Earthquake 1000bx excessive current while playing

[damage]

The amp draws excessive current when playing. At idle, only draws 1 amp. But when just one channel plays (left or right) it draws 4 amps just to make 1 watt. All the outputs test good, I know one channel is because I replaced all the outputs. Also replaced all the PS FETS with IRFZ44 and 125 ohm gate resistor.

Any ideas?

TIA!
Tristan

[Perry Babin]

Can you reduce the input voltage to the amp to about 10v? If you can, do so. Does the current draw increase when you reduce the voltage?

[damage]

Well my variable PS is not regulated. But if I input 10V, then input the sine wave, the voltage goes down and the current goes up pretty rapidly.

[Perry Babin]

If it's adjustable, it's regulated. When you decrease the input voltage to 10v (no signal, no load), does the idle current increase?

[damage]

Starting at 13.8V and descreasing, the current goes up from 1.3A to 1.6A until 11V then the current continues to go down fairly rapidly.

I dunno about the PS. I thought it was a variac type. It's a Brodhead Garrett. But I've never opened it so I dunno. Seems to get dragged down fairly easily. It'll pump out about 9 amps at ~13.6 knob turned to full power. Unloaded it will do 25V. I only use it during repairs, not during completion testing as it's the only adjustable one I have.

[Perry Babin]

I could be wrong about the power supply regulation. I've never seen one that does what you described.

Post a photo of the gate drive signal on the power supply FETs.

[damage]

Here is a shot. Not exactly perfect.

[damage]

Gate resistors are 68 ohms and FETs are IRFZ44N.

[Perry Babin]

Set the DC voltage lower (near 10 or 11v) and post another image.

[damage]

Looks the same at 11V as it does at 10V.