passive/active inputs?

Wade10987 · #1 10-08-2011, 10:36 PM

Hey fellow bassists,

Quick question: why is it that bass amplifiers sometimes have passive and active inputs for your instrument cable? Does it alter the tone knobs or something if you already have tone control present on the bass? I was thinking of the new Acoustic USA 360/361 stack in particular, but I have seen the seperate outputs elsewhere.

GrowlerBox · #2 10-08-2011, 10:46 PM

Quote:

Originally Posted by Wade10987

Hey fellows bassists,

Quick question: why is it that bass amplifiers sometimes have passive and active inputs for your instrument cable? Does it alter the tone knobs or something if you already have tone control present on the bass? I was thinking of the new Acoustic USA 360/361 stack in particular, but I have seen the seperate outputs elsewhere.

The active input generally just has a pad on the gain, often in the order of -6 dB. Not sure about that particular amp. No harm in using the passive input with an active bass, you just won't need as much gain. Should have no effect on your bass' tone controls.

SurferJoe46 · #3 10-08-2011, 11:33 PM

Typically, just think of any active guitar (one that needs a battery) a stomp or effects pedal or an auxiliary pre-amp that you have before the amp input, as a spurious voltage source that needs to have some of the power taken off it - or blocked, depending on the type of actual 'pad' on the Active input.

It just keeps the input signal from swamping the preamp and it has nothing to do with the adjustments of the amplifier's EQ or other adjustable parameters.

You will be going into a pre-pre-amp overdrive that way, so watch your clipping light if you have one.

Although it's not totally harmful to overdrive the pre-amp, you'll get a lot more mud - or in the case of clipping, if that's what you want, then go for it in small-ish doses.

I prefer to run an un-stomped signal into the Passive side.Consider that an Active bass - is, er: active and has a fairly hot signal already that may need to be crippled a little to protect the pre-amp.

JimmyM · #4 10-08-2011, 11:44 PM

I own a couple active basses and a couple that are very hot passives. Number of times I've used the active input: 0. I consider them useless unless your bass is so hot there's just no other way to make it work. Number of times I've played a bass that hot: 0.

SurferJoe46 · #5 10-09-2011, 09:13 AM

Yup - a very good point - but it takes an astute operator to know when/if there's damage being done.

A n00b should try to observe the promulgated instructions at first until their 'ear' opens to the sounds of distress though.

Smoke is always a bad sign - not that it's likely - but in time ------.

I imagine that a manufacturer could save untold millions of dollars by not putting both jacks there with the extra circuitry if they weren't a good or necessary idea though.

GrowlerBox · #6 10-09-2011, 01:22 PM

Quote:

Originally Posted by SurferJoe46

I imagine that a manufacturer could save untold millions of dollars by not putting both jacks there with the extra circuitry if they weren't a good or necessary idea though.

??. Perhaps they should start by not making them out of platinum

.

**B-string** · #7 10-09-2011, 02:14 PM

A lot of designs use the "input volume" after the first gain stage. If the signal from the active bass is too high it will overload the input stage. How many would complain if they could not turn up the "volume" on their active bass without the amp "crapping out". Show of hands please

bongomania · #8 10-09-2011, 02:56 PM

Quote:

Originally Posted by SurferJoe46

Typically, just think of any active guitar (one that needs a battery) a stomp or effects pedal or an auxiliary pre-amp that you have before the amp input, as a spurious voltage source that needs to have some of the power taken off it - or blocked, depending on the type of actual 'pad' on the Active input.

Baloney. Absolute, unfiltered baloney.

An active device may have ANY output level, including much lower than a passive bass. Back in the 80's there was a tendency to make active basses have higher output than passives, but that was just a fad that passed. I have owned a couple of passive basses with remarkably high output, too.

On top of that, what do you mean "blocked, depending on the type of pad"? The pad on an "active" amp input is just a resistor. Let's not make more of this than it is.

Quote:

Originally Posted by SurferJoe46

You will be going into a pre-pre-amp overdrive that way, so watch your clipping light if you have one.

"Pre" preamp overdrive? What exactly do you think is getting clipped, if it's not the preamp? The jack itself?

Quote:

Originally Posted by SurferJoe46

Although it's not totally harmful to overdrive the pre-amp, you'll get a lot more mud - or in the case of clipping, if that's what you want, then go for it in small-ish doses.

There is no possible harm to the preamp from any active bass, even with very high output. None of this "not totally harmful"--try "zero chance of any harm whatsoever". Clipping does not inherently result in "mud"--that depends on the preamp circuit design. As far as "smallish doses", tell that to the thousands of people that crank their amps into high drive all the time, and love the sound, and have never ONCE had their preamp damaged by it.

Quote:

Originally Posted by SurferJoe46

Consider that an Active bass - is, er: active and has a fairly hot signal already that may need to be crippled a little to protect the pre-amp. ... it takes an astute operator to know when/if there's damage being done. ...Smoke is always a bad sign - not that it's likely - but in time ---.

I thought I smelled smoke...

rodl2005 · #9 10-09-2011, 03:04 PM

I take no notice of the separate/active inputs, or pad buttons either, & I've got passive basses that are way hotter than active basses.
I s'pose they could be handy for some situations, but I've probly used one 2 times ever!

RickenBoogie · #10 10-09-2011, 03:12 PM

+1 to the no need to use a padded input crowd. A hot signal in front of your preamp is avoidable by setting each stage to unity gain, or close to.

SurferJoe46 · #11 10-09-2011, 03:14 PM

Quote:

Originally Posted by bongomania

Baloney. Absolute, unfiltered baloney.

An active device may have ANY output level, including much lower than a passive bass. Back in the 80's there was a tendency to make active basses have higher output than passives, but that was just a fad that passed. I have owned a couple of passive basses with remarkably high output, too.

On top of that, what do you mean "blocked, depending on the type of pad"? The pad on an "active" amp input is just a resistor. Let's not make more of this than it is.

"Pre" preamp overdrive? What exactly do you think is getting clipped, if it's not the preamp? The jack itself?

There is no possible harm to the preamp from any active bass, even with very high output. None of this "not totally harmful"--try "zero chance of any harm whatsoever". Clipping does not inherently result in "mud"--that depends on the preamp circuit design. As far as "smallish doses", tell that to the thousands of people that crank their amps into high drive all the time, and love the sound, and have never ONCE had their preamp damaged by it.

I thought I smelled smoke...

Who kicked your food dish?

All I was trying to say is to follow the manufacturer's recommendations and plug active devices into the active jack and passive devices into the passive jack - or throw a switch - whatever they provide.

bongomania · #12 10-09-2011, 03:46 PM

Quote:

Originally Posted by SurferJoe46

All I was trying to say is to follow the manufacturer's recommendations and plug active devices into the active jack and passive devices into the passive jack - or throw a switch - whatever they provide.

It's just that it doesn't help anyone for you to make up imaginary stuff, in support of following directions without understanding them.

There is no reason to use the active input, or flip a switch, unless you are getting bad sounding clipping--completely regardless of whether the bass is active or passive.

JTE · #13 10-09-2011, 05:46 PM

Most active basses have outputs that are nominally the same as most passive basses. Based on my experience with playing and selling active instruments since my first StingRay in 1978, no active bass I've ever experienced was at all hotter than my Precisions. That includes two pre EB StingRays, two Guild Pilots (both with EMG's active PUPs, one with passive V/V/T, the other with a Mighty Mite active EQ preamp), three US Lakland 4-94 with Bart electronics, and a Fender with the Duncan/Basslines Steve Bailey 2-band pre. The basses I've played with the absolute hottest outputs have been the early '80s G&L basses with the original MFD pickups- the L-1000 was passive and MUCH louder than my '78 StingRay with both EQ controls nailed wide open.

The "active" input on most amps is simply a padded input with a simple resistor to cut the amount of signal hitting the first stage of the amp. If you boost all the EQ on your active bass it might be enough hotter than the normal input is able to handle without distortion. So the best thing for optimum signal to noise ratio is to plug into the passive input. If you simply can not get the signal undistorted, then try the active input or pad. You won't hurt anything by running the preamp with a hotter signal.

The only exception I know of is that some early Trace-Elliot amps had a different input impedance on the active inputs- this was to better match the typically low impedance outputs of many active basses at the time. In that case it MIGHT make a difference in tone if you use the "wrong" choice. But again, you won't hurt anything.

John

JazzbassArt · #14 10-09-2011, 06:50 PM

2004 Americam Deluxe Jazz. BBE 383, Yamaha PB1. Both are barely able to be off zero, without a HUGE jump in gain. IMO, with THIS bass, there needs to be a padded input.

bongomania · #15 10-09-2011, 07:07 PM

Are you having an issue with clipping?

KJung · #16 10-10-2011, 04:18 AM

Quote:

Originally Posted by SurferJoe46

Who kicked your food dish?

All I was trying to say is to follow the manufacturer's recommendations and plug active devices into the active jack and passive devices into the passive jack - or throw a switch - whatever they provide.

This is, unfortunately, bad advice and incorrect. I wish manufacturers would eliminate the outdated discriptors of 'active and passive' to identify input padding or not. It gets confusing for noobs.

Interestingly, the only time I've ever had to use a padded input was with an extremely hot passive instrument (the old Reverend basses).

While, in rare cases, the input impedance of the active/passive inputs are different, that still doesn't really matter, since active basses really don't care much about input impedance, and passive basses would most likely be run unpadded (like most active basses) anyway.

So, better to not think about 'active/passive' in the old, outdated way. Use the non padded or 'passive' input for every bass, and only move to the padded 'active' input if you preamp clips at very low gain settings.

SurferJoe46 · #17 10-10-2011, 08:31 AM

This still doesn't address the issue of using an effect pedal or some sort of tube-pre device and putting it into the passive jack input.

As an example, I get some very serious (what I am about to say is prolly wrong, terminology-wise) 'overdrive' when I put my MXR80 in the passive jack.

To use it at all, I have to use the active input.

I bet they actually have more output than an active system in the bass, so what about them?

KJung · #18 10-10-2011, 08:34 AM

Quote:

Originally Posted by SurferJoe46

This still doesn't address the issue of using an effect pedal or some sort of tube-pre device and putting it into the passive jack input.

As an example, I get some very serious (what I am about to say is prolly wrong, terminology-wise) 'overdrive' when I put my MXR80 in the passive jack.

To use it at all, I have to use the active input.

I bet they actually have more output than an active system in the bass, so what about them?

Again, that is a pure gain issue, and has nothing to do with active or passive. If, for whatever reason, you have a super hot signal going into an amp that you can't control by turning the gain control down on the amp, then the padded signal (sometimes mistakenly labeled as 'active') would make sense.

SurferJoe46 · #19 10-10-2011, 08:50 AM

Is 'gain' not voltage?

KJung · #20 10-10-2011, 08:59 AM

Quote:

Originally Posted by SurferJoe46

Is 'gain' not voltage?

Not sure what your point is there.

Again, there is NO reason AT all to use a padded input due to the nature of the input signal (active, passive, effects, whatever). ALL the mistakenly labeled active input does is pad the gain down with a capacitor prior to the signal hitting the input stage of the amp.

You will do no harm running any signal into either input of an amp (or with the pad switch engaged or not with amps that pad the input that way). If you don't have a particularly strong signal, running your bass into the active input can sound just a touch different due to the extra circuitry and lower gain (which doesn't help a weak signal in any way).