ZenV4 oscillations problem

pro · 7th October 2004, 02:32 PM

Hi averybody.
I have controlled the output of my ZenV4 with a scope, and I discovered that there is an oscillation at about 300KHz with 25mv amplitude. Is this normal, or could it be a problem?
The only differences respect to the original schematic, is the feedback loop resistor modded in 470K and input resestor in 34K for a gain of about 22dB. Feedback capacitor is 4.7p silver mica.
Thank you.

Nelson Pass · 7th October 2004, 06:05 PM

This is not normal. You will probably want to consider
the values of C3 and C12, both frequency compensation
caps. Also you did not mention what load it might have
been connected to.

PMA · 7th October 2004, 06:50 PM

How about LW transmitters near to your facility?

pro · 7th October 2004, 10:29 PM

C12=4.7p
C3=1n
Load 8 hom
No LW emitter (I am in a bunker 7 foot underground.
Amplitude is 10mV on one channel and 25mV on the other.
Any suggestion?
Thanks.
Ciao.

till · 7th October 2004, 10:39 PM

Did you measure only at the output or did you test if its the regulator thats oscillating?

pro · 8th October 2004, 06:29 AM

I havn't measured the regulator, but I have seen that no oscillation occurs until signal RCA arn't attached.
Ciao.

PMA · 8th October 2004, 06:46 AM

Is the input signal clean? (must be measured at the input of an amplifier, not the generator alone).

pro · 8th October 2004, 06:59 AM

Hi PMA.
I don't know. The generator is a CDP transformer coupled.
This evening i'll try to measure the source signal.
Thank you for now.
Ciao.

PMA · 8th October 2004, 05:50 PM

OK. In case you find no oscillations in the input it is Nelson to answer. I do not know how the Aol vs. FB Bode plot of this amp looks like.

Nelson Pass · 8th October 2004, 07:39 PM

Try increasing C3.

Also look at ground with your probe and make sure you
don't see the oscillation there.

7th October 2004, 10:29 PM	#4
pro diyAudio Member Join Date: Feb 2004 Location: Milano	C12=4.7p C3=1n Load 8 hom No LW emitter (I am in a bunker 7 foot underground. Amplitude is 10mV on one channel and 25mV on the other. Any suggestion? Thanks. Ciao. __________________ Michele

8th October 2004, 06:29 AM	#6
pro diyAudio Member Join Date: Feb 2004 Location: Milano	I havn't measured the regulator, but I have seen that no oscillation occurs until signal RCA arn't attached. Ciao. __________________ Michele

8th October 2004, 06:59 AM	#8
pro diyAudio Member Join Date: Feb 2004 Location: Milano	Hi PMA. I don't know. The generator is a CDP transformer coupled. This evening i'll try to measure the source signal. Thank you for now. Ciao. __________________ Michele

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7th October 2004, 06:05 PM	#2
Nelson Pass The one and only Join Date: Mar 2001	This is not normal. You will probably want to consider the values of C3 and C12, both frequency compensation caps. Also you did not mention what load it might have been connected to.

7th October 2004, 06:50 PM	#3
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	How about LW transmitters near to your facility?

7th October 2004, 10:39 PM	#5
till Banned Join Date: Apr 2002 Location: Germany, Clausthal	Did you measure only at the output or did you test if its the regulator thats oscillating?

8th October 2004, 06:46 AM	#7
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	Is the input signal clean? (must be measured at the input of an amplifier, not the generator alone).

8th October 2004, 05:50 PM	#9
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	OK. In case you find no oscillations in the input it is Nelson to answer. I do not know how the Aol vs. FB Bode plot of this amp looks like.

8th October 2004, 07:39 PM	#10
Nelson Pass The one and only Join Date: Mar 2001	Try increasing C3. Also look at ground with your probe and make sure you don't see the oscillation there.

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