External preamp?

JordanAnthony · #1 06-07-2021, 10:30 AM

Hi. A bit of a novice to acoustic rig setup. Wondering if I need a preamp for DI out to a powered speaker for my fishman loudbox? Basically, are the onboard preamp (aura and ES) sufficient for this? What are the benefits of an external preamp (pedal or box)? Thank you.

4wheeljive · #2 06-07-2021, 11:12 AM

Are you asking if you need a pre-amp between your guitar and the Loudbox, or between the Loudbox and a separate powered speaker? If it's the latter, I'm pretty sure you wouldn't need anything additional, as the Loudbox has its own DI output. But even if you're asking about the former (i.e., guitar to Loudbox), I don't think you'd need anything, unless you have a really long cable run. I think the onboard Aura and ES pre-amps both send a pretty strong signal. I believe external pre-amps/DI boxes are most useful when you have a passive pickup.

JordanAnthony · #3 06-07-2021, 11:32 AM

Thank you. I assumed this but I see people online with an acoustic preamp on their pedal board. Seems a bit unnecessary if you have a good onboard preamp. I've been thinking about using a soundhole pick up running to a separate channel for a little overdrive. I can see how a preamp would be necessary in that case.

Lost Sheep · #4 06-07-2021, 11:51 AM

I am also a novice to acoustic amplification.

I have passive piezo pickups (Barkus-Berry) from the '60's in a couple of my guitars and passive Fishman pickups in a couple others. (No electronics - no battery). They do not have enough wattage to make themselves heard to most amplifier inputs, so benefit by a little boost. Essentially a preamp that most modern acoustic-electrics with piezo pickups have in the guitar body.

Impedance matching, volume, loudness and signal strength are fairly mysterious to me.

tbirdman · #5 06-07-2021, 12:01 PM

The choice comes down o do you want an inboard pre-amp or external. My two reasons for going with an external was I wanted the least mount of stuff inside the guitar so I have only the pickup. 2nd is the external preamp can be used for multiple guitars. If you have internal preamps, no need for an external premap.

Mandobart · #6 06-07-2021, 02:06 PM

The real reason for a preamp or DI is for impedance matching. Piezoelectric pickups have an output impedance in the meogm (million ohm) range. Traditional amplifiers, PA's and powered speakers have an input impedance in the kilohm (1000 ohm) range. An unmatched interface in any type of transmission system (fluid, mechanical, electrical, signal) will result in reflection and phase shift and poor transmission of whatever you're trying to transfer.

The often maligned "piezo quack" is usually caused by this simple impedance mismatch.

IF your amp, PA or powered speaker has a high impedance input (designated HI Z) you don't need any preamp or DI, but using a decent quality one never hurts.

Br1ck · #7 06-08-2021, 05:03 PM

Quote:

Originally Posted by Lost Sheep

I am also a novice to acoustic amplification.

I have passive piezo pickups (Barkus-Berry) from the '60's in a couple of my guitars and passive Fishman pickups in a couple others. (No electronics - no battery). They do not have enough wattage to make themselves heard to most amplifier inputs, so benefit by a little boost. Essentially a preamp that most modern acoustic-electrics with piezo pickups have in the guitar body.

Impedance matching, volume, loudness and signal strength are fairly mysterious to me.

To me, onboard systems can vary a lot, no mystery a $400 guitar won't have the quality of a $3000 guitar, and even then, manufacturers have compromises. Cole Clark's three way is the best I've heard. But if I were starting with a guitar with no pickups, I'd go with a passive piezo unless I had a band with a drummer, them I'd cry uncle and go magnetic soundhole.

If you put a SBT in your guitar that is passive, I'd go with an outboard pre every time. You can pick a pre without compromises like SunnAudio products that will serve you well for multiple guitars for a long time. Even a RedEye will likely sound better than most factory units. There I am, jaded as all get out. The RedEye is very good.

Without getting technical, a piezo pickup reacts to the value of the input impedance of the devise next in line. By itself into a mixer input of 880 ohms, a piezo is going to be very high end ice picky. Piezos react best to 1Meg Ohm or so. Much smoother sound. Something as simple as a passive DI can do this, but most people want some gain and some EQ. Hence the pre, which generally have a DI incorporated into the devise.

Now a word about gain. A well designed devise like a SunnAudio or RedEye will have a linear gain stage. All that means is no peaks and valleys in the frequency curve. A lot of the need for EQ is to compensate for a poor gain stage ( caused by built to price point cheap parts), the rest for non linear response of the pickups themselves. But even good devices have a ceiling at the upper end of their volume range where performance drops off, and gain amplifies everything(hum), so you generally leave that to the amp at the amplifier or PA level. All you need is a signal strong enough the next devise can work in it's sweet spot, not too much or too little.

When someone says studio grade, they are referring to good design and good parts. Good parts cost. A potentiometer can cost $20 each. Easy to see where a $150 devise with five knobs would have to cut corners.