Adding Fans Circuit

MM54 · 05-08-2010, 08:11 PM

I don't fully understand how rectification circuits work, so please bear with me

If one were to add a couple of fans to their amp head, it would make the most sense to run them on the heater supplies, right?

Since computer fans (which would work well) are DC, you need to rectify the power before it hits them. I don't fully get how a rectifier circuit, but I think this makes sense to work at least.

(Do I need two diodes in each one or would one work?)

I assume the heater tap that comes off of pin 9 of v1 is not the main live one, as it is a black wire (as opposed to red

) and I know 4/5 are what run the heater. With that I assumed that if I put the diodes in that fashion, the 6.3v would be rectified into around 8.9v DC, with minus being on the lower wire there.

Would a fan need a filter cap? I don't see why since it is in no way affiliated with the signal chain, and if it cuts 60 times per second it won't really hurt it, no?

Am I correct at all? Is this just a horrible idea I should drop? Thanks in advance for the awesome help.

TwinACStacks · 05-09-2010, 07:06 AM

DC current always flows - to +. I definitely wouldn't **** with a heater tap but that's just me. I'd get a 120V 4" computer fan and wire it through the power switch.

TWIN

MM54 · 05-09-2010, 08:24 AM

Okay, thanks

***Adwex*** · 05-09-2010, 10:04 AM

I installed cooling fans in my power amp, 120VAC, tapped into the main power feed, right after the fuse.

Fans come in all shapes, sizes, and voltages. Get an AC fan.

Just a further suggestion....get a finger guard (if it's gonna be externally mounted), and a vibration dampening mounting gasket.

Wilder Amplification · 05-09-2010, 12:33 PM

Basically D3 and D4 pass negative current ("send" current) while D1 and D2 pass positive current ("return" current). Electrons flows through D3 and 4 first, through the fans, then returns through D1 and D2. When it tries to reverse the other way on the negative cycle of the AC, the diodes "turn off" and no current flows. It's essentially a 1/2 wave rectifier, meaning that current can only flow during 1/2 of the AC cycle/sine wave.

Most computer fans I think are 12V fans, which won't work on a 6.3V supply. You'll have to see if you can find a 6V fan for that circuit to work. I would also consider installing a filter cap across the supply after the diodes as well.

Shouldn't need 4 diodes as you're dealing with low voltage...you could actually get away with just one diode on the positive side of the supply with the cathode (silver band) facing toward the + terminal of the fans.

MM54 · 05-09-2010, 01:17 PM

I've run 12V computer fans on a AA battery before (they just don't spin really fast), so it is possible.

I'm going to look at all my options and maybe just toss the whole idea

If I come up with something, I'll draw up another schem and post it.

Thanks, guys.

PaoloJM · 05-11-2010, 08:46 AM

Rectify the heater tap and run the fan from that.
Your rectifier circuit above is wrong. It'll work, but extremely poorly and produce vast amount of noise.
Just use a normal full wave rectifier, there's loads of schematics for this available online. Two dioes will be sufficient.
Use a decent amount of capacitance for filtering as fans are normally inductive loads. In the region of 4,700uF is appropriate at this voltage level.
The fan will run slower, = less mechanical noise which is a good thing, you probably don't need it running at full whack anyway.

BTW, why do you need one?

Wilder Amplification · 05-11-2010, 10:50 AM

Quote:

Originally Posted by PaoloJM

Rectify the heater tap and run the fan from that.
Your rectifier circuit above is wrong. It'll work, but extremely poorly and produce vast amount of noise.
Just use a normal full wave rectifier, there's loads of schematics for this available online. Two dioes will be sufficient.
Use a decent amount of capacitance for filtering as fans are normally inductive loads. In the region of 4,700uF is appropriate at this voltage level.
The fan will run slower, = less mechanical noise which is a good thing, you probably don't need it running at full whack anyway.

BTW, why do you need one?

Um....if you did a FWCT rectifier with only two diodes you'd only have 3.15VAC. For 6.3 you'd have to do a FWB rectifier and make it a floating supply (i.e. floating = neither side of the fan circuit is referenced to ground).

Something like this should suffice -

***Adwex*** · 05-11-2010, 11:54 AM

Is there a compelling reason to not use an AC fan? Seems like it would be much easier. I installed a pair of AC fans in my power amp, tapping into the main power in, after the fuse, and it worked out great. I mounted them with rubber vibration gaskets to keep the noise down.

tonefreak · 05-11-2010, 12:03 PM

so with an AC fan, you'd wire it in somewhere after the mains fuse?

PaoloJM · 05-11-2010, 12:11 PM

Quote:

Originally Posted by Wilder Amplification

Um....if you did a FWCT rectifier with only two diodes you'd only have 3.15VAC.

Which would be around 4.4Vdc, plenty to get the fans spinning to move some air.
Plus you'd need to add a reasonable amount of capacitance to the circuit you've drawn.

The reason I asked why he needed the fan was to see what exactly the heating problem was.
Guitar amps shouldn't really need a fan unless there's an underlying problem.

The slow moving air provided by a 12Vdc fan run @ 4.4Vdc should be enough to remove any heat. If more is required then I think there's a bigger problem that needs looking at.

***Adwex*** · 05-11-2010, 12:15 PM

Quote:

Originally Posted by tonefreak

so with an AC fan, you'd wire it in somewhere after the mains fuse?

Yup. Piece o' cake.

I even used a quick disconnect type of connector, so I could unhook the fan easily.

TwinACStacks · 05-11-2010, 03:43 PM

Other than an Ampeg SVT which has about 1000 tubes in it, What amp runs so hot as to need 2 fans for circulation? AC30's are a blast furnace and most aren't equipped with fans. Just curious.

TWIN

***Adwex*** · 05-11-2010, 05:37 PM

Quote:

Originally Posted by TwinACStacks

Other than an Ampeg SVT which has about 1000 tubes in it, What amp runs so hot as to need 2 fans for circulation? AC30's are a blast furnace and most aren't equipped with fans. Just curious.

TWIN

My Marshall 9005 rack power amp doesn't have any factory fans like the 9200 or EL34 100/100 family of pwr amps. When sitting in a rack, the damn thing gets as hot as an oven. Without forced cooling it would melt whatever component was installed in the rack space above it. Stupid design.

MM54 · 05-11-2010, 07:22 PM

Again, thanks for all the help guys

I'm working on an amp now that I may put a fan or two in just to help keep it cool, but there's a lot of other things I need to decide on before that

lespaulr0cker · 05-12-2010, 07:11 PM

I reccomend using "brushless" fans to prevent noise.

05-08-2010, 08:11 PM	#1 (permalink)
MM54 Senior Member Join Date: Feb 2010 Location: Penn State Behrend, Erie PA Posts: 7,771	Adding Fans Circuit I don't fully understand how rectification circuits work, so please bear with me If one were to add a couple of fans to their amp head, it would make the most sense to run them on the heater supplies, right? Since computer fans (which would work well) are DC, you need to rectify the power before it hits them. I don't fully get how a rectifier circuit, but I think this makes sense to work at least. (Do I need two diodes in each one or would one work?) I assume the heater tap that comes off of pin 9 of v1 is not the main live one, as it is a black wire (as opposed to red ) and I know 4/5 are what run the heater. With that I assumed that if I put the diodes in that fashion, the 6.3v would be rectified into around 8.9v DC, with minus being on the lower wire there. Would a fan need a filter cap? I don't see why since it is in no way affiliated with the signal chain, and if it cuts 60 times per second it won't really hurt it, no? Am I correct at all? Is this just a horrible idea I should drop? Thanks in advance for the awesome help. __________________ -Matt If you don't understand what I'm saying, assume I'm making a joke. Trust me. Lachesky Amplifiers - Home of the CA10 Orders for 2013 CA10s are now being accepted! "... And I come from a place where they drag your hopes through the mud because their own dreams are all dying"

05-09-2010, 08:24 AM	#3 (permalink)
MM54 Senior Member Join Date: Feb 2010 Location: Penn State Behrend, Erie PA Posts: 7,771	Re: Adding Fans Circuit Okay, thanks __________________ -Matt If you don't understand what I'm saying, assume I'm making a joke. Trust me. Lachesky Amplifiers - Home of the CA10 Orders for 2013 CA10s are now being accepted! "... And I come from a place where they drag your hopes through the mud because their own dreams are all dying"

05-09-2010, 10:04 AM	#4 (permalink)
*Adwex* Super Moderator Join Date: Sep 2006 Location: I'm not sure. Posts: 8,423	Re: Adding Fans Circuit I installed cooling fans in my power amp, 120VAC, tapped into the main power feed, right after the fuse. Fans come in all shapes, sizes, and voltages. Get an AC fan. Just a further suggestion....get a finger guard (if it's gonna be externally mounted), and a vibration dampening mounting gasket. __________________ http://www.youtube.com/MarshallLesPaul

05-09-2010, 12:33 PM	#5 (permalink)
Wilder Amplification Senior Member Join Date: Oct 2009 Location: Fresno, CA Posts: 6,165	Re: Adding Fans Circuit Basically D3 and D4 pass negative current ("send" current) while D1 and D2 pass positive current ("return" current). Electrons flows through D3 and 4 first, through the fans, then returns through D1 and D2. When it tries to reverse the other way on the negative cycle of the AC, the diodes "turn off" and no current flows. It's essentially a 1/2 wave rectifier, meaning that current can only flow during 1/2 of the AC cycle/sine wave. Most computer fans I think are 12V fans, which won't work on a 6.3V supply. You'll have to see if you can find a 6V fan for that circuit to work. I would also consider installing a filter cap across the supply after the diodes as well. Shouldn't need 4 diodes as you're dealing with low voltage...you could actually get away with just one diode on the positive side of the supply with the cathode (silver band) facing toward the + terminal of the fans. __________________ Jon Wilder Wilder Amplification - The official home of the 80s cock of the walk "Schwank" http://www.wilderamps.com http://www.facebook.com/wilderamps

05-09-2010, 01:17 PM	#6 (permalink)
MM54 Senior Member Join Date: Feb 2010 Location: Penn State Behrend, Erie PA Posts: 7,771	Re: Adding Fans Circuit I've run 12V computer fans on a AA battery before (they just don't spin really fast), so it is possible. I'm going to look at all my options and maybe just toss the whole idea If I come up with something, I'll draw up another schem and post it. Thanks, guys. __________________ -Matt If you don't understand what I'm saying, assume I'm making a joke. Trust me. Lachesky Amplifiers - Home of the CA10 Orders for 2013 CA10s are now being accepted! "... And I come from a place where they drag your hopes through the mud because their own dreams are all dying"

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05-11-2010, 08:46 AM	#7 (permalink)
PaoloJM Senior Member Join Date: Jun 2008 Location: Cork, Ireland Posts: 1,519	Re: Adding Fans Circuit Rectify the heater tap and run the fan from that. Your rectifier circuit above is wrong. It'll work, but extremely poorly and produce vast amount of noise. Just use a normal full wave rectifier, there's loads of schematics for this available online. Two dioes will be sufficient. Use a decent amount of capacitance for filtering as fans are normally inductive loads. In the region of 4,700uF is appropriate at this voltage level. The fan will run slower, = less mechanical noise which is a good thing, you probably don't need it running at full whack anyway. BTW, why do you need one? __________________ www.youtube.com/paolojm I'm no poindexter, I'm ****ing awesome like this guy

05-11-2010, 11:54 AM	#9 (permalink)
*Adwex* Super Moderator Join Date: Sep 2006 Location: I'm not sure. Posts: 8,423	Re: Adding Fans Circuit Is there a compelling reason to not use an AC fan? Seems like it would be much easier. I installed a pair of AC fans in my power amp, tapping into the main power in, after the fuse, and it worked out great. I mounted them with rubber vibration gaskets to keep the noise down. __________________ http://www.youtube.com/MarshallLesPaul

05-11-2010, 12:03 PM	#10 (permalink)
tonefreak Senior Member Join Date: Jan 2010 Location: Larsen WI. Posts: 12,068	Re: Adding Fans Circuit so with an AC fan, you'd wire it in somewhere after the mains fuse? __________________ Why waltz when you can Rock n Roll?

05-11-2010, 07:22 PM	#15 (permalink)
MM54 Senior Member Join Date: Feb 2010 Location: Penn State Behrend, Erie PA Posts: 7,771	Re: Adding Fans Circuit Again, thanks for all the help guys I'm working on an amp now that I may put a fan or two in just to help keep it cool, but there's a lot of other things I need to decide on before that __________________ -Matt If you don't understand what I'm saying, assume I'm making a joke. Trust me. Lachesky Amplifiers - Home of the CA10 Orders for 2013 CA10s are now being accepted! "... And I come from a place where they drag your hopes through the mud because their own dreams are all dying"

05-12-2010, 07:11 PM	#16 (permalink)
lespaulr0cker Junior Member Join Date: Jan 2010 Posts: 19	Re: Adding Fans Circuit I reccomend using "brushless" fans to prevent noise. __________________ lespaulr0cker http://www.sunsetbetty.net

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