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Old 23rd November 2007, 10:42 PM   #1501
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Wow......

and you've double, triple, quadruple checked your components, connections, soldier joints, no soldier bridges, etc.?

You're running the correct power fets?

Describe your tranny. etc.


edit: raise the value of that little resistor you changed several thousand ohms and see what happens.
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Old 24th November 2007, 12:46 AM   #1502
DaveM is offline DaveM  United States
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Yup.... No solder bridges that I could see. Parts were double checked on assembly and there were no leftovers. I did screw up the fets on, but caught that long before I put power to it. The trannies are 750 VA 18 volt double taps. Massive overkill, but they happen to be on the bench and not in use.

I will try and bump it to 7K. I believe I can do that without ordering parts. I will need to dig in the spares.

I guess I could try re-flowing the solder joints on the board, but I was pretty thorough the first time and use a good Hakko solder station. It makes it kind of hard to screw up with the right tools.
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Old 24th November 2007, 01:01 AM   #1503
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Quote:
Originally posted by DaveM
I was pretty thorough the first time and use a good Hakko solder station. It makes it kind of hard to screw up with the right tools.

You'd be surprised how often a bad solder joint is the reason for people having problems. If you don't solder pretty much every day, you either never gain the experience, or loose the touch. Either way, it's an issue.


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Old 24th November 2007, 02:50 AM   #1504
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Quote:
Originally posted by skseah
Hi,
Here is my F4 with Conrad Heatsinks..bias set at 200mV..hot but seems OK for the hot temperature in Singapore.[IMG]http://[/IMG]

Skseah,

That's a beautiful amp with mirrored boards.
Congrats for the nice work youve done, wish I could do something as nice.

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Old 24th November 2007, 02:59 AM   #1505
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Quote:
Originally posted by DaveM
Yup.... No solder bridges that I could see. Parts were double checked on assembly and there were no leftovers. I did screw up the fets on, but caught that long before I put power to it. The trannies are 750 VA 18 volt double taps. Massive overkill, but they happen to be on the bench and not in use.

I will try and bump it to 7K. I believe I can do that without ordering parts. I will need to dig in the spares.

I guess I could try re-flowing the solder joints on the board, but I was pretty thorough the first time and use a good Hakko solder station. It makes it kind of hard to screw up with the right tools.
How about some voltage around the board: above and below TL431, or the rails, etc.

Anything around 7k will do... series a 2.2k alongside the 5k.
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Old 24th November 2007, 03:13 AM   #1506
DaveM is offline DaveM  United States
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Well, I diverted my attention to firing up the second channel and seeing how that went, hoping that if it worked as it should I would have a model to work from. No such luck. The second channel is a repeat of exactly what the first did. 50mv max bias and no DC offset. At least I am consistent. It also rules out something like a solder joint unless I screwed up the same joint in the same place twice. Not likely. Now I need to go back and double check my components and verify values.

I just turned things off and am packing it in for the night. I find that anything after 11 had better not need the use of my brain.

Thanks for the help. I will try again tomorrow night and let you know what I find.
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Old 24th November 2007, 03:19 AM   #1507
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Oh man, it would only take a "second" to series in that 2.2k ohm resistor........
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Old 24th November 2007, 08:16 PM   #1508
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Is r0 6/4/07 the latest F4 schematic?

I'm purging my F4 folder of all unnecessary/obsolete data.

Please save me the effort of rereading this entire thread.

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Old 24th November 2007, 08:24 PM   #1509
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Ok so, I changed out the 5K for an 8k. Now I can get the DC offset at 0 with a bias of about 130mv. If I drive the bias up to 200mv, the DC offset comes up to about .4 V. Certainly better than when I started, but I must be missing something.

The rails are +23.8, -23.8.

Voltages around tl431 are 4.24 V to the IRFP240's, 4.27 V to the IRFP9240's and 1.8 V on the top side
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Old 24th November 2007, 08:31 PM   #1510
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Ah Damn. Ok. Carpenter. You ask that for your own purposes of course and then I say, hmmm I wonder which version is on my bench? Nope.

Changes I notice are the resistors R10-R15 are 100R instead of 150R on the latest. Also R3+4 are 22.1R instead of 10R

Everything else matches the schematic. Will those value changes cause the problems I am seeing? Hmmmm. I guess there is one way to find out.
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