The objective here is to build a portable guitar preamp that I can carry around and gig with different people. It can also replace the preamp section of my guitar amp, which is a Peavey, and borrow the sounds of Fender/ Marshall/ Vox from its tonestack.
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Signing UpStep 1: Schematics
I did not design the schematics myself. Since my objective is to make this preamp portable, I searched for the simplest preamp design and found this from www.redcircuits.com . This is called a "Solid-state Fender Blackface Preamp", which is a transistor version of the original valve circuit from the "Fender Blackface".
http://www.redcircuits.com/Page120.htm
I then borrow the tonestack from the Tonemender that is found at www.runoffgroove.com . The Tonemender is a booster with a very flexible tonestack, which can re-create the Fender, Marshall and Vox responses.
http://www.runoffgroove.com/tonemender.html
Details of these schematics can be found at the links above, which explain clearly what these circuits do and how they work.
http://www.redcircuits.com/Page120.htm
I then borrow the tonestack from the Tonemender that is found at www.runoffgroove.com . The Tonemender is a booster with a very flexible tonestack, which can re-create the Fender, Marshall and Vox responses.
http://www.runoffgroove.com/tonemender.html
Details of these schematics can be found at the links above, which explain clearly what these circuits do and how they work.
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1 I will be using a larger enclosure so that I can fit a mains transformer with 24 volt secondary and a filtered power supply with a 7824 regulator that I have. Can you foresee any problems ?
2 Is there any need to have all the offboard shielded?
3 I am confused with 2 input wiring. Obviously the jack sockets are switched but I am not sure how to wire them
I think this is a very good circuit and is just what I need
1. I am not experienced with power supply. One reason I do not want to get into it is because of the high voltage. Second reason is that I did built some power supplies in some other projects and found that many unforeseeable issues may happen. For instance, shielding of the transformer is important or the magnetic field may interfere with the signal. You may want to put it as far from the circuit and wiring as possible.
2. It is always better to have them shielded.
3. You need mono jacks with switch. http://www.guitar-parts.com/catalog/jack-14-inch-female-choose-style-1. the middle one in the image of this link. Once you get the jack, check its connectivity with a multimeter by inserting a jack. You need to figure out which pin is the switch (one that will be disconnected from the tip when the jack is inserted). Once you figured out how this switch works (it is easy when you can and play around with it physically), you should be able to connect according to the circuit.
Good luck!
to design your circuit board? THAMKS!!!
It was already routed to accept a DC power adapter. However, from experience, unless you have a very clean power source, batteries sound better.
Actual wiring depends on the DC jack you buy. You can use a multimeter to check for the connection.
You can refer to the wiring diagram for any guitar effects. They are all the same for the DC jack/ battery part.
http://www.generalguitargadgets.com/pdf/ggg_sgo_lo_wiring.pdf
and better labels of what the component are(Like value of resistors and cap.)
where do the transistors go ?
thanks for the input..
Why not up the voltage from a single cell? Or run at 9v?
The tonestack is the section I highlighted in red in the new photo. This is the part that shape the sound.
If you look at the Blackface's circuit, coming out of the 1st set of transistors, the signal goes into the tonestack, then the signal goes to the vol (P4) with or without the C6 (bright switch) to enter the 2nd set of transistors.
So instead of going into the original tonestack, in my version, the signal comes out of the 1st set of transistors to the Tonemender tonestack (the red part), then to vol (P4) and the 2nd set of transistors.
If you look at the Tonemender circuit again, the signal comes out of the 1st opamp, then into the tonestack, then into the 2nd opamp.
So if you look closely, both circuits are actually doing very similar things.
The tonestack is totally passive and it does not use any power. Vref in the Tonemender = Earth = 0V. Hope it helps!
In a couple of days I'll start to work on it. I'm interested on make a bass version, so I need to tweek the voicing in the tone section and some caps here and there, you know.
Thanks again for your kindly response!
I let you know as soon as I get positive results.
Cheers!
The guy at the store gave me the stereo plug , how do i wire it for mono ?
Ill post the link to m 'ible as soon as it's up.
P.D: Cool project, could you upload some videos or sound to have a listen on it???
Looking forward to your instructable!
P.S.: I will try to get some sound clips when I've got the time.
for the big amount of gain you can remove the C8 cap and put the Jfet buffer like on the red circuit page,
just replace the output résistor by a 100k log pot and you get a master volume.