High Low Amp inputs???

[Davey]

ok.. i browsed the JCM800 mod page on tone lizard and i havent read it all yet, but it made me wonder again, why do some amps have two inputs??

what does the high mean and do and what is the low input for? there was a false belief around the guitar players that i know that the high one focuses more on the high notes and the low one on the bassy side

so, can you please shed some light on this manner? go all out if you have to, i just want to get it, what is what and which one is used for what

thx for any input

 

[Benjy_26]

Re: High Low Amp inputs???

On some amp designs, one input is brighter than the other while on other amp designs, the one labeled high is straight to the gain stage while the low input has a pad to make the signal cleaner.

 

[TwilightOdyssey]

Re: High Low Amp inputs???

It's the sensitivity of the input.
The HI input is more sensitive, as the name implies ...
I have had great success plugging into the HI input directly on my amps, and using the LO sensitivity input when using an OD pedal.
The HI sensitivity will distort faster, too.

I have found that at high volumes, the input can also make or break it in terms of feedback.

 

[Sabe]

Re: High Low Amp inputs???

I find that when I play my semi-hollowbody, (which has tons more output than any of my solid electrics), it feeds back pretty easily in the regular input, but when I plug it into the lo input, it stays cleaner.

 

[Davey]

Re: High Low Amp inputs???

so the HI input is more sensitive/hotter so to speak and the LO input is like said, cleaner?

 

[TwilightOdyssey]

Re: High Low Amp inputs???

Yep, that's correct!

 

[Davey]

Re: High Low Amp inputs???

so they function independantly from eachother? one does not interfere with another.

what would happen if you plugged the guitar into both of them?

and why did the marshall JMP have 4 of them? what were they for?

sorry if i ask too much, but i'd like to know as much as possible bout this stuff as amps are really not my strong point (meaning i know jack bout em)

 

[TwilightOdyssey]

Re: High Low Amp inputs???

Depends on the amp, Davey ...

On my Knucklehead, they're looped together, so you can plug into the LO input, and use the HI input as an INPUT into another (slave) Knucklehead.

For the life of me, I can't imagine what kind of lunatic would need TWO Knuckelheads running at once, but it can be done, apparently.

 

[Zerberus]

Re: High Low Amp inputs???

On a JCM 800 (specifically mine), the Hi input has more gain but I find it also has less punch, a more fizzy tone, and is missing depth in the bass, as well as less headroom.

The Low input on the other hand has herculean dynamics, punches like Holyfield and the bass is bottomlessly deep, particularly on preamp settings between 3 and 6 o´clock. Tradeoff is less gain, about 25dB IIRC.

I never use the High Input, I run my V-Twin (everything on max) into the low input, put everythiing on max on the JCM (IT´s A freaking Marshall goddamnit, what did you expect?? ) and Voilá: My Tone :headbang:

As far as 2 axes: No go on a JCM. IIRC the High has priority, I know one of them does.......

 

[Kent S.]

Re: High Low Amp inputs???

Without reading the responses (warning upcoming repeated info), the low input is a padded input it knocks some of the gain down (normally -6dB in comparison to the other input) ... in reference to the classic design (ala Fender), there is also an impedance change on the input to ground, meaning the lo input has a lower input impedance, hence it isn't as bright ... generally speaking, you plug in the high input, unless you are having trouble getting a clean sound on chords (hot humbuckers), then you use the lo input. Of course, you use whichever you want to of course. If you plug in both, and if memory serves, you either have both inputs become the lo input, or they are the lower impedance, but one is louder than the other. This also appears to be a holdover from the early days of two players plugging in one amp.
It depends on the exact design(how they are wired) though, a pad switch is often a better option, although that too can be the exact same thing electrically speaking.

 

[No effects]

Re: High Low Amp inputs???

so the HI input is more sensitive/hotter so to speak and the LO input is like said, cleaner?

That is the case in my plexi RI: more gain and volume from the top input and when two guitars are plugged in (top/bottom), each drops a little volume. With the LP, I'm liking the bottom one better.

 

[Davey]

Re: High Low Amp inputs???

thanks guys you rock!

 

[Sabe]

Re: High Low Amp inputs???

On my Fender Princeton Chorus, it allows both jacks to be used at once, so 2 guitars can share the same amp.

The owners manual says that when used this way, that the input becomes equal in both jacks, and I guess that somehow overrides the normal set up of having one jack being high output, and one being lower.

I've never actually tested this as I can't play 2 guitars at the same time, and nor have I ever had to share it with an ampless guitar player, but it seems like a versatile feature nonetheless.

 

[Kent S.]

Re: High Low Amp inputs???

On my Fender Princeton Chorus, it allows both jacks to be used at once, so 2 guitars can share the same amp.

The owners manual says that when used this way, that the input becomes equal in both jacks, and I guess that somehow overrides the normal set up of having one jack being high output, and one being lower.

I've never actually tested this as I can't play 2 guitars at the same time, and nor have I ever had to share it with an ampless guitar player, but it seems like a versatile feature nonetheless.

It's crappy feature, trust me ..., two guitars may get way with it clean, but overdriven ... sounds horrid. Yours is a newer amp also ... Again, just depends on how they are wired, probably still lowers the input Z (of course maybe not also, that is if Fender was actually serious about designing that as a real feature ... not just *hey you can plug two instruments in*. Now one in one channel of an old Fender, and one in the other channel, that worked well, except one player wouldn't have reverb (unless they modded it for both channels to have it). I believe that the original intent of that second channel on the old Fenders was as a monitor type of thing for another guitar player.
To get back to the original topic, I believe on the old fenders, and marshall (the new ones are the same I believe, check the schematic), the hi input has an input impedance of 1 Meg and 34k into the grid, the lo input had an input impedance of 68k and 68k into the grid, again I'd have to check as to what the combined use of both jacks would be, but one could always plug an extra cable into the other jack just to see what effect it had on either jack.

 

[Sabe]

Re: High Low Amp inputs???

wow, Kent, you know you're stuff for sure, but that's a bit too techy over my head.

What I have done in the past, is plug in a mic (I have an old one with a 1/4" jack instead of a regular mic prong thing) into that second jack. The vox sound muddy and muffled, but it got me through in a pinch when we jammed and had no PA. Better than nothing, in that regard.

Its an old amp, I got it in 87. I really don't use it anymore. Just a spare in the basement these days.

 

[Pandemonium]

Re: High Low Amp inputs???

I agree with everything Zerb said about the Hi and Lo inputs on a JCM 800. I plug into the Lo side and crank it up which gives me more than enough grind for my purposes. I slam it with an OD when needed for solo work.

 

[TwilightOdyssey]

Re: High Low Amp inputs???

I agree with everything Zerb said about the Hi and Lo inputs on a JCM 800. I plug into the Lo side and crank it up which gives me more than enough grind for my purposes. I slam it with an OD when needed for solo work.

This is the de facto ground work for getting a great metal tone. I do the same: Lo input, 1/2 gain, overdrive ...

 

[Kent S.]

Re: High Low Amp inputs???

wow, Kent, you know you're stuff for sure, but that's a bit too techy over my head.

What I have done in the past, is plug in a mic (I have an old one with a 1/4" jack instead of a regular mic prong thing) into that second jack. The vox sound muddy and muffled, but it got me through in a pinch when we jammed and had no PA. Better than nothing, in that regard.

Its an old amp, I got it in 87. I really don't use it anymore. Just a spare in the basement these days.

In regard to the first point, all it means is that you have less high end in the lo input ... now there are two ways of looking at this ... one, a classic example that I give is that if you plug in a strat,you wnat that to have the most gain available compared to a Les Paul, the LP can stand to lose some gain if you are trying to keep them withing reason to each other ...problem, the lP will be a bit darkr than the strat ... if anything you would want to maximize the LP's brightness, and warm the strat up some. however, the other side of the coin, at high gain the padded input will be a bit less noisy (hissy) do to it rolling off some of the upper range ... more of a pro/con thing.
I still stand by the fact that the the lo input should have a higher impedance than the hi input, or ideally, that both be the same.

On the second point, a guitar is roughly classed as being -20dBu in output, where as a microphone is roughly -50dBu~-60dBV ...translation the preamp of a guitar amp is not hot enough, nor it's input impedance designed for microphone use ... you won't hurt anything, but coupled with not enough gain, restrictive frequency response, and other factors, well like you said it works, just barely ... Now the harmonica players using those Shure green bullet mics into small tube amps are delibrately taking advatange of the limitations, but in a favourable way.