High and Low gain inputs on a Valve amp

Manfred-Klose

something i am wondering about, but cant find info i can trust on the internet.

Can you run an A/B box into a valve amp's low/high gain inputs without any problems?
switching between the 2 of course.

i've read that due to different circuit designs you can do it with a fender amp but would get a popping noise with a marshall, is this true?

bottledtone

The hi-lo inputs of fender types rely on one jack being used so that the other is switched to ground. If in the hi input then the signal is about 1M resistance from ground and if in low input only it is 68k resistance from ground. If both jack are inserted at same time, then they are both 1M resistance from ground and equal. So A/B would be the same!
Of say a Marshall 2203/4 jcm800 then placing a jack into Lo disconnects the switch/link from the first gain stage. So if you A/B'd it, the signal would never go through the first gain stage because the jack you inserted is breaking the chain.

FenderBender

+1 the JCM800 only reacts to the low input when both inputs are used together.

Manfred-Klose

thanks. thats was the reply i was looking for.

Gearhead

You might also want to consider the "Hi" and "Lo" aren't for high gain and low gain.

Manfred-Klose

is this one of your riddles ? ???

AlanRatcliffe

High and low are references to the impedance of the input.

Manfred-Klose

i knew that.

i thought gearhead had something else up his sleeve.

Gearhead

Sorry if I came across like a riddler. I was just trying to make it clear for forumites who don't know what the Hi and Lo stand for that they should not take your original question to mean you were thinking about gain:

Manfred Klose wrote: Can you run an A/B box into a valve amp's low/high gain inputs without any problems?