LF: guitar preamp suggestions for use with soundcard

[J.R.Freeman]

Hello everyone,

I am using the line-in port of a generic PC soundcard to plug in my electric guitar. I am using a software based effects suite, and I have to crank the gain to get reasonable output. The signal to noise ratio is awful at the moment, understandable as I do not have a preamp in-line.

So, I realize I need a preamp but what types of specs are needed? What is the typical output level and impedance of guitar pickups? Do I need lots of gain or really just impedance matching? I've tried a tube-based "mic" preamp, but it doesn't seem to work very well in this application.

There are some interesting commercial products, but they usually come with EQ and compression and all that stuff, along with a hefty price tag. I want to keep the analog chain short and simple, so maybe I can accomplish this with a clean opamp and a potentiometer. Any thoughts would be appreciated!

Thanks all,

Jim

 

[famousmockingbird]

Passive pickups have a high output impedance and output voltage varies (even just picking harder puts more voltage out).

I don't know what tube preamp you used but it could still have a high or even higher output impedance than the passive pickups. For example a common 12AX7 gain stage can have an output impedance of 38k ohms and a guitar pickup can have an output impedance of 10k ohms. You normally want the input impedance to be at least 10x the output impedance driving it.

I recommend an active opamp unity gain buffer, they usually have output impedance under 100 ohms and that will drive almost anything. I use one to drive my true bypass effects pedals and it only cost me like $20 bucks to make form stuff at radioshack.

If you need tubes than a cathode follower buffer say with a 12AX7 will have an output impedance of 1k.

 

[Nigel Goodwin]

Or just a simple FET source follower, one FET, two resistors (gate resistor and source resistor), three capacitors (two coupling, one battery decoupling) and a 9V battery.

It doesn't get much simpler 😀

 

[fastfolkert]

....like described here: http://guitarnuts2.proboards.com/thread/3150

 

[ATAUDIO]

You might try
THIS.
It works to a boombox, and I suppose it would be (more than) enough for a PC
LINE input. You can use TL 074 ICs if you want something more common (but a little bit more noisy).

 

[tinitus]

There are some interesting commercial products, but they usually come with EQ and compression and all that stuff, along with a hefty price tag...

Jim

check booster pedals, etc

this one looks sweet, and not expencive 🙂

but you could also get a small combo for the same money
but check carefully if it has pre out, or DI out

gosh, that little Orange Micro Crush combo with 4" speaker is really funny ... and there is even a stereo version for music, cool 😀

 

[ArcticBreaze]

Hav you tryed the mic input on your pc, it works ok for my software guitar tuner.

 

[jjman]

If you have any Boss pedals you can test if a mere buffer will resolve the issue. All Boss pedals (and many others) have buffering, even when the effect is "off." (I place a Boss in front of my DIY Fuzz pedal to avoid loading issues.) The eq is likely to improve with this but volume may not increase measurably. Buffered is the alternate to "true bypass."

Play thru the pedal in "off" mode and you are playing thru a buffer. For a volume boost, which also seems appropriate, get a "boost" pedal that has a low impedance/buffered-output as mentioned by others. I suspect they are all low(er) impedance on their output than a guitar. DIY for such can probably be low cost.

This can also be called a preamp IMHO.