F4 power amplifier

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jleaman

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Peter Daniel said:


That ground connection is only when C5/C6 are installed, otherwise it's not being used. I explained it here: http://www.diyaudio.com/forums/showthread.php?postid=1324572#post1324572
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ok, Fair enough,

However im still not able to get this amp working :( ive just checked all the resistors to the schematic, ive checked the pot's and i have checked the psu boards :( this is so bizzar. My alephs have never been this hard to figure out.

GRR
 
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jleaman

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lykkedk said:
What now jleaman, how much voltage on pwr resistors now ? I mean do you only got voltagedrop on left or right side now? As you mentioned before, you figured the GND thing out ?

Jesper.
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I haven't figure out the gnd thing yet, im totally lost now. where am i suppose to get the ground from now, i mean you have to have 3 wires from the psu, positive negitive and gnd. where does ground go if its not at the end of the board.
 
Peter Daniel

Peter Daniel

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Peter Daniel said:
If you look at F4 amp schematic, you will notice that power ground is not there, only the input signal ground.

The power ground is located on PS board, and this is where speaker ground connects. Signal ground reference is taken from PS board, with a separate wire, and connects to GND point on amp board which is beside SG point (SG is used for ground connection from input RCA).

The GND on the opposite side of the board is only for C5/C6 and if those caps are being used you need another ground wire from PS board.
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jleaman

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ok so the psu ground is beside the input ground, the speaker ground is off the psu, now when turning up the variac, i get 5V on the speaker ouput, i can turn the P2 down all the way to 3.5V but then it clicks ( meaning im at the end) but the voltage is still high. I don't have my variac turned up hi because i don't want to blow up this amp and cook these fet's that cost a fortune.
 
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jleaman

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lykkedk said:
First thing is to adjust the voltagedrop on pwrresistor's, then DC-offset(P2) adjust when done... Do you still got 1v(P1 ~middle) on pwrresistor's, cause then something else is wrong. Maybee time for closeup picture.

Jesper
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Here you go, when i power it up and have 5v on the speaker i have about .27v on the output.
 

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J

jleaman

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lykkedk said:


You mean 0,27v on resistor's (all 6 ???), and 5vdc between +out/gnd right ???

Jesper.
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correct, and that is not even at full power on the rails. I can hear my 1kva variac humming lots at 60V ac, im not sure of the rail voltage on the amp i can check that if needed also.

Jase
 
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audiorasp

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jleaman, it looks in your picture that the caps C1 through C4 are not insulated. It's just a guess, but I think if the metal can touches the bare unused pads it could cause a short. Usually the rubber gasket on the bottom of the cap will prevent this, but it's hard to see in your picture. Again, just a guess.
 
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jleaman

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cherhit said:
jleaman, it looks in your picture that the caps C1 through C4 are not insulated. It's just a guess, but I think if the metal can touches the bare unused pads it could cause a short. Usually the rubber gasket on the bottom of the cap will prevent this, but it's hard to see in your picture. Again, just a guess.
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I too checked that, however the black plastic part of the base of the cap is touching the board, and preventing the short :p good eye tho :)
 
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jleaman

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lykkedk said:


jleaman, that's the problem, then the bias go crazy, and it won't work for sure... sry to hear that you got the wrong part's... the q6,q7,q10 MUST be 100% for sure p-channel aka' irfp9240...

Jesper.
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Well this is cool, i paid close to 160$ for parts that are uesless, how come no one else caught this ? others bought parts for their F4's and have not complained :(
 
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jleaman

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lykkedk said:
You got a stereokit right ??? --- have you checked the other kit, to see if there is hiding 6pcs. of irfp9240 ??? just a guess...

Jesper.
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yes i just checked, i have 24 fets for 2 stereo moo blocks me and a friend put money into to buy parts for all 4 channels, i see that i have 24 IRFP240's :( what a waste of time and money. Now to explain this to the other guy that we have to put more money into this. I'm not happy at all.
 
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jleaman

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carpenter said:



Good catch, Jesper!:) :)

It's late and I just logged on. Sorry to read of your purchase, jleaman, but at least you know where to go from here.
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I just re-opened the other kit for scott, and it looks like his kit is all ok, so he has 6 p's and 6 of the others, Oh well. I'm not worried about my self, im only worried about him, Ill get some more and fix this all up :p


Thanks for your help guy's.

Jase
 
lykkedk

lykkedk

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jleaman... please don't be so angry, i see that you ofcause is frustrated, but no one did this for irritating you... maybee you and you're friend could buy the missing irfp9240 and match them your self... it's not very difficult... and they dont have to match the irfp240 parts at all... (i think :D) You only have to have some 3match between the irfp9240... I have build 2 F4monoblock's with only 25pcs of irfp9240, from same batch... no problem.

When done, meassuring the voltagedrop ~250mv on each resistor, assures you that the matching was done proberly... mine was in the area of 230 - 255mV.

Jesper.
 
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