circuit requiring hitting to work

[antonis]

My nails are very short so let's take a deep breath and try to lightly scratch the surface of "bias"..

A BJT can be set to work on 4 regions:
1. Cut-off (no current through it, dead..)
2. Saturation (full current, alive till its death comes very quickly ..)
3. Reverse-active (like in your schematic, zobie of good intentions..)
4. Forward-active mode (alive and well, you can call it "amplifier" ..)

All 4 above regions can be obtained via proper bias configuration..
(we order transistor to do a job, hopping it will obey us..)

That order is, in his vast majority, implemented by adding a DC voltage on transistor's Base..
This voltage "activates" a Collector current (of h_FE times Base current) so we can set any of the above 4 regions (working conditions)..
(well, almost 'cause region 3 needs more than this..)
Now, we have to deal with transistor type (n-p-n or p-n-p)
Conventional current flow is considered from Collector to Emitter for n-p-ns and from Emitter to Collector for p-n-ps..
The above said, we also have to take into account power supply polarity in conjunction with BJT type..
(even if we DO wish region 3 operation..)

For an effective bias orded implementation, there are various resistive configurations (read attachments below), all of them having to do with famous/notorious Quiescent point..(the "idle" working state..)
This DC Q point is set according to the intented use and Collector voltage (for CE amp) can vary above & below of it..
(more of DC & AC line in attachments below) 

https://www.electronics-tutorials.ws/amplifier/transistor-biasing.html
https://www.electronics-tutorials.ws/amplifier/transistor-biasing.html
https://en.wikipedia.org/wiki/Bipolar_transistor_biasing
https://www.allaboutcircuits.com/textbook/semiconductors/chpt-4/biasing-techniques-bjt/

All in all, we can't just kick, in cold blood, the Base of a BJT without, at least, some explanation for our impolite action..
(in case of our explanations are fairly good, we might get forgiven - we even might meet our task with success, who knows..)

[11-90-an]

Thanks  @antonis !! 

[antonis]

To stay close to your original design..




P.S.
Define the role of all resistors (R5, R6 excluded..)
(weekend homework..)

[willienillie]

^


And maybe move C7.

[11-90-an]

To stay close to your original design..




P.S.
Define the role of all resistors (R5, R6 excluded..)
(weekend homework..)

THANKS !!!!  :icon_lol:But there's a problem though, i happen to not have a 100k pot, can i use a 10k pot instead? also, can the 470k resistor be replaced with a 560k ? otherwise, I already have everything else.

and for the resistor uses, 
1, 2, 7, 8 - voltage divider bias circuit
4, 9 - collector feedback bias circuit

[antonis]

And maybe move C7.

Do you mean move it before diode pair of delete it..??

Thank's for the coffee - Q2 Collector should feel grateful also..

[antonis]

You shouldn't ask about 470k/560k replacement in case you've indeed read about feedback bias configuration..
(its value is depended on particular BJT current gain and is set by [(Vcc/2 - 0.7) X h_FE]/I_Collector..)

So, 470k is a safe "estimation" for h_FE of about 200 - 560k should also do the job fine..
(it might move Collector quiescent voltage up or down a bit but, afer all, we deal with fuzzy stage..)

10k pot should be OK after an Emitter folower (buffer) but here it "loads" R4..
(you can considered either in parallel with Q2 Collector resistor or in parallel with next effect imput impedance - in both considerations, its low value dominates Q2 stage Gain..)

You can try it as it is but, IMHO, you'll not get satisfactory results..
One modification could be the use of much higher gain Q2 (much lower R4 value required..) to be "immune" or R6 low value..
Another (lousy enough) mod could be the addition of a series resistane (47k -56k, say) with R6 upper lug..
It will cut down Volume setting range significantly so proceed under your own risk - do not try it using headphones..)

P.S.
Pay attention to  willienillie's cup of coffee and move C7 before D4/D5 pair..

[11-90-an]

So.. I finished desoldering everything from the pcb and all the parts still have long legs(i anticipated having to desolder everything from the start) so this pcb was the last one that i have, and also i have near-0 solder left. Would it be better to reuse this pcb, buy another prototype circuit board, or design and print specifically for this application? After breadboarded everything of course...

Here are some pics

[antonis]

I don't presume there is need for printed board for such a simple buid..
I don't suggest also re-usage existing board..
(it needs very scrupulous cleanup both for solder residuals and oxidized/corroded pads..)

[jfrabat]

Listen, do not fret.  I have been exactly where you are at (and not long ago!).  Most of what the pro's discuss here is WAAAAY over my head (like trying to understand how transistor works!  Sorry, Anotnis, but even your explanation was tough for me to follow!), but every day, I learn something new that is useful, and I keep going. 

If you allow me, I would recommend you read and maybe breadboard this:

https://www.premierguitar.com/ext/resources/files/Oct14_PGDistortion_BuildGuide_Final_R2.pdf

I thought it was a great introduction to guitar pedal building, and I even ended making my second pedal from this one (my first pedal "sort of worked" and I still keep it, but in all honesty, it sounds HORRIBLE!  This one is still in the pedal board - with many tweaks, of course!!!).  It will teach you what each part does, and allows you to play with different choices (like caps, transistors and resistors) to teach you to tailor to your tastes.

And do not feel bad about your soldering; practice makes perfect.

This was me starting to solder:



This is the same circuit (different board layout, but same circuit) some time later:



I still make a mess of things in that type of PCB you are using, though, which is why I taught myself Eagle and now I have my PCB's printed.  But that is a different topic!  A good soldering iron helps A LOT here too.  But you do not need one to start.

The other word of advice I can give you is that if it does not work perfectly on the breadboard, do not even bother with it on a PCB.  It will only make chasing the issue more difficult.  Other advice include making yourself an audio probe, and getting a multimeter with a continuity sensor.  And lastly, only about 10~20% of my PCB's work right out of the gate.  Typically I made some stupid mistake with polarity, have a solder bridge or some other issue that I have to troubleshoot.  People here have been great at helping me solve these, but they need info, which means voltage readings at different points, which, again, means a multimeter...

[11-90-an]

Listen, do not fret.  I have been exactly where you are at (and not long ago!).  Most of what the pro's discuss here is WAAAAY over my head (like trying to understand how transistor works!  Sorry, Anotnis, but even your explanation was tough for me to follow!), but every day, I learn something new that is useful, and I keep going. 

If you allow me, I would recommend you read and maybe breadboard this:

https://www.premierguitar.com/ext/resources/files/Oct14_PGDistortion_BuildGuide_Final_R2.pdf

I thought it was a great introduction to guitar pedal building, and I even ended making my second pedal from this one (my first pedal "sort of worked" and I still keep it, but in all honesty, it sounds HORRIBLE!  This one is still in the pedal board - with many tweaks, of course!!!).  It will teach you what each part does, and allows you to play with different choices (like caps, transistors and resistors) to teach you to tailor to your tastes.

What transistors did you use for this? The 2n3904? I am thinking of ordering that online because it seems like a very useful transitor...

[11-90-an]

So now im gonna order some parts online...
Any other essential transistors other than 2n3904, 2n3906, bc547, bc557, that i should get?

[garcho]

Get some MOSFETs like 2N7000 and BS170

[11-90-an]

Get some MOSFETs like 2N7000 and BS170

No MOSFETs only BJTs

[antonis]

No MOSFETs only BJTs..

THAT'S THE SPIRIT..!!! 

P.S.
Waiting for Sir Mike to slap our hands..

[11-90-an]

THAT'S THE SPIRIT..!!! 

hahahaha...
what i mean is that the place that im ordering doen't have any MOSFETs. They only sell BJTs...




anything useful for pedals here?

[antonis]

Almost all of them..!!! 

(although, many of them can be considered of "equivalent" usability - like BC547 to 550, BC556 to 558, etc..)

[11-90-an]

in some circuits that require a tl072 or a tl074, is it possible to just use 2 or 4 transistors like 2n3904s?

or any others in this list?

[antonis]

Unfortunantely, you'll need much more transistors for TL07X simulation..
( JFETs included..)

In general, you could build basic op-amp stages (differential input, voltage amplifier, emitter follower(s) output but I'm pretty sure you shouldn't wish to mess up with all those nasty blocks for the time being..

[11-90-an]

Unfortunantely, you'll need much more transistors for TL07X simulation..
( JFETs included..)

In general, you could build basic op-amp stages (differential input, voltage amplifier, emitter follower(s) output but I'm pretty sure you shouldn't wish to mess up with all those nasty blocks for the time being..

Thanks @antonis!
Right now i will buy:
8 x 2n3904
2 x bc547
2 x bc557
5 x 2n3906
Do you think this is enough? Or more transistors needed?