Trying to connect fans to the amp and got a huge spark!

rg12 · 02:23 AM

I decided to add two computer fans to blow on the cooling fins of my
amp's transistors.

I decided to try to find a 12v source in the power stage of the amp.

So, i decided to get a multimeter and try to explore the amp.

I connected the amp and fired it up (no music playing) and i put
the amp on the side with the pcb's copper tracks facing me.

I connected one probe to the chassis ground and started touching
random points (which was a big mistake).
I found out that most of the amp's voltage is 37.3, so i kept on going
and one time i touched with the positive probe one of the ends of
somekind of bridge in the power stage of the amp (what i mean by
bridge is a stripped wire that is soldered like a resistor) and bam!
i see a blue spark with a loud noise.
Everything still works well (the multimeter, the amp and thank god, me!).
The positive probe's tip coating broke, it was a big zap!

What did i do wrong?

The spark was kind of what this stupid guy does with the cap and the pliers http://www.youtube.com/watch?v=UvSwI...eature=related
Could it have been something with the power caps?

benb · 27th September 2010, 03:53 AM

You surely shorted something with a lot of current across the probe tip, apparently one of the main filter capacitors. I doubt the probe on the chassis ground had anything to do with it.

From your description the "bridge" is a jumper wire that one end may not have been soldered well, and wasn't making a connection until you touched it.

As far as 12V for fans, you'd probably want to pull that off the main voltage and drop it down rather than some random point that happens to be at 12V. Post pics and a schematic, and let's see.

That video looks scary. Presumably that's rather high voltage. He's trusting the rubber insulation on the tool to keep him from being shocked. He's holding the cap in one hand and the tool in the other. If something goes wrong the current from the capacitor will go through his chest. Holding each of the charging wires in each hand isn't something I'd do either.

rg12 · 27th September 2010, 04:35 AM

When you say jumper i imagine the computer's motherboard jumpers
which are removable (to open the circuit) and in that case it was
only a permanent connected wire and it was and still is soldered well,
if it wasn't then the amp wouldn't work right or wouldn't work at all.

Here is a link to the schematic:
http://www.milkbands.co.il/Pioneer-SA-7300-int-sch.pdf

And here is a link to a thread with many of my amp's pics:
My whole amp mod and rebuild log Pioneer SA-7300 with 26 pics!

What do you mean from the main? the main is 240v from what i know.

chlorofille · 27th September 2010, 05:04 AM

Try to find an old double insulated SMPS power pack (9-12V DC) to run the fans.
Much safer !

benb · 27th September 2010, 09:04 PM

Yes, that's one common meaning of jumper. Another is a wire connecting two traces on a printed circuit board.

By the main voltage I mean the 37.3V, the main supply voltage to the amplifier from its power supply. On the schematic, this would be across C67 or C68.

I really like clorifille's idea, though I'd prefer an older 50/60Hz-transformer-based "wall wart" supply rather than using a modern SMPS, a potential source for noise, inside audio gear.

rg12 · 28th September 2010, 06:01 AM

I don't know where can i get an old transformer, the only thing i see
in stores are those 12v plastic transformers that connects to the wall.

Wouldn't it make a noise connecting the fans to the mains?
And how can i drop the 37.3 to 12v?

mace1337 · 28th September 2010, 07:14 AM

Instead of randomly prodding around, you should just measure the voltages that the power supply inside the amp gives. If your fan causes the supply to sag on one side of the dual supply you can create a dangerous DC offset that can fry your amp and/or your speakers!

If you ask me, it's much better to get an old LCD monitor power supply (The aforementioned SMPS) and use that, much safer.

infinia · 28th September 2010, 07:27 AM

IMO AC Fans are more reliable than cheap PC 12 VDC fans.
A.C. Fans | AllElectronics.com

rg12 · 28th September 2010, 10:46 AM

Quote:

Originally Posted by mace1337

Instead of randomly prodding around, you should just measure the voltages that the power supply inside the amp gives. If your fan causes the supply to sag on one side of the dual supply you can create a dangerous DC offset that can fry your amp and/or your speakers!

If you ask me, it's much better to get an old LCD monitor power supply (The aforementioned SMPS) and use that, much safer.

Sounds convincing, where can i get a good transformer elsewhere?
I don't have anything i can throw out that has a 12v transformer.

Quote:

Originally Posted by infinia

IMO AC Fans are more reliable than cheap PC 12 VDC fans.
A.C. Fans | AllElectronics.com

I already bought DC ones, but quality quiet ones and also the AC ones
are deeper in size and don't fit my needs.

Original Burnedfingers · 28th September 2010, 10:52 AM

Quote:
I decided to add two computer fans to blow on the cooling fins of my
amp's transistors.

Why? Are the outputs running hot? If so investigate why the output stage is running hot instead of trying to band aid the situation. In proper operating condition the amplifiers heat sinks are capable of taking care of the situation.
Have you changed the heat sinks or done some modification which would cause them to run hot?

27th September 2010, 02:18 AM	#1
rg12 diyAudio Member Join Date: Aug 2010	Trying to connect fans to the amp and got a huge spark! I decided to add two computer fans to blow on the cooling fins of my amp's transistors. I decided to try to find a 12v source in the power stage of the amp. So, i decided to get a multimeter and try to explore the amp. I connected the amp and fired it up (no music playing) and i put the amp on the side with the pcb's copper tracks facing me. I connected one probe to the chassis ground and started touching random points (which was a big mistake). I found out that most of the amp's voltage is 37.3, so i kept on going and one time i touched with the positive probe one of the ends of somekind of bridge in the power stage of the amp (what i mean by bridge is a stripped wire that is soldered like a resistor) and bam! i see a blue spark with a loud noise. Everything still works well (the multimeter, the amp and thank god, me!). The positive probe's tip coating broke, it was a big zap! What did i do wrong? The spark was kind of what this stupid guy does with the cap and the pliers http://www.youtube.com/watch?v=UvSwI...eature=related Could it have been something with the power caps? Last edited by rg12; 27th September 2010 at 02:23 AM.

28th September 2010, 07:27 AM	#8
infinia diyAudio Member Join Date: May 2005 Location: Californication	IMO AC Fans are more reliable than cheap PC 12 VDC fans. A.C. Fans \| AllElectronics.com __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Little dot 2+, got spark	lawrencechin	Tubes / Valves	0	10th June 2010 01:19 PM
Sudden spark.	crashman	Tubes / Valves	4	5th May 2010 04:43 PM
on/off spark	rgrayton	Chip Amps	4	27th March 2007 01:06 AM
amp fans	sriegel	Pass Labs	4	5th January 2002 11:10 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

27th September 2010, 03:53 AM	#2
benb diyAudio Member Join Date: Apr 2010	You surely shorted something with a lot of current across the probe tip, apparently one of the main filter capacitors. I doubt the probe on the chassis ground had anything to do with it. From your description the "bridge" is a jumper wire that one end may not have been soldered well, and wasn't making a connection until you touched it. As far as 12V for fans, you'd probably want to pull that off the main voltage and drop it down rather than some random point that happens to be at 12V. Post pics and a schematic, and let's see. That video looks scary. Presumably that's rather high voltage. He's trusting the rubber insulation on the tool to keep him from being shocked. He's holding the cap in one hand and the tool in the other. If something goes wrong the current from the capacitor will go through his chest. Holding each of the charging wires in each hand isn't something I'd do either.

27th September 2010, 04:35 AM	#3
rg12 diyAudio Member Join Date: Aug 2010	When you say jumper i imagine the computer's motherboard jumpers which are removable (to open the circuit) and in that case it was only a permanent connected wire and it was and still is soldered well, if it wasn't then the amp wouldn't work right or wouldn't work at all. Here is a link to the schematic: http://www.milkbands.co.il/Pioneer-SA-7300-int-sch.pdf And here is a link to a thread with many of my amp's pics: My whole amp mod and rebuild log Pioneer SA-7300 with 26 pics! What do you mean from the main? the main is 240v from what i know.

27th September 2010, 05:04 AM	#4
chlorofille diyAudio Member Join Date: Jul 2008 Location: Christchurch	Try to find an old double insulated SMPS power pack (9-12V DC) to run the fans. Much safer !

27th September 2010, 09:04 PM	#5
benb diyAudio Member Join Date: Apr 2010	Yes, that's one common meaning of jumper. Another is a wire connecting two traces on a printed circuit board. By the main voltage I mean the 37.3V, the main supply voltage to the amplifier from its power supply. On the schematic, this would be across C67 or C68. I really like clorifille's idea, though I'd prefer an older 50/60Hz-transformer-based "wall wart" supply rather than using a modern SMPS, a potential source for noise, inside audio gear.

28th September 2010, 06:01 AM	#6
rg12 diyAudio Member Join Date: Aug 2010	I don't know where can i get an old transformer, the only thing i see in stores are those 12v plastic transformers that connects to the wall. Wouldn't it make a noise connecting the fans to the mains? And how can i drop the 37.3 to 12v?

28th September 2010, 07:14 AM	#7
mace1337 diyAudio Member Join Date: Aug 2005	Instead of randomly prodding around, you should just measure the voltages that the power supply inside the amp gives. If your fan causes the supply to sag on one side of the dual supply you can create a dangerous DC offset that can fry your amp and/or your speakers! If you ask me, it's much better to get an old LCD monitor power supply (The aforementioned SMPS) and use that, much safer.

28th September 2010, 10:52 AM	#10
Original Burnedfingers diyAudio Member Join Date: Nov 2002	Quote: I decided to add two computer fans to blow on the cooling fins of my amp's transistors. Why? Are the outputs running hot? If so investigate why the output stage is running hot instead of trying to band aid the situation. In proper operating condition the amplifiers heat sinks are capable of taking care of the situation. Have you changed the heat sinks or done some modification which would cause them to run hot?

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)