply. (2) drive the Amp into hard clipping. (3) have the bass Boost in the On posistion when applying power to the amp.

If you can live with these limitations then The AD-843 will give you the best sound available from an op amp. this is why i recomend the Newer AD-8610/20 devices. you get alot of the AD-843 Qualties in alot more user frendly Almost fool proof device.


Note (3) is applicable for my amp designs using the Feedback Bass boost topology Like the PPA

 

[jamont]

Quote:

Originally posted by ppl However the AD-843 is not for Amps with sloppy or not well bypassed PC layouts. it is also one of the most ineffecient Op amps i have used. With +/- 15 volt supplys you will only get about 6-7 Volts RMS output. most other opamps will Do 10 Volts On the same supply voltage. to make matters worse the AD-843 will lock-up to one of the supply rails if the max. input voltage is exceaded. this condition will put half of the powersupply voltage into your headphones if (1) you slowly power up the amp from a current limited power supply. (2) drive the Amp into hard clipping. (3) have the bass Boost in the On posistion when applying power to the amp.

I'm wondering if anyone else using the AB843 has experienced this "latch-up" condition in the course of normal listening?

I have a META42 that uses the AD843 with a high-quality 24V mains-fed power supply. I have not observed any misbehavior in several months of heavy use, mostly with HD580 and K501's. Indeed, the sound is consistently excellent.

Thanks to ppl for pointing out this unpleasant possibility, hopefully it's rarely encountered...

 

[ppl]

This has for me been a consistent issue with the AD-843 for over a decade. The Latch up will happen only upon hard clipping, and with High resistor values in the feedback loop Values i use that still show this problem are above 1 K for the smallest resistor value in the feedback loop. the lock up on applying power with Bass boost on is only when the Boost is at a rather high +20 dB leaving only 10 or so dB of feedback at DC.

It is a Potential problem and can be delt with by building an Amp spicificaly with the AD-843 in mind and using a normal non current limited Power supply. with enought rail voltage to totaly avoid Hard Clipping. Mild clipping will not cause latch up However.

 

[sTaTIx]

Quote:

Originally posted by puppyslugg The ad8610/20 are not 'bright'. They have great air and detail, and clarity, without being strident or harsh. The bass ain't too bad either. Not 'dark' sounding like the opa627.

Hmm... if the OPA627 is "darker" than the AD8620/10 as you say, then it should logically follow that the AD8620 is "brighter," wouldn't it? Whether something is bright or dark is subjective, imo, and it's all about the "degree" of those qualities. I'm just wondering if I like the "dark" BB sound, would I in turn be put off by the comparatively "bright" (or faster) signature of the AD8620.

 

[puppyslugg]

Quote:

Originally posted by sTaTIx I'm just wondering if I like the "dark" BB sound, would I in turn be put off by the comparatively "bright" (or faster) signature of the AD8620.

It's possible, but I doubt it. You may not like the sound of the ad8610/20, but you won't be 'put off' by it.

To me, the ad8610/20 is just more musical. If you like the sound of the opa627, the ad843 may be more to your taste. Which is the one I ended up using in my maxed Corda HA-1.

 

[tangent]

I wouldn't think of the AD8620 as "bright". The AD823 is "bright". The OPA627 is darker than either chip, and I'd say that it's on the dark side of natural. The AD8620 is closer to natural, I think.

Another thing to consider is whether you're using a buffer with the op-amp. If you're using the BUF634, that will darken any op-amp's presentation, whereas the EL200[12] tend towards a more natural presentation, and the HA-5002 is a bit on the aggressive side. Combine an aggressive op-amp with an aggressive buffer and listen with Grados and you'll be in for a lot of pain. Combine dark op-amps with dark buffers and laid-back headphones and you'll go to sleep.

As for AD843 latch-up and such, you won't encounter that kind of behavior in a simpler amp with normal use. The reason ppl and I have seen it so much is because we experiment with lots of strange things and we use current-limiting power supplies as a matter of course (bench supplies). People just building META42 or CMoy variants with wall wart power supplies won't likely ever see this problem.

 

[ppl]

Thanks tangent for pointing this out in your easy to understand post. In normal operation the AD-843 works great. I mentioned this type of problem just in case someone elce runs across this and the solution is simply power down and re apply power.