MiniBooster

[aziltz]

i apologize for the barrage of questions, i'm a newbie and completely unorganized.  I'm currently working on Jack Orman's Mini Booster.
i couldn't find the specified value for the C4 cap which goes from the gate of Q2 to the source of it i believe.  I substituted what i had on hand, and i have this on breadboard and it has TONS of gain, way too much i'm afraid. i'm not sure what i have on their now, its either 10uf or .1uf.  how does C4 effect the gain? should i try as close a value as i can find for C4? my selection is limited.

-Austin

[davebungo]

The mini-booster is a rendition of a not so well known type of amplifier known as a mu-amp.  It relies on the FET in the drain circuit behaving almost like an AC constant current source i.e. a very high impedance at AC and therefore very high gain.  If high gain is not what you want then this circuit (at least in an un-modified form) is not what you are after.

Modifying the capacitor you refer to will not make much difference although it will affect frequency response (lowering it will result in an increased -3dB LF roll-off point.  You will still get high gain at high frequencies.

[aziltz]

yeah i know its high gain, it just seemed pecular that i'm getting an amp on 5/6 sound when its set on 1.5 with the pedal volue set at 3.

[stm]

You can check the following info:

http://www.geofex.com/Article_Folders/modmuamp/modmuamp.htm
http://muzique.com/amproj.htm
http://www.geofex.com/Article_Folders/mosboost/mosboost.htm

[MetalUpYerEye]

it just seemed pecular that i'm getting an amp on 5/6 sound when its set on 1.5 with the pedal volue set at 3.

Dude, thats what a booster pedal does; boosts the signal going into the amplifier. If nothing else, it's bound to make everything louder.

[aziltz]

it just seemed pecular that i'm getting an amp on 5/6 sound when its set on 1.5 with the pedal volue set at 3.

Dude, thats what a booster pedal does; boosts the signal going into the amplifier. If nothing else, it's bound to make everything louder.

dude, i know what a booster does, but it doesn't make sense to get a HUGE sound out of an amp thats barely on with a pedal thats barely on.

[R.G.]

Dude! Kewl! You go!

Everybody knows that it doesn't matter how big the signal is, it's WHERE THE KNOBS ARE SET that matters.

[davebungo]

 ...

OK, lets go back to basics.  I assume that you have a volume pot on the output?

If so, when it is set to one end you should have full volume and when set at the other end you should have zero volume.  If that is not the case, then you probably have a wiring fault. 

There is no gain control as far as I can remember, so any decent signal going in will probably sound distorted at the output regardless of volume level.

[erick4x4]

Did you put in C6? I find many people are surprised by how loud, and how "dirty" this pedal can be, especially with C6. Try taking C6 out.

[aziltz]

C6 is there.  I found out that on the output pot (on the bread board circuit) i was using a linear version of what the schematic calls for (100k audio) so i think that my explain why i'm getting a lot of volume so quickly?

I've got some small hex shaped risers screwed to my pcb, whats the best way to secure those to the inside of the box? epoxy? what about making the board secure but removable?  i will probably transfer this to a different box some time down the road.

[Alex C]

Keep the knob set at 3, and use a sharpie to label "10" next to it.  Problem solved.


JB Weld is a good quick and easy epoxy for securing standoffs to the enclosure.  There exist some metal standoffs with threading on the inside, which can be used with small bolts through the PCB and into these standoffs.  This will hold it securely, but it can be easily removed in the future.

There are also smaller plastic (nylon?) standoffs which attach to the enclosure with adhesive and "clip" the board into place.  Small Bear has one or both of these, but appears to be down at the moment.

[RDV]

Dude! Kewl! You go!

Everybody knows that it doesn't matter how big the signal is, it's WHERE THE KNOBS ARE SET that matters.

ROTFLMAO! 

RDV

[aziltz]

Alright so my first build is complete, its in the box, and it works.  it is kinda sloppy but from the outside its fine. it does what its supposed to and its exactly what i was looking for in a booster.

however,
a) if i back off my guitar volume to halfway, with the pedal or amp gain up (not cranked, just not at minimum) i pick up radio stations, ? that doesnt happen with my other pedals.

b) sometimes the switch pops, i think if the switch moves in the hole and the threaded section loses contact with the enclosure.

c) if the box gets knocked my my hand or foot or whatever, the noise is heard through the amp.

this is my first build and i'm not sure how to handle these problems, any advice would be greatly appreciated.

[trevize]

b)
place a big resistor (let's say 1M-2M at least), on the input between the signal and ground, if you don't have room on the pcb do it directly on the jack.
that should prevent popping. for more explanations look at the articles on fuzzcentral http://fuzzcentral.tripod.com/.

He does two things that should be applied to every guitar stompbox related circuits: polarity protection and pulldown res to prevent popping.

[aziltz]

But that 1M is already on the pcb.

[aziltz]

i just openned it up, and my ground wire from the output has come loose from the board, and it looks as though another ground wire is scraping against the box itself, this could cause the handling noise maybe, and i think the loose ground wire for the out put could be whats picking up radio?

[aziltz]

Also, another question about the wiring up of boxes, i used the wire we had in lab, and it seemed to be breaking alot at the solder joint,  it wasn't braided, it was solid core.  Is braided the way to go? what gauge?

[steve b.]

i always use braided ---22 gauge or small bears solid core and u gotta read arons facts -----alot of info in there

[petemoore]

  Solid core...I use only resistor leads on the bottom of perfs..where it'll stay exactly straight or how it's installed, never getting moved at all.
  Just the act of bending solid core, can crack the 'outside walls', OT?: this is where all the electrical activity happens, almost completely, no electrical activity takes place under the surface of ...anything... including especially, wire, this is why there is stranded and tubular wire...the surface area of these types of wire is much greater than with thicker strands....
  Even before it breaks off, it is becoming more resistant, and 'wierd'...because those cracks go around the wire where bent...
  Suffice it to say that overbent [with stress cracks] solid core wire should be avoided or eliminated in general.

[tubewhimper]

Just the act of bending solid core, can crack the 'outside walls', OT?: this is where all the electrical activity happens, almost completely, no electrical activity takes place under the surface of ...anything... including especially, wire, this is why there is stranded and tubular wire...the surface area of these types of wire is much greater than with thicker strands....

Sorry to be so disagreeable...
but the 'skin' effect that you are talking about here only begins to be a problem at radio frequencies.  Audio signals (and DC voltages) simply do not exhibit this effect at all.  You can get some distortion of the wire's cross section, but most wire formulations won't 'crack' under normal circumstances.  I use 19-strand braided 99%-silver over copper for my amp work... but still prefer a lot of solid-conductor wire in FX boxes.  Ever look inside a box made by David Barber?  You will find a lot of solid-core buss-wire used and he is very highly respected in the stompbox biz. So you gotta ask yourself why he would take a chance like that if it were mechanically unsound.

There is more of a problem with wire detaching itself (by flexing) in and around the pedal from the controls to the PC-board in my experience. YMMV!