Soft starter for amplifier, PDF or module

[sdk]

Completed assembly of my amp project today and started testing to come across a problem during start up.

The amp starts and runs beautifully when connected to the series board with a 100W bulb

But when connected to the mains directly usually one on phase or rarely both fuses blow with the inrush current. Good thing I bought a box of a hundred 4A fuses!

The transformer is 45-0-45V 8A secondary supplying two 10,000 UF capacitors

Can anyone help me with a PDF of a soft starter PCB that I can etch and make or a resource where I can buy one for a 400 RMS amp?

Thanks

 

[manniraj]

I use a readymade relay based soft start module in couple of my class A amplifiers. This one comes with heat/temperature sensing module built-in to cut off the amplifier power and very useful for Class A amps. There are different boards on similar lines in different price points.

Other simplest soft start for power amps is to use the Thermistors like the NTC ones - refer to this detailed build guide of Aleph J amp where I think this is discussed along with the wiring.

 

[sdk]

I use a readymade relay based soft start module in couple of my class A amplifiers. This one comes with heat/temperature sensing module built-in to cut off the amplifier power and very useful for Class A amps. There are different boards on similar lines in different price points.

Other simplest soft start for power amps is to use the Thermistors like the NTC ones - refer to this detailed build guide of Aleph J amp where I think this is discussed along with the wiring.

There are many soft start boards on AliExpress. Any suggestions for a 400W amp? Or go for the one you bought, which is a little pricey compared to others.

 

[manniraj]

There are many soft start boards on AliExpress. Any suggestions for a 400W amp? Or go for the one you bought, which is a little pricey compared to others.

If you do not want to use the temperature sensor module, you can go with other ones as well like this one.

 

[jls001]

4A fuse seems puny for a 400W amp. I think you need much higher amperage. My 50W PeeCeeBee V4 uses 16A fuses.

Theaudiocrafts (Delhi based) sells ready made soft starter. It comes with temperature sensor too.

 

[sdk]

4A fuse seems puny for a 400W amp. I think you need much higher amperage. My 50W PeeCeeBee V4 uses 16A fuses.

Theaudiocrafts (Delhi based) sells ready made soft starter. It comes with temperature sensor too.

Well, newbie that I am. I follow to a T the instructions of the site/maker of the circuit. I checked the box and these fuses are the fast blow type. I'll try and buy slow blow type this week and give them a try too.

I have a lot of voltage fluctuations in the main line and I've noted that the fuse blows more often when the voltage is above 245V

Between 180 to 230V it blows less often.

 

[quad]

You can limit the in rush current by having a cheap NTC thermistor in the input. This will
stop the fuses blowing

https://www.circuitbread.com/ee-faq/how-do-i-protect-my-circuit-from-inrush-current
https://www.amwei.com/ntc-thermistors/inrush-current-limit-surge-suppress-power-ntc-thermistors/

https://www.electroncomponents.com/10D-11-Ohm-Thermistor

 

[sdk]

4A fuse seems puny for a 400W amp. I think you need much higher amperage. My 50W PeeCeeBee V4 uses 16A fuses.

Theaudiocrafts (Delhi based) sells ready made soft starter. It comes with temperature sensor too.

You can limit the in rush current by having a cheap NTC thermistor in the input. This will
stop the fuses blowing

https://www.circuitbread.com/ee-faq/how-do-i-protect-my-circuit-from-inrush-current
https://www.amwei.com/ntc-thermistors/inrush-current-limit-surge-suppress-power-ntc-thermistors/

https://www.electroncomponents.com/10D-11-Ohm-Thermistor

Update

Purchased a box of 4A slow blow fuses and installed one on the phase line. Now wondering if i use slow blow on neutral too or keep that as fast blow and phase only as slow blow as that's the only one blowing.

No blowouts in the first few attempts

So that gives me a little breathing time to build my soft starter once i find a PCB layout

 

[jls001]

Fuse on the live wire. Not required on neutral. The current on the live completes the circuit via the neutral, so in effect you're putting two fuses in series.