Zen amp turn-on thump.

vdi_nenna · 13th October 2000, 09:15 PM

I recently built the Zen amp from the original article. No modification from the second article. What I'd like to know is- can I use a Thermistor to impede the in-rush of current to stop the speaker cone from extreme excursion at turn-on. Will this alter the sound in any way? What effects could it have on the amp? I don't want to add another circuit. I just want to keep it simple.

Any suggestions??

Thanks in advance for your help!

pixie · 16th October 2000, 07:06 PM

I've seen large capacitors used for this purpose.

Someone correct me if I'm wrong, but the capacitor will
charge to the peak voltage then act as an open circuit.

Something like a 3000uF capacitor should do.

Don't take my word for it. I graduated three years ago and
have been a digital programmer since then. My analog electronics is a bit rusty.

Pixie

ebrewste · 22nd October 2000, 07:27 PM

You can set up a relay to short the speaker outputs for a bit on start up. With the current source in the Zen, it won't hurt anything. If you set the relay closed with the power off and open it after a short delay, the thump will go away.
It is an additional circuit, but it does remove itself from the signal path when it is not in effect.
This isn't my original thought. It was in a reader comment in Audio Electronics, I believe.

Erik

16th October 2000, 07:06 PM	#2
pixie diyAudio Member Join Date: Oct 2000 Location: Austin, Texas, USA	Capacitor I've seen large capacitors used for this purpose. Someone correct me if I'm wrong, but the capacitor will charge to the peak voltage then act as an open circuit. Something like a 3000uF capacitor should do. Don't take my word for it. I graduated three years ago and have been a digital programmer since then. My analog electronics is a bit rusty. Pixie

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13th October 2000, 09:15 PM	#1
vdi_nenna diyAudio Member Join Date: Oct 2000 Location: PA, USA	I recently built the Zen amp from the original article. No modification from the second article. What I'd like to know is- can I use a Thermistor to impede the in-rush of current to stop the speaker cone from extreme excursion at turn-on. Will this alter the sound in any way? What effects could it have on the amp? I don't want to add another circuit. I just want to keep it simple. Any suggestions?? Thanks in advance for your help!

22nd October 2000, 07:27 PM	#3
ebrewste diyAudio Member Join Date: Oct 2000 Location: Sunnyvale, CA	You can set up a relay to short the speaker outputs for a bit on start up. With the current source in the Zen, it won't hurt anything. If you set the relay closed with the power off and open it after a short delay, the thump will go away. It is an additional circuit, but it does remove itself from the signal path when it is not in effect. This isn't my original thought. It was in a reader comment in Audio Electronics, I believe. Erik

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