[Magic77]

Does anyone know if an AD825 can be replaced with an AD8610? I have a Cary Audio Nighthawk amp and it uses 2 AD825's on browndog adapters. Could I possibly try 2 AD8610's?

 

[jcx]

you have to check the supply Voltage
 
AD8610 is unusual in only having +/-13 supply V max limit - many op amp circuits use +/-15 or even 
+/-18 V to squeeze out the most headroom
 
OPA827 would be a "safer" substitute since it accepts up to +/-18 V supplies
 
at low supply V differences in the input common mode range and output swing can become critical
 
 
but the exact circuit application is really needed to determine which specs are critical, which potential replacements offer improvement in performance in the specific circuit
 
does the application benefit from the 825's 40 MHz GBW product, or suffer from lack of open loop audio frequency gain of only 76 dB?
 
require the 50 mA output? care about the awful 1/f noise corner?

 

[Magic77]

The supply voltages measure +15 and -15, so I guess I can't use the AD8610. The OPA827 looks interesting. I was also looking at the OPA209.

 

[EniGmA1987]

Check out the AD797B, it is somewhat similar to the AD825. The 797 is better in some ways than the 825 and worse in others, so it depends on the circuit and position of the op amp for if it will be better suited or not. The "B" version sounds significantly better than the regular "A" model, so if you try it out be sure to go for the better model. It has much lower input offset voltage and bias current.

 

[jcx]

the AD797 is an awful suggestion for rolling in place of a fet input op amp
 
in fact the AD797 pretty generally unsafe for rolling since its not exactly unity gain stable and the high input noise current can make noise worse dropped in with typical circuit impedances designed for a fet input op amp

 

[EniGmA1987]

the AD797 is an awful suggestion for rolling in place of a fet input op amp


 


in fact the AD797 pretty generally unsafe for rolling since its not exactly unity gain stable and the high input noise current can make noise worse dropped in with typical circuit impedances designed for a fet input op amp

 


It was offered as a suggestion for something similar to the 825 that would work with the voltage of the amp. It offers DRASTICALLY lower input voltage and current noise than the 825, and since when is 2 picoamps (2 million millionths of an amp) considered high noise? It also offered very low THD in the audio range, significantly lower than the 825, and significantly better common mode noise rejection. So as an alternative to the 825 that was originally asked about it seems like a good alternative for some circuits. The place it looses is gain bandwidth and slew rate, but it still have enough slew for proper performance.

 

[jcx]

the "not exactly unity gain stable" rules out the AD797 as a blind rolling candidate unless you have a 50 MHz oscilloscope
 
it simply won't work stably with some feedback and impedance combos often found in circuits designed for unity gain fet input op amps - not recommended with a local lead C feedback - needs series R - read the datasheet carefully
 
the current noise is hugely larger than the 825 - use a AD797 with a 50 kOhm volume pot on its input and you get up to 25 nV/rtHz Vnoise which is twice the 825 input noise spec
 
 
the AD797 is a fine part in the right circuit conditions - few of which occur in line level home audio electronics
 
it could be used to some advantage in moving coil phonograph preamp or ribbon mic preamp, possibly a few audio DAC I/V circuits - not in line level input headphone amp with a volume pot