Amp on - no input or speaker?

si_blakely · 7th July 2005, 07:11 PM

I have 2x150W Mosfet amps (Maplin kitsets). They have seperate power supplies, but a single Stereo Speaker Protection/Dethump circuit. The main use for this will be driving one or two 12" bins as personal stage monitors.

The question is, when this is running mono, can the unused amp channel be powered up with no input/output, or should I switch power to each channel seperately. I would rather not do this, as my bass playing 14yo daughter will be the prime user and I do not want to stress her too much by having too many don'ts.

Of course, the other option is to have two mono amps, but that means building a second Speaker Protection circuit (and another case etc).

Any thoughts

Si

Tekko · 7th July 2005, 07:13 PM

Paralell the channels, double power and no risc that a unhooped channel can break.

djQUAN · 7th July 2005, 08:03 PM

I think connecting the unused input to ground via a 1k resistor would keep the amp stable.

if you would like to make it useable, use two separate gain controls for each channel, turn the unused channel to min and don't worry about it. works for the amps I have built.

si_blakely · 7th July 2005, 08:13 PM

and fry my bins which will not handle 300W :-)

Si

Brion55 · 7th July 2005, 08:36 PM

Most pro sound amp mfgs use switched input jacks that short the input to ground when it's not in use.

Like this:

si_blakely · 7th July 2005, 08:41 PM

How would that be implemented - just a pot across the amp inputs?

Si

Frank Berry · 7th July 2005, 09:00 PM

"Paralell the channels, double power and no risc that a unhooped channel can break."

I suggest that you DO NOT ever do this. Paralleling the outputs can damage the amplifier.

I've never had a problem with using only one channel of a two channel amplifier. If you're really worried about damage to the idle amplifier, insert a plug into the input with the tip shorted to ground.

si_blakely · 7th July 2005, 09:16 PM

Thanks guys - I'll change the inputs from RCA to switched jacks.

Si

anatech · 8th July 2005, 09:33 PM

Hi si_blakely,
To be honest, don't worry about it. An unloaded channel will not cause any trouble unless it's a tube amp (transformer output). So don't change anything. Frank Berry has made a good point & I agree totally.

-Chris

7th July 2005, 07:11 PM	#1
si_blakely diyAudio Member Join Date: Jul 2005 Location: SouthWest England	Amp on - no input or speaker? I have 2x150W Mosfet amps (Maplin kitsets). They have seperate power supplies, but a single Stereo Speaker Protection/Dethump circuit. The main use for this will be driving one or two 12" bins as personal stage monitors. The question is, when this is running mono, can the unused amp channel be powered up with no input/output, or should I switch power to each channel seperately. I would rather not do this, as my bass playing 14yo daughter will be the prime user and I do not want to stress her too much by having too many don'ts. Of course, the other option is to have two mono amps, but that means building a second Speaker Protection circuit (and another case etc). Any thoughts Si

7th July 2005, 09:00 PM	#7
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	"Paralell the channels, double power and no risc that a unhooped channel can break." I suggest that you DO NOT ever do this. Paralleling the outputs can damage the amplifier. I've never had a problem with using only one channel of a two channel amplifier. If you're really worried about damage to the idle amplifier, insert a plug into the input with the tip shorted to ground. __________________ Frank

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7th July 2005, 07:13 PM	#2
Tekko diyAudio Member Join Date: Jan 2005	Paralell the channels, double power and no risc that a unhooped channel can break.

7th July 2005, 08:03 PM	#3
djQUAN diyAudio Member Join Date: May 2004 Location: manila	I think connecting the unused input to ground via a 1k resistor would keep the amp stable. if you would like to make it useable, use two separate gain controls for each channel, turn the unused channel to min and don't worry about it. works for the amps I have built.

7th July 2005, 08:13 PM	#4
si_blakely diyAudio Member Join Date: Jul 2005 Location: SouthWest England	and fry my bins which will not handle 300W :-) Si

7th July 2005, 08:41 PM	#6
si_blakely diyAudio Member Join Date: Jul 2005 Location: SouthWest England	How would that be implemented - just a pot across the amp inputs? Si

7th July 2005, 09:16 PM	#8
si_blakely diyAudio Member Join Date: Jul 2005 Location: SouthWest England	Thanks guys - I'll change the inputs from RCA to switched jacks. Si

8th July 2005, 09:33 PM	#9
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi si_blakely, To be honest, don't worry about it. An unloaded channel will not cause any trouble unless it's a tube amp (transformer output). So don't change anything. Frank Berry has made a good point & I agree totally. -Chris

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