more amplification questions from db beginner

[Fenderjazz1]

hi, i posted a few weeks ago regarding starting gigging a cheap db with a cheap pickup through a markbass head and a phil jones cab ( my electric set up). advice was to get a preamp but i havent got pennies yet and started gigging the bass 3 weeks ago. soundwise its ok and keeps up with drummer etc in 5 piece band though any louder and it feedsback.
anyway in another thread on amps someone mentions possibility of using the balanced connector on the front of the little mark 2 for double bass. Is this true and would i get any benefit in running the lead from the bass to this? sorry if this is a dumb question but i dont know nowt about the dark side of how it all works! cheers stu

[Gareth Hughes]

[size=4][font=verdana,geneva,sans-serif]I'm not sure if the balanced connector trick will work but here's something to consider that might shed some light on what's going on. Piezo pickups have a completely different output compared to magnetic pickups, and until recently most bass amps were designed with electric bass in mind. Markbass heads (Little Mark and F1/F500 heads anyway) have an input impedance of 50,000 ohms.[/font][/size]

[size=4][font=verdana,geneva,sans-serif]Here's what Bob Gollihur at www.gollihurmusic.com has to say about it all:[/font][/size]

[color=#4b0082][size=3][b]Do You Need a Preamp?[/b]

Your amp or other device you plug your pickup into will determine that -- the [i]input impedance[/i] of the amp affects how a pickup sounds.

Piezo (most common) and similar acoustic instrument pickups are very different from the magnetic pickups you find in electric guitars and basses, and most amps are aimed at that market. Keep in mind that when you plug something into an amplifier, it becomes part of the circuit, and that circuit is designed for a specific impedance range. If there is a mismatch, problems result. There are three general impedance values, as follows: [/size][/color][list]
[*][color=#4b0082]Most bass amplifier inputs usually aim for around 50,000 ohms, which is considered "high impedance" -- electric guitar/bass pickups and general use dynamic microphones' impedances are designed to be compatible with that input impedance.[/color]
[*][color=#4b0082]Low impedance (like condenser mics and higher quality mics with XLR connectors (three pins inside a circular shell) match best with an input around 600 ohms.[/color]
[*][color=#4b0082]Piezo transducers want an input load in the 1-10 [i]million+[/i] ohms (1-10 megohms) range. ULTRA-High impedance.[/color]
[/list]
[color=#4b0082]So it's no wonder odd things happen. They can also often have a frequency response bump that further contributes to the odd sound -- that brittle, raspy, all highs and no lows sound that makes you think you have a bad pickup. Probably not -- you just need a buffering/impedance matching preamp. You can improve the sound by EQ'ing it to death, but it still isn't the same.

[b]Here are some reasons why you should have or should consider using a preamp between the pickup and amplifier:[/b] [/color][list]
[*][color=#4b0082]the input impedance specification of your amplifier is under 1 megohm
[i]...also expressed as 1,000,000 ohms or 1Mohm; being close to that value, like 800K, is usually ok. This is probably the most common reason for using a preamp. [/i][/color]
[*][color=#4b0082]there are features available from the preamp that are not on your amp, that can enhance or help with problems
[i]...like more precision or flexible tone controls, phase reversal, a DI output, high pass filter, etc.[/i][/color]
[*][color=#4b0082]you want/need a convenience volume control (and tone controls?) close to you, for when your amplifier is not at your feet
[i]since at higher volumes you will likely need to place the amplifier further away from you, so avoid feedback and other undesirable sounds[/i][/color]
[*][color=#4b0082]your pickup's output is very low, so you need a preamp to increase its signal level to better match your amplifier[/color]
[/list]
[color=#4b0082]Even with an amp that seems to handle the ultra-high impedance of a piezo pickup, I often like the buffering/matching effect of a preamp, and I think in most cases they are necessary for the best and most realistic-sounding results. They can also give you convenient control of volume and tone without having to move towards your amp, which can cause feedback problems depending on volume. I have experimented and found the Bass Max can be more "acceptable" without a preamp, but the Double Big Twin really benefits/needs a preamp for best results. Acceptable? that's a call you'll have to make - if you buy without a preamp, try to borrow one to try.

I've also experimented with the K&K Twin Spot on my old '27 "the gibson" tenor guitar, and while it is more acceptable than the bass pickup experience (it's tuned very high), the warmth and improved character that a preamp adds confirms my personal decision to never plug into an amp without one, unless it is designed to handle the ultra-high impedances of piezo-based pickups.

So, unless you have one of those special amps* that are designed to accommodate piezo pickups, I suggest that you use some sort of buffering preamp with [i]any[/i] piezo pickup, or you won't be getting everything these and other pickups have to offer. Some "stomp boxes," when not in bypass mode (turned off) and other preamps may be ok; check the input impedance specification of your device. If it is 1 megohm or higher, it should do the buffering/matching job. [/color]

[size=4][font=verdana,geneva,sans-serif]Back to me speaking - here's something else to consider: I used to think that the higher the impedance the better as it would let all the low frequencies through that I wanted. Trouble is that in amplifying a double bass there's a lot of those low frequencies that are completely unnecessary and only serve to make your gig life hell. I had been using a Fishman Dual Parametric DI, with an input impedance of 10Mohms - doing what I was told - but I was constantly fighting feedback and using the parametric eq to take out all the low frequencies. Then I tried using something with a lower impedance in an effort to get rid of some of those lows. Tried a BOSS pedal, with an input impedance of 1 Mohm and it cleared things up so much. In effect it acts like a high pass filter. I don't know what frequency it cuts at but it works a whole lot better for me than what I had been using. So before you go buying a preamp with a 10Mohm impedance I'd try something like a BOSS pedal (any one will do, they're all 1 Mohm) and see if that helps - oh, and the pickup has to be plugged into that first, or else it's irrelevant.[/font][/size]

Edited January 22, 2012 by Gareth Hughes

[Fenderjazz1]

thanks Gareth for your time to put that together, very helpful, I have some Boss pedals somewhere from my 6 string days and will give it a go in the house tonight. cheers stu