| The AD 826, AD827 are dirty opamps, they should be avoided. The circuit must either have some local cap across the feedback resistor or the chip may oscillate. Some wideband parts don't like being used as followers, like the LM6172 for example. Any opamp change must be viewed on a scope to determine if it's operating in a linear region. Local psu .1 uf ceramic bypass caps must be fitted close to each opamp. Input legs must not run long lengths or phase margin will collapse and oscillations at worst, ringing at best may occur. Audio band parts like OPA2134, AD 8599 are usually safe, the LM4562/LME49720 is a 55 mhz bandwidth part, watch out. The LM6172 is a 100 mhz part.
This is not like swapping the tubes on your old color TV, one can quickly make things worse without knowing it.
Jim Williams
Audio Upgrades |