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Post by Boomzilla on Mar 12, 2020 15:41:48 GMT -5
The fan in my "pro" power amp is worn out. I bought a replacement 110VAC, ball-bearing fan from parts-express. But the replacement is ALSO too loud, and has more than twice the air flow of the original fan. How does one drop the fan speed for an AC fan? A simple dropping resistor works for DC fans, but this is an AC one, and the resistor won't work.
Thanks - Boomzilla
Plan B occurs to me... Ventilate the top panel & just remove the fan entirely. The only reason the 40 CFM fan was there in the first place is because the amp was intended to be rack mounted. Without rack mounting, natural draft ventilation should be sufficient. Further, the fan was designed to keep the amp cool while it produced top power output for hours at a time. For home use (and particularly at the volumes I listen at), the amp will be essentially idling. Even if the amp DOES overheat, there are thermal shutdowns built into the circuitry. The MOSFET output stage is not prone to thermal runaway as are bipolar transistors, so I'm thinking that the fan is probably superfluous for my needs?
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Post by SteveH on Mar 12, 2020 17:01:11 GMT -5
AC motors are controlled best by a variac, which basically is a variable transformer, but they are a bit large, it would have to be external to your amp. The fan would actually plug into the variac and you could vary the speed to your liking.
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Post by knucklehead on Mar 12, 2020 17:46:54 GMT -5
Post the model of your pro amp. Someone has probably modded an amp or two and know which fans to buy. I've done it with a couple of Behringer amps in past years. It's easier to buy a 110v fan by CFM than to buy just any old fan and then modify it.
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Post by garbulky on Mar 12, 2020 17:53:14 GMT -5
The fan in my "pro" power amp is worn out. I bought a replacement 110VAC, ball-bearing fan from parts-express. But the replacement is ALSO too loud, and has more than twice the air flow of the original fan. How does one drop the fan speed for an AC fan? A simple dropping resistor works for DC fans, but this is an AC one, and the resistor won't work. Thanks - Boomzilla Plan B occurs to me... Ventilate the top panel & just remove the fan entirely. The only reason the 40 CFM fan was there in the first place is because the amp was intended to be rack mounted. Without rack mounting, natural draft ventilation should be sufficient. Further, the fan was designed to keep the amp cool while it produced top power output for hours at a time. For home use (and particularly at the volumes I listen at), the amp will be essentially idling. Even if the amp DOES overheat, there are thermal shutdowns built into the circuitry. The MOSFET output stage is not prone to thermal runaway as are bipolar transistors, so I'm thinking that the fan is probably superfluous for my needs? Gosh I don't know enough, but what you are proposing sounds dangerous. I wouldn't proceed until I know the the thermal output of this amp at idle without a cooling fan. Also in the Ashly manual, it mentions they don't use thermal protection circuitry. From page five of the manual ashly.com/wp-content/uploads/2016/05/ftx1001-1501-2001-amplifiers-r07.pdfThe IDLE CURRENT CONSUMPTION IS 0.5 Amps (95 watts of heat!) It consumes less than 12 AMPS (!!!) when operating in to 2 ohm loads at only 12% of its max power output. Sounds like there was a reason for that big ol fan. |
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Post by Boomzilla on Mar 12, 2020 19:44:35 GMT -5
AC motors are controlled best by a variac, which basically is a variable transformer, but they are a bit large, it would have to be external to your amp. The fan would actually plug into the variac and you could vary the speed to your liking. That's exactly what I thought. Thanks SteveH! |
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Post by Boomzilla on Mar 12, 2020 19:46:40 GMT -5
...Sounds like there was a reason for that big ol fan. I plan to shoot the case with a laser thermometer at two minute intervals after startup and see what temperature it stabilizes at. Based on those numbers, I'll fan or not. |
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Post by Boomzilla on Mar 12, 2020 19:48:19 GMT -5
Post the model of your pro amp. Someone has probably modded an amp or two and know which fans to buy. I've done it with a couple of Behringer amps in past years. It's easier to buy a 110v fan by CFM than to buy just any old fan and then modify it. It's an Ashly FTX-2001. The Parts-Express guy was worse than useless. |
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Post by Ex_Vintage on Mar 12, 2020 21:17:04 GMT -5
With respect to fan noise, the determining factor of how loud it will be is not CFM, but fan speed. Lower RPM fans are generally much quieter.
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Post by adaboy on Mar 12, 2020 21:54:03 GMT -5
The fan in my "pro" power amp is worn out. I bought a replacement 110VAC, ball-bearing fan from parts-express. But the replacement is ALSO too loud, and has more than twice the air flow of the original fan. How does one drop the fan speed for an AC fan? A simple dropping resistor works for DC fans, but this is an AC one, and the resistor won't work. Thanks - Boomzilla Plan B occurs to me... Ventilate the top panel & just remove the fan entirely. The only reason the 40 CFM fan was there in the first place is because the amp was intended to be rack mounted. Without rack mounting, natural draft ventilation should be sufficient. Further, the fan was designed to keep the amp cool while it produced top power output for hours at a time. For home use (and particularly at the volumes I listen at), the amp will be essentially idling. Even if the amp DOES overheat, there are thermal shutdowns built into the circuitry. The MOSFET output stage is not prone to thermal runaway as are bipolar transistors, so I'm thinking that the fan is probably superfluous for my needs? Boom, I'd replace with one of these guys. They have a built-in speed controller or you can link a thermal controller to them for auto cooling functions. Link below AC Infinity Quiet USB Fans |
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KeithL
Administrator 
Posts: 10,273
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Post by KeithL on Mar 13, 2020 9:58:17 GMT -5
You will also find major variations in the details...
For example, some bearings types are noisier than others, and some fans have specially shaped blades that are quieter than others. (Most fan manufacturers actually spec the noise at various speeds... or, at least, at top speed.)
With respect to fan noise, the determining factor of how loud it will be is not CFM, but fan speed. Lower RPM fans are generally much quieter. |
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