Generic NPN Booster Project, Tips.

[Hallmar]

I just made this today and it works!
I breadboarded it and simulated it in Workbench and it works.

Also, i forgot to add two 1Mohm resistors on the input and output to earth to prevent switchpoping. You do the imagination.

Any tips on it?
I'd like to add a little more distortion to it, just a little. How do i go around doing that? Add a second stage? Or just do diode clipping?
It's a clean booster as it is now.

Thank you!

Voltage Measurements
C: 5.6v
B: 0.7v
E: 27mv(practically 0v)

[Hallmar]

On a side note: i tried putting the emitter directly to ground and it changed nothing.

So i don't even need that 220ohm resistor?

[LucifersTrip]

try ~1K - 5K+ resistor in series with ~5uF - 50uf cap from emitter to ground ...if too much, increase the 1K - 5K+ resistor.

[PRR]

What does Workbench say the pin voltages are?

They look wrong to me. Like C and E are swapped.

Yes, one transistor amp fed e-guitar "usually" won't distort. Use it as a booster to make a *second* stage distort.

[Thecomedian]

this schem is basically screaming bird booster or bass booster from muzique. It looks like you're getting the hang of it. I usually find a feedback resistor on E or adding a feedback cap in parallel with Resistor E magically makes the circuit work when it wasn't before.

[Hallmar]

What does Workbench say the pin voltages are?

They look wrong to me. Like C and E are swapped.

Yes, one transistor amp fed e-guitar "usually" won't distort. Use it as a booster to make a *second* stage distort.

Hmmm. I'll swap it later today and see if it changes much.

[Hallmar]

I changed the orientation on the tranny on the breadboard and it didn't work.

So i guess the orientation is right. Maybe i got the voltage readings wrong.

Edit: i raised RC to 33k to get more voltage amplification.
Raised the output voltage by 1v.

[allesz]

+ 1 on Lucifero's post. For my taste it will shape the sound good, and you can even lower a little the input cap in this case.

Removing the emitter resistor will, mostly, give more noise and maybe a little bit of distortion too  (but nothing to scream about...).

For more grit I would add some diode to the output mostly silicon (1n4148 for example) or even a couple of leds.

1K seems a too little value for the volume pot, try something more. And you don't need a antipop resistor on the output, the volume pot does the work already.

[Thecomedian]

One of your problems is too little resistance at the output past the DC decoupler. 1k is really tiny.

http://www.youtube.com/watch?v=LuMD3-iKjKk

watch this and you can see that the resistances across the circuit can be added together to simplify the circuit, a bit like simplifying equations in middle school math.

If you simplify the entire circuit down to two resistors, the output volume pot resistance and the rest of the circuit being one resistance value, you can then compare this to a simple voltage divider formula and see that the voltage will be incredibly weak. For this, only the paths where AC can flow through resistances inside the DC circuit matter, I believe.

100k volume
http://www.muzique.com/schem/bird.gif
http://www.muzique.com/schem/mole.gif

500k volume
http://www.muzique.com/schem/fuzzface.gif

55k ish minimum between low frequencies and ground, with some treble bleeding low pass filtering.
http://www.muzique.com/schem/sonic.gif

Basically, you want the signal to "pass" to the output to the next stage or amp. With too little resistance to the ground, the next stage can force your signal to ground instead of having the signal forced on it. It'll use up batteries fast and sound lifeless probably.

[mac]

I'd put a multi switch at the input to choose among various input caps --> treble to mid to full boost.

A hotter transistor, bc550c or 2n5089 or mpsa18 or darlington, emiter grounded, will distort a little more.

mac

[Hallmar]

One of your problems is too little resistance at the output past the DC decoupler. 1k is really tiny.

God damnit!

I forgot to change the value on that. It was supposed to be 100k.

Derp

[gjcamann]

I'm in the middle of messing around with the same circuit and have had some great results, I recommend 1N914's for clipping.

If you put a cap (4.7uF-470uF) in parallel with your emitter resistor and add a pair of clipping diodes to ground after the output cap, you'll have some variation of a Lovepedal (COT50 AC Les Luis). Then you can put a 1k pot in series with the emitter cap and/or resistor to change their effectiveness. For some more fun, try a 10nf input cap for a very twangy sound. Try a bunch of different clipping diodes (symettical, asymetrical, also try them in series). Put a cap (47nF) in parallel with your diodes for soft clipping. Maybe even try adding a high cut next to your clipping section just to see how it works, that would be a resistor (10k) and cap (10nF) in series to ground.

I'm not knocking lovepedal, they guy does a good job showing how good simple circuits can sound and how versatile they can be.

Have FUN!

[Thecomedian]

One of your problems is too little resistance at the output past the DC decoupler. 1k is really tiny.

God damnit!

I forgot to change the value on that. It was supposed to be 100k.

Derp

lol. problem solved, then.

[chromesphere]

Hey Hallmar,

I'm currently learning common emitter amplifiers at the moment and put your circuit on breadboard.  I couldn't get it to work with the bias resistors of 100k and 220k.  Did you get this circuit to work?  With this combination I got no output at all.  Swapping the values to 1m and 100k (aka -> the lpb1) gave an voltage amplification of about 27 times and a current gain of 24.  200mv signal input and 5.44v output, with a dc offset of about 1.6v on the output.  I'm observing all this on an oscilloscope btw. 

Also, I tried removing the emitter resistor.  I know that lowering Re will cause an increase in gain.  I currently only have a square wave as an input which can be difficult to view clipping, but im pretty sure it clips.  maybe it wont clip with a lower input signal, but it looks like its clipping with the 200mv input.

Anyway, just thought I would share those observations.  I had it all in front of me and thought I would just type it up / you might find it interesting.
Cheers,
Paul

[Hallmar]

Hey Hallmar,

I'm currently learning common emitter amplifiers at the moment and put your circuit on breadboard.  I couldn't get it to work with the bias resistors of 100k and 220k.  Did you get this circuit to work?  With this combination I got no output at all.  Swapping the values to 1m and 100k (aka -> the lpb1) gave an voltage amplification of about 27 times and a current gain of 24.  200mv signal input and 5.44v output, with a dc offset of about 1.6v on the output.  I'm observing all this on an oscilloscope btw. 

Also, I tried removing the emitter resistor.  I know that lowering Re will cause an increase in gain.  I currently only have a square wave as an input which can be difficult to view clipping, but im pretty sure it clips.  maybe it wont clip with a lower input signal, but it looks like its clipping with the 200mv input.

Anyway, just thought I would share those observations.  I had it all in front of me and thought I would just type it up / you might find it interesting.
Cheers,
Paul

Hmmm, i got it to work on the breadboard but i'll try that resistor change see if it changes anything drastically.

So R2 is 100k and R1 is 1M?

[Thecomedian]

There must be something wrong with your values on schematic.

The voltage drop between base and emitter is only ~.6v and it needs to be at least ~.7v to turn on. I checked it in LTspice. The bigger you make Re from 220 to 20k, the larger the output signal is, from 10 microvolts to 2.0 millivolts by 20k on Re, which is still a de-amplified signal compared to the source.

Im getting 200mv Emitter with your original values.

I can change R1 in the voltage divider at the Base to 10k to have a 10k/100k voltage divider, and the output voltage rises to 155mv from the original circuit's 10MICROvolts, 10uv. Emitter voltage drops to 150mv, base voltage swings between 792 and 801mv.


I noticed that you forgot to put in the 1meg resistors to earth from input and output, so I simulated those as well, and got a Zero to 40 microvolt input from a 5mv source, and a -120+130nV output using all the other original values.

Collector voltage is ~247mv with .002mv variation due to the de-amplification.

removed the 1meg to ground input and output resistors against and it's 247mv on collector.

Changing the voltage divider of the resistors on base.


changing the size of emitter resistor

[Hallmar]

There must be something wrong with your values on schematic.

The voltage drop between base and emitter is only ~.6v and it needs to be at least ~.7v to turn on. I checked it in LTspice. The bigger you make Re from 220 to 20k, the larger the output signal is, from 10 microvolts to 2.0 millivolts by 20k on Re, which is still a de-amplified signal compared to the source.

Im getting 200mv Emitter with your original values.

I can change R1 in the voltage divider at the Base to 10k to have a 10k/100k voltage divider, and the output voltage rises to 155mv from the original circuit's 10MICROvolts, 10uv. Emitter voltage drops to 150mv, base voltage swings between 792 and 801mv.


I noticed that you forgot to put in the 1meg resistors to earth from input and output, so I simulated those as well, and got a Zero to 40 microvolt input from a 5mv source, and a -120+130nV output using all the other original values.

Collector voltage is ~247mv with .002mv variation due to the de-amplification.

removed the 1meg to ground input and output resistors against and it's 247mv on collector.

Changing the voltage divider of the resistors on base.


changing the size of emitter resistor

What program are you using to simulate?

Maybe workbench isn't exactly that good and i'm just bullshitting here.

[Thecomedian]

LTspice, a generic free spice simulator.

The sine waves are of 400hz frequency from 5mv in and taken between 1 and 100k output, which is a simulation in itself of a potentiometer, wherein you would decrease the lower resistance in direct propertion to increasing the upper resistance, such that the total series resistance to ground stays at 100k while the resistance to output goes from 0-100k.

What are you using as an input voltage?

[Hallmar]

I usually use 1v since a guitar pickup produces 1v rms normally(atleast with humbuckers).

[Thecomedian]

I have 2 humbies and active electronics on mine and it produces 5mv. This value also happens to work exceptionally effectively When playing through a typical Fuzz face, both literally and simulated.. soft distortion and "easy" hard clipping. If I run the sim for fuzz face again with a 1v signal it essentially becomes a square wave and there's no partial clipping on one side of the signal from one transistor and partial clipping on the other side of the signal when it passes through the second transistor, which is what leads to an evenly hard clipped sine wave as opposed to bricking the Sine into square waves, which is what a 1v input gave me   ...

note that I took this value by plugging in the cable, which activates the battery in circuit, putting two leads of a voltmeter against the tip and the ground, and then recording the averages of voltage output while hitting between 1 and 5 strings.

I wandered off to find some pictures.



The hard clipping signal is the "usual" one I can get from Fuzz face while using 5mv in. This is still a sine wave, but with the ends of it's peaks and troughs "clipped".



The square wave in this picture is what I get at 1v input... however it's not an even wave. There are massive lengths of peak, and very narrow trough, imagine the low/negative voltage side compressed 10x while the high/positive voltage side of the square wave is expanded 10x.