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Old 18th October 2004, 12:24 AM   #1
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Default Do i need a preamp?

I am purchacing a bass guitar soon. What i am wondering is, if i want to hook it through a regular stereo RCA inputs, do i need to build a preamp? is that what they are called? or what do i need? any information would be helpful. if i do need a preamp(or whatever else i need) can anyone tell me where to get the schematics that i would need? I dont want one that has any effects on them, just a 'straight through' that will make it compatable with a stereo input. thanks
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Old 18th October 2004, 02:53 AM   #2
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you can plug a bass guitar into a RCA connector by simply using a plug that makes the two compatible..
but if the rca plug is on a hifi or straight power amplifier then you will need a preamp to increase the gain from the bass guitar to an acceptable level. there are preamp schematics all over this forum and the internet, you would be after a gain of around 10 i imagine (100mV guitar output level?)
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Old 18th October 2004, 02:57 AM   #3
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Default Re: Do i need a preamp?

Quote:
Originally posted by silentblackhat
I am purchacing a bass guitar soon. What i am wondering is, if i want to hook it through a regular stereo RCA inputs, do i need to build a preamp? is that what they are called? or what do i need? any information would be helpful. if i do need a preamp(or whatever else i need) can anyone tell me where to get the schematics that i would need? I dont want one that has any effects on them, just a 'straight through' that will make it compatable with a stereo input. thanks
Well, it depends. I have 11 basses (and a box full of other pickups) and they all produce varying signal levels due to the differing designs of the pickups and whether or not they have a preamp onboard. Before you spend any money, try plugging the bass directly into the line stage and see what it's like, but beware of the levels; start low and wind the volume controls up slowly.

If you decide to build a buffer/preamp all that you'll really need is a small buffer using an opamp. The type of opamp really doesn't matter (LM833, TL071, NE5534 etc, ie any modern opamp), but I would suggest adjusting the feedback resistors to get you in the gain range you want to use when you plug it in to your stereo (line inputs). Simply 'Y' cable it into the two channels and away you go.

If your bass has a preamp, or active pickups like EMGs, then a buffer might not be neccessary as they should be able to drive the lowish input impedance of most line stages. Passive basses won't like the low impedance and will give a lower output signal and sound very thick, but won't be damaged in the test.

I've added a schematic below. Make R3=1M, R1=20k, R2=1k - 5k (vary gain roughly 20 - 4x) and add a 10u cap on the output.

If you haven't chosen your bass yet, spend as much time as you can in stores, and play everything to find what feels good to you in terms of balance, position on the body when sitting and standing and especially neck shape and width. All will make a big difference. If you can, take your teacher along, or an experienced bassist friend to help you choose. I'd also suggest having it set up properly by a pro, to get the action right; it'll make a big difference in how you play and how much you enjoy learning to play (I'm assuming you're a new player). Later, look for a small combo amp secondhand.
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Old 18th October 2004, 06:18 AM   #4
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on the output there is only one line, is that connected to the posative part of the output connector and the other end is just to the batteries negative terminal? cna someone explain how to piece that together? i know it sounds dumb, if i just get this then i will nkow how to connecte everything else. i know how to put hte resistors and all, but on terminal 4 on the IC, is htat to the negatice terminal of the battery also?(isnt that called the ground)
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