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problem about decoupling capacitor

post #1 of 6
Thread Starter 

Hi

 

I am new in DIY some amp and want to design circuit by myself. Now I want to add two buffer in my design. I don't know should I use separate decoupling capacitor on two buffer or share same set of cap since they are connect to same node. Please help! :D

post #2 of 6

my 1st post here biggrin.gif

 

Hi

just my experience,  seperate decoupling caps for each part of the curcuit give u cleaner /more powerful power supply and  will make it sound better, but different person has different  taste. So the best way to figure out this question is to try and listen ,and goodluckcool.gif

post #3 of 6
Thread Starter 
Thanks for sharing your experience! Maybe I should try minimizing the circuit to spare the space for those coupling caps! biggrin.gif

BTW, this is my first post:P
post #4 of 6

Use separate decoupling caps.  If you combine them, they would need to be twice as large, and would also tend to cause cross-coupling between the buffers' signals.  Combining them would also make it difficult to achieve a good-enough layout, for minimal inductance (and impedance in general) as seen by the power pins.

 

The decoupling caps are like a small point-of-load power supply.  They are there to supply demands for fast-changing transient currents.  Their layout is very important, since too much inductance will make the transient response less accurate, and will also restrict the ability of the feedback loop to remove higher-frequency harmonics.

 

It is best to use more, but smaller, decoupling caps, in parallel, and place them all as close as possible to the power pins, with short-as-possible connections to both the power pin and (usually) the device's load's ground.

 

How have you calculated the capacitance values needed for decoupling?

 

You will also want a physically-small bypass cap for each power pin, which should be connected extremely close to the chip's power pin.  Its purpose is to short-circuit high frequencies to ground, to defeat the hidden high-frequency positive feedback loop that exists in most transistor amplifier cicuits, through the power rail.  Otherwise the circuit could oscillate or ring at high frequencies.

post #5 of 6

On subjects such as this "gootee" definitely knows of what he speaks!

 

With decoupling caps, a fraction of an inch in extra lead length can be important.

Use caps designed for decoupling.

Don't use boutique audio film caps.

post #6 of 6

Or better still build two PU .keep them separate [mono-block] use star earthing .Use quality smoothing caps Buffers amplify small signals so make sure ripple current is low.Use quality voltage regulators .These are usually rated at 1 AMP rather than unregulated . Unregulated in big Power-Amps 100W up. are better due to instant current available, But not in buffers.

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