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gaetan8888 10th January 2008 12:29 PM

About PCB layout

To check if a PCB layout are good and don't do oscillations or stray capacitance, is it enough to pass a 10k hz square wave into the finished amp and look if it is oscillate ?




Jan Dupont 10th January 2008 02:06 PM

Since you post here, I assume that you are talking about a solid state amplifier PCB........

10 kHz will only show if something is completly wrong with your layout. Not if oscillation could or will occour when feeding the amp with higher frequencies, and it won't say anything about the behavier for stray capacistance at high frequencies....

If the upper Fo for your amp is 20 kHz it could work, however if your amp has a higher Fo, you have to test it at the Fo limit frequency or even higher.

Also remember that stray capacistance depends on the power going through the tracks, so you should test it under load.

gaetan8888 10th January 2008 04:01 PM

Hello Jan

I forgot to specify that it was for transistors amps.

The amp would go up to about 50k hz, so since a square wave can have high harmonic do a 20 kz square wave can do the job to check oscillation cause by the PCB ?

I can go up to 30k hz square wave but it seem quite high and can be hard on the amp.

Btw, is there any web site about how doing good PCB layout ?



wg_ski 10th January 2008 04:15 PM

You can check for overshoot and ringing with a much lower frequency square wave. Feed it with a 1Khz square with fast rise and fall times and look for funnly stuff on the leading and trailing edges. Both at the output and at internal nodes.

A 20 KHz sqaure will probably smoke your zobel. :D

Jan Dupont 10th January 2008 04:18 PM


That doesn't show all problems with stray capacistance.......:att'n:

gaetan8888 10th January 2008 04:29 PM


Any other way than square wave ?

Because even a small oscillation can degrade the sound quality of an amp.



Jan Dupont 10th January 2008 04:34 PM

What do you mean by:


I can go up to 30k hz square wave but it seem quite high and can be hard on the amp.
Your amp wont suffer from that....... The square wave may not be nice to look at, but your trannies won't be damaged because of that....

gaetan8888 10th January 2008 04:36 PM

Hello Jan

It won't fry the zobel ?



Jan Dupont 10th January 2008 04:50 PM

I didn't say that you should go full power ;)
Try with an output of 1 Volt into 8 Ohms.

What's your zobel frequency ?

gaetan8888 10th January 2008 05:01 PM

Hello Jan

My zobel are 10 ohm with 100nf, how about just disconnecting it for the time of the test ?

Btw, do you want the schematic of a Audiotec amp for your web site ?



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