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Alembic Club » Alembic Basses & Guitars » Archive: 2007 » Archive through November 26, 2007 » Active vs. Passive « Previous Next »

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Username: aquaman

Post Number: 23
Registered: 9-2006
Posted on Sunday, September 09, 2007 - 7:10 pm:   Edit Post

Here is a beginner's question: Does anyone know why my passive practice bass sounds louder on my Hartke 100 watt combo amp than my Spoiler? Does a passive bass generally sound louder than an active?
Advanced Member
Username: hb3

Post Number: 250
Registered: 2-2005
Posted on Sunday, September 09, 2007 - 7:40 pm:   Edit Post

Generally, no. As far as I know, it should be the opposite, as active EQ will boost low end, etc.
Senior Member
Username: adriaan

Post Number: 1600
Registered: 6-2002
Posted on Monday, September 10, 2007 - 1:53 am:   Edit Post

The Spoiler has trimpots in the control cavity that adjust the output level of each pickup. Check out the FAQ section of the Club.
Senior Member
Username: crgaston

Post Number: 427
Registered: 11-2005
Posted on Monday, September 10, 2007 - 5:19 pm:   Edit Post

It does vary, though. I've got a G&L SB-2, and the output of the passive P pickup is slightly more than that of my active 18 volt Modulus with the EQ set flat.

What kind of passive bass are you comparing it to?
Username: aquaman

Post Number: 24
Registered: 9-2006
Posted on Monday, September 10, 2007 - 7:01 pm:   Edit Post

My practice bass is a Steinberger copy (passive).
Senior Member
Username: crgaston

Post Number: 428
Registered: 11-2005
Posted on Tuesday, September 11, 2007 - 4:55 am:   Edit Post

Rich, if you are plugging the passive bass into the passive input and the active bass into the active input, then that will make a big difference as well. The active input jack usually has around 6 dB of gain reduction on it. Is it still louder if you compare them using the same input?
Username: aquaman

Post Number: 25
Registered: 9-2006
Posted on Tuesday, September 11, 2007 - 12:31 pm:   Edit Post


Interestingly enough, they sound the same when in the passive input jack. Do you know why I would need to use the active input jack when the output is lower? I still need to see if adjusting the trimpots will increase the output. Thanks for your help.
Senior Member
Username: 811952

Post Number: 1131
Registered: 10-2003
Posted on Tuesday, September 11, 2007 - 1:04 pm:   Edit Post

Impedance loading (I think that's the term). It will affect the tone as well in many cases. The "active" input jack just has a pad on it, based upon the typical "active" bass having more output than the typical "passive" bass..

Also, you can easily adjust an Alembic (or many other active basses) to have a lower output than many passive basses, and yes there are sometimes valid reasons one would do so.

Hope this helps..

Advanced Member
Username: dfung60

Post Number: 272
Registered: 5-2002
Posted on Saturday, September 15, 2007 - 6:23 am:   Edit Post

As has been mentioned, your Alembic has output level trim pots so the active output level can be set to whatever level you like. It's probably set low now, or your battery is weak if the output level is low relative to a passive bass.

If you set the output level too high, you may overdrive your preamp and get a distorted tone at all volume levels. This was why Hartke added the active input - it has less gain, so the hotter signal won't overdrive the preamp. If you plugged your passive bass in there, it might not be able to generate enough input to drive the power amp to full power.

The pad circuit on most instrument amps is very simple - just pair of resistors. The input impedance (you can think of impedance as "AC resistance" although it's actually more complex than a variant of DC resistance) may be slightly different at the two inputs, but won't be significantly different.

Your brain perceives things in interesting ways. By nature, if two things are close to each other in volume, you will almost always prefer the louder one, even if the sound quality of the softer one is better.

Modern amps have a lot of dynamic range at the inputs, so you can use the passive input unless it sounds distorted when you are playing harder at the bass. If you were playing a 1960's Ampeg B-15, you might find it hard to get a clean signal with a modern active bass - the output level is just too high. The good part about active instruments is that you can turn the volume down at the bass with no change in tone.

If you used level-sensitive effects (like an envelope follower or compressor) in your signal chain, then it's great to have the output level trimpots, so you can set your Alembic up to match the output of your passive bass. If you didn't, then you'd have to reset all your effects when you switched basses.

Impedance matching can affect the tone of your instrument, but is not a factor for the passive/active inputs or your instruments. High frequency signals (like your cable TV feed) have very specific requirements for each part of the system to insure minimal signal loss, including very specific input impedances. Audio-type systems work on a different principle, where you want to have the input impedance of the preamp significantly higher than the output impedance of the pickup or microphone. The output impedance of a passive pickup would be on the order of a couple thousand ohms; from your active circuit, tens to hundreds of ohms. The input impedance of a normal amp will be 50-100K ohms, so there shouldn't be an issue in either case. Impedances will come into play when you have a very, very high impedance pickup like a piezo. They will often have output impedances in the millions of ohms, which is higher than a regular guitar amp input impedance. In this case, the effect will be to filter out the bass, which is why some acoustic guitars sound scratchy and thin when they're plugged into an instrument amp. You don't see this much anymore because they put a suitable preamp in the guitar now which solves the impedance mismatch.

David Fung
Username: somatic

Post Number: 65
Registered: 11-2003
Posted on Monday, September 24, 2007 - 1:56 pm:   Edit Post

The input impedance of a normal amp will be 50-100K ohms

Excellent post David, except add an order of magnitude to those numbers for the input Z of many amps. 100k is low for a passive input.
Advanced Member
Username: hydrargyrum

Post Number: 291
Registered: 3-2004
Posted on Monday, September 24, 2007 - 2:06 pm:   Edit Post

David would you just go ahead and write a book explaining instrument electronics for us? Please?
Username: anarchyx

Post Number: 12
Registered: 10-2007
Posted on Sunday, October 07, 2007 - 8:13 am:   Edit Post


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