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Non ADA Gear => Amps => Topic started by: Dante on July 12, 2016, 10:51:22 AM

Title: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: Dante on July 12, 2016, 10:51:22 AM
I thought I'd ask. What's the diff?

Is the HI for a stronger signal? Like humbuckers? Whereas LO would be for single coils?

Or, is the HI for plugging my rackmount preamp in (because it's a hotter signal and I have no FX loop), and the LO for standard signals like a plain ol' guitar?

Or...something else entirely?
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: PrimalScream91 on July 12, 2016, 11:30:32 AM
I believe that the Hi input attenuates the signal, the low input does not.

That is a criminally simple way to put it, but it's what I've always understood. Some will tell you that your pickup type (active/passive/single/hum) determines what input you should go into, but I've never bought into that.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: MarshallJMP on July 12, 2016, 12:18:15 PM
Normally the Hi means HIgher sensitivity, so in guitar player language more gain  >:D
And lo ,well LOwer sensitivity.In the old marshall heads the difference between both is 6dB (voltage ratio of 2)
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: vansinn on July 12, 2016, 12:41:16 PM
One is High, the other is Low.
You use the Hi when you wanna get High, you choose the Lo when you wanna chill, no?  :dunno:

Oh well, one is a high impedance input, the other has a lower impedance.
They're used for matching different sources with different impedance.
Depending on how you source behaves, you may see/hear not too much difference, or one may sound/work better than the other.
Or as MJMP just stated it (annoying how often those university folks tends to right so often :lol: )

EDIT: Oh, I was sure I'd seen different impedance levels too; actually pretty sure my Sunn Model-T had it this way, but schemos are packed down, so won't be checking up on this.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: MarshallJMP on July 12, 2016, 12:58:53 PM
The impedance doesn't change much.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: rnolan on July 12, 2016, 04:15:55 PM
It very much depends on the amp (preamp) and the era, it can mean hi and low sensitivity (initial input gain) as MJMP said or it can also mean low and hi impedance (though this is not common these days).
Early amps had multiple inputs to handle the whole band, guitar, mic, bass .. as PA's were still relatively rare, reasonably primitive and very expensive, so their inputs were designed to take the common signals from all the band.
When more specific PA style amps came out (with their associated column speakers) they accommodated (sometimes) hi and lo impedance mics.  This changed when mixers and multicores came along, hi impedance looses top end after 25 feet (ish) and mics (mostly) went to 600ohms and balanced (came a bit later ?).
The hi and lo inputs on guitar and more commonly bass amps came with the uptake of active PUs which generally had higher output than passive PUs which overloaded the preamp input (in not a nice way). So it's very much a read the manual thing.  These days I see it mostly on bass amps to accommodate the hi output signal from active bass PUs.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: MarshallJMP on July 13, 2016, 03:32:38 AM
Well I was talking about guitar amps in general but yes R has a point.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: Dante on July 14, 2016, 09:51:35 PM
I see that every post has a different answer. Each is logical enough to believe

I thought the Hi was on top and the Lo was on bottom, but these are side-by-side, so that got me wondering  ::)
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: rabidgerry on July 15, 2016, 02:08:38 AM
the guys have already explained this, but I hit upon it when talking about my bass players bass amp on another thread which has a high and low input.

My basic understanding of it has always been, the "Low" input is some DB lower volume and therefore more suitable say a guitar with active pickups.

The "High" input is for guitars with passive pickups and therefore is a little louder.

So the low is lower signal volume to compensate for the active pickups extra volume.

So since I have no active pickups I always use high inputs on any equipment that has it, such as my Peavey Rockmaster preamps which have high and low input.

I got my definition for these inputs from the manuals for certain gear, and the have always said, "active pups for low inputs" "passive pups for high inputs".

If this is wrong someone correct me. :facepalm:
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: rnolan on July 15, 2016, 02:34:26 AM
The terms Hi and Lo get used for a few things in different ways (e.g. my MB1s have Hi and Lo or Full outputs for bi Amping or not).  To be sure what it means for a particular unit, check the manual/specs.
RG what you are describing is (I think) the most common but I'd think of it as Hi gain (coz lower output PUs so need more input gain) and Lo gain as the active PUs are generally (not always) higher output.  In the input circuit the difference is probably just some "pad" resistors between the Lo jack and where it meets the input circuit.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: rabidgerry on July 15, 2016, 06:33:08 AM
well in the context of what Dante is asking Richard, the MB1 info isn't to do with the hi and lo inputs on guitar amp

RG what you are describing is (I think)

uh yes, so one is more suitable for passive pickups and the other active pickups (without nit picking and making things convoluted - he wants a basic understanding of what these are for unless I'm mistaken)

I've never viewed the hi and lo inputs as one has more gain than the other, but I guess gain is volume and not distortion as is generally thought so in a round about way I AM thinking one has more gain than the other so that's a good way of looking at it Rn.

My actual experience of using hi and lo inputs is always been, the guitar sounds quieter when using the lo.  My first amp (which I still own) had the hi and lo inputs and I just used the hi always because I didn't have to turn the volume knob up so much as I did when I used the lo input.  There was no extra distortion using the hi as opposed to the lo, only a difference in volume.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: rnolan on July 15, 2016, 07:03:49 AM
Hey RG, I used the MB1 just as an example of other places those terms/words are used. Obviously they have to be taken in context.  Although even then I've seen examples (not often) of them used the other way around e.g. Lo means the inst has low output so boost more, Hi it has high output so boost less...

In the end it's like a simplistic "fixed" version of the gain control on a mixer channel, Lo = knob turned down (as plenty of signal), Hi = knob turned up as signal needs boosting, so pick 2 ballpark points (which cater to most insts') and fix/set them in the circuit.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: rabidgerry on July 15, 2016, 07:28:16 AM
Hey RG, I used the MB1 just as an example of other places those terms/words are used. Obviously they have to be taken in context.  Although even then I've seen examples (not often) of them used the other way around e.g. Lo means the inst has low output so boost more, Hi it has high output so boost less...

In the end it's like a simplistic "fixed" version of the gain control on a mixer channel, Lo = knob turned down (as plenty of signal), Hi = knob turned up as signal needs boosting, so pick 2 ballpark points (which cater to most insts') and fix/set them in the circuit.
having the lo and hi the other way around would totally confuse me, mainly because I have only ever come across the examples that have the Hi input for passive/quieter pups and lo for actives.  But I'm not surprised there is someone somewhere who has varied the usual meaning of each input.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: Kim on July 16, 2016, 11:55:30 AM
The QuadTube has an Input Sensitivity Switch on the front panel next to the Input jack that may or may not do what other amps use separate Hi and Lo Input jacks for.

So, according to that QuadTube manual:  "Input Sensitivity Switch -  Sets the input sensitivity of the QuadTube 150M.  If you see the Input Clip LED coming on when you play hard, then switch to Low."

I notice a change in the actual sound when I switch this to Low:  seems like there is a bit less Gain and also a bit less of the higher EQ freqs in that Low setting than what I hear in High. 

FWIW, plenty of amps have had the option of using High and Low Inputs long before active pickups were invented, and it's also entirely possible that each amp manufacturer had their own different ideas in mind when designing the Input jack circuitry.   The Input jacks on say a Supro, Sunn, HIwatt, etc. may not have the same intentions as say a Marshall, Fender, Dumble, etc.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: MarshallJMP on July 16, 2016, 03:02:41 PM
Well now I think of it,with a JCM800 master volume (or the older JMP) 2203 and 2204 models the lo input bypasses one half tube.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: Slimjim on November 27, 2016, 02:39:07 AM
https://robrobinette.com/How_The_AB763_Deluxe_Reverb_Works.htm

Here is an exceptional article on the details and possible mods for the AB763. It covers the Hi/Low topic very well, as well as all of the other sections of an amp circuit. Much to learn, as always.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: Dante on November 27, 2016, 09:30:40 AM
Awesome! Thanks SlimJim  :thumb-up:

I think this page sums it up pretty good, and explains the "bright" vs. "normal" on Fender amps (https://robrobinette.com/How_Fender_Input_Jacks_Work.htm)

^^ That is a link ^^

Quote
The Hi and Lo inputs differ in signal intensity, input impedance and grid stopper resistance. The Lo inputs form a voltage divider using the two 68k grid stopper resistors. This voltage divider cuts the source signal in half (-6dB)--yes, half of the guitar signal is bled to ground. The Lo inputs are attenuated by slightly more than -6dB to offer less gain and more clean headroom. If you find you prefer the Lo inputs I recommend you try using the Hi inputs and turn down the guitar's volume control. You get pretty much the same outcome but you have control at the guitar but the Low jack's low input impedance can remove some high frequencies from the guitar pickup so the guitar tone is typically a little less bright when compared to the Hi jack.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: Kim on December 10, 2016, 11:40:39 AM
Well now I think of it,with a JCM800 master volume (or the older JMP) 2203 and 2204 models the lo input bypasses one half tube.

I was checking out some other unrelated things, and came across this from the JCM800 2203 User Manual:   :lol:

9. High Sensitivity Input
This is the High Sensitivity input of the amp – in theory,
such an input is supposed to be used for low-output
pickups. This said, 99.9% of all 2203 users ignore this
and plug guitars loaded with high-output pickups into this
input, because it enables them to drive the pre-amp even
harder.
10. Low Sensitivity Input
This is the Low Sensitivity input of the amp, which was
designed for hot (high-output) pickups; we would
suggest you try both inputs and then decide which one is
best for you.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: MarshallJMP on December 10, 2016, 03:46:45 PM
Great finding Kim  ;D
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: Dante on December 13, 2016, 08:17:45 AM
Sounds like each amp manufacturer had a different approach

Who woulda thunk?
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: vansinn on December 13, 2016, 08:25:16 AM
Sounds like each amp manufacturer had a different approach

Who woulda thunk?

Mmnn..  you didn't expect DIN standards for tube amp inputs, did you now.. :lol:
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: rnolan on December 14, 2016, 01:14:32 AM
Seems so  :facepalm: .  IIRC hi and low inputs started when active PUs and built in preamp circuits took off. And the first I recall seeing were bass amps (Alembic were probably one of the first in the active space  :dunno: ).  I remember EMGs coming out way back but there were also a few others (Ovation ?, wow they had some bight  >:D , interesting guitars not sure if the PUs were active but they had a mean built in preamp circuit).  Played one through a BAEZ stack (great amps BTW made in my home town), you could mow the lawn with that setup  :metal: .

So seems some are just a PAD (cool the signal down by xdb) and some for impedance matching, or both.

Anyway, the advice in Kims post is good, try both, use the one you like that works for you  :thumb-up: , or use a Y lead and plug into both  >:D :whoohoo!:
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: Harley Hexxe on December 14, 2016, 08:21:35 AM
   I don't know if  a "Y" lead is such a good idea.

   Do you remember the old school amps with all the input jacks, supposedly to be able to plug the whole band into? When you did that, the instruments would fight for dominance in the input section.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: vansinn on December 14, 2016, 11:44:52 AM
   I don't know if  a "Y" lead is such a good idea.

   Do you remember the old school amps with all the input jacks, supposedly to be able to plug the whole band into? When you did that, the instruments would fight for dominance in the input section.

Well, that actually could be seen as an advantage, as it would force everybody to play correctly, and drop the ego ride :banana-guitar: :nono:  (yup, was a real  POS)
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: rnolan on December 15, 2016, 02:41:56 AM
Who knows what a Y lead would bring ? with just one input source it shouldn't be a problem, it will depend what's behind both inputs and then how they combine, so worth a try, may be good, may not be  :dunno: .  With my 73 Marshall, it has a lead and a bass input (well 2 jacks of each, old school small writing Marshall).  Input 1 is lead, 2 is bass.  So I bridge 1 & 2 (they each have a vol knob  :whoohoo!: ) and wind in some cleaner bottom end into the sound.  I know not the same as high/low inputs, but then depends how they work (many and varied it seems)
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: Harley Hexxe on December 15, 2016, 05:03:17 AM
Hey Richard,

    Give it a bash and let us know what you think
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: rnolan on December 16, 2016, 12:41:29 AM
Hey Harley, I don't have any amps/preamps with high/lo inputs to try.  I've always bridged the Marshall lead and bass inputs inputs and dialed in a fair bit of the bass channel (it has its own vol knob).  The lead channel in these heads is very toppy but including the bass channel rounds it out nicely (for me anyway). But no master vol on these babies, and crap does it mooove some air  >:D .
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: Harley Hexxe on December 16, 2016, 04:08:59 PM
Richard,

  What model is that Marshall head? I used to have a 73 Super Lead 100 a long time ago, but I don't remember it having a bass channel. Mine was modified with a rheostat in one of the inputs to act as a master volume. I'm assuming the input that was modified was one of the low inputs, but plugging my guitar into the input above the modified jack didn't give me more bass tone, just a weaker signal.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: rnolan on December 16, 2016, 06:04:28 PM
Initially I thought it was a 1972 JMP 50w lead head.  When I changed the input tubes a while ago I noticed it was built in 1973.
It has 2 inputs (1 and 2) with 2 jacks each (paralleled) and a vol control for each input.  Also has presence, bass, mid and treb.
Output tubes are 2 x EL34 (6CA7).
I now have the bottom bass input jack wired direct to the power amp (as MJMP does with his 100 watters)
I think the super leads were a bit different  :dunno: (MJMPs area here  :thumb-up: ).  It was also around the time gear makers stopped having lots of different inputs, mic, bass, guit etc (ie run the whole band off one amp). But we used to have to do this, as a 14year old, I couldn't afford much of anything. I used to repair broken strings etc... and we made do with whatever we could get our hands on (and I soo wanted a Marshall or BAEZ (local amp maker) stack).
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: vansinn on December 17, 2016, 02:32:07 AM
Erm.. are you sure about the two EL84's?

If so, I'd love to know which technology can make those produce 50 Watts.. :dunno:
Like, 1 Kv on the plates, -150 Volt cathode bias, 48 volts to the heaters, a power transformer featuring negative loss - and using liquid nitrogen cooling :lol:
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: MarshallJMP on December 17, 2016, 10:06:33 AM
The old Marshall 4 input heads have 2 channels, each with their own volume controls. One side is the bright channel, the other one is the normal channel. Each channel has 2 inputs with one low and one high sensitivity (they differ 6db from each other). And the preamp circuit changed a bit over the early years.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: Harley Hexxe on December 17, 2016, 10:08:22 AM
Richard,

    The model isn't printed on the back of the chassis? That's a bit strange for Marshall.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: Harley Hexxe on December 17, 2016, 10:11:20 AM
The old Marshall 4 input heads have 2 channels, each with their own volume controls. One side is the bright channel, the other one is the normal channel. Each channel has 2 inputs with one low and one high sensitivity (they differ 6db from each other). And the preamp circuit changed a bit over the early years.

   Yes, the Super Lead 100 I had was like that, Two jacks were marked with "I" and the other two "II" and both were guitar inputs. I didn't think there was a bass input on that amp.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: MarshallJMP on December 17, 2016, 11:30:55 AM
Yes normally it should say,  super lead, bass or PA on the back. Also the serial nr states what it is.

http://www.superiormusic.com/page024.html

Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: rnolan on December 17, 2016, 06:49:33 PM
Erm.. are you sure about the two EL84's?
  :facepalm: Fixed

On the back of the chassis mine has a piece of dynotape label that says Lead.  I never knew the bottom jacks were -6db, I thought they were the same.  I've never tried plugging into the bottom jacks, I just ran a short patch lead from the bottom jack of input I to the top jack of input II and plug signal into the top input I jack.  The bright (input I) channel is very bright.
Title: Re: What's the Difference Between Hi and Lo input jacks on some amps?
Post by: Harley Hexxe on December 17, 2016, 09:00:18 PM
Yes, I thought input I was very bright also, and with a Strat in the bridge pickup, it just wasn't meaty enough to cut through.