Bonkers MOSFET Amp

For the three and more legged things
brig001
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#16

Post by brig001 »

The Nemesis PDF makes interesting reading. I kinda like the "if it sounds better to me, then it must be better" philosophy. Your design also reminded me of this http://www.audiophonics.com/audiophonic ... about.html although it actually isn't much like it :D
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Mike H
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#17

Post by Mike H »

Yep. As philosophies go, that's a good one.
 
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Mike H
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#18

Post by Mike H »

Well finally got a supply box working ~ problem is amplifier is unstable without a really stiff supply rail. Straight off the bridge > reservoir is OK but it hums like buggery:

Image


A CLC filter or even a resistor >= 100R in CRC, and off it goes into LF oscillation. Since it was originally powered off a regulated bench supply (SMPS at that, I think) the only sensible recourse seemed to be duplicate that kind of approach and add a LM317 regulator, see Velleman board at top right in the following:

Image

Turns out reservoir Volts is 56 so can afford to drop 5 - 6V
 
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#19

Post by brig001 »

Hi Mike, could you just regulate the supply to R6?
Then again, with 70mA, you might as well regulate the lot I suppose.
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Mike H
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#20

Post by Mike H »

That did occur to me afterwards, though not sure it would help actually as bear in mind it's effectively decoupled to ground by C2, or would be if pot is turned down to zero anyway. And if it isn't....?

Also ripple would still come down through the transformer making the hum, the main problem would still apply I think i.e. the resonance which is Q2 & Q1 trying to compensate for "wobbles" on the supply rail, coming down R1 and aggravated by transformer inductance. :?:

So as you say may as well regulate the whole lot, it's not like much power is involved for that :D

Anyway it's still happy like that and working well.

Did I mention it sounds bluddy good BTW? Well it does. :D
 
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Mike H
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#21

Post by Mike H »

Here is the power supply for it (transcribed from paper!):
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Nick
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#22

Post by Nick »

Err, how do you stop the reg dying at the turn on when its output is 0v and its input is 60v ish.
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Mike H
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#23

Post by Mike H »

Image


 
 
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Mike H
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#24

Post by Mike H »

A more sensible answer to the foregoing enquiry .. :D
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brig001
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#25

Post by brig001 »

I think Nick meant the other way. The Absolute Maximum Input-Output Voltage Differential is 40V, and you will exceed this briefly on power up.
Mike H wrote:Did I mention it sounds bluddy good BTW? Well it does. :D
That's what we really wanted to know :D
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Nick
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#26

Post by Nick »

Yep, but making that diode a 35V Zener will solve the problem (and provide a discharge path)
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Mike H
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#27

Post by Mike H »

Tried that, current through the Zener is too high. All I'm trying to do here is charge up C2 as fast as C1 which forces the output on, which in turn keeps In vs Out within spec. by itself.

Although having said that, it's still wired up like this ~ Zener hasn't blown yet, or if it has, it's done so unobtrusively ~ if so then we're back where we started but it still works :D
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