Using only one side of the Quad pre?

[The Magic Hoof]

I'm running a Quad pre and a 50/50. I was wondering if you could use only one side of the Quad pre at a time, like channel A or channel B which would in turn only be using the left or right 2 speakers in a 4X12 cab.

Is that safe? I read about it somewhere and I think it said something about just turn the knobs to 0, or something...

 

[mr_fender]

The Quad is a preamp, so there is no problem with using just one side. There is no need to have a load present on a preamp. The 50/50 is another story. You MUST have a load of some kind (speakers, dummy load, etc.) on a tube power amp. The 50/50 is basically two separate power amps in one unit, so you must have a load on both left and right channels when in use. The exception would be to pull the two power tubes for the channel you don't want to use. That will stop any current from flowing through the output transformer for that channel, and it would then be safe to not have a speaker attached to that channel.

 

[crane]

$as said in the manual you can use one channel of te 50/50 by turning the other one to "0". I've used mine for years in that configuration without any problems.

 

[The Magic Hoof]

Thanks for the replies. It'd be great to quiet down everything and not have both sides blasting. I kinda wish I had a 2X12 cab since I've got a smaller room, but ah well. So does that mean I should turn down an output on the Quad and the 50/50 (say channel A on both the Quad and 50/50) but just leave the cables connected? Or just leave both sides of the 50/50 powered up but turn down a channel of the Quad?

 

[crane]

Be shure to plug nothing in the unused channel's input. Simply plug only what you are using.

 

[mr_fender]

Be shure to plug nothing in the unused channel's input. Simply plug only what you are using.

Not a bad idea. However, I've always strayed away from using a stereo amp with one channel turned down. It is safe as long as no signal goes to that channel, but it's too easy to accidently turn that volume up. Assuming the amp has switching input jacks, leaving that channel's input unplugged would shunt any input to ground when not in use.

Keep in mind though, if an input tube stage were to go microphonic, a possibly large signal could be going to the power section without you knowing it, even with the input grounded and/or volume turned down all the way. That's why I like to pull the tubes just to be safe. That way I know for certain there is no current flowing throught the output transformer. You could also pull the phase inverter tube for that channel too, but that often requires opening the amp. Power tubes are just easier to get to.

 

[The Magic Hoof]

Be shure to plug nothing in the unused channel's input. Simply plug only what you are using.

Not a bad idea. However, I've always strayed away from using a stereo amp with one channel turned down. It is safe as long as no signal goes to that channel, but it's too easy to accidently turn that volume up. Assuming the amp has switching input jacks, leaving that channel's input unplugged would shunt any input to ground when not in use.

Keep in mind though, if an input tube stage were to go microphonic, a possibly large signal could be going to the power section without you knowing it, even with the input grounded and/or volume turned down all the way. That's why I like to pull the tubes just to be safe. That way I know for certain there is no current flowing throught the output transformer. You could also pull the phase inverter tube for that channel too, but that often requires opening the amp. Power tubes are just easier to get to.

So I should pull a couple of the tubes from my 50/50 eh? I'm not sure which one(s) to pull. That'd be great to do though since I seriously only need one side. I record at home and it'll help with volume.

 

[desertdweller]

Wait, with the 50/50 in half drive, try turning the volume knobs up from zero until the sound is just barely audible. It should be pretty darn quiet. Do you really need to go quieter than that? It's just barely audible with most preamps.