need some help with buff n' blend + muff fuzz pedal

[Kipper4]

Ooops

Here's the article


https://learn.sparkfun.com/tutorials/how-to-read-a-schematic

[okuzster]

Let's look at a bit of the circuit

In this post I'm using the schematic from Guitarpcb

Link to the doc
http://www.guitarpcb.com/PDF%20Files/Buff%20N%20Blend.pdf

R1 is a large resistor to discharge the charge held by the capacitor c1 when the effect is switched to bypass, so as the true bypass switch does not pop when you turn the effect back on

C1 the input capacitor (cap for short) somewhat shapes which freqauncies go through from the guitar to the circuit.

R2 R3 are two equal value resistors. One hooked up to the positive rail +9v the other is hooked up to ground (gnd) this is called a voltage divider.
Ohms law (google it) the single most important piece of math theory a stomper will use.
Ohms law tells us that the node (place where the two resistors meet in the middle)
Will be half of our supply voltage.
When using +9v
This shows us that the gate of the fet which is connected to the same node will sit at 4v5 (another way of saying 4.5V)
So now we know that the transistors gate should sits at 4v5
Now look at the drain Q1 it is directly hooked to the positive rail +9v
So we know what two of the voltages on the fets legs are.


Can you see anymore voltage dividers?

For info capacitors block the passage of DC volts. But let AC volts through.

Please note this is not an exhaustive explanation of what everything does. It is just aimed at getting the reader interested enough to want to know more.
An exhaustive explanation would be beyond my pay grade.

I hope this helps someone, if anyone else wants to chip in feel free and if I'm wrong about anything
Chip in too.

Rich

on my schematic there is no switch, so no need for r1 i think.

about c1, is it work like tone caps on guitar tone pots? if so lower/higher value for lower/higher freq?

i am getting the voltage divider slowly, but on my scheme 9v goes to drain same as the scheme on guitarpcb, but my 4v5 goes to source, not gate. thinking this is my problem.

about voltage dividers, is 50k pot and r7 works as voltage divider for return? and also, my pot is 22k if i remember right, how is its value effect? is it ok as long as it's smaller than r7?

gonna sleep now and will dig more tomorrow

[Kipper4]

The true bypass switching is often omitted on schematics. It's how most of us switch the effect on and off.
So I'm not surprised.

The tone cap on a guitar functions like a RC filter (google that too)
The C1 cap if made bigger will allow more of the Lower freqauncy through and vice versa.
Once you have the breadboarded circuit working you can change the C1 cap and see what a difference varying this cap will do to your signal.

The R2 R3 node should definitely go to the gate. Consider the gate like a fets input.
The source is going to gnd via the resistor.

Yes the pot 50k and R7 form a voltage divider. And R5 R6 also form a voltage divider.
Well spotted.

As for the 22k pot maybe your using a different schematic.
Even so if you used a 22k pot in the schematic I posted it should still pass signal.
You can always adjust r7 on the breadboard later to compensate.
Meantime let's get it working.
I can't wait to see how you get on when you get back to the workshop.

[duck_arse]

okuzster - I love this diagram, I'm sure it makes perfect sense to you, and your pcb looks very well done - is it cnc milled/router-ed?


but I can't read it. there are programs for laying-out and making pcb's (DIYLC is one example) and others that do both schematics and boards (Eagle, not for beginners tho) and still others that are web based for circuit diagrams only ( fritzing or something?) (there are even simulation programs, will let you draw a circuit, then run it on the computer to see what does.) when you use those agreed upon squiggles, we all speak the same language, and there are plenty people here can/will help you get good using those programs.

when you say:

.... transistor is 40v, looks exactly like this ....

do you mean it is marked J201?

[okuzster]

i have a small laser cutter(cnc). painted pcb to black and draw the lines with laser (it removes paint but cant do anything to copper). then put pcb to HCl+H2O2.

i just googled DIYLC and watch a tutorial, looks easy, will check it soon. thanks, i was aware of this kind of programs but didn't want to go for a learning process but now i can see it's worth to go for it. fritzing is also looks nice. can you say what is best software for simulating for a beginner? i would like to try them also.

and yes, it's marked J201. and also other letters/numbers same as the one on the picture.

[okuzster]

i re-arrange breadboard circuit with this schematic only missing r1 and led part,



while battery attached, drain is 9.7v, gate is 3.25v and source is 0.

that 0 is not sound right to me, 3.25 is also meh, is it my resistors? my multimeter is very cheap one, so i cant truly trust it but when i test 1m resistors it jumps between 800k to 1200k, so they should be fine also.

by multimeter from source to ground is 3.2k ohm also.

on the output, there is no guitar signal this time (with battery or not), but there is more noise when pot is on the middle position.

what can be the problem here? is it some component not working right? is it me that making a mis-wiring. since i never made a stompbox yet, it can be the most basic thing i must know but cant figure it out now.

edit: when i connect out to gate, i can get the sound. but when i connect it to source, nothing. so is it transistor?

[okuzster]

i put a jumper from gate to source and disconnect battery. now it's kinda blends.

[okuzster]

i was thinking about simplest blender without buffer, so thought that;



just like a splitter and a pot, and for the feedback a diode maybe? what would be the negative side of this?

i just tried it with 1n4007 diode but sound signal is not go through it. is it because voltage is too low?

[Kipper4]

Double check the 3k3 is connected to both gnd and the source.
I can't remember what voltage I'd expect to see at the source off hand and im away from home so can't breadboard it to check.
I guess though one would expect to get a source voltage around 2v7 if your gate is around 3v5.

A jumper form gate to source is just bypassing the transistor altogether.

You could make a passive blender but I don't think t would work out too well.

Maybe someone else can confirm the type of voltage one would expect to see in a working circuit.
Just for kick try another fet too in case you fried it in an earlier experiment.

[PRR]

Your OUT jack has big DC on it. This is rude to whatever it goes to. Some goes-to will load-down the DC and make Q1 very unhappy. Put a cap in there.

[bluebunny]

just like a splitter and a pot, and for the feedback a diode maybe? what would be the negative side of this?

i just tried it with 1n4007 diode but sound signal is not go through it. is it because voltage is too low?

The diode won't start to conduct until you reach its forward voltage, V_F.  This is 1.1V for a 1N400x.  And of course it won't conduct at all when the signal swings the other way (which it does, half the time).  So you'll only ever get half your signal, if it's loud enough.

[okuzster]

Your OUT jack has big DC on it. This is rude to whatever it goes to. Some goes-to will load-down the DC and make Q1 very unhappy. Put a cap in there.

sorry, i couldnt follow. which schematics are we talking here, and where to put cap?

The diode won't start to conduct until you reach its forward voltage, V_F.  This is 1.1V for a 1N400x.  And of course it won't conduct at all when the signal swings the other way (which it does, half the time).  So you'll only ever get half your signal, if it's loud enough.

i got it. so what is the best way for what i am trying you think?

[duck_arse]

in the Bruce R circuit, the "send" jack tip is directly connected to the fet source, which is supposed to be some volts DC. the thing attached to the send jack won't like all the DC fed to its input, so you need a cap between the jack tip and the R4//C2 junction to block DC, and allow the AC.

[okuzster]

so it's like this



should the cap value be like c1 or c2? (nf/uf scale) or should i test and see?

[Kipper4]

C1 value will be fine r a 100nf no need to go bigger.

[okuzster]

i ve tried everything i can think. i am thinking whole batch of j201 is broken. i am a bit confused on how to test them. anyone can help me on that?
i also try another transistor, 2n3904, dont know if it should work that way but still not working.

[duck_arse]

I hate to tell you, but the best way to test your fets is to put a circuit just like this on the bb, plug in the parts and see what voltages you get, then put audio and listen to the result.

is there something connected to the "send" jack? disconnect the send jack and C2 so you have just three resistors and a cap and the fet. remeasure your voltages. also measure the resistance to ground from the fet source pin - NOT on the resistor legs.

[duck_arse]

the 2N3904 should work, if you connect the collector where the drain should be, and the emitter where the source should be. if you put that in and measure the voltages, it may dis/prove something.

[okuzster]

I hate to tell you, but the best way to test your fets is to put a circuit just like this on the bb, plug in the parts and see what voltages you get, then put audio and listen to the result.

is there something connected to the "send" jack? disconnect the send jack and C2 so you have just three resistors and a cap and the fet. remeasure your voltages. also measure the resistance to ground from the fet source pin - NOT on the resistor legs.

i didn't get why you hate it.

so i should test it when there is only the fet, a cap and 3 resistors, and battery of course. what values should i get for it?

[Kipper4]

It's gonna take 5mins at the breadboard.
Try it and see, report back with the voltages.
Thanks

J201 pinout is in reply no3 here

http://www.diystompboxes.com/smfforum/index.php?topic=62210.0