DIY guitar preamp for PC recording

[PenPen]

Well, all you have to do is mentally cut everything out to the right on the blue line from the second input pot, where those three trace cut squares are. That will net you just one of the input stages.

[nightingale]

+1 for the LPB trick.
I think it adds a little character to interface mic pre's. A couple of my friends have  s*undcraft consoles [ghost/spirit]. It seems like 50% of the time we end up re-amping a track through the LPB and blending it with the original to give to make the track sound a little more interesting.

Hope is helps,
ry

[drazenmob]

Well, all you have to do is mentally cut everything out to the right on the blue line from the second input pot, where those three trace cut squares are. That will net you just one of the input stages.

So should it look like this?

If that's it I think i will try to build this first because its simple. And i got all the parts needed.
Only thing I will change is to replace J201 with BF245c. 

[Somicide]

just my 2 pennies here:

The OP said something about using guitar rig 2 for his tracks.  My advice?  Get a DI box.  Cheap ones can be found for ~$30.  This is how I record my guitar parts for use in GR2, and they always sound great, IMO.

[drazenmob]

just my 2 pennies here:

The OP said something about using guitar rig 2 for his tracks.  My advice?  Get a DI box.  Cheap ones can be found for ~$30.  This is how I record my guitar parts for use in GR2, and they always sound great, IMO.

Thanx for advice but I can't find DI boxes here and can't afford to order and buy one

[PenPen]

Well, all you have to do is mentally cut everything out to the right on the blue line from the second input pot, where those three trace cut squares are. That will net you just one of the input stages.

So should it look like this?

If that's it I think i will try to build this first because its simple. And i got all the parts needed.
Only thing I will change is to replace J201 with BF245c. 

This is correct. I am unsure about those JFets, I've never heard of them, you may need to rebias it (use a different resistor value instead of 22k on the drain there). Gimme a sec, I have that jfet model in my spice library, I'll try out simulating that circuit with that jfet in there. Biasing fets is normally a pain, but we'll see how this turns out.

[alextheian-alex]

J201 behave *kinda* like an MPF102, but have higher voltge tolerances and lower Gm and input capacitances.

[PenPen]

Again, simulators are tough, and don't account for variance in parts, so your actual result may vary a bit, but I had to lower that 22k resistor on the drain to 5k in order to get a full voltage swing and proper biasing with that Jfet. SO, if you build it up and it sounds wrong, try lowering that resistor until it does start working properly.

[drazenmob]

This is correct. I am unsure about those JFets, I've never heard of them, you may need to rebias it (use a different resistor value instead of 22k on the drain there). Gimme a sec, I have that jfet model in my spice library, I'll try out simulating that circuit with that jfet in there. Biasing fets is normally a pain, but we'll see how this turns out.

Again, simulators are tough, and don't account for variance in parts, so your actual result may vary a bit, but I had to lower that 22k resistor on the drain to 5k in order to get a full voltage swing and proper biasing with that Jfet. SO, if you build it up and it sounds wrong, try lowering that resistor until it does start working properly.

Thanx a lot PenPen!!! for simulating this preamp with BF254c and giving me advice what to do to rebias it to work properly.
Only thing to do now is to make this circuit and tryout which resistor on the drain will work good. I will buy several different ones from 22k to 5k maybe 1k. I cant wait to build and to try it! YEAH!

[drazenmob]

Hey!
i've built this preamp 90% and now im looking at this picture and i dont understand one thing...
If red wire is (+) from dc 9v or 9v battery where is (-) wire?
I'm going to use 9v battery. Please look at picture and tell me if i am wrong... or something... 
please come with advice soon! Thanx!

[Seljer]

the negative wire from the battery would go to where any of the green wires are in that diagram (just hook it up to the bottom row of the veroboard)
(you'd probably want to use a switch to turn the thing off in this setup)

or you could use a stereo input jack for channel one, and you'd hook up the batter to the ring section of the jack, so the circuit would be turned on whenever you plugged a guitar or any other 1/4" mono plug into channel one

[Minion]

Another Simple Preamp idea is to just use a basic Dual Opamp with the First half as a High impedance buffer and the second as a adjustable Gain stage, You can even add overdrive by adding a couple Inverted Diodes in Paralell with the Feedback resistor of the second opamp....

Something like this:




Cheers

[drazenmob]

the negative wire from the battery would go to where any of the green wires are in that diagram (just hook it up to the bottom row of the veroboard)
(you'd probably want to use a switch to turn the thing off in this setup)

or you could use a stereo input jack for channel one, and you'd hook up the batter to the ring section of the jack, so the circuit would be turned on whenever you plugged a guitar or any other 1/4" mono plug into channel one

OK, i did it that way. connected with green wires, and tried it but output signal is very vary weak!

[PenPen]

Change the biasing on the drain of the fet then. What resistor do you have there now? As I said, biasing fets is tricky, and every part is different. What voltage are you reading on the drain of the FET?

[drazenmob]

Change the biasing on the drain of the fet then. What resistor do you have there now? As I said, biasing fets is tricky, and every part is different. What voltage are you reading on the drain of the FET?

I've put a 4.7k resistor instead 22k as you said and voltages on jfet are:
D: 6.02v
S: 5.96v
G: 5.70v

Battery: 8.97v

[PenPen]

That drain voltage is a bit low compared to the model. Variances in parts causes that, I mentioned that fets can be tricky. Try upping that drain resistor, like a 6.8k, or even just adding a 2.2k in series with the 4.7k resistor. I apologize this is being difficult, it just really hard to predict what a FET is going to need.

[drazenmob]

I've changed drain resistor 4.7k with 6.8k and now voltages are:

D: 5.35v
S: 5.29v
G: 5.13v

Battery: 9.09v

[drazenmob]

NOWI've changed drain resistor to 1.1k and now voltages are:

D: 8.13v
S: 8.02v
G: 7.78v

Battery: 9.09v


I hope that someone can help me i need this preamp working soon 

[Meanderthal]

 Is the transistor in the right orientation? BF245c is flat on the opposite side of a J201, so in this case the flat side should be facing right.