Diy bench power supply snag help

[diy didi]

I built this power supply years ago. Its 0-50V and 0-4Amp.
Its been serving me well.
I recently built a mosfet amplifier and decided to test it with my dual bench power supply.
I connected an 8ohm load and 1khz input signal to the amp, and powered it up.
Works great until i reach a certain output level. Then my bench supplies start dropping the voltage and my current limit drops down to 2 Amps from 4 amps.
I did notice that if I bypass the current sense resistor R8 with a piece of wire, the current shoots back up and I regain my full 50v output.
This tells me that there is an issue with the current limit circuit.
I can see a slight oscillation equal to the 1khz fed into the power amp input on the supply rails of my power supply.
I suspect that this is feeding into my current control circuit.
Is there a way to fix this on my circuit??. See attached.
I know its not a fault on my amp board as it powers and works fine on a commercially bought power supply.
Thank you!!

 

[rjenkinsgb]

I'd try adding small caps across D1 & D2, and/or D9. Try 0.1uF and see if that has any effect?

I suspect the +/- 10V supply may not be tracking the output fast enough when there is high frequency noise or pulses present.

 

[unclejed613]

check C1 with an ESR meter. or increase the size of C1.

 

[diy didi]

#3​
	I think I might have cured the issue. I changed C2 with the use of a decade box. The power supply is completely stable with a 100nf in the place of C2. Does this look like a good solution?. Cant explain it theoretically.