buffer step down

[Ted205]

I've had a search but couldn't really find anything.

What is a good way to step the higher dc voltage used for the amplifier, down to something that can be used for a buffer, i.e 15-20v.

Or do people simply use another transformer & power supply

thanks

ted

 

[AndrewT]

best to use a twin secondary transformer of the correct voltage.

Or use a dropper resistor and Zener from your existing HV supply. Or something a bit more complicated.

search reg or Vreg or regulator

 

[woody]

It might be best to tell us what you realy need. Like how much
current do you need, how tight do you need this voltage regulated, how much noise can you tolerate, do you need a
single supply voltage, is it located in the amp ect.

 

[Nuuk]

If sound quality is the goal, I recommend a separate PSU for the buffer.

This may give you some pointers.

 

[Ted205]

assuming i have a large enough transformer. Is there any 'audio' downside to using one tranny for the amp and the buffer, each with their own PSU feeding from it?

Or if i take a feed from the original PSU output and regulate it down to what i need?

i realise more heat will be generated dropping a high voltage.

 

[Nuuk]

The problem is when the power amp modulates the supply to the buffer/pre.

You can take separate secondaries off the same transformer and build separate supplies from them.

 

[Ted205]

unfortunately my transformer is completely sealed so i'll have to use a regulator

 

[AndrewT]

unfortunately my transformer is completely sealed so i'll have to use a regulator

or a small 10 to 15VA 15Vac transformer + regulator.

 

[artquake]

or also a ..:: DC/DC Regulator Module ::..

 

[Ted205]

wold this be acceptable?

Picture

 

[AndrewT]

r5=680 is too big.
If the supply runs at 24Vdc (this will vary with mains voltage and amplifier load) then you have just 13mA available.
At max mains voltage and min amplifier draw the Zener should be near maximum dissipation. That makes more current available at other operational conditions.
If Zener dissipation is a problem then use a zener+medium power transistor to make more current available for the low level stage when mains is at minimum and amp load is maximum.

 

[Ted205]

thanks for your help andrew.

can i ask how you calculated 13mA

 

[AndrewT]

17*sqrt(2)=24, [24-15]/680=0.013

 

[Ted205]

Thanks for you help

 

[Ted205]

It might be best to tell us what you realy need. Like how much
current do you need, how tight do you need this voltage regulated, how much noise can you tolerate, do you need a
single supply voltage, is it located in the amp ect.

I'm making the additional power supply for a discrete buffer (Andrew Rothwell's design from Decibel dungen)
which i need to investigate as to what current is needed.

 

[AndrewT]

the negative and positive rails draw similar current of ~6mA while no signal is present.
But the positive rail current is modulated with a signal passing.
Allow at least +6mA and -6mA.
but probably better to go to +12mA and -6mA, to ensure that current limiting does not occur on asymmetrical peaks. i.e. 0mA to 18mApk in +ve rail and 6mA continuous in -ve rail.

This analysis depends on R1=120r & R2=27k with +-15Vdc to +-20Vdc supply.

I suggest you add an RF filter to the buffer input. 300uS should be sufficient. 470pF & 680r are about right, but there is much leeway in these values.