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Converting from guitar level to line level

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joecool85

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I want to build some sort of preamp to go from guitar level signal to line in level. Right now to run my lm3886 amp I need to plug into my practice amp and line out from it. Any sort of booster circuit that would bring it up to line level easily?
 
joecool85 said:
I want to build some sort of preamp to go from guitar level signal to line in level. Right now to run my lm3886 amp I need to plug into my practice amp and line out from it. Any sort of booster circuit that would bring it up to line level easily?

Just a simple opamp is all you need, but you need one with a high impedance input to match a passive guitar (1Mohm or so). Using non-inverting format is best, you don't need much gain, 5 or 10 times should be plenty.
 
joecool85 said:
So I'm thinking about using the TL072 preamp my dean markley uses.

The TL072 would be fine.


Again, that looks fine - notice that the first opamp gives a gain of about 5?, which is what I suggested. If all you want is a basic preamp, the first opamp part is all you need.

Can anyone help me get all the values, it seems some aren't listed. Also, whats the difference between a A10k pot and a B10k pot? Is the B one linear? And if so, why would the mid and bass EQ be alpha (log) and the treble be linear?

Which parts are you having problems with?, it looks pretty clear to me?.

It looks to me like B pots are log (as the volume is a B one). The reason the tone control pots are different types is because it's the strange 'Fender' type guitar tone control system - with baxendall tone controls the pots would be all the same, all linear for active, and all log for passive.
 
Is there any other opamp that would be easier to work with or something? Or just better in general?

And I think there was a cap I couldn't figure out, but now I don't know which one lol.
 
This shows another guitar pre-amplifier design:

**broken link removed**

The TL072 is pretty decent, I often use it. I have used the NE5532 recently too, and its noise performance seems excellent to me, though its not always a suitable alternative (internal diodes and needs an input resistor I believe). Anyhow, breadboard it and just try some you have, a 741 and other cheap/old ones will probably be too noisy.
 
joecool85 said:
Is there any other opamp that would be easier to work with or something? Or just better in general?

How could it be easier?, it's an 8 pin opamp, it's easy to use - there's no opamps easier than that.

And I think there was a cap I couldn't figure out, but now I don't know which one lol.

I didn't notice anything, it all looked very straightforward.

As for noisy opamps, it's not at all a problem, MANY guitar amps have used them in the front end, as have microphone inputs, perfectly happily.

In fact I changed a couple of 741's in the front end of a mixer/amp the other year before a gig (to keep Audioguru happy!) - I couldn't tell any difference, and that was using 600 ohm mike inputs.

NOT that I suggest you use a 741, you can get far better opamps for less money, the TL072 series are FAR better chips.
 
Cool. I think I will do the dean markley preamp. It seems the easiest and best solution. Besides that, I know I like the sound, because I already have one :)

**edit**
The caps I didn't know about are listed as 333M and 222M, whats that mean?

**edit again**
Think its perfable? I want to do it on perfboard since I don't make PCBs.
 
A cap marked "333M" is 33,000pF which is also 33nF or 0.033uF. "M" is a tolerance of 20% (K is 10% and J is 5%).
"222M" is 22nF or 0.022uF at 20%.

Use Veroboard or stripboard instead of plain perfboard since half the wiring is already done for you on the copper strips.
 
I'm thinking of doing a PCB for it since it seems several other people are interested in using this as a preamp for their chipamps.
 
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