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Old 22nd January 2013, 10:42 AM   #1131
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Ittien,
At work now, so hopefully typing will be better. What I would suggest is to remove them and rearrange them to where the Vdrop are more closely aligned.

If you have 350, 370 on one side and 355 and 375 on the other, locate the similar ones on the same side. Report back.
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Old 22nd January 2013, 10:48 AM   #1132
omishra is offline omishra  India
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I can see 2 possibilities either power supply capacitors inadequate or that P3 trimmer not in middle. I would suggest not to use that P3 if you do not have distortion analyzer.
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Old 22nd January 2013, 10:52 AM   #1133
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I guess it is possible, although something is funny, as the F5 is a very wide bandwidth amplifier. Hf shold not be an issue. I am not sure that even badly mismatched devices would cause bandwidth limiting.
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Old 22nd January 2013, 12:08 PM   #1134
ittien is offline ittien  Viet Nam
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Thanks all for your input, it's really good for me to solve my issue, i think.
Attached is my current board.
All resistor is KOA 5%, but i'm NOT do measure before plugin, that would be a mistake.
I'm not install P3.
I'll do and report back all of your input. capacitor for power supply i used is Nichicon Gold Tune 10000uF/35V. as i think it good enough(?), and used 4 STTH6002 diode to make bridge for power supply. all thing i tried to do the best.
but as sangram said. power supply 500VA for both channel maybe an issue.
i will update more infor above lost HF and narrow bandwidth.
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Old 22nd January 2013, 05:23 PM   #1135
ittien is offline ittien  Viet Nam
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OOps... not a lucky day. after swapped FET i made it short circuit with heat sink on both channel
some may dead already...need time to check...
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Old 23rd January 2013, 09:14 AM   #1136
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Default F5 Resistors

Hi There!
Maybe a stupid question? But cdoes it matter, if I use 1 watt resistors instead of 1/4 watt resistors for the F5? Thanks for the answer, Teake
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Old 23rd January 2013, 09:16 AM   #1137
AndrewT is offline AndrewT  Scotland
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too big to fit most PCB layouts.
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Old 23rd January 2013, 01:01 PM   #1138
6L6 is online now 6L6  United States
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Quote:
Originally Posted by intense-tavda View Post
Hi There!
Maybe a stupid question? But cdoes it matter, if I use 1 watt resistors instead of 1/4 watt resistors for the F5? Thanks for the answer, Teake
Not a stupid question at all! This is DIY -- we are all learning and nobody knows it all.

You may always use more dissipation rating and/or voltage rating.

The 1W resistors will be very de-rated in the spots for the smaller resistors, and will be fine.

As AndrewT says, there may be a fit problem, but you can mount them 'soldier-style' if there is an issue. See photo -

Click the image to open in full size.

You can see that most of the small resistors are mounted that way, this PCB is made for very, very small resistors. Again, this way of mounting works very well.
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Old 23rd January 2013, 01:06 PM   #1139
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Quote:
Originally Posted by ittien View Post
Thanks all for your input, it's really good for me to solve my issue, i think.
Attached is my current board.
All resistor is KOA 5%, but i'm NOT do measure before plugin, that would be a mistake.
I'm not install P3.
I'll do and report back all of your input. capacitor for power supply i used is Nichicon Gold Tune 10000uF/35V. as i think it good enough(?), and used 4 STTH6002 diode to make bridge for power supply. all thing i tried to do the best.
but as sangram said. power supply 500VA for both channel maybe an issue.
i will update more infor above lost HF and narrow bandwidth.
Attachment 325646
Before you fire up any amp, check for proper isolation of the Fets by connecting one probe of the DMM to the drain pin of the fet and the other probe to the heatsink surface. Set it to measure resistance and you should get an open loop reading if all is OK.
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Old 23rd January 2013, 01:40 PM   #1140
sangram is offline sangram  India
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Quote:
Originally Posted by AndrewT View Post
No, it should read:
given that 4 +-1% resistors give a worst case matching of 2%.
Or, probably 1% when resistors are in parallel and 4% when they are in series. If it was only one resistor it would be 2%.

The only insight I can offer to ittien on his problem is that I tend to agree that even severely mismatched current sharing will be less of a probable issue than fake input devices (setting bias properly is not an indicator), a failed input stage, or a problem in the power supply. I ran a F5 off a 150VA transformer for each channel and while it worked, the results weren't as pretty as I hoped. Switching those out for 400VA units, one per channel, really boosted the performance.
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