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Building guitar preamp!!!

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3/24/2003 7:04 PM

Building guitar preamp!!!

Hey guys,

I don't know a lot about electronics at all, but I've decided to build a guitar pre-amp in the next few days. I've found a pre-amp kit that I can get hold of, at:

http://www.dse.com.au/cgi-bin/dse.storefront/3e7f53ca0a9cf5d0273fc0a87f9c0779/Product/View/K5608

Does this kit look like it'll be acceptable, in terms of, will it introduce noticable noise into the circuit, etc?

It says it'll give up to 40dB gain, which is too much for me... so I'm just wondering what type of resistor I'll need to drop it down without compromising the noise levels...

Your help would be GREATLY appreciated, thanks in advance

3/24/2003 7:06 PM
Jon	Oh yeah, and by the way the noise issue is really important to me, if there's one thing I hate, it's too much noise coming through my amp heh thanks

3/24/2003 8:18 PM
Luijo	Hi Jon: The preamp you posted doesn't seem like a regular guitar circuit,looks rather large and amateurish,i guess u can get better things out there on the net,but for a little more money though. Any more help feel free to contact me, Luijo P.S.:Have you considered putting one together yourself?There lots of schematics available for that!

3/25/2003 4:41 AM
Chris B	Jon, What is it you're trying to accomplish with the preamp? More volume from the guitar (to overdrive the amp) or a lower output impedance (reduces treble loss through long cables)? Chris B

3/25/2003 6:09 AM

Hi guys,

First of all, thanks heaps for answering.

Basically, I'm going to use the preamp for overdriving the 1st stage on my existing amp a little more...

I've looked at building my own preamps and found heaps of schematics, but I don't know which one to use!!! If you know of any that will suit my purpose (low noise, increase by about 24db). I'm not sure if 24db will be the right increase in level, but I can change that once I try it, with resistors anyway, can't I?

That link of the pre-amp I posted, apparently it's smaller than a 9v battery, which is just fine by me... my main concern is, will it introduce any noticable noise into the circuit?

Thanks heaps :_

Jon

3/25/2003 1:42 PM
Anthony Noel	Take a look at the LPB1(2) and The AMZ Booster. YOu can find the LPB1 at http://www.generalguitargadgets.com do a google search for the other one.

3/25/2003 2:09 PM

IIRC, a 3dB increase is equal to a 10x boost in gain. So, for 24dB increase, you'd need a gain of 80. If you use an OPAMP like a low noise version of a LM741, you can set the gain by adjusting the ratio between two resistors. The circuit would be simple, and small. You would need a 9V battery to operate it.

I'd go with a non-inverting amplifier and use a 1k and an 82k resistor to set the gain. Then you'd have to build a +/- 4.5V supply using the 9V battery. I'd use two 100k resistors in series from +9V to the - terminal, and ground the junction of the two resistors so that you have + & - 4.5V. There's probably a schematic very similar to this on the web somewhere. The Distortion + is similar to this, but has a few extras thrown in.

Check this schematic:

http://www.play-hookey.com/analog/experiments/non-inverting_amplifier.html

Put a 82k in place of Rf (or use a 100k linear pot, so you can adjust the gain), and a 1k in place of Rin. Then you just have to worry about the power supply.

If you're using single coil pickups, noise could be a problem, but that's the pickups, not the OPAMP circuit.

Chris B

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