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Old 29th July 2008, 02:43 PM   #1
cufunha is offline cufunha  Brazil
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Default First guitar preamp... teake a look please.

I'm graduating this year (electronics engineering) and I play guitar for a long time. I like to play metal (symphony X, angra, metallica).

I don't know much about guitar amplifiers; all I know came from google. It seems like guitar pickups act like a lowpass system with a ressonant frequency varying from 1kHz to 5kHz, and this transfer characteristic must be compensated (how?) in the pre-amp stage.

I'm trying to design a pre-amp, as simple as possible, just to start learning about guitar electronics and, in the future, design my own pre-amplifier for my guitar.

I have scketched a very simple pre amp based on poor solid state components, and it has a very good sound.
All I want now is suggestions on what to do next or what is wrong in this schematic and should be changed.

Please take a look:

Click the image to open in full size.
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Old 29th July 2008, 03:58 PM   #2
lineup is offline lineup  Sweden
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Hola!

I think your little guitar ampifier is good.
You say: 'sound is good'
Why you want to change?
Some problem?

Only thing I do not know about is where you connect output?
Some power amplifier?
What is input impedance of your power amplifier = The Load?


What would I change?
I do not know.
TL081 / TL082 / TL084 will be good for this type of guitar amp.
12 Volt.
What power supply you use?
------------------------------------------------

You want to use battery?
You can use TL06X variant: >>> takes only 200uA supply current! ( 0.2 mA )
And you use one 9 Volt Battery.
And you can put Battery + Guitar Amplifier inside your guitar!
Then you can turn and control, when playing.

Datasheets .. for VARIANT of Op-Amplifiers:
http://focus.ti.com/lit/ds/symlink/tl084.pdf
http://focus.ti.com/lit/ds/symlink/tl064.pdf


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Old 30th July 2008, 12:54 AM   #3
cufunha is offline cufunha  Brazil
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thankx for the answer. I forgot to mention some things. First, the output is connected to a standard stereo amplifier, I think a load impedance of 20k to 100k (which is connected to the 22k resistor shunt to the diodes).

the reason of 12V: it's the source I have here... it could be 9V without any problem...

about the 'good sound': the sound is clean (not noisy). It has a good distortion, but it doesn't have that metal sound i want. I have read about pickup electronics and pre-amp pickup corrections. What kind of corrections (filtering) are made in guitar preamps?

and the last question: what do you suggest to add to this schematic and how it is done?

thankx again for the answer.
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Old 30th July 2008, 01:06 AM   #4
lineup is offline lineup  Sweden
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Quote:
Originally posted by cufunha

about the 'good sound': the sound is clean (not noisy).
It has a good distortion, but it doesn't have that metal sound i want.
I have read about pickup electronics and pre-amp pickup corrections. What kind of corrections (filtering) are made in guitar preamps?


and the last question:
what do you suggest to add to this schematic and how it is done?

thankx again for the answer.
I do not see anything add to your schematic, besides some metal effects you want.

One idea I have used,
when have mono signal input + output to stereo:
Put 2 output capacitors and output level potentiometer:
to left + right stereo channel


Same as using a mixer with 1 microphone (mono mic) input.
- you have 2 output to left/right.
- can use those 2 potentiometers to put this sound source into LEFT/RIGHT panorama
... when reording in stereo.
It is like panorama studio mixer.


I give you one good link to find metal guitar effect ... and some other good electronics circuits.
Because I know only little about guitar circuits.

Here I hope you will find a lot links for Guitar Circuits applications
http://www.epanorama.net/schematicsf...uits/index.php
http://www.epanorama.net/links/music.html



Regardas honores.
Lineup
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Old 3rd August 2008, 06:59 AM   #5
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Default from a relative newbie to guitar stuff..

but a seasoned analog engineer;

C2 can be decreased. 0.22, or even 0.1uF, smaller and cheaper

C5 should be incresed, this is rolling off your gain st 160Hz right now. Becuase there is a fixed DC offset, a 22uF or 47uF electrolytic can be used.

R8 will not provide a reasonable volume range due to its interaction with the feedback diodes.

You will never get more than about 0.6Vpp out of this. Is that enough?
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Old 3rd August 2008, 04:15 PM   #6
cufunha is offline cufunha  Brazil
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i changed R8 to 500k now and now i can clearly hear the overdrive effect i want (but too noisy because of the very high gain). the capacitors are now changed as you pointed.
Can u explain me what should be the low cutoff frequency of this amp? I thought it was about 200Hz or more, but you´re talking abaout 160Hz.. and how about the high frequency cutoff? 10KHz is fine?

PS: inductor and capacitor near source simulates guitar pickup plus cables.
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