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Advanced Member
Username: mint_bass

Post Number: 269
Registered: 1-2004
Posted on Monday, November 06, 2006 - 3:55 am:   Edit Post

hi guys

havnt posted in a while but i have been watching from the sidelines.

hope you are all well.

my question regards external preamps. i was recently told that because Alembics are low impendence it is a good idea to have an external preamp prior to your amp head. i have noticed in the past that quite a few use rack systems is that because i really good preamp helps with the alembic or just personal preference?

Also i heard with basses with piezo pickups this is also a good idea to level out the sound like you would with a double bass.

what do you think then guys? any truth in these statements or have i been mislead?


Senior Member
Username: adriaan

Post Number: 1111
Registered: 6-2002
Posted on Monday, November 06, 2006 - 5:18 am:   Edit Post

Couple of issues to look at ...

In general, modern instrument amps have passive and active inputs, so you can choose the appropriate one for your instrument. You can even use the passive input for an active instrument, and it will produce a slightly different sound. A passive instrument into the active input will probably sound anemic.

For a rig with a power amp, if you have a passive instrument (no built-in preamp) then the signal must go through a preamp, otherwise the power amp doesn't have enough signal to work with. You could plug an active instrument straight into the power amp - Jimmy Johnson style.

IIRC, piezos have a rather hot signal, even compared to active instruments, so if you switch between instruments on the same rig, you need an attenuator to level out the signals. You could use a preamp for that.

A completely different issue is the tone shaping facilities that preamps give you.

Senior Member
Username: lbpesq

Post Number: 1758
Registered: 7-2004
Posted on Monday, November 06, 2006 - 6:06 am:   Edit Post

I've never heard the part about piezos having a hot signal. FWIW, all of my acoustics with piezos require a battery for the on-board pre-amp. Both my Alembicized Fernandes and my Godin LGXt have RMC piezos (9V battery powered) to go along with the magnetic pickups (passive on the Godin, Alembics on the Fernandes). I've never noticed a remarkable difference in signal when I switch between the mags and the piezos on either guitar. As for external pre-amps, I believe that most people using such, (FS-1, F-2B), are running them into power amps. People not using an "external preamp" are usually then using an amp that combines the preamp and power amp sections. You can still put a preamp in front of a preamp/power amp combo amp. Set with a little gain, you'll get a hotter signal. Turn up the gain on the preamp and you'll start getting distortion. Most overdrive/distortion stomp boxes are essentially preamps, as I understand it.

Bill, tgo
Advanced Member
Username: dfung60

Post Number: 211
Registered: 5-2002
Posted on Monday, November 06, 2006 - 7:24 am:   Edit Post

Piezo pickups are super high impedance, so they generally require a buffering preamp before the "regular" preamp in your amplifier otherwise they will have odd frequency response, often very shrill and trebly. Usually that preamp is inside the instrument, making it active and low-impedance by the time it gets to your amplifier. Having the preamp in there usually leads to a very high output level after the buffering amp. That's why you hear that piezos have both high and low output - with the internal preamp it's high output and without it would be low.

Regular passive magnetic pickups are "high impedance". Amps are set up to expect this kind of output, so the level and frequency response are acceptable, but you may experience high frequency losses with a long cable (or a poor cable with high capacitance). You'll generally also find that the volume and tone controls interact somewhat (often turning down the volume causes a loss of highs).

An active instrument has regular magnetic pickups and an onboard buffering preamp which eliminates the tonal effects from the cable and can boost the signal to a much higher level. The higher output level raises your signal above the noise in the environment, so they often seem quieter. There's no more interaction between volume and tone and you can have certain features like blend controls and EQ that boosts as well as cuts. Finally, because you know that output level depends on the preamp, not the design of the pickup, you can tweak the pickup so it has less magnetic pull or wider frequency response.

You almost never will gain any benefit from an outboard preamp with a low-impedance instrument since you've already got that preamp internally. You can gain some benefits of active systems by adding an external preamp to a high-impedance system (this will solve treble loss over a long cable). You almost always will want to use a preamp with a piezo pickup, but chances are good that you already have one in most modern instruments.

David Fung
Senior Member
Username: lbpesq

Post Number: 1759
Registered: 7-2004
Posted on Monday, November 06, 2006 - 11:21 am:   Edit Post

David, better explained than I could. One point of disagreement, though. As a guitarist I gain mucho benefit using an external preamp in the form of a stompbox for lead tones. See my recent thread in Miscellaneous about the Seymour Duncan Twin Tube preamp pedal.

Bill, tgo
Senior Member
Username: keith_h

Post Number: 606
Registered: 2-2005
Posted on Monday, November 06, 2006 - 11:36 am:   Edit Post

"I have noticed in the past that quite a few use rack systems is that because i really good preamp helps with the alembic or just personal preference?"

The advantage of separate preamps and ampilfiers are you can pick the tonal characteristics of each one. By going separates you can also upgrade portions individually as needed. This has nothing to do with playing an Alembic (although the clearer Alembic tone does make one want to upgrade everything).

So in a nutshell it is personal preference.


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