Accuphase P-266: replacing the NTC to limit the inrush current

[fox]

Hi everyone!

I completely recapped the Accuphase P-266. Once the amplifier is on, it runs great! But charging 4x 22,000uF filter capacitors causes a high inrush current.

Every time I first start it, the circuit breaker is trips because the inrush current is too high. This also happened before restoring the amplifier.

The 10A fuse, which is installed in the amplifier, never blows, which is good! So it makes me think that the circuit breaker is old and is set off easily.

Regardless, I would like to explore the possibility of reducing the inrush current so that the circuit breaker does not trip every time I attempt to power the amplifier. According to some research I did, this can be mitigated using an NTC and a relay which I think the amplifier already has. But it doesn't seem to do too good of a job in reducing the inrush current.

This is the NTC (or a capacitor?) that is currently in the amplifier:


For more information, the only relay I have not replaced in this amplifier is this one:

I am guessing this relay is combined with the NTC to limit the inrush current, but I am not sure. Does someone know the purpose of this relay, and should it be replaced as well?

Does anyone have an idea how to reduce the inrush current in this power amplifier? I had an idea to replace the NTC, but do not know which one to choose or whether that would solve the problem.

Edit: I am actually not sure whether the component on the photo I posted is an NTC or a capacitor. It kind of looks like an NTC, but looking at the schematic, it may as well be a ceramic capacitor?

 

[llwhtt]

That relay switches the secondaries of the power transformer, 49V secondary for NORMAL mode and 23V secondary for CLASS A mode. Nothing to do with turn-on surge.

Craig

 

[Bill Ferris]

Hi everyone!

I completely recapped the Accuphase P-266. Once the amplifier is on, it runs great! But charging 4x 22,000uF filter capacitors causes a high inrush current.

Every time I first start it, the circuit breaker is trips because the inrush current is too high. This also happened before restoring the amplifier.

The 10A fuse, which is installed in the amplifier, never blows, which is good! So it makes me think that the circuit breaker is old and is set off easily.

Regardless, I would like to explore the possibility of reducing the inrush current so that the circuit breaker does not trip every time I attempt to power the amplifier. According to some research I did, this can be mitigated using an NTC and a relay which I think the amplifier already has. But it doesn't seem to do too good of a job in reducing the inrush current.

This is the NTC (or a capacitor?) that is currently in the amplifier:
View attachment 3106449

For more information, the only relay I have not replaced in this amplifier is this one:
View attachment 3106448
I am guessing this relay is combined with the NTC to limit the inrush current, but I am not sure. Does someone know the purpose of this relay, and should it be replaced as well?

Does anyone have an idea how to reduce the inrush current in this power amplifier? I had an idea to replace the NTC, but do not know which one to choose or whether that would solve the problem.

Edit: I am actually not sure whether the component on the photo I posted is an NTC or a capacitor. It kind of looks like an NTC, but looking at the schematic, it may as well be a ceramic capacitor?

That disc shaped device in your picture, is not a NTC !
But looks to be a input electrical line noise suppression ceramic disc capacitor.
The circuit breaker, I`m thinking, has possibly become surge weakened over time from all the large power current inrush every time that that unit has been powered up over the many yrs.

The relay is probably used to remove internal power if the circuit that controls the relay detects a serious output circuit fault, like excessive DC voltage on the output, to save the connected speakers from being burned up.

 

[llwhtt]

That's capacitor C001 which is across the AC line.

 

[fox]

Thank you for all the replies! Does anyone know why power amplifiers don't come with a circuit that reduces the inrush current? Is it hard to design?

 

[llwhtt]

Many do, especially ones with big toroids, Pioneer Spec 2 comes to mind. My SUMO Power and Half Power amplifiers use a relay and large resistor to cope with the initial turn-on surge.

 

[Bill Ferris]

Thank you for all the replies! Does anyone know why power amplifiers don't come with a circuit that reduces the inrush current? Is it hard to design?

In some cases they have.
My Metron 500 wpc @8ohms, power amp has a 20 or so watt input inrush current surge limiting low ohm value resistor.