Weird crackling sound without B+ applied

arnoldc · 9th January 2007, 04:41 AM

Hi,

Over two nights I made a simple UL EL34 amplifier. I don't have a schematic now, but the driver section is a 1/2 5687 with 10mA diyAudio CCS on the plate, 750R (bypassed) on the cathode to give ~8V bias, cap coupled to EL34 with 1K series on the grid and 220K grid resistor. The UL tap of the transformer is connected to the EL34 G2 via 1K resistor. 470R (bypassed) on the cathode of the EL34 to give 20V bias.

The power supply is a simple full-wave with FR107 -> 470uF -> 500R 10W -> 470uF and I installed a switch (on the negative leg) for standby.

When power is applied, but no B+ (standby on), there's crackling sound coming from the speakers. When B+ is applied, it goes away and the amp is playing well.

Any thoughts? I'm sorry but this is the first time I have experienced such.

EC8010 · 9th January 2007, 07:54 AM

Arcing across your (open) standby switch.

arnoldc · 9th January 2007, 09:51 AM

Ooooh! My bad...

Thanks!

EC8010 · 9th January 2007, 10:02 AM

You're welcome.

9th January 2007, 04:41 AM	#1
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	Weird crackling sound without B+ applied Hi, Over two nights I made a simple UL EL34 amplifier. I don't have a schematic now, but the driver section is a 1/2 5687 with 10mA diyAudio CCS on the plate, 750R (bypassed) on the cathode to give ~8V bias, cap coupled to EL34 with 1K series on the grid and 220K grid resistor. The UL tap of the transformer is connected to the EL34 G2 via 1K resistor. 470R (bypassed) on the cathode of the EL34 to give 20V bias. The power supply is a simple full-wave with FR107 -> 470uF -> 500R 10W -> 470uF and I installed a switch (on the negative leg) for standby. When power is applied, but no B+ (standby on), there's crackling sound coming from the speakers. When B+ is applied, it goes away and the amp is playing well. Any thoughts? I'm sorry but this is the first time I have experienced such.

9th January 2007, 07:54 AM	#2
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	Arcing across your (open) standby switch. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

9th January 2007, 10:02 AM	#4
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	You're welcome. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

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9th January 2007, 09:51 AM	#3
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	Ooooh! My bad... Thanks!

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