DC Servo MOSFET Amplifier

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still4given

still4given

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Joined 2004
prasi said:
I had a good look at both of the boards, cant find any thing amiss (BTW nice soldering), dont have eagle eyes.
Non-working board:
1.Pl check the pin 2 and 3 of op amp for any short, which may not be an issue anyway. try reflow of joints if you haven't done that already.
2. see if any of the transistor is exchanged, MPSA 42 to 92, BC327 to 337, IRFP9240 to 240, etc. + you may like to see if any of the semi is dud.

Working board.
1. like I said resistor values check based on the schematic for expected value (if any of the resistor are in parallel.

hope that someone like Mr. Mile is able spot something.
how is the DC offset behavior , might give some indication if the problem like with servo ckt.
Click to expand...

Hi Prasi,

What cap did you plan for C10 and C11? That is on the low voltage circuit. You have it marked as 100u but it is a large footprint.

Thanks, Terry
 
prasi

prasi

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sites.google.com/site/analogdesign1234/
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still4given said:
Hi Prasi,

What cap did you plan for C10 and C11? That is on the low voltage circuit. You have it marked as 100u but it is a large footprint.

Thanks, Terry
Click to expand...

I wanted to see if using higher value there could give better supply to i/p ckt like 470u being used in Bimo mod of FX-8. (But I never actually got around to testing it)
Just my thought, Mr. Mile's ckt uses 100u.
reg
Prasi
 
still4given

still4given

Member
Joined 2004
prasi said:
I wanted to see if using higher value there could give better supply to i/p ckt like 470u being used in Bimo mod of FX-8. (But I never actually got around to testing it)
Just my thought, Mr. Mile's ckt uses 100u.
reg
Prasi
Click to expand...

Actually, Mile didn't use a big cap on the low voltage section.
 

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prasi

prasi

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Joined 2014
sites.google.com/site/analogdesign1234/
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still4given said:
Actually, Mile didn't use a big cap on the low voltage section.
Click to expand...

Ok my bad. It was my addition. Also added individual electrolytic caps on D of mosfets as a little reserve. Got the idea from one of the slewmasters. Amp will work just fine if one doesnt populate those electros as per Mr. Mile's orginal design.
 
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