high and low input on an amp

T

the dairy giant

New member
Hi, does this high/low thing mean anything in particular?

i sometimes plug my guityar into the instrument input on a mixer, it goes into my computer and amplitube. I have bee told I'd never get a good sound like this coz the impedance is wrong (i think), but I have recorded some songs where people listening have thought it was a mic'ed up tube amp!

So is this low/high input thing something specific?, I have just tended to use whichever I felt sounded best at the time. I currently use a big old Yamaha solid state amp from the 70s or 80s with a 15" speaker, can't remember the model, but my 90s peavey amp which was a bit nasty had them too..

thank you. I ahvee been playing for years by the way, but can never get to tied up into these finer details of equipment etc.
 
The high and low inputs are part of the amp's design which allows you to use either active pickups or passive. While either input will work, high is for passive, and the low input is for active.
 
Dani Pace said:
The high and low inputs are part of the amp's design which allows you to use either active pickups or passive. While either input will work, high is for passive, and the low input is for active.
Click to expand...
That's not really quite right though it may end up working that way. But high and low inputs were on , for instance, Fender amps WAY before there were gits out there with active electronics.
Basically the high input runs the signal straight thru into the preamp section while the low input attenuates the signal ...... the point was to keep instruments that had an especially high output from overloading the preamp.
So since actives generally have a much higher output than passives, they often match up better with the low input.
But that wasn't the specific intent ..... they were just two different gain level choices.
 
My acoustic 370 has two inputs, labelled only "1" and "2". I learned somewhere that if I insert an open dummy plug into input "2" and plug my bass into "1", I get a pretty good increase in output.

Dunno if it applies to any other amps, but it works on mine...

Eric
 
I didn't mean to imply that was the only reason, just a quick simple explanation of how the high and low inputs are most commonly used.
 
Hmm...I'm thinking you're both right but I thought I'd throw my 2 cents in there too.

I'm looking two different amplifier schematics. One is a new school high gain amp and the other is an old school single ended amp. They share a similar idea in how the high and low inputs are used. Both the high and the low input go to the V1 pre-amp tube which is a 12AX7 type tube. The 12AX7 tube is really two amplifier circuits in a single enclosure. The "high" jack seems to go through both stages of the input preamp tube while the low only goes through one stage. That kinda makes sense in how you get a cleaner sound when you go into the low input. My feeling is that you get a little more headroom and less preamp gain quality when in the low input. In both amps, the high and low inputs have different tone shaping components as well as resistie impedance loading components giving a different flavor of sound as well.

I don't see a technical reason why both inputs couldn't be constructed with matching impedances but then what would be the fun in that? Also, considering the input impedance and how it would interract with the pickups in the guitar, that too makes for some interesting combinations. I'm willing to bet that the reason for the different impedances isn't for matching purposes but rather for some tonal variety. The impedance differences determine how hard the input amp will be hit and how tightly or loosely the guitar signal will be coupled. I'm thinking that a variable input selector would be cool.

Just thought I'd add a little mud to the waters.

Aint these things fun? :D
 
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