[PinkFloyd]

Hi,

Does anyone have experience of either the AD823 or AD712 op amps?

Would either of these be suitable drop in replacements for the OPA2132 & OPA2604.

Comments appreciated.

Thanks.

Pinkie.

 

[KTpG]

In my CMoy, I tested an AD823. The main difference I heard was a very slight less bass and more present highs. I didn't like it. If you mixed it with a Burr-Brown BUF634, the results could be quite favorable, though I didn't take a listen. I also listened to the AD648, but cannot remember my thoughts on it.

 

[was ist los?]

I didn't like the sound of the ad823 compared to the ad8620 or opa2132p. I found the ad 823 a bit too foward and as KTpG said, lacking bass.

 

[SFbayArch]

Check out the following thread regarding this opamp:

the cmoy slayer - the AD823


also, check out Tangent's own site...the following link is his expert opinion on the qualities of different audio opamps:

Tangent's Notes on Audio Op-Amps

 

[ppl]

If between the AD-823 and the AD-712 i think that is your question then i would go with the AD-712. for a cmoy type amp. the AD-823 is not able to drive low impedances as well as other op amps including the Old AD-712 because of different output stage topolgies

 

[tangent]

I found that with high-impedance headphones, bass was slightly better with the AD823 than the OPA2132. But with low-impedance headphones, this low-output op-amp will be starved for voltage. That's why Apheared built the original #42: by adding EL2001s to the output of this op-amp, you retain its sound qualities while increasing output current, so that it works well into any load the buffer will handle.

 

[aos]

>>But with low-impedance headphones, this low-output op-amp will be starved for voltage

You mean starved for current, right?

On a somewhat sidenote, what happened to AD825? This chip was all the rage for a while, but nowdays it's not often mentioned.

 

[ppl]

The AD-825 is still considered an Audiophile Grade op Amp, However it's agressive High End can be a distraction with Can's like Grados, Otherwise a nice detailed and fast sounding op amp. moreover for cmoy type of applications the AD-825's input stage is layed out to minimise thermal distortions.

 

[aos]

Ah, so the chip is optimized to perform well when driving a non-negligible load. That's why it should be used to replace opamps in CD players and soundcards, instead of using AD8620. I found that some chips that sound great when driving a buffer might not sound that good if forced to drive a pair of RCA cables by themselves.

 

[ppl]

The AD-8620 is great at driving cables and is a great device to replace most op amps used in Soundcards and the Like. This is also true of the AD-825, but the AD-823 has an output stage that is not so great at High capacitive or low impedance loads.

 

[rickcr42]

Quote:

I found that some chips that sound great when driving a buffer might not sound that good if forced to drive a pair of RCA cables by themselves.

simple current limitations of the output stage

I have found that when i want to drive a discrete mosfet output stage for an opamp gain stage that the mosfets like to see a good amount of current drive to thier gates.No wimpy opamps need apply

 

[ppl]

Hi Rick glad to hear from Ya, yes you are so Right with Mosfets having large current drive requirements. This is because of the unreal high Input capacitence of the Mosfets. heck 1000 pF per device is quite normal so then you add a few in parralell.

The big advantage perported by Mosfet manufactures is the easy drive requirements since the input impedance is in the Meg ohm range rather than a few K ohms of Bipolar devices.

Most designers of mosfet Audio Amps rushed to the ocasion by replacing the Heafty! power hungry, Mini power Amp driver stage used in quality Bipolar designs. This resulted in alot of Mosfet based Amps to not sound as good as thay could.

 

[rickcr42]

hey ppl

yeah ,mosfet need a good "nudge' to get going.

i never really got my early szekeres amp moving and grooving until I hit the gate with another mosfet configured with jfets as a sort of dicrete op-amp.


The limitations noted by others is in reality an inability to drive the gate correctky due to the high capacitance which is not just limiting the drive but the upper frequencies as well.

Version two was an5687 SRPP tube stage ,also very high current drive though a bit on the high impedence side.

so yeah,these beasts like current-they need it to work and they put it out in spades

 

[ppl]

Verry true. years ago at a CES i was listening to the Biggies in the Industry speak of the sound of this paticular Mosfet Power Amp, driving a pair of Sould lab electrostatic lounspeakers placed in a large closet to inhance the bass. the Overall reproduction was superb. Nothing beats electrostatics for giving you real goos-bumps, Be it headphones or loudspeakers. However I noticed a distint Tsshhh sound throught the upper mids and high's and this was gone on subsaquent auditions of this set up with Other solid state Bipolar amps or even tube units. These bigwigs were comenting on the same thing and this is where i first heard the term mosfet mist. this Hit me, as an exact discription of what i was hearing. What a way to spend a day in vegas, I tell ya. That was also the first time i heard stax Electrostatic headphones with there Tube Amp and boy thay sure sounded better than my Koss ESP-9B's

 

[rickcr42]

I have an old pair of "Realistic" branded Stax headphones and they never were right until i built Kevin Gilmore's All Triode Tube Amp .

they really sing now

Damn fine sounding design