I need a fan to cool my amps heatsink, which do you think is better, AC or DC powered fan? Fan noise is not an issue but if I use an AC(Mains) powered fan, will it cause noise in my amp?
How many blades does a fan need to give more air? Someone once told me that a fan with 3 blades pushes more air than a fan with 5 blades. Is this true?
Jojo
How many blades does a fan need to give more air? Someone once told me that a fan with 3 blades pushes more air than a fan with 5 blades. Is this true?
Jojo
I am planning to use 2 12v fans in my amp,but they run from a seperate supply , isolated from the amp ( they run off the 12v rail that the soft-start / amp monitor cpu uses ) . In my case it's essential to use 12v computer fans which have a tacho feedback - in case either fan fails the cpu shuts down the amp.
AC fans typically use a brushless 'squirrel cage' type of induction motor, but even these can induce noise onto the supply.
as for the airflow, look at the manufactures figures, they should tell you the airflow in cfm or l/min . the number of fan blades is not normally an issue , but try to get a fan which has an odd number of blades with respect to the supporting struts for the motor - i.e. 5 blades/4 struts , or 7blades/3 struts etc.
This minimises vibration, noise and resonances.
Try looking at some of the computer overclocking websites for lots of info on fans, there are some real keen folks out there.
you might be able to add an additional secondary winding to your psu transformer ( e.g. toroidal one especially ) and power your 12v fan from that via a diode bridge. This keeps the fan supply nicely isolated.
Ive done this trick once or twice myself to cool amps.
ray
AC fans typically use a brushless 'squirrel cage' type of induction motor, but even these can induce noise onto the supply.
as for the airflow, look at the manufactures figures, they should tell you the airflow in cfm or l/min . the number of fan blades is not normally an issue , but try to get a fan which has an odd number of blades with respect to the supporting struts for the motor - i.e. 5 blades/4 struts , or 7blades/3 struts etc.
This minimises vibration, noise and resonances.
Try looking at some of the computer overclocking websites for lots of info on fans, there are some real keen folks out there.
you might be able to add an additional secondary winding to your psu transformer ( e.g. toroidal one especially ) and power your 12v fan from that via a diode bridge. This keeps the fan supply nicely isolated.
Ive done this trick once or twice myself to cool amps.
ray
fans are specified for SPL's
my one budding architect son has a very "overclocked" computer for doing his CAD work, and purchased a pair of low SPL fans -- these are easy to find on the web.
Unless you are a complete head-banger, you might wish to consider using a controller chip for the fans which would respond to the temperature on the heat sink. If you are driving the amp to high levels of output the ambient noise from the fan will rise, but the s/n ratio is going to remain pretty low. If OTOH you are listening to something quiet the fan noise will be at a low level also.
there are quite a number of fan controller chips. Analog Devices has one with built in thermistor and it only costs a buck or so.
Jack
my one budding architect son has a very "overclocked" computer for doing his CAD work, and purchased a pair of low SPL fans -- these are easy to find on the web.
Unless you are a complete head-banger, you might wish to consider using a controller chip for the fans which would respond to the temperature on the heat sink. If you are driving the amp to high levels of output the ambient noise from the fan will rise, but the s/n ratio is going to remain pretty low. If OTOH you are listening to something quiet the fan noise will be at a low level also.
there are quite a number of fan controller chips. Analog Devices has one with built in thermistor and it only costs a buck or so.
Jack
there are quite a number of fan controller chips. Analog Devices has one with built in thermistor and it only costs a buck or so.
you might as well build your own controller, it only takes a thermistor , a darlington transistor (e.g. TIP120) and a couple of resistors...
as for the fan, brand new they cost about 6UKP ( maybe $8 ), much less from surplus outlets ( last lot I got were about $2 each)
ray
you might as well build your own controller, it only takes a thermistor , a darlington transistor (e.g. TIP120) and a couple of resistors...
as for the fan, brand new they cost about 6UKP ( maybe $8 ), much less from surplus outlets ( last lot I got were about $2 each)
ray
What do you mean when you say soft start?
if you use large psu transformers - especially toroidal ones - the inrush current on powerup can be excessive and blow fuses.
In the amp I'm building I have a 1KVA toroid which destroys any sensibly rated fuse , so I have to use a 'soft-start' arrangement to turn on the supply.
This works by supplying the initial mains power through a resistor to limit the inrush current. The resistor is removed from the circuit automatically after a couple of seconds ( effectively shorted out by a relay ) once the current has dropped to a sane value.
Some designs use a Thermistor to do the same thing. The cold resistance is high, and drops as the current causes it to heat up, thus restoring full power to the transformer.
I actually use both ideas. by shorting across the thermistor after a couple of seconds I prevent the thermistor staying hot. this means that it's instantly ready the start the cycle again if the amp is switched off and on quickly, and reduces the heat inside the amp slightly.
ray
if you use large psu transformers - especially toroidal ones - the inrush current on powerup can be excessive and blow fuses.
In the amp I'm building I have a 1KVA toroid which destroys any sensibly rated fuse , so I have to use a 'soft-start' arrangement to turn on the supply.
This works by supplying the initial mains power through a resistor to limit the inrush current. The resistor is removed from the circuit automatically after a couple of seconds ( effectively shorted out by a relay ) once the current has dropped to a sane value.
Some designs use a Thermistor to do the same thing. The cold resistance is high, and drops as the current causes it to heat up, thus restoring full power to the transformer.
I actually use both ideas. by shorting across the thermistor after a couple of seconds I prevent the thermistor staying hot. this means that it's instantly ready the start the cycle again if the amp is switched off and on quickly, and reduces the heat inside the amp slightly.
ray
Thanks guys
Thank you very much for the info! Fan control will be my first project since my amp can power up safely as it is. But I will be experimenting on that soft start circuit.
I still need to understand soft start more religiously since it involves tinkering with the mains powered lines.
Thank you very much for the info! Fan control will be my first project since my amp can power up safely as it is. But I will be experimenting on that soft start circuit.
I still need to understand soft start more religiously since it involves tinkering with the mains powered lines.
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