Recently I acquired a Peavey 1.3k power amp from my local church. Whenever I would turn it on,the cooling fan did not want to start spinning on it's own so I gave it a nudge and it would spin fine.Then I decided to replace the fan with a computer desktop 120mm fan,installed the desktop fan and turned on the power amp,fan started up just fine. Thirty minutes later,the fan stopped working and the power amp started to get really hot.I turned it off,opened the cover and found a blown resistor.
This it what the resistor would look like in it's normal state:
I turned on the power amp back on and it just makes a buzzing sound on left and right channels.
I'm guessing the mismatching voltage of the desktop computer fan made the resistor blow,i have no idea.
My question is,is it just a matter of replacing the resistor and installing the proper voltage cooling fan or did i kill the power amp?
This it what the resistor would look like in it's normal state:
I turned on the power amp back on and it just makes a buzzing sound on left and right channels.
I'm guessing the mismatching voltage of the desktop computer fan made the resistor blow,i have no idea.
My question is,is it just a matter of replacing the resistor and installing the proper voltage cooling fan or did i kill the power amp?
You must find out first what actually this resistor is doing. If it is powering the fan then replace it and use a fan with the same voltage or You can even get a mains voltage fan.
As what the buzzing concerns, this amp needs some cleaning... Measure for DC on the output, if there is no DC probably it's fine.
As what the buzzing concerns, this amp needs some cleaning... Measure for DC on the output, if there is no DC probably it's fine.
Recently I acquired a Peavey 1.3k power amp from my local church. Whenever I would turn it on,the cooling fan did not want to start spinning on it's own so I gave it a nudge and it would spin fine.Then I decided to replace the fan with a computer desktop 120mm fan,installed the desktop fan and turned on the power amp,fan started up just fine. Thirty minutes later,the fan stopped working and the power amp started to get really hot.I turned it off,opened the cover and found a blown resistor.
This it what the resistor would look like in it's normal state:
I turned on the power amp back on and it just makes a buzzing sound on left and right channels.
Looking at this
I'm guessing the mismatching voltage of the desktop computer fan made the resistor blow,i have no idea.
My question is,is it just a matter of replacing the resistor and installing the proper voltage cooling fan or did i kill the power amp?
Attachments
I took the power amp to the local audio shop and they told me the resistor blew because i put a mismatching cooling fan in the power amp.
As for the amp itself ,it is fine,both channels fully function.
The buzzing sound was coming from a faulty speaker wire as i found out later after further inspection.
Really living up to your nick with all that helpful info.... are you???
Indeed!.... you should always speak truthful.
It is an 120 VAC fan. I think it says that on the label, whereas computer fans are usually 24 VDC. Also usually says that on the label.
The resistor is to slow the fan down for quiet when the amp is not hot. A thermostat shorts the resistors. Buzzing could be form interference from the open AC line running around the case.
You need to check the speaker connections for DC to make sure you have not blown the amp before connecting any speaker to it. About 100 mv max DC.
I fixed one of these badly blown, but it took 20 output transistors, 3 drivers and 101 cheaper parts. OTOH I fixed a PV-4c (low power cousin) with 4 output transistors and some new mains filter caps. It was a good education in PA amp features. I used the schematic from eserviceinfo.com, a DVM and an analog VOM with a 2 vac scale to trace the music through the front end. No scope required.
I usually get my parts from newark in SC, although digikey is closer to westerners to MN and mouser is closer in TX. Only the 3180 transconductance amp is unavailable. Peavey even has that but you have to call them on the phone to get parts.
Put a filter over the fan grill; dust is what kills these amps usually if a speaker wire short doesn't get them. Don't use 1/4 phone plugs in temporary setups, they short if pulled out. Use dual banana plugs.
The resistor is to slow the fan down for quiet when the amp is not hot. A thermostat shorts the resistors. Buzzing could be form interference from the open AC line running around the case.
You need to check the speaker connections for DC to make sure you have not blown the amp before connecting any speaker to it. About 100 mv max DC.
I fixed one of these badly blown, but it took 20 output transistors, 3 drivers and 101 cheaper parts. OTOH I fixed a PV-4c (low power cousin) with 4 output transistors and some new mains filter caps. It was a good education in PA amp features. I used the schematic from eserviceinfo.com, a DVM and an analog VOM with a 2 vac scale to trace the music through the front end. No scope required.
I usually get my parts from newark in SC, although digikey is closer to westerners to MN and mouser is closer in TX. Only the 3180 transconductance amp is unavailable. Peavey even has that but you have to call them on the phone to get parts.
Put a filter over the fan grill; dust is what kills these amps usually if a speaker wire short doesn't get them. Don't use 1/4 phone plugs in temporary setups, they short if pulled out. Use dual banana plugs.
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Try to get the mains powered fan.
Besides matching voltage, they typically blow 2 or 3 times mor air (CFM=Cubic Feet per Minute) than same size DC ones.
Cooling a PC supply is light duty; but a couple pounds worth of aluminum heatsinks plus lots of heat dissipation is for the grown ups only
When you say "mains powered fan",what are you referring to?
Can you post a picture of a mains powered fan?
Thank You
What he's saying is that the fan is powered by "the mains", AKA 120 volts AC.
In your post you replaced it with a 12 Volt DC fan - utterly wrong and dangerous to do.
In due respect, it's obvious that you don't understand basic electrical terminology, AC from DC, and the dangerous voltages involved.
So, in reality, you're embarking on dangerous territory, and my strong suggestion to you is to have that amp checked and serviced by a qualified service tech. - for your own well being.
The voltage and ac/dc numbers have to match. 120 vac could sub for 115 vac, but 12 versus 115 is way far off.
It is not that hard to learn this stuff. I learned a lot from a sears roebuck pamphlet when I was age 8. I started changing tubes in TV's 1958, worked up to power supplies in car radios age 14. Now we have the internet. Take some electronics courses or read some tutorials.
Basic safety - don't touch metal with two hands, current across your heart can stop it. Use one hand. Wear no metal jewelry on hands or neck, current through that can burn your skin to charcoal. Electronics repair is more thrilling than web surfing, less dangerous than cycle acrobatics. Also sticks it to all those big consumer companies that design their gear to be replaced in 6 years. **** my new 32" Samsung TV from ****-Mart lasted 1 year and 50 weeks. Won't turn on now. ****!@#$@#$%^%^& It's summer, I don't have time for this.
Peavey gear from the nineties was designed for more like 15 years life IMHO, a bit better than consumer ****.
It is not that hard to learn this stuff. I learned a lot from a sears roebuck pamphlet when I was age 8. I started changing tubes in TV's 1958, worked up to power supplies in car radios age 14. Now we have the internet. Take some electronics courses or read some tutorials.
Basic safety - don't touch metal with two hands, current across your heart can stop it. Use one hand. Wear no metal jewelry on hands or neck, current through that can burn your skin to charcoal. Electronics repair is more thrilling than web surfing, less dangerous than cycle acrobatics. Also sticks it to all those big consumer companies that design their gear to be replaced in 6 years. **** my new 32" Samsung TV from ****-Mart lasted 1 year and 50 weeks. Won't turn on now. ****!@#$@#$%^%^& It's summer, I don't have time for this.
Peavey gear from the nineties was designed for more like 15 years life IMHO, a bit better than consumer ****.
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Amp has been thoroughly checked by qualified technician at my local audio repair shop.
Currently running at full blast with no problems using a 12 volt fan wired from a 12V mains power adapter.
Ok, don´t come crying when it starts overheating and cutting off because of insuficcient cooling.
There is a reason Peavey chose a 3X more expensive AC fan instead of a cheesy DC powered one, but hey, maybe you know more than them
The DC powered fan I installed powered by the power adapter plugged into the wall blows just as hard as the original installed fan if not harder.Besides,they are both made by the same company :Nidec
Aire es aire,porque tan serio?
AC:
DC:
You chose a beefy DC fan, that´s to be commended, but still weaker than the original AC one
Until I see datasheets showing both move same amount of air I´ll have to go by only parameter shown so far: motor power.
AC one shows 115V and either .26 or .21A so nominal 30VA or 24VA; while DC one is 12V and 1.4A for nominal 17W .
Again, that is a beefy 12V fan, hope it´s enough.
Saludos, amigo
They are probably both 105 CFM. The TA 450 is the reason that hi-if enthusiasts hate PA amps. What kind of computer did you say it came out of? It had to sound like a low flying plane.
30 VA is not 30 watts - the power factor of a shaded pole motor is not just low, it is very low. Gets even worse if you lower the voltage (with the resistor, in low speed mode). AC fans often fail to start up when you do that, especially when there is the least little bit of resistance in the bearings. DC fans have the advantage of being more well behaved when slowed down at low voltage. Most of them do have awful bearing systems and wear out quickly, but good ones can be had. A good DC fan is more expensive than a good AC fan.
30 VA is not 30 watts - the power factor of a shaded pole motor is not just low, it is very low. Gets even worse if you lower the voltage (with the resistor, in low speed mode). AC fans often fail to start up when you do that, especially when there is the least little bit of resistance in the bearings. DC fans have the advantage of being more well behaved when slowed down at low voltage. Most of them do have awful bearing systems and wear out quickly, but good ones can be had. A good DC fan is more expensive than a good AC fan.
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