My turn to ask for help - Basic Fuzz Face

[italianguy63]

Gator finally got me.  I have a regular white bread fuzz face (no part subs) that no worky.  PNP positive ground.

Powered by a charge pump, and that portion works.  I am using Russian trannies, with a twisted pin-out, but I have another proto I built that works.  So I am 99% sure I have the trannies in right.

Getting nothing but buzzing (noise). strangely noise in bypass mode too.

I have +9.22V at battery
-8.89V coming out of the back of the Charge pump section.  So, OK there.

Q1
B:  -.19V
E: 0V
C: -.92V

Q2
B: -.92V
E: -.84V
C: -8.76V

Adjusting bias resistor (pot - 10K) gives me a range of voltage at Q2 - C from -8.65V to -8.86V 

Ideas?

MC

[PRR]

Q2 is not conducting.

A possible cause is a way-wrong (high) value for Q2 emitter resistor. Tack a 1K fixed resistor in there and see if anything changes.

[italianguy63]

From where to where Paul?

[italianguy63]

I don't know where my post went.  But I figured out the buzzing.  Bad ground on the output jack.  Wiring and solder joints look fine.  Maybe a bad wire somehow.  When I jumpered the jack to ground-- the noise all cleaned up.  But, now silent when the effect is on.  Same voltages prevail.

MC

[italianguy63]

Getting somewhere.  Paul, used the 1K jumper from Q2E and poked around.  Nothing until I crossed the .01uF pass capacitor at the Level Pot.  Once I go on the other side, all kinds of signal.  No signal passing the cap.  Maybe a solder bridge (although I don't see one) or a bad cap.  I will desolder it and throw another in and see what I get.

MC

[italianguy63]

Not the cap.  Replaced it, same situation.

[italianguy63]

Bad Q2?

[italianguy63]

If it matters... when I jump signal-- bias pot makes changes in tone.  Level pot works.  But, Fuzz pot has no effect.

[LucifersTrip]

To get nearly 9V on Q2 C (should be around 4 - 6V) you must have a bad/wrong joint or bad/wrong component in the Q2 area.   If you can't find it, post a clear closeup pic.

[MaxPower]

Did your voltage at the Q2 collector change when you connected the 1k resistor on the emitter (to ground presumably)? If not:

If memory serves me correctly the Q2 base is connected to the Q1 collector. So, did you take the Q2 base and Q1 collector readings from one spot, or did you check the voltages directly at each pin? It could be that Q2 base is not connected to Q1 (and not conducting as Paul suggests). This happened to me when I built an Axis Face (forgot to connect the base to the collector and the collector voltage was stuck near Vcc).

[italianguy63]

Taking the parts in and out of the enclosure-- wires started breaking off (don't like that wire-- won't use it again), and tough to unsolder this board for some reason.  Swapped Q2.  Still problems.  Spent way too much time on it yesterday... just tossed it aside, and started on a fresh one.

I may go back to it if I have gumption.  I have to have a solder bridge or something.  The board is pretty tight, and the pads have very little relief.  I am looking forward to my own boards in a few days.  I will probably just junk this board and use one of mine.  Fixing it will just make it look boogered up.

[italianguy63]

I've determinied that God got even with me for the Eddie Van Halen crack yesterday.    

[italianguy63]

It gets more interesting.  I built another.  Put it together-- same symtoms.  High Q2 collector voltage.  This one at least has a little bit of output.  But, weak and farty.  I only get anything with all the knobs cranked.  And the output is low -- but all the controls do work.

Just to be sure, I checked the values of all the resistors and caps to make sure I didn't grab the wrong bin.  This is really strange because I "bench built" a prototype, and it has no issues.  Only difference is this one has the LED and 3PDT switch circuitry added.  Just to be sure I disconnected the LED and ground to be sure it wasn't that.  Nope.

Makes me wonder if the trannies are suspect?  I tested them, and although weak  (Hfe 35-60 consistantly) they should still work.

I think I am going to table this project until my own PCBs get here-- it will be easier to mount some transistor sockets and take another stab at it.  Right now I am feeling very burned out.

MC

[italianguy63]

Max-- BTW I did measure on both trannies, so the connection between Q1 and Q2 is good.

I am very frustrated with it.  I don't like the board a whole lot.  The solder pads have very little space from nearby traces.  And a double sided board.  It is one of those boards that the field is ground or some common factor like power on the other side.  Just way too many ways to get a solder bridge on a good joint.  My eyesight is not as good as it used to be.  I will probably switch this build to my own boards instead of dycking with it further.  I need to test those anyway. 

Just so I could feel better about myself.  I finished my DynaComp build tonight.  Came out nice.  Works real well.

MC

[LucifersTrip]

good way to avoid solder bridges

[italianguy63]

Good point!  I might try one of those.  I can get those binding boards at my local surplus house for like a buck.  And I have a gang of self-contained charge pump boards here.  Should not be to hard to slam them together.  Maybe another afternoon project!  

Will it fit in a 125B?  MC

[italianguy63]

I am going to try making some home-made eyelet boards and try this.

Lucifer's Trip-- BTW.  The polarity on the 2.2uF in the diagram is reversed!!!  The (+) should be to the input on the positive ground PNP.

MC

[italianguy63]

Anyone who has done this-- is there a preference between 1/16" or 1/8" eyelets?

[italianguy63]

Super cool.  A good sized piece of Norplex cost me about $2, and 200 eyelets cost me less than $3.  So, I made an eyelet board in about 30 minutes for 50 cents.  Throw in some big mojo components... Old school fuzz.

It has a pink LED and knobs.  Why not?

[LucifersTrip]

That looks great...very cool & no more solder bridges!  You may have found your new preferred technique.  Remember to take voltages when it sounds best to you.