Audio amp quiscent current

[Paul_J]

I replaced a STK3062 in a Marantz PM-52SE power amp with another module.
The output DC offset voltage is 0 but the quiscent current in 700mA. 
What should I do to reduce it to 70mA?

Here's a list with the values of the components of the replacement module:

R1______________47K  1/4W Resistor
R2_______________4K7  1/4W Resistor
R3______________22K  1/4W Resistor
R4_______________1K  1/4W Resistor
R5_____________330R  1/4W Resistors
R6_______________1K5  1/4W Resistor
R7______________15K  1/4W Resistor
R8______________33K  1/4W Resistor
R9_____________150K  1/4W Resistor
R11_____________39R  1/4W Resistor

C1_____________470nF  63V Polyester Capacitor
C2_____________470pF  63V Polystyrene or ceramic Capacitor
C3______________100uF  63V Electrolytic Capacitor
C4_____________100nF  63V Polyester Capacitors
C5______________10pF  63V Polystyrene or ceramic Capacitor

Q1,Q2,Q3,Q4,Q5_____MPSA42  300V 500mA NPN Transistors
Q6___________MJE340  200V 500mA NPN Transistor
Q7___________MJE350  200V 500mA PNP Transistor



STK_3042-3062-3082-3102-3122-3152_III_-_Sanyo.pdf

 

[audioguru2]

If your amplifier circuit has a trimpot to adjust the amount of idle current then it will connect to a transistor or couple of series diodes connected to the outer of the 3 pins of your new module. Probably the new module passes a different amount of current through the adjustment part so it causes a higher idle current.

Attach a schematic of the output circuit to see the adjustment trimpot and what can be changed to get a better current adjustment range.

 

[Paul_J]

Because it's a rare amp I don't have a schematic. It's hard to guess it by looking at the PCB tracks because there's also a circuit that detects if there's DC at the output.

I think the value of the trimpot is too large. The trimpot connects to a transistor.
If this doesn't work I'll use a couple diodes.

 

[audioguru2]

I think the value of the trimpot is too large. The trimpot connects to a transistor.

Maybe Marantz copied Sanyo's circuit. Increasing the value of the pot turns on the transistor, then the idle current is reduced. A resistor is on the other side of the transistor to turn it on, reduce its value to reduce the idle current.
It would be difficult to find a trimpot the same physically but with a higher resistance.

 

[Paul_J]

The circuit is different from Sanyo's. The trimpot is an ordinary one, nothing special. I could easily find a replacement if I had to. The output stage seems to be a triple Darlington - all TOSHIBA.
I'll find a way to fix this. Thanks anyway.

 

[audioguru2]

Marantz was an extremely high quality [q]American[/q] hi-fi equipment manufacturer, probably the very best. Now they are Japanese-owned and use cheap Sanyo and Toshiba parts. Their owners also bought McIntosh and Boston Acoustics. Amazing.