Weird pedals

[ambulancevoice]

for any chance doug, do you still have the old red poorly drawn version of the rng?
i would just like to see how the 2nd pot is wired

[calculating_infinity]

Ok I took the time to read how to wire the pot up right  .  So you can ignore that question.  Still trying to figure out which 100k to sub out (at work).  I read an old post saying it was "the bottom one".  I am going to assume that it is the 100k in the bottom of the schem that comes from collector of the pn2222, which goes to the .01 output cap.  I'm still kind of a newb but really I'm trying to learn  . 


Thanks,
-Jonathan

yep thats the one!
so just wire up the pot as a variable resistor and put it in the place of the fixed resistor.
i wouldnt worry about not getting this circuit and being a "NOOB" 
the circuit doesnt really make much sence to begin with, i didnt really have to much design knowledge when i came up with it, and it was a whole lot of sticking stuff in randomly till i got something cool.
but it does sound pretty insane and unique.

I wired it up with both pots and I like the extra pot, it really makes a difference in my build.  At one end its really trebly high pitch with some glitchy lower octaves randomly.  At the other is almost a constant lower octave and less random glitchyness still fun!  I'm just waiting for some enclosures to get in the mail and finish the build.  I actually made one then desoldered when I found out about the 2nd pot.  I couldn't get it to work so I set it aside and made another one.  I ended up getting the other one fixed so now I have two!     I use all 2N9304s and there is constant noise.  I think I need to get lower hfe trannies like doug suggested in an earlier post.  IIRC the 2N3904's I put in had hfe's ranging from 220-320 which I assume is pretty high.   Anyways have good luck and have fun! 

-Jonathan

[Hambo]

It is really excellent to see people pushing this design around a bit. I always liked the sound but find it a bit hard to use other than in controlled bursts, so I'm really interested to see what happens here . I did build a second myself with sockets for all the transistors, but I found it made little difference what was in there.. then when I put the specified trannies in, technically it should sound the same.. but no, its totally different to the first one I built, in a not very excellent sort of way... I gave up a bit then to mess about with some other stuff (Uglyface )

Might have to dig this out again if I can get some time.

[ambulancevoice]

yep thats the one!
so just wire up the pot as a variable resistor and put it in the place of the fixed resistor.

I found that this pot didn't made much difference to the sound on mine. Since I had the space on the side of the box, I removed it and put in pots in place of the collector resistors on the first 3 transistors. Lots of different sounds now - and the overall output is so huge you can cut the voltages right down and it still makes a huge noise. Reducing power to 1st resistor cuts some of the ear-blistering highs, but maintains the roar. Liking it!
I've tried lots of diff transistors in mine and they change the sound a LOT, especially 1 & 2. Worth messing with.

which collector resistors?
the ones coming from the base to collector
or the ones going off the collector
(not the power supply ones btw)

[doug deeper]

ok here is an updated schematicwith the second pot.

[doug deeper]

and youcan hear a clip of how it should sound here:
midfielectronics.com

[smnm]

which collector resistors?
the ones coming from the base to collector
or the ones going off the collector
(not the power supply ones btw)

... sorry to be so imprecise, I didn't have the schematic in front of me when I posted - I did mean the resistors going from the power supply TO the collectors - having three pots does make any kind of consistent control difficult, but that's hardly the point for this pedal, and it's good for maximum variability - I'm digging the starved transistor sound, reminds me of the horrible/great Swell Maps (uk punk/post-punk/avant band of the 70s) gtr sounds.
Pots on the base to collector resistors you mention would also alter the interaction of the 3 also, though (I don't know how, but you could try it....)

[ambulancevoice]

so you replaced the fixed power to collector resistors with pots right? and that yielded interesting results?
sorry, id like as many pots of possible to get as many sounds as possible
since with the "music" i do involving alot of knob twiddling

[caress]

i think what smnm meant was to add a voltage starve pot...if you want to add more knobs you can always add a switch and pot wired between the in/out for feedback control.  also try adding diodes in feedback loops in various parts of the circuit, maybe a cap to ground at the end, send the collector of one transistor to the base of an earlier one, etc etc...

[ryanscissorhands]

My suggestion would be an Uglyface with an optional footpedal to control the frequency. That would certainly give you a sick-sounding, controllable nasty fuzz-like sound.

[mattpocket]

Seems like some interesting ideas floating around here.

if you want to add more knobs you can always add a switch and pot wired between the in/out for feedback control.

what is feedback control? and what would this pot do for the sound. where would I connect it?

also try adding diodes in feedback loops in various parts of the circuit,

what does this involve a simple diode in line, where would I hook each end of the diode up to?

maybe a cap to ground at the end

what would this achieve?

send the collector of one transistor to the base of an earlier one

again, what would this do? would you have this as an additional connection or as a sub for the other collector-base connections.

Matt

[caress]

all of those "mods" that i offered may or may not do something interesting... 

using feedback is super simple - wire the input to the output with a switch and pot in between.  this may do nothing, create some subtle instability or just start the pedal oscillating.

adding diodes...just experiment with this.  you can add two diodes (ge, si, leds) in a feedback loop (neg end of one facing the pos end of the other) from the base to collector, from emitter to ground, from any point in between two transistors to ground, after the last .01uf to ground...?  i don't know if this will do anything significant...might just add some different harmonics in the clipping?

a cap to ground after the last .01uf makes one of doug's other pedals (garagefuzzz) freakout and start oscillating and creates octave drops, etc...so i figured it's worth a try.

the collector to base is just another form of a feedback loop.

EDIT: *most of these additions will make a pedal kind of freakout or start oscillating in some way...maybe this is useful to you , maybe not.  it's worth noting, too, that in the past i've added feedback loops and diodes to ground in pedals and the diodes act as a gate for the oscillation so that it stops when you're not playing.  that was definitely useful...*
for any of these, i would recommend trying some different ideas out without actually soldering anything.  if you find something you like, add a switch or a pot.  i wish i could technically tell you what was happening in these circumstances, but i don't know enough to say...i'm just trying random shit out.     hope this helps...?

[mattpocket]

trying random shit out... this is the way forward!

I love experimentation... if you do it to a toy, its arseing around with circuitbending, if you do it to a pedal, its design! haha

[doug deeper]

the cap to groud thing only work in the garage fuzzz because the last stage is a negister (a type of oscillator)
and with out the extra cap its set to oscillate just out of hearing range.

[caress]

ahhh ok

[2wm]

hello. i'm new here and i just attempted to make a pcb design for the random number generator. can you guys tell me if this looks right?

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[mattpocket]

The trace coming down from C3 heading to the pot/feedback resistor is going to ground. This should not be the case. Also the grounds from Q1 & Q2 go to one trace, and then there is a ground trace running underneath. This is unessecary. You could fill in the space to make a larger ground plane, or just remove the top trace and connect the grounds to the bottom one. The way in which you have connected Q3 and Q4 is also a bit suspect. You have connected the emitters and then took the emitter of Q3 to ground. This might cause problems, although I am unsure of how. I would try to make a more direct route to ground.

I dont know if you know this, but when there is a "hump" in a schem where two "wires" cross it means that they are NOT connected. If there is a dot or no "hump" then they are connected. This could be why you ran into problems with the feedback section.

The feedback resisitor is a problem when creating a small layout. I made a really tiny layout for this, unfortunately I have lost it. It involved bending the transistor legs so that they are in the triangular position (rather than in line). In this case you can then "thread" the feedback loop through the legs of the transistors.

You also dont need the connection between r9 and c4. just connect r9 to the collector (as it is now), leave c4 where it is and just break the trace as shown on my drawing.

R6 also needs to be connected to the collector of Q3.

The feedback pot should also have two of the pads connected together although there is an easier way around this which I talk about below.

I have doctered your layout to show you where you've gone wrong. The change will mean you need to wire your pot differently. To make a variable resistor (as is required for the feedback loop) you wire one outside lug to the middle lug. Then just take one wire from the middle lug, and one wire from the outside lug (this must be the one that isnt jumpered to the middle lug). This means you only need two pads on the pcb, instead of three (as one connection is made at the pot).

You have also put three pads on for the volume pot, when you only need two. One pad by c4 (which you already have) and one pad on the ground plane (which you already have). One outside lug is connected to each of these pads, and the middle lug then becomes the board output which you wire to your stompswitch.

Also here is some advice about pot lugs on schematics that someone gave to me:

If they are not numbered on the schematic then it is not certain, but most of the schematics here use a convention that the lugs are numbered 1,2,3 from the bottom to the top:

  | 3
  |
  \
  /
  ---- 2
  \
  /
  |
  | 1

Then if you are looking at the back of the pot with all lugs pointing down, they are numbered 1,2,3 from right to left.

Take a little look at this, I might have made mistakes too, its pretty early, I havent finished my coffee and just got to work! haha



Hope it helps,

Matt

[Dan N]

Whille your pot lug numbering is correct, lug #1 should go to ground so the volume gets louder when you turn clockwise.

[mattpocket]

Lug one does go to ground? 

[Dan N]

Lug one does go to ground? 

Yes. You have it going to C4. Your way will still work, but it will get louder as you turn counter clockwise. Maybe more fun that way?