[KWS]

Recently,i have built up a PPA-like 3-channel amp called "Walker"which was designed by a "Hong Kong"er.You can see the original schematic at the 4th pic while i modified it and replaced the buffer by ha2-5002-5 in stead of buf634.

It works very well with opa134 and opa627.However,when i replace them by opa128sm,the buffers are getting really hot ( i think the buffers are oscillating ) that i can't touch them last for 2s.So I tried to find the solutions in Tangentsoft.net (actually,the amp should be a simplified PPA 1.1).Well,i can found that the bandwidth capacitor is 20pf in it while PPA 1.1 is 20pf and the output resister between the opamp and buffer in this amp is 100R while it is 1kR in PPA1.1.
Tangent's site stated that"These resistors balance the current from the op-amp among the buffers, and reduce electrical ringing in the amp. R11 goes with BUF1, R12 with BUF2, etc.

There is some wiggle room on the value of this resistor, but for most purposes 1 KΩ is a good value."
I have built PPA1.1 before and the OPa128sm worked very well in this amp so please let me know if i replace the 100R by 1KR and 20PF by 10pf,then opa128 can works in WALKER?Thank you so much.=']

 

[FallenAngel]

I don't think dropping from 20pF to 10pF will help, that's there to keep the ground channel opamp stable and going higher is where it becomes more stable. This also doesn't sound like your problem.

Increasing the opamp output resistor might help.

 

[KWS]

Thank you for your reply.
Today,i changed the opamp output resistor vaule from 100R to 1K.
However,the buffers are still getting hot but not as hot as before.
I am so confused now and what should i do?