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Author Topic: Yamaha PC4002M blowing fuses/output transistors  (Read 1585 times)

phatt

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #30 on: August 20, 2017, 08:29:39 AM »

No you don't need 10 or 20 watt resistors,, maybe 2 watt resistors will be fine. :tu:
Here is my Laney KB schematic clearly showing both a HP output as well as a line out (DI) from the power amp section. There would be many SS amps with similar setups if you search. 8|
Phil.
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ilyaa

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #31 on: August 21, 2017, 01:42:35 AM »

and that rig will be sufficient even for a much higher power output amp like this Yamaha?
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phatt

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #32 on: August 21, 2017, 02:56:19 AM »

Well try a 220R then if the signal is too hot swap to 470R.
Like most of these things you have to Select on test.
Phil.
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ilyaa

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #33 on: September 09, 2017, 11:05:17 PM »

so this thing was working fine and then blew again WTF...

doing some research I came across this:

"The one limiting factor is the design of the amplifier output. If it is a single-ended design, meaning that the negative side of both the left and right output channels have a common reference (ground) and as a result the positive side of each channel is the only audio energy source, all you have to do is connect the sleeve to the common reference, the ring to the right channel positive speaker output, and the tip to the left channel positive speaker output. But   if the amp is a dual ended design and both the positive and negative speaker outputs are presenting audio energy, you cannot sum the negative outputs from each channel (which is what happens when you connect to the sleeve of the headphones) or you will fry the amp."

(found on this thread: https://www.gearslutz.com/board/geekslutz-forum/54486-powering-headphones-power-amps-how.html)

now this Yamaha is a dual-ended design and it was being used in the studio for the stereo headphone mix - meaning that the sleeve of the headphone jack on the output was indeed connecting both negative poles of the Yamaha's output. is this why the amp is blowing up???
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Enzo

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Re: Yamaha PC4002M blowing fuses/output transistors
« Reply #34 on: September 10, 2017, 01:45:25 AM »

I think what they mean is most amps we see have a split supply, as in V+ and V-, all referenced to ground.  The output is ground and hot, the hot swings pos and neg.

But some amps are bridged in nature.   ON a conventional amp in bridge, we use the hots of the two channels out of phase.  neither speaker post is ground.   Some amps are built this way for each channel.  Some popular Crown amps come to mind.  Each channel is already two power amp stages facing each other, and neither speaker post is ground.   In a stereo amp, then the negative speaker posts are NOT ground and you cannot connect the left and right together.

Your amp looks to me to be a conventional plain old vanilla V+ and V- design.  The output is ground and hot.  SO I do not think you are facing the phones grounding something.

Generally when an amp works for years, then blows up, you fix it, and it keeps blowing up, it means you are not completely repairing it each time it blows up.  I have no idea what you are missing.  I always check and resolder the drivers, if I didn;t already replace them.  That is Q219,220.  How are you setting bias?  What is idle current draw from the mains?
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