Is a Pre-Amp REALLY necessary?

Double Daddy · #1 03-05-2003, 06:29 AM

I am using a Fishmn BP-100 with the plates placed under the bridge feet. I go 1/4 cable direct to a Behringer MX802A mixer, then out to a Yamaha MS400 active speaker. I also mix in keyboard, vocal, and horns (when present).

I want to try a new pickup. In reading posts here, and at http://www.jonaslohse.de/doublebassg...t_2_gear.html, use of a preamp is deemed recommended or mandatory.

My question is, since I go direct into a mixer, which has a trim pot, do I really need a preamp in any case? Doesn't the trim pot in the mixer effectively replace a preamp? (As compared to going pickup into instrument amp).)

**Francois Blais** · #2 03-05-2003, 07:03 AM

Depends on the input impedance of the device you plug the pickup into.
As a general rule, 1 Megaohms is a minimum with piezo pickups.

Double Daddy · #3 03-05-2003, 08:13 AM

Francois, thanks for the reply.

Following is from the mixer spec sheet: "Mic E.I.N. (22Hz-22kHz): -129dBu, 150 Ohm Source; -117.3dBqp, 150 Ohm source; -132.0 dBu, inputed shorted; -122dBqp, input shorted"

I don't know how to decode all of that. Does that clue you in as to the input impedance you mentioned? - Double Daddy

**Francois Blais** · #4 03-05-2003, 09:16 AM

I suppose you plug the pickup into the line level input, and not the mic input?
In that case, check the line input specs.

Double Daddy · #5 03-05-2003, 09:28 AM

Yes, into 1/4 unbalanced line input. Those specs are for line input.

I do have a passive direct box; I suppose I could plug into that and go into the PA XLR input for impedance matching. Ne c'est pas?

**Francois Blais** · #6 03-05-2003, 11:42 AM

Gee, 150 ohms is far from 1,000,000 !
A passive direct box is not a solution either. It usually uses a simple transformer.
You need an active device.
I suggest you try to find a simple preamp like the Fishman B-II from a friend and get a try with it.

Marty Forrer · #7 03-09-2003, 03:48 AM

Your Behringer mixer already contains a preamp for each mic channel, so there is no need for an extra preamp. Having said that, the Fishman pups are notorious for needing a preamp and may benefit some from a buffer preamp, although my experience with them is in the normal position, not under the bridge feet.

Double Daddy · #8 03-09-2003, 05:14 AM

I went ahead and got this new Fishman preamp yesterday from Guitar Center. I can return it in 30 days if not satisfied. Tried it at a gig last night (first time opening the box - pretty chancey, eh?)

It really helped with the arco. I did not have to crank the volume down at all and still had a smooth sound. I need to play around with the eq settings to get the most "natural' sound. Will repost as I get more experience with it, and let all know my decision to keep it or not.

Barefoot Larry · #9 03-09-2003, 06:24 AM

Quote:

Originally posted by Double Daddy
Doesn't the trim pot in the mixer effectively replace a preamp?

No.

Most piezo pickups have an impedance of about a million ohms (literally 1 mega-ohm), and if you don't at least approach it, you're going to have a thin too-trebly sound. That's one of the things a preamp does... Ultra High impedance IN, Pretty High impedance out.

Some bass amps have preamps built into them.

Some PA heads will work "acceptably" with some piezo pickups, but you will get a fuller more natural sound when going through a pre-amp, even into one of those.

I use a K&K BassMax which is one that works pretty well into most PA systems (especially Mackie powered mixers, it seems), but still it sounds better every time with a preamp, even one that has no EQ adjustment.

Don't depend on trim pots or mic preamps. The only rig so far that the BassMax didn't work with at all, was a Behringer Eurorack mixer going into a power amp, rather than an actual powered mixer head. Fergot my preamp.

By the time they got the bass eq'd so that it didn't sound like someone blowing their nose, almost all of the highs and mids were cut out, and I think the low-end was way boosted too.

That left me plenty of muddy dark sounds that were worse than you'd get out of a Casio synth, and allowed me to keep the beat... not much else. It was marginally better than having no bass player.

Christopher · #10 03-12-2003, 01:51 PM

I have a Realist that reacts well to most amps that I've run it through. On rare occasions when it doesn't like the amp, I bust out a Sansamp Acoustic DI to cut out crispiness and feedback.

mje · #11 03-12-2003, 02:52 PM

Ideally you want an amplifier with an input impedance greater than or equal to pickup you're using. You also want to keep the leads between the preamp and pickup as short as possibly. This minimizes the effects of cable reactance (capacitance and inductance) on the signal. Ever hear a cable crackle as you flexed it? This can happen in very high-impedance systems, where the cable acts like a big capacitive transducer.

Double Daddy · #12 03-31-2003, 07:24 AM

Ok, so I've used the Fishman Pro pre-amp for a few weeks now and offer this follow up report.

In the weekly piano-bass duo gig it weemed to help. In particular, the arco sound was much smoother at any given volume. My piano player says it generally sounds better to him.

However, in a loud quintet gig last Saturday at a jazz club in Newnan, Georgia, the pre-amp was a detriment. I actually had hoped that it would help me crank out the loud volume I need without sounding so much like an electric bass. But, alas, 'twas not to be. The problem was that I was getting a hiss sound from the preamp. I unplugged and went direct from my bass (with Fishman BP-100 mounted under the bridge feet) to my Behringer PA, like I used to do before I got the preamp. I had much more presence, although the one arco solo would have sounded scratchy if I had not done the unison vocal skat thing with it (a la Slam Stewart).

So, I guess I'll keep the preamp for small gigs, and maybe try it again in a loud setting.

Double Daddy · #13 03-31-2003, 09:14 AM

Well, he uses a keyboard (no acoustic piano in the palce), and I use a mic for vocals, so might as well plug in the bass, too. If I didn't, the bass wouldn't project well enough to the back of the room. It's a weekly jazz thing in a restaurant in Peachtree City (i.e., Augustino's Italian Cuisine).

I never expected jazz in Newnan, either. But this fancy continental cuisine restaurant ("10 East") sponsors a jazz club once a month where we get a quintet or sextet together. The pay sucks, but it's fun, and it's an "exposure" gig (don't ya just love those!). No big deal - I've got a day job.

**Pacman** · #14 04-01-2003, 12:43 AM

Quote:

Originally posted by Ed Fuqua

Jazz club in Newnan was (unfortunately) a phrase I never heard uttered when I was living in GA. Glad to see there's more gigs happening.

Me either, Ed. I lived in Ptree city till a couple years ago, twarnt nothin' happnin'....

and my ole lad taught high skool in Ptree... no jazz to be had there, for sure.....

times, they are a' changing...

chadds · #15 04-20-2003, 07:05 AM

I use the same pickup under the bridge feet in a Eub. The Preamp makes all the difference. Make sure you have the right pu under the right bridge foot etc as they will phase cancel each other . If the fishman doesn't work try the Ravens labs mdb-1. great ohms blance but no eq. In fact try the fishman I because we know that works well. I dial out a lot of treble and things get wonderful. Your cabinet choice also might be amplifing frequencies you don't want to hear. (not produced by the body of the bass)

oliebrice · #16 04-26-2003, 12:11 PM

I just got a K&K Bass Max, after reading threads on this site. Didn't get a pre-amp with it, mainly cos I couldn't afford it.
I've only used it once so far, through another bassist's GK combo (can't remember what model), which sounded great. Do some GK combos have built in pre-amps? or does this mean that I don't need a pre-amp when playing through a good amp?

How do DB amps such as a GK compare to a PA for needing/not needing a pre-amp?
cheers

Barefoot Larry · #17 04-26-2003, 03:39 PM

Quote:

Originally posted by oliebrice
How do DB amps such as a GK compare to a PA for needing/not needing a pre-amp?
cheers

Some bass amps have a pre-amp built in, some (I think most) don't. I don't know for sure about the G-K, specifically, but I believe it's among the "Don'ts"

As piezos go, the BassMax is pretty good about not absolutely requiring a preamp in most applications. It it almost always sounds a little better with a preamp, though.

Aside from one nightmare with a Behringer Eurorack mixer running into a power amp, I've never ABSOLUTELY had to have a preamp with my BassMax.

Running into powered mixers, it seems to work acceptably most of the time, depending on your notion of "acceptable".

oliebrice · #18 04-26-2003, 04:14 PM

cheers
I was really hoping that'd be the answer!

steve in tampa · #19 04-11-2006, 04:51 AM

A stompbox compressor like a Boss CS-3 can be a nice addition.

mesmithnm · #20 04-11-2006, 07:42 AM

Quote:

Originally Posted by Barefoot Larry

Some bass amps have a pre-amp built in, some (I think most) don't. I don't know for sure about the G-K, specifically, but I believe it's among the "Don'ts"
....

All bass amps have some sort of preamp. I don't think any bass pickups are capable of line level output - the question is one of input impedance. As Francois pointed out, piezo pickups need a high input impedance to keep from being "loaded". In simple terms (which is all I understand), the pickup can only make so much voltage from the piezo element as it compresses/uncompresses under the acoustic load. If the load on the other end doesn't have enough impedance (resistance to current flow), the voltages produced by the pickup get "drained" from the input end too fast. I think this is why they get "quacky" or harsh when the input impedance is too low. The fast signals (high frequencies) aren't as susceptible to draining (they don't last long enough) whereas the low frequencies are, so all you get is a bunch of harsh sounding highs with an impedance mismatch. Theoretically, an infinite input impedance would give the truest results, but then none of the signal would get through to the amp. Still, the best results are with an input impedance as high as possible - the tradeoff is that the gain stage of the preamp is trickier to build when the input signal is less.