Electrical – Using an Op-amp buffer to Power Amplifier unit


I have an old amplifier unit that runs on A.C and I'm trying to make it a battery powered amp
I understand that the A.C voltage get rectified to 15+/15- D.C with a common ground so I used a 36v li-ion battery pack and the following circut to get a virtual ground

enter image description here

the circuit works but when it's connected to the amp power rails the virtual ground voltage drops to 0.8 V , is it because of capacitive load instability ? is there any solutions ?

Note : I'm using a LM324N Opamp I.C and the unit uses a NJM4558 DUAL OPERATIONAL AMPLIFIER I.C

Best Answer

The circuit you show is almost guaranteed to oscillate. The 1K resistor makes it worse. It also can't handle much ground current before the op-amp saturates (due to the 1K).

Something more like this has a better chance of working:


simulate this circuit – Schematic created using CircuitLab

Since we don't know how much ground current there is, it's hard to design it properly. You may need a beefier buffer than an LM324 which is only capable of 10s of mA. If the load is grounded vs. a bridging amplifier it's probable unsuitable for anything more than a headphone amplifier. On the other hand, if the 4558 directly drives the output, it may be okay.