No sound at all on double-checked superbasic distortion circuit...

Thread Starter

Vicc

Joined May 24, 2020
13
Hiya all,

Decided to build my very first distortion pedal and found this easy-to-follow DIY guide with schematic and all (attached here); the circuit needs a 2N3904 transistor, two 104 capacitors and three 1/4-watt resistors (470R, 68K and 2.2M). As I couldn't find all the exact same components, I bought a 2N4001 instead as well as 1/2-watt resistors. I'm in the breadboarding phase (see attached photo) and I've double checked everything from properly identifying the CBE terminals to continuity issues using my multimeter, battery charge if full, guitar/amplifier connections, settings, etc. OK. I'm assuming the problem lies with those 1/2-watt resistors although I don't understand the reason why there's no sound at all when signal goes through the circuit...

Any help would be greatly appreciated.
 

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Papabravo

Joined Feb 24, 2006
13,728
There is no bias on the transistor base. Where did you get the circuit? Better Homes & Gardens?
Use voltage divider bias and set the Q-point at Vcc/2.
One more thing, you might want to reduce the collector resistor and bypass the emitter resistor.
 

AlbertHall

Joined Jun 4, 2014
9,873
There is no bias on the transistor base. Where did you get the circuit? Better Homes & Gardens?
Use voltage divider bias and set the Q-point at Vcc/2.
One more thing, you might want to reduce the collector resistor and bypass the emitter resistor.
The transistor gets its base bias from the collector. This method stabilises the bias against differences in transistor gain (to some extent).
LTspice using a 2N3904 gives about 1.46V DC on the collector and a gain of just short of 100. So the circuit should work.
I can't see from the photo just how the components are connected on the breadboard so I can't tell if it matches the circuit.

[EDIT] using 0.5W resistors will not affect the circuit at all.
 

Papabravo

Joined Feb 24, 2006
13,728
The transistor gets its base bias from the collector. This method stabilises the bias against differences in transistor gain (to some extent).
LTspice using a 2N3904 gives about 1.46V DC on the collector and a gain of just short of 100. So the circuit should work.
I can't see from the photo just how the components are connected on the breadboard so I can't tell if it matches the circuit.

[EDIT] using 0.5W resistors will not affect the circuit at all.
There wont be much bias current through the 2.2MΩ resistor and as soon as the transistor starts to conduct that current will drop like a brick in the rain
 

Audioguru again

Joined Oct 21, 2019
1,491
How can you see which connects to what in that messy tangle of breadboard parts and wires all over the place??
I simulated it with a low impedance signal source with levels of 12mV peak and 100mV peak. No load.
Of course the low input level produced low distortion and the high input level produced severe clipping.
 

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Thread Starter

Vicc

Joined May 24, 2020
13
Awesome man! Thanx for the simulation...

I'll try changing that 2.2M resistor as indicated by Papabravo with say a 68K or 10K...
 

Audioguru again

Joined Oct 21, 2019
1,491
Your circuit does not work probably because the mess of wires on the breadboard are connected wrong. You never said the level of your input signal or what it comes from (a guitar pickup without a preamp?).

Reducing the value of the base bias resistor will result in the transistor turning on more therefore its collector voltage will be less.
The bottom of the signal waveform will be badly clipped and the output level will be low.
 

MisterBill2

Joined Jan 23, 2018
6,071
Hiya all,

Decided to build my very first distortion pedal and found this easy-to-follow DIY guide with schematic and all (attached here); the circuit needs a 2N3904 transistor, two 104 capacitors and three 1/4-watt resistors (470R, 68K and 2.2M). As I couldn't find all the exact same components, I bought a 2N4001 instead as well as 1/2-watt resistors. I'm in the breadboarding phase (see attached photo) and I've double checked everything from properly identifying the CBE terminals to continuity issues using my multimeter, battery charge if full, guitar/amplifier connections, settings, etc. OK. I'm assuming the problem lies with those 1/2-watt resistors although I don't understand the reason why there's no sound at all when signal goes through the circuit...

Any help would be greatly appreciated.
For this circuit to do anything at all the input signal needs to have an amplitude high enough to drive the transistor into conduction. The output from an electric guitar pickup is not high enough to do that with the circuit shown.
AND I could not tell anything from the photo of the prototype.
If there was any description of the application of the circuit, that should have included something about the required driving voltage.
It does seem like the value of the base bias transistor is much too large.
 

AlbertHall

Joined Jun 4, 2014
9,873
Awesome man! Thanx for the simulation...

I'll try changing that 2.2M resistor as indicated by Papabravo with say a 68K or 10K...
If this is supposed to produce distortion leave the values as they are. For low distortion you bias the transistor so the collector sits at half the supply voltage, but when distortion is the aim then having the collector at a low voltage helps.
 

Audioguru again

Joined Oct 21, 2019
1,491
My simluations show that the circuit works fine with both transistor numbers. The distortion is high when the input signal is only 100mV peak which is easy from an electric guitar pickup but impossible from a microphone. The transistor biases itself.
 

Thread Starter

Vicc

Joined May 24, 2020
13
As stated, the connections on the breadboard were double-checked, so that was not the issue. I replaced the 2.2MΩ with a 470R though, still nothing. But when I changed that back and then decided to use the 470Ω as the R2 resistor, I could now hear sound through the speaker, almost imperceptible, even if I crank up my amp's volume from 10 to 11 it's definitely not distortion at all! The only logical explanation, at least for me, lies in those 1/2-watt resistors I'm using.

I want to thank everyone for your input. I'll post any update as long as I acquire some of those pesky 0.25-watt resistors...
 

AlbertHall

Joined Jun 4, 2014
9,873
As stated, the connections on the breadboard were double-checked, so that was not the issue. I replaced the 2.2MΩ with a 470R though, still nothing. But when I changed that back and then decided to use the 470Ω as the R2 resistor, I could now hear sound through the speaker, almost imperceptible, even if I crank up my amp's volume from 10 to 11 it's definitely not distortion at all! The only logical explanation, at least for me, lies in those 1/2-watt resistors I'm using.

I want to thank everyone for your input. I'll post any update as long as I acquire some of those pesky 0.25-watt resistors...
Changing the power rating of the resistors will not make any difference at all.
 

djsfantasi

Joined Apr 11, 2010
6,427
It’s like replacing your low voltage wiring (22g) with 10g wire. The wire is doing it’s job regardless of the wire gauge, electrically connecting two points.
 

Audioguru again

Joined Oct 21, 2019
1,491
Problems:
1) You say you used a 2N4001 transistor and it has an old metal case but your photo shows a plastic case transistor. 2N4401?
2) You said the transistor pins are CBE but a 2N3904 and a 2N4401 have EBC.
3) You did not say what (an electric guitar pickup?) produces the input and its level.
4) You did not say the output load resistance.
5) You did not measure and say the battery and collector voltages.
6) We cannot see which connects to what on the breadboard.
 

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MisterBill2

Joined Jan 23, 2018
6,071
Problems:
1) You say you used a 2N4001 transistor and it has an old metal case but your photo shows a plastic case transistor. 2N4401?
2) You said the transistor pins are CBE but a 2N3904 and a 2N4401 have EBC.
3) You did not say what (an electric guitar pickup?) produces the input and its level.
4) You did not say the output load resistance.
5) You did not measure and say the battery and collector voltages.
6) We cannot see which connects to what on the breadboard.
7) ALSO, most of the folks participating have poor mind-reading ability, and so there is a whole lot about the project that we are not able to know.
 

Thread Starter

Vicc

Joined May 24, 2020
13
Problems:
1) You say you used a 2N4001 transistor and it has an old metal case but your photo shows a plastic case transistor. 2N4401?
...
Could you please indicate WHERE EXACTLY did I state the 2N4001 had an old metal case?

7) ALSO, most of the folks participating have poor mind-reading ability, and so there is a whole lot about the project that we are not able to know.
Would you care ELABORATING on what else would you want to know about this project besides being a distortion circuit for my very first distortion pedal?
 

Audioguru again

Joined Oct 21, 2019
1,491
You said 2N4001 transistor that I never heard about before so I searched for it in Google. Here is a photo of the old thing.
The best way to troubleshoot a single transistor circuit is to measure the battery and collector voltages.

What is feeding its input and with how much signal?
What is connected to its output and what is its resistance?
 

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