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.

UPDATE 20.12.2010':
Ive uploaded some examples with different Pickups and Gain settings.
Youll' need a mediaplayer that is able to encode AAC Music Files. Apple Quick Time Player should do the Job.

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
Solder
Wirecutters + Strippers
Needle Nose Pliers could be helpfull
Drill to drill holes in your Case

Comments

[fender-electric-guitar]

Very good job!! I have a question can you wire two of these together to make a two stage pre amp because if you could i can use the Hammond 262B12 transformer to wire the tube filliments together in series and that remaining 60v in series to use the 120 from the secondary

[Lenny24]

Thanks!
Yeah, you could easily do that, just leave out the Gain pot, from that point the Volume Pot would be the Gain pot.
With two additional Gain stages you are able to get some Rock tunes and maybe some High-Gain distortion, depending on how exactly you combine the two stages.
The 262B12 is a pretty neat Transformer for this application, Just make sure you use Capacitors with a voltage rating thats high enough to take the 170 or more Volts DC. But that shouldnt be a problem.

Have Fun Building it!

[plasmashears]

I am having trouble reading the values on your schematic, could you post a better image of it please? Really want to try this one out!

[Lenny24]

Well, here you go, check out the last step for the Schematics!

[arussell-wilkes]

Hey there, I'm just starting to get into this kind of stuff and im a little bit confused on your power supply set-up. I'm mostly getting confused with how to make the transformer/ power supply. Would you know of what kind of power transformer I could buy so that I can bypass the making of one right now?

[Lenny24]

You could use a Preamp- Power Transformer. You should be able to get them at your local electronic shop.
It should have something around these Values:
Primary: 110 or 230V Input (Depending on where you live)
1. Secondary: 6.3Volts @ 1 Ampere
2. Secondary: 100 - 200 Volts @ 50 mA (Note: the DC-Voltage will be multiplyed by the Factor 1.41, If you have a Output of 100 Volts AC, youll have a DC Output of
141 Volts)

[arussell-wilkes]

Would I need to add anything different to the circuit like a choke or something? Also would I just connect the transformer to an IEC socket for power, and where in the circuit would be a good place for a fuse to be put in?

[Lenny24]

The first Fuse should be in series with the Primary of the Transformer, the second Fuse in series with the 100 - 200 Volt Secondary.
You should use Fuses with a Value twice the Amperage,which you drain through it. Otherwise, it will blow, even if theres no Failure.

Youll need a CLC or CRC filtering supply. I Prefer CRC, they are easier.
For a simple preamp, you should use a Bridge rectifier, after that a charging Capacitor (the first C), that one should be around 47µF and rated 1 and 1/2 Volts more than your Filtered DC Voltage.

Example:
You got a 100 Volt AC Secondary.
After the Rectifier you got very Unsmooth 141 Volts, the next Voltage-rating on Caps should be 200 Volts, so use one 47µF @ 200 Volt Type.

After your Charge-Cap, youll need a resistor and another Capacitor, to complete the CRC - supply.

The Resistor should be a 2 Watt type and should have a value around 10 - 22 Kilo Ohms.
After that, use another cap to finally smooth out any spikes, that are in the Supply voltage.
For that, you can use another 47µF @ 200 Volt type.

[arussell-wilkes]

Thanks for being so helpful with questions! But I do have a problem with finding a transformer. The local radio shack doesn't have what I need, and I've looked through a lot of different transformers online trying to find one with the right specifications. I don't know how far off the numbers can be from the specs you gave me. I've found some that are close, but Im not sure if they're usable-

http://www.bottlehead.com/store.php?crn=221&rn=439&action=show_detail

http://www.tubedepot.com/tr-pw-13.html

http://www.hammondmfg.com/261.htm

If you could look through these and let me know your thoughts on them, it would be much appreciated!

[Lenny24]

No problem, man!


The first one looks pretty Solid, the second one looks a bit Underpowered for me (It could get very warm in use).
And with Hammond-transformers, you can do nothing wrong.
You could use the Hammond 262B12, but then youll have to connect the Filaments of the 12AX7 in series instead of parallel, thats just one Wire less, so easy to do.

[alexthemoose]

out of curiosity, how much did it cost you to do this build?

[Lenny24]

Pewh, Well, I had a lot Parts laying around, I think about 10 - 20 €.

[chypsylon]

Thanks for the schematic, it really helped me with another project :)
With what values have you actually ended up using for the inductors?
Would one of those here work? 

[Lenny24]

Hey!
Sorry, I have no Exact values of the Inductor. I winded it myself, I think 50 Turns of 25AWG Copper Wire... I would use a 330 µH Type, just to be Safe.

Which kind of Project is it? Normally, they should work.

[carpe_noctem]

Great job! I've been waiting for something like this since i read gmoon's amp 'ible and wanted to do it small scale first. You probably know this but for anyone else to whom this might not be clear, this preamp (or any) will not perfectly replicate an overdriven all-tube amp, because the power stages also affect the tone. Also, based on my research, good iron(transformers) can make a really big difference, so as a mod someone could do this using trannies instead of the regulated switchmode Power supplies.

[Lenny24]

Thanks! Yeah, thats right.I think my next 'ible will be a 5 Watt All-Tube Amp. Ive ordered some 12AX7 and EL84 Tubes, and I want to try that.
But If you only have got an Transistor Amp (Like me, until I finished my Tube Amp) this is a good option to bring some soft drive in your Songs.

Well, I dont have big Transformators at home, so now Im' thinking of Building the 5 Watt amp with a Switchmode, too. But in that case, I would build myself a step up transformer or I have to look for an ooooold TV. Otherwise, the big advantage of SMPS is, they have a much higher Frequency, which means you have no 50 - Hertz humming in your Powerline. SMPS handle frequencies, which are muuuuuch higher than the Human ear could Recieve.

[carpe_noctem]

yeah, i've just been drooling over all the guitar instructables. I moved and couldn't bring my guitar with me, so now all i have to play is some old classical guitar i picked up. Plus, i'm kinda broke too (studying hard with no time to work) so it'll probably be quite awhile until i can afford a guitar, let alone decent amp. I've been thinking of using a preamp like yours going into my computer. Using audacity (freeware)and headphones i can monitor myself and record loops to jam with...

[Lenny24]

Cool Idea! For use with Computer, you could just put in a 3.5mm Stereo Jack as the output Jack in this design and mess around with it.But maybe you have to make some changes in the Input and Output stages. Use a 100 Ohm instead of a 10k ohm resistor in series with the 1M ohm resistor to make clean sound Possible and Use a 100k insted of a 10k series with the 100k output pot. That will decrease the outputlevel and makes it easier to handle with a Computer sound card.

[carpe_noctem]

I'll definitely keep this in mind for when I can finally get my guitar back. Thanks.

[robot797]

do you have a sircut that is more understandable (paint)
includien the step up converter?

if not
send me a better drawn one and i will draw it for you (high qualety)

[Lenny24]

I will make another 'Ible only for the Step-Up Converter in a Few Days.

Well, the Schematic ive drawn have a very high resolution ( I think 7k x 3k Pix)
And I gonna put some Eagle Schematics online.

[robot797]

well okey
i just found the enlarge button (sorry)

i sm so gonna build this
i have 5 of thos those here
i can get them for 10$ new

[Lenny24]

Hehe... No Problem! :DD

Well, it has to be the 12AX7 or the 12AU7. The AX has a Higher gain so it will overdrive faster.

[Aud1073cH]

With the 12AU7 you could try the matsumin valvecaster. Made by matsumin, well documented by beavisaudio

[robot797]

what if you used a tube transformer and put 250V + on the circut?

[Lenny24]

Well... I think the Anode Capacitor would explode... Its only rated at 100 Volts. So at first youll have to change some of the Parts, but if you got it to work, it will overdrive totally heavy, I think.

[robot797]

that would be cool
so if all parts are +300 V it should work

[Lenny24]

Well, not All parts. The Cathode Bypass Caps should be Around 50 volts.
The Anode Caps something like 400 Volts and 2.2µF Elkos.

In my new Full-Tube Amp, I got the 12AX7 powered with 270 Volts, it sounds great!

[robot797]

wel okey
i will try (i will make all the parts 500V so it is always good) :P

[Lenny24]

Thats a Bit Overkill but If you want to, do it! (;

Good Luck!

[Aud1073cH]

Will you have a schematic and part sources for the power supplies?

if you want to make nice schematics, ray wilson made some free web tools that make schematics that export xml - tools section at musicfromouterspace.com

[Lenny24]

Hey, I just Put up the Schematics for the PSU! Check it out, If you like to.
I made them as Easiest as possible for me...
Ask me if you have any questions!

[Lenny24]

I could Upload them, If you want me to! Basicly, they are just 2 PWM-Controller plus Some MOSFETs an Inductors...

Thanks for the Link! That Tool looks great!

[Aud1073cH]

That would help.
I don't know much power supply design yet. Just the LM78xx regulators and smoothing caps to step down wall warts.

thanks :)

[Lenny24]

You could use a 7806 (in addition with some diodes, because you need 6.3 Volts, not 6) for the Filaments.
Or you could look for a 7 Volt Step Down converter, it think there IS a 7807, but im not sure, and put a 1N4001 in series with the output connection, which should drop the voltage to about 6.2-6.4 Volts.

And If you want to build the Step-Up Converter, youll need those parts:
PWM Controller IC: I used the MC34063
IRF740 MOSFET
Ferrite Core + Magnet wire (Around 22 AWG or so) or a inductor (something around 220 - 470uH)
0.47Ohm 2Watt or higher Resistor
820 Ohm Resistor
38k Ohm Resistor
180 Ohm Resistor
330 Ohm Resistor
1.5nF Ceramic Capacitor
1 UF4007 Diode
And some Filtering Caps... Rated at 100 Volts or Higher. Youll have to mess around with these to filter out as much ripple current as possible.
I used(one of each) 470 uF, 0.22uF,1uF and 47uF.


Hope that helped a bit, Ill draw the Schematics a quick as possible.

[Aud1073cH]

Ah- something in my area-

XLRs (microphone) pinout is

pin1 - ground (reference)

pin2 - hot (signal +)

pin3 (center pin) - cold (signal inverted)

most pro microphones are about 600 ohm impedance.

with 48v phantom power both pin2 and pin3 are at +48V DC in reference to pin1 ground. no DC potential across 2 and 3 However - some phantom power can only supply 14mA, and better supplies up to possibly 200mA. Not enough to supply a tube preamp.

all Tube preamps I've seen (external, or internal in the microphone) have had external power supplies.

[Lenny24]

Oh Thanks!
I got the pinout out of the internet before, but I didnt know about the Phantom power. Thanks again for that! I think if you didnt said that, I would have killed my mixer...

Well, 14 mA should be enough for at least one half of the 12AX7, because of the High On-State resistance of tubes (Pentodes - At least a few kOhm, Triodes - a few hundred Ohms).Well, With a 100k anode resistor...
48V/100100Ohm ~ 0,0004795 = 0.4795 mA , If im right.
^(100 Ohm of the Triode, normally would be higher than 100, I think)

Oh and I think it would be easier to use a OpAmp for supplying the grid of the Tube, because OP have an Inverting and an Uninverting input,which makes it a lot easier to use them with a XLR Jack.

Ive got your Supply-Schematics nearly finished! Ive made a new Version with a power tranfsormer that works a bit better. Which one do you like to use?

[Aud1073cH]

As far as power supplies,
With guitar effects, I think the answer first is whatever sounds better.
But cost and efficiency are also factors. Not only cost ($) but difficulty in finding parts.

How much better is your new design?

It may be nice to see the transformer version, and let the viewer decide. :)

Anyhow- Thanks very much for drawing up the power schematics. Much appreciated.

[Lenny24]

Yeah, thats right. I build a Tube Power Amp with an EL84 and I had to use a big Transformator instead of a planned SMPS, because it had drained too much current of the Battery and switched of every time I tried. But for a Preamp, its more than enough.

Yeah, but youll have to know that youll have to wind the Transformator yourself.
Oh, I think you could use the Tranny out of an old Computer PSU backwards. I think if you get he right pair of Pins, youll get something around 250 Volts.

Its better because you could add an bridge rectifier which will increase the effency of the circuit a bit.
Yeah, I will desing the Transformer-SMPS and upload it to the last Page,too. Well, maybe even today.

[Tekker]

Awsome! Thanks for the help and quick replies! New weekend project in the works : )