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Old 14th August 2010, 04:57 PM   #1
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Default Elemental Designs Nine.1

I recieved this amp in for repair. Inoticed the outputs were shorted (IRF640s')

The 9640's tested fine.

So i replaced the irf640's in the amp. Put it back together and amp powers up fine sits and idles perfect.

So i tested for audio.

The output is very quiet and when a speaker is connected the amp will start drawing excessive like to the beat of the music.

Wondering what might cause this and what do i check for?
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Old 14th August 2010, 05:49 PM   #2
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Ok did some checking around in this amp.

On the power supply fets ( IRFP064N)

Theese are the voltages i came up with.

Leg1:0.62

Leg2:13.90

Leg3:0

Shouldnt i have around 5 volts on leg 1??

What do i need to check for at this point?
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Old 15th August 2010, 08:53 AM   #3
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Location: Louisiana
An amp with a regulated power supply can have very low gate voltage (DC measured with multimeter). The reduced pulse width reads lower than the near-full duty cycle.

Do you have ±regulated voltage on the op-amps?

What is the ±rail voltage on the output transistors?
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Old 15th August 2010, 04:07 PM   #4
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The rail voltages i got are

IRF640

1:-67.8
2:-1.04
3:-70.3

IRF9640

1:68.4
2:-1.04
3:70.3

I have + 12.2 volts and - 11.8 volts on all op-amps
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Old 15th August 2010, 05:24 PM   #5
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Ive got + - rail voltage and + - regulated voltage.

Amp idles perfect. The 640's are new

But as soon as i connected a test speaker to the amp it draws excessive current .

I swapped test speakers but the amp does the same thing.

Wondering what might cause this problem .

I check for dc on the outputs and get like .04 so that normal.

Where would i go at this point?
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Old 15th August 2010, 09:03 PM   #6
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Location: Louisiana
Look at the speaker terminals with your scope. Do you see any high frequency oscillation?

If not, monitor the signal on the speaker terminals when you touch the speaker wires to the speaker terminals.
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Old 16th August 2010, 12:52 AM   #7
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Scope set to 10 MS .5 div? or what?
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Old 16th August 2010, 01:16 AM   #8
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Perry,

Never mind i have this amp fixed. What the problem was is that i had speaker wire that got pinched inside the encloser causing it to short together.

Thanks
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