F4 power amplifier

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#1,502
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.
 
#1,505
DaveM said:
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.
Click to expand...

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.
 
#1,506
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.:smash:
 
#1,509
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
 
#1,510
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.
 
#1,513
Has this been asked before? I don't remember reading it.

How closely matched are your output MOSFETS?. What are the voltage readings across each output source resistor? If there is a large enough imbalance you might have a difficult time reaching 0 volts offset.
 
#1,514
carpenter said:
I'm finishing the interior of my hobby room before I begin the F4 and the Pumpking/Shunty project. My "great-room" is currently a "great-closet".

Ohhhh how I wish I were as far along as some of you folks.😀
Click to expand...


you have your own hobby room too ! Cool, me too! However im slowly getting out of audio and geting into my new hobbie, R/C Helis Just ordered 2 of them 🙂 about 1200$ for 2 🙂

Jase
An externally hosted image should be here but it was not working when we last tested it.
 
#1,515
BDP said:
Has this been asked before? I don't remember reading it.

How closely matched are your output MOSFETS?. What are the voltage readings across each output source resistor? If there is a large enough imbalance you might have a difficult time reaching 0 volts offset.
Click to expand...


It's my understanding that the opposing banks don't need to be matched to one another. How do you feel about this?

I plan to match to within .01 volts, but haven't given cross matching (9xxx to xxx) much thought.
 
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