Differences between Low and High inputs in theory

[andrius]

What is the difference between Low and High inputs in theory: is it only their resistance that differ or something more? Does the effect result in only different levels of input volume or does it also result treble frequencies differ too? Are there any more differences between Lo and Hi inputs?

[Steve Conner]

It depends on the amp. In some Marshalls, the high input had a whole extra stage of gain.

The arrangement I'm familiar with is from Fender's silverface era. The high and low jacks are combined with 68k mixing resistors, and the high jack has a grounding switch. So, when you plug into "high" your guitar is loaded with 1M ohms. Plug into "low" and it is loaded with 136k ohms and the signal strength cut in half. To my mind anyway, these are two useful tonal options. The different load resistance modifies the resonant peak of the guitar pickups and changes the response of the guitar volume and tone controls.

Other amps had a similar arrangement but with both jacks grounding. In this case you can stuff a dummy plug in the other jack and get the equivalent of "high".

[mooreamps]

I was told once, because you plug your pedal into the low Z input jack..

-g

[Chuck H]

I tried the "low" input once... When I was young. It made my guitar sound dull and less dynamic. I never did it again

It's lower impedance input intended for higher output devices. Like a keyboard. As Steve noted, most high/low input schemes change the resistance on the load resistor. Not usually the series resistor.

[riz]

I used to feel the same way as Chuck, but I've been using input 2 (LOW) on old Fenders a lot lately... I find the clean sounds are more even, less responsive to dynamics (less spikey on the attack, like a limiter I guess), and sometimes that's just what I'm looking for. Plus, getting the volume knob up a little just makes me feel better for some reason!

[tedmich]

why no variable resistors at the input to dial in the gain? I always wondered... A 1963 Strat set to the bridge PU and a Dual EMG 18v slabbucker have very different outputs but are apparently equivalent...?


what is the definition of a High and a Low input source??

[Tom Phillips]

why no variable resistors at the input to dial in the gain? I always wondered...

Some old amps did that. Usually low end practice amps. Gain control up front will increase the background noise you hear at the output. Especially when the amp is played at low volumes. This is because the output of the pre-amp first stage is then running at full gain into the next stage. You could leave in the volume control in the normal location (After the tone stack before the second gain stage) but then I think there are too many operator controled variables for the average person to deal with. Bottom line is that the commonly used Hi/Low input circuit satisfies the needs of just ablut everyone.

[andrius]

Thank you for the answers. I'm not good at electronics, so I want to clarify one thing. "The different load resistance modifies the resonant peak of the guitar pickups" - does it mean that the High input will sound brighter?

By the way, maybe someone knows how Laney amps behave when in Low/High inputs?

[pdf64]

'"The different load resistance modifies the resonant peak of the guitar pickups" - does it mean that the High input will sound brighter?'

Yes, 'high' input will be louder and, if connected directly to a regular passive guitar, brighter. Any fx between guitar and amp, unless true bypass, may have buffers that provide a constant load to the guitar, usually equivilant to an amp's 'high' input. That (ie buffers in the signal chain) would then greatly reduce tone differences between high and low inputs.

'how Laney amps behave when in Low/High inputs'

Need to specify the model.

'Plus, getting the volume knob up a little just makes me feel better for some reason'

If the volume control has a bright cap, then turning the vol up will reduce the relative boost from the cap, thereby further reducing spikiness.
Pete.

[andrius]

Thanks. It's Laney Lionheart amp.

[pdf64]

Right, that's different again, similar to the situation Steve mentioned. The inputs aren't a mixing type, only one can work at a time, can't use both at same time.
The jack sockets have a switching arrangement, so that a treble / mid boost (probably about 6dB) at the input stage (ie cathode bypass cap) is engaged when the HI input is used, the boost being turned off when the LO input is used. Whichever is used, the input impedance is the same.
The LO input will be more resistant to overload, eg higher headroom / lower gain/ bigger maximum input signal before overload.

Schematic:-
http://www.gearslutz.com/board/attac...-schematic.pdf
Pete.

[hasserl]

I tried the "low" input once... When I was young. It made my guitar sound dull and less dynamic. I never did it again

It's lower impedance input intended for higher output devices. Like a keyboard. As Steve noted, most high/low input schemes change the resistance on the load resistor. Not usually the series resistor.

Actually, with the typical Fender input arrangement the Hi input only sees 34k series resistance (two 68k resistors in parallel), the Lo input sees 68k. Same with Marshall.

[Steve Conner]

The arrangement I'm thinking of is something like this. I think they meant 136, not 134.

[g1]

why no variable resistors at the input to dial in the gain? I always wondered... A 1963 Strat set to the bridge PU and a Dual EMG 18v slabbucker have very different outputs but are apparently equivalent...?

Some Ampeg had a 3 position input attenuator:

A friend borrowed my V4 once. No matter what he did he could not get a clean enough tone from his strat. It was driving him nuts. When I got there I switched the sensitivity switch from 0db to -9, he was happy.
Some guys won't turn down their guitar volume beyond a certain point they feel is acceptable. With the standard amp volume after the first tube stage, they are overdriving it no matter how low they set the amp volume .

[andrius]

Maybe someone can take a look at this Laney Lionheart schematic and see if there is anything special going on in the inputs? I don't understand all that stuff