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Diode in Amplifier

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Hello Forum,

I have an amplifier design, in which a number of diode in it, that I do not understand, I have circled the diode operation in the schedule, I hope there is someone who can explain it to me.

Sincerely,

Pim
 

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I'm guessing that D11 and D12 ensure the input stages have a supply voltage if the 40V/-40V supply drops below 28V/-28V one (perhaps at power-down). No idea what the other diodes are for.
 
Thank you for the response, so I had not yet viewed.
perhaps this is a given, the output transistors are switched in Class A, there is approximately 1.7 A quiescent current, this still affect your view.

greeting,

Pim
 
I think D9 and D10 just clamp the gates of Q18 and Q19 to prevent the driver stage (running from +-40v) from driving the power stage above its +-28v supplies.
Again, this is probably something that would not happen under "normal" operation.
 
Thanks for your reaction, does it have something to do with the protection circuit Q 17 and Q16,

No, it's simply to prevent the output transistors getting over-driven, a consequence of the rather bizarre idea of using FET's to drive bi-polar output devices.

D11/12 are probably for something similar, protecting the outputs (by maintaining some kind of preamp/driver supply) in case of failure of the 40V rails.

Presumably the 40V and 28V rails are fused, and it 'might' have come to light that when a 40V rail fuse blows it caused damage, and D11/12 possibly prevent that?.

But as a design it seems vastly over-complicated for probably little or no gain.
 
Looking at the schem again I agree with Nigel's and tomizett's assessments.
 
Dear Mr. Goodwin, I read now that you find it strange to use as control transistors MOSFETs, the original design has transistors in the output stage, which is a better idea?, the Mosfet output stage amplifier was my own idea.

Greeting,

Pim
 

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Sir, Mosfets give me a positive feeling when it comes to the sound of the amplifier, this is purely instinctive.
Do you think that is possible with a mosfet driver stage and MOSFETs in the output stage.

greeting,

Pim
 
Sir, Mosfets give me a positive feeling when it comes to the sound of the amplifier, this is purely instinctive.
Do you think that is possible with a mosfet driver stage and MOSFETs in the output stage.

I seriously doubt you could hear any difference in blind tests, but if you want MOSFET's then go for it :D

But generally you would use MOSFET's as the final output devices, and the design you've posted is seriously overcomplicated, which doesn't mean it's any better than far simpler designs - there's plenty of MOSFET designs out there, but they have never been particularly popular (until the recent class-D designs, where they seem to have become popular - perhaps because they don't different to bipolar in class-D?).
 
Dear Sir,

I have a power supply design with some zeners, two reference D1 and D2, and two at the base of Q 8.

The output of the power supply give noise could be seen through the oscilloscope 50 mv.

Look for the noise cause I discovered that the noise of the zener D3 and D4 came.
I find the place of the zener even strange!.

And found out that a resistor of 1K worked without noise.

I also noticed that some small zener in series 4 pieces 4.2 volts also solved the problem of noise.

Can you explain why the designer has placed there that zeners.

Is replaced the Zener by a resistor good opportunit.

Sincerely,

Pim
 

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Again, it's vastly overcomplicated, for no reason or advantage whatsoever - where do you find these weird crazy designs?.

But you certainly can't replace zener diodes with resistors, a zener is there to provide an accurate voltage reference, a resistor does nothing of the kind.

But why are you concerned with 50mV of noise on a 33V rail anyway?, I suggest you try working out what percentage that is :D

Incidentally, zeners are inherently noisy, which is why they are used in noise generators.

Have you actually built and tested this, or are you just using a simulator? (particularly bearing in mind the crazy component values) - you should be aware that simulators aren't real life, and may bear little resemblance to it.
 
Dear Sir, I find that there is no noise may stand on a power line, maybe 1 mv is OK, a little Perfectionist, :).
I have tested with occiloscoop the power supply.

But is the location of the zener diode is not placed oddly.

Geeting,

Pim
 

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  • Voeding 10 juni 2014.pdf
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Sorry, I've just noticed you were referring to D3 and D4, you could quite happily replace those with a resistor, just as you could Q9 (and much of the rest as well).

D1 and D2 are the reference zeners, and there are two in series because zeners of that voltage have low temperature coefficients.
 
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