Relay or switch mains

magnetman · 15th July 2012, 11:08 PM

Hi all,
I am working on a amplifier build, it's still in the cerebral stage. I had the idea to put a relay in the back of the chassis for mains switching. I like the idea that 240 ac doesn't travel to the front of the box for noise reasons. What do you think?

Cheers

DF96 · 15th July 2012, 11:16 PM

A relay won't do any harm if the right relay is used in the right way, but a front-panel mains switch is the usual way of doing it. Just keep the mains wire away from signal circuitry.

indianajo · 12:08 AM

Peavey uses a TO3 package triac on the main hot with the heat sink screwed to the case. Legs are .250" spade pointed in. Front panel switch is light duty. Jameco.com sells the triacs in that case but they don't stock in Aust. Peavey might stock in Aust., one amp using it is the PV1.3k. It is not on the schematic so I don't have a part number. Don't forget an EMI snubber on the gate and MOS transient supressor clamps on the main line. .

DF96 · 16th July 2012, 09:43 AM

If you use a triac you add switching transients which you then have to get rid of again. Transients are much worse than plain mains AC. Guitar or PA is less worried about a bit of noise, though.

jacco vermeulen · 16th July 2012, 10:11 AM

Or use a triac and a relay in parallel with a delay, the relay avoids the triac misbehaviour at the crossover points, the triac saves the relay from wearing down.

bullpeters · 16th July 2012, 10:16 AM

surely the transients are only when you turn it on or off?

jacco vermeulen · 16th July 2012, 10:22 AM

It's AC, goes through the zero crossing twice every cycle, makes 100-120 times a second for a triac.

bullpeters · 16th July 2012, 10:31 AM

good to know!

bullpeters · 16th July 2012, 11:05 AM

sorry if i seem a bit dim here but this knowledge also applies in another part of my life,
I assumed a Triac is on or off and not switching each cycle.I also assumed a relay would be good for 1000's of switches? As i hope I imply,I don't know and it would helpful with a non audio applicatition,a packaging machine that needs to switch "silently"
Thanks

Mooly · 16th July 2012, 11:32 AM

There are many ways to drive a triac. It's best to trigger the device constantly using a "high" frequency gate drive.

Eva has a brilliant example of this here,
Soft-start circuit with no relays and no aux. transformers

I think this was the original diagram as the image seems to have disappeared,

15th July 2012, 11:08 PM	#1
magnetman diyAudio Member Join Date: Jun 2011 Location: Hobart Australia	Relay or switch mains Hi all, I am working on a amplifier build, it's still in the cerebral stage. I had the idea to put a relay in the back of the chassis for mains switching. I like the idea that 240 ac doesn't travel to the front of the box for noise reasons. What do you think? Cheers

16th July 2012, 12:04 AM	#3
indianajo diyAudio Member Join Date: Jan 2010 Location: Jeffersonville, Indiana USA	Peavey uses a TO3 package triac on the main hot with the heat sink screwed to the case. Legs are .250" spade pointed in. Front panel switch is light duty. Jameco.com sells the triacs in that case but they don't stock in Aust. Peavey might stock in Aust., one amp using it is the PV1.3k. It is not on the schematic so I don't have a part number. Don't forget an EMI snubber on the gate and MOS transient supressor clamps on the main line. . __________________ Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300 Last edited by indianajo; 16th July 2012 at 12:08 AM.

16th July 2012, 10:11 AM	#5
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, Rotterdam or Curaçao	Or use a triac and a relay in parallel with a delay, the relay avoids the triac misbehaviour at the crossover points, the triac saves the relay from wearing down. __________________ Not so much,.......if it says "ZM" in the corner.

16th July 2012, 10:22 AM	#7
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, Rotterdam or Curaçao	It's AC, goes through the zero crossing twice every cycle, makes 100-120 times a second for a triac. __________________ Not so much,.......if it says "ZM" in the corner.

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15th July 2012, 11:16 PM	#2
DF96 diyAudio Member Join Date: May 2007	A relay won't do any harm if the right relay is used in the right way, but a front-panel mains switch is the usual way of doing it. Just keep the mains wire away from signal circuitry.

16th July 2012, 09:43 AM	#4
DF96 diyAudio Member Join Date: May 2007	If you use a triac you add switching transients which you then have to get rid of again. Transients are much worse than plain mains AC. Guitar or PA is less worried about a bit of noise, though.

16th July 2012, 10:16 AM	#6
bullpeters diyAudio Member Join Date: Apr 2009 Location: Right next to beach, a potatoe toss to the whitewater	surely the transients are only when you turn it on or off?

16th July 2012, 10:31 AM	#8
bullpeters diyAudio Member Join Date: Apr 2009 Location: Right next to beach, a potatoe toss to the whitewater	good to know!

16th July 2012, 11:05 AM	#9
bullpeters diyAudio Member Join Date: Apr 2009 Location: Right next to beach, a potatoe toss to the whitewater	sorry if i seem a bit dim here but this knowledge also applies in another part of my life, I assumed a Triac is on or off and not switching each cycle.I also assumed a relay would be good for 1000's of switches? As i hope I imply,I don't know and it would helpful with a non audio applicatition,a packaging machine that needs to switch "silently" Thanks

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