Guitar Tube Pre Amp




Introduction: Guitar Tube Pre Amp

Hello Again!
I'm back with a new Instructable! Wheeyy!
In this 'able, I'll show you how to make a Low-Voltage (Around 60 Volts) Tube Pre Amplifier for your Guitar!

Youll need, lets say Basic Electronics Knowledge for this.

Step 1: Parts Youll Need

I've listed all parts youll need here.
One thing I have to say before I write further.
I cant' tell you the exact sizes of the holes etc you need to drill because it depends on which parts you use and what kind of housing you choose.

So, Youll need :
A Case.
1 12AX7 or ECC83 Tube
1 9 Pin Tube Socket + Screws
1 200V 470uF Electrolytic Capacitor
1 1M Ohm Logaritmic Pot
1 100k Ohm Logaritmic Pot
2 Switches, 1 DPDT and 1 SPDT
2 35 V 2.2uF Electrolytic Capacitors
2 6.3mm Jacks
1 400V 0.68uF Polyester Capacitor
1 100V 1uF Poly Capacitor
Lots of wire.

Resistors :
2 4.7k  Ohm 1/4 Watt or Higher
1 68k Ohm 1/8 Watt or Higher
2 100k Ohm 1/2 Watt or Higher
3 10k Ohm 1/4 Watt or Higher
1 1.5k Ohm 1/4 Watt or Higher
1 100k Ohm 1/4 Watt or Higher

Tools :
Soldering Iron
Wirecutters + Strippers
Needle Nose Pliers could be helpfull
Drill to drill holes in your Case

Step 2: Prepare Case

At this step, I couldnt help you much.
You need holes for :
Tube Socket
2 Pots
2 6.3mm Jacks
2 Switches
and for some Wiring that goes outside the case.

Step 3: Insert Sockets Etc in the Case

I think its easier if you put in the Parts first and then solder everything up.

Step 4: Prepare to Solder!

Bend the pins of the Socket a bit apart. That makes soldering a bit easier.
Then, put solder on every pin.

Step 5: Schematics

I'm sorry for the Hand-drawn Schematics, but I couldnt find any kind of software which could draw Tubes. If you dont' understand something, post a Comment. I'll try to Answer ASAP.

Oh. One thing. I forgot to add the Bypass switch ( the DPDT type).
I will explain that in the next step.

Check out the last Page for the new, better Schematics.

Step 6: Beginn the Work

Grab the following parts :
2 100k Ohm 1 Watt resistors
1 68k Ohm Resistor

And Join together like shown on the Pictures.

Step 7: Adding Next Parts

Grab the following parts (According to the new schematics):
Jumper Wires
400v 1uF Cap
220k Resistor

Step 8: Cathode Resistors and Bypass Caps

... and the Coupling Capacitor between the two halfs of the 12AX7. And other connections...?
Get these Parts:
2 4.7k Ohm Resistors
1 35v 2.2uF Cap
1 63v 0.47µ Cap

400v 10nF Cap
100k Resistor

Step 9: Ground Those Things

Get some Jumpers out. And some Wire.

Step 10: Power Anybody?

You've got it nearly finished! Time to add... High.. er LOW Voltage!
Youll need a 60 Volt PSU for it.
And something around 6.3 Volts for the Filaments.

Step 11: Add the Tube and Some Knobs.

Well. Because this whole circuit wont Work very well without the Tube, Plug it in! Dont force it. it MIGHT take a while until you get it in.

Then, trimm the Pots and put some Fancy Knobs on them.

Step 12: Test It Out!

Now, youll have to apply power to it. Ive done that by Building some regulated switchmode Power supplies.
One Step-up Converter for 60 Volts and one Step-Down Converter fpr 6.3 Volts. Ive used the MC34063 For that. Not the perfect choice but it works.
I have applied 80 Volts to it, but that doesnt sound quite good. A little too thrashy. At 60 volts, the Gain is much better controllable and the distortion is a bit more harmonic.

Hope You Liked' it and Please Comment!

Step 13: Step Up/Down Converter

If you are interrested in the SMPS,I got the Schematics for you.
The Step Up converter is a bit more complex, but it aint as mind-breaking as it might look.

I uploaded the eagle-files for those who have got eagle, but youll also need the MC34063 Library file, which you can get at the Homepage.
Scroll down to M, it should be there.

Step 14: UPDATE 24.10.'11

Just made some tweaks at this Preamp and updated the Schematics.
Now you got beautiful Computer-drawn schematics (;

C2 is only if you want a brighter tone.
R8 should be choosen according to your Amp.
If it has a high gain, use a higher value to prevent unwanted Clipping.



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    112 Discussions

    This is kind of confusing to me, I am by no means an expert. I have all this stuff

    So, Youll need :
    A Case.
    1 12AX7 or ECC83 Tube (not sure which 1 I have)
    1 9 Pin Tube Socket + Screws
    1 200V 470uF Electrolytic Capacitor
    1 1M Ohm Logaritmic Pot (not 100% sure which is witch mixed the two up)
    1 100k Ohm Logaritmic Pot
    2 Switches, 1 DPDT and 1 SPDT
    2 35 V 2.2uF Electrolytic Capacitors
    2 6.3mm Jacks
    1 400V 0.68uF Polyester Capacitor
    1 100V 1uF Poly Capacitor
    Lots of wire.

    Resistors :
    2 4.7k Ohm 1/4 Watt or Higher
    1 68k Ohm 1/8 Watt or Higher
    2 100k Ohm 1/2 Watt or Higher
    3 10k Ohm 1/4 Watt or Higher
    1 1.5k Ohm 1/4 Watt or Higher
    1 100k Ohm 1/4 Watt or Higher

    Although some of the capacitors are a bit off.

    But anyways I am just trying to see how much space to size for my box and laying it out, and I noticed the section for the PSU. Which I only see a schematic but not how to make it.

    So I am wondering whats the exact input in VOLTS and AMPS that this preamp uses? Is it better to find a cellphone charger that matches the settings or something to use?

    As a new person to this, any suggestions as to following along with making the psu? I would rather like to run this with a PSU used for a phone charger, or run on a 9v battery in a way that wont ruin the sound. I read some of the comments but it all sounds so technical, I cant make head or tails of some of it.

    any help please would be great!

    plsss. reply

    how can connect this to guitar

    Mine keeps squealing, tried different tubes, different power supplys nothing fixes it. Any ideas?

    BTW Really good instructable very straight forward

    Hi... random question here but I have a random ECC82 Tungsram tube kicking about and I am looking into making this.. I can follow the instructable with no probelms because of the images but I am not too hot on schematics when it comes to the transformers... What is the input voltage for them and would you be able to put a picture up so I can see what it is meant to look like?

    Thanks in advance...

    Craig :)

    I am looking for more information on the step-up converter, is there a source for how to build it, a BOM or any other information available? Thanks

    can someone help me out with the switches, becouse I whant to solder it all on a pcb but dont know where the switches go on the schematic

    is there any way i could make this to run on a 9v power supply rather than making the step up/down transformers?

    Thanks for sharing this simple tube amp circuit. I am new to diy amps so I have some questions with the build.

    I just happen to found a power supply unit at home that gives 350mA on 12 volts, so Is it possible to make this preamp run on 12volts 350mA? i have reduced the resistorstors to the cathode to 50kΩ. Also where do I connect the ground to? Should I connect it to the negative end of the power supply?

    1 reply

    You should be able to convert the circuitry so it runs with your PSU; first, you should wire the filaments of the tubes in series and directly tie them to your psu, thus powering the filaments with 12V/150mA (as described in the tube datasheet); further, reducing the anode resistors is the right way, 47k sounds about right, if you're unsure just fool a little around. And yes, your psu negative goes to signal ground.

    Have fun!

    HI, Lenny24 ! Great work !!! Let me ask you some questions...Do you have a pdf version file for the PCB's step up/down converter ? I'm not a pro in electronics and I;m a little (dazed &) confussed. (I don't speak English either...I'm doing my best so, sorry and thanks a lot !)

    Hello, your project is very inspiring! Thank you alot.
    Im having
    questions about your psu, i havent built any smps and am researching the
    chip you used. and your schematic seems different than all the examples
    ive found( diode and inductor in different places) could you please help me with calculations for 9v 1% input and 60v(0,01a??? or what ever amps your anode eats?)0.01vripple out for the schematic like yours?(since you probably didnt use the datasheet example schematic for a reason)

    also when using multiple regulators(notswitchingmode) in a single output, does the adding up of input filter caps do any harm to the regulators?

    5 replies

    Hello, thanks!
    The schematic used is just a simple boost-converter using an inductor, a switching-FET and the chip as switching regulator. The output Voltage is more or less independent of the input voltage as of the fact that its a regulated supply. The output voltage is set by the voltage divider R7 R3.

    Do you want to connect multiple regulator outputs together? There may be some difficulties with that.

    thx for explanation! is there a need to use a fet, couldnt the chip supply enough power by its own? are there any improvements for this kind of low current application? if there is, maybe you could help me with the calculations. i used an online calc for the mc34063 and it gave me these values in the schematic ive added. and i have access to 470uh coils that i could use both between the pins 1 and 8 and also the low pass on the output with the 100uf cap.
    about the regs- no i do not want to connect the outputs, just the inputs and on the back of my mind i remember something about max input capacitance for regulators and for instance if id use 5 from the same power source and only one would be used at the occasion it would have 5 times the input capacitor, wouldnt it be problematic?

    i am working on a 9v psu for my addac and the stuff that connects with it and the plan was to put 3 separate regulators for 3 outputs @9v and it would be nice to power a preamp like yours with this same transformer, so 2 extra regulators for 6.3and60v.
    also how much current does the 60v line needs to supply?

    step up.png

    Hey there!

    The chip itself could deliver enough power, thanks to the 1.5Amps switching current of the transistor, but: its only rated at 40 Volts Uce, which means it would definitly die because of overvoltage. If you have one on hand, you could surely use any transistor which is rated with Uce > 80 Volts and switches enough current for your application.

    Connecting the inputs of different regulators together shouldnt be a problem as long as the power source is able to deliver enough current for all circuits, including 10 - 20% buffer. In case one of your regulators then starts unwanted oscillation, you could try decoupling the regulators with a small inductor (eg. 2µ2H, depending on your current) and a 100nF ceramic (!) capacitor in front of the switching type regulators.

    R4 is the gate pulldown-resistor, its used to switch off the mosfet, because only the 'on'-state is driven by the internal Transistor of the chip.

    R5 creates a voltage divider with R7, which determine the output voltage of the regulator. It shuts off, as soon as the input voltage at pin 5 (which is connected to the tap of the voltage divider) reaches 1.25 Volts (Vref).

    C2 should be used if your regulator is oscillating; if you double the resistance of the voltage divider, the capacitance should be roughly halved.

    hope i could help!

    as i understand you had a 12v supply so ive changed the Vsense resistor to a one for 9v and also changed the coil and Ct accordingly. and do i have change some other values like R4,r5,c2? you think this schematic below would supply 60v?