Zen V4 - square wave with real load

wish · 15th February 2005, 11:22 AM

Hi All!

My Zen V4 have some "slow" overshoot in output signal when connected to real loudspeakers.

My test signal at input is 2KHz square wave. Output load is 8Ohm louspeakers said to be tube friendly. Right after raising front in output wave there's a fall, then rise and then wave settles until falling front. The value of overshoot is about 3% of impulse amplitude and peak of overshoot is delayed for 80 microseconds from raising front of wave. So it isn't fixed with feedback capacitor, which fix first microsecond(s) of square wave.

There's no overshoot when load is 8Ohm resistor. Top of output wave is flat.

Is this usual?
What's the reason for this?
Is there any advice to fix this?

Thanks!

Nelson Pass · 15th February 2005, 05:15 PM

Quote:

Originally posted by wish
Is there any advice to fix this?

You can adjust C12, for starters.

wish · 16th February 2005, 05:15 PM

Mr. Pass! Thank you for response.

I've adjusted C12 already. Doing this I removed short overshoot which starts right after square wave front and lasts for 1 microsecond. This one existed with any load, resistor or loudspeaker.

Values of C12 from 3pf to 50 pf don't affect another, "long" overshoot. It appears only when loudspeaker is connected. It doesn't exist when power 8Ohm resistor is connected instead of loudspeaker. It's peak is 40 us from square wave front (80 us in previous post is mistake).

Nelson Pass · 16th February 2005, 07:39 PM

Sounds like the finite output impedance of the amp is
seeing the inductance of the driver. You can use an
output RC "Zobel" network to ground to correct it, if
that's the case.

wish · 21st February 2005, 07:54 PM

Mr. Pass!

Thank you for support!

I tried to connect RC network in parallel with loudspeaker. I used R=2 Ohm, C=0.22 uF; R=8 Ohm, C=1uF and some other combinations. It doesn't help. "Long" overshoot is still there.

During my experiments I noticed that I can change wave form changing R16 value. As I wrote, "Long" overshoot peak is 40us after wave front. Changing R16 from 3K to 1K I can make level of wave before and after this 40us position lower or higher than level in this 40us position. With R16 less than 1.3K overshoot peak becomes a fall. With R16=1.3K value of overshoot is minimal. But I couldn't make top of wave flat this way.

Earlier I tried to set current source gain as you wrote on the forum. I've got 50% with R16=2,2K.

Any advice?

15th February 2005, 11:22 AM	#1
wish diyAudio Member Join Date: Jul 2004 Location: Perm	Zen V4 - square wave with real load Hi All! My Zen V4 have some "slow" overshoot in output signal when connected to real loudspeakers. My test signal at input is 2KHz square wave. Output load is 8Ohm louspeakers said to be tube friendly. Right after raising front in output wave there's a fall, then rise and then wave settles until falling front. The value of overshoot is about 3% of impulse amplitude and peak of overshoot is delayed for 80 microseconds from raising front of wave. So it isn't fixed with feedback capacitor, which fix first microsecond(s) of square wave. There's no overshoot when load is 8Ohm resistor. Top of output wave is flat. Is this usual? What's the reason for this? Is there any advice to fix this? Thanks!

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16th February 2005, 05:15 PM	#3
wish diyAudio Member Join Date: Jul 2004 Location: Perm	Mr. Pass! Thank you for response. I've adjusted C12 already. Doing this I removed short overshoot which starts right after square wave front and lasts for 1 microsecond. This one existed with any load, resistor or loudspeaker. Values of C12 from 3pf to 50 pf don't affect another, "long" overshoot. It appears only when loudspeaker is connected. It doesn't exist when power 8Ohm resistor is connected instead of loudspeaker. It's peak is 40 us from square wave front (80 us in previous post is mistake).

16th February 2005, 07:39 PM	#4
Nelson Pass The one and only Join Date: Mar 2001	Sounds like the finite output impedance of the amp is seeing the inductance of the driver. You can use an output RC "Zobel" network to ground to correct it, if that's the case.

21st February 2005, 07:54 PM	#5
wish diyAudio Member Join Date: Jul 2004 Location: Perm	Mr. Pass! Thank you for support! I tried to connect RC network in parallel with loudspeaker. I used R=2 Ohm, C=0.22 uF; R=8 Ohm, C=1uF and some other combinations. It doesn't help. "Long" overshoot is still there. During my experiments I noticed that I can change wave form changing R16 value. As I wrote, "Long" overshoot peak is 40us after wave front. Changing R16 from 3K to 1K I can make level of wave before and after this 40us position lower or higher than level in this 40us position. With R16 less than 1.3K overshoot peak becomes a fall. With R16=1.3K value of overshoot is minimal. But I couldn't make top of wave flat this way. Earlier I tried to set current source gain as you wrote on the forum. I've got 50% with R16=2,2K. Any advice?

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