Fuzz Face Foolery...

[modsquad]

Okay built an Arbiter Fuzz based on:

http://www.aronnelson.com/gallery/v/album171/Dallas_Arbiter_Fuzz_Face.gif.html?g2_imageViewsIndex=1

I know Q2 is supposed to be biased at 4.5v but It's way to high.   Here are the voltages

Q1
E - .003v
B - .110v
C - .781v

Q2
E - .735v
B - .781
C - 7.88

So as you can see the Collector is double the voltage basically of the input.   I checked all the components and they seem to be the right resistances. 


I am using 2n1305 germs from Small Bear.   I am assuming they are oriented as EBC from the tab on the can.   Any light anyone could shed would be helpful.

[Solidhex]

Did you use the resistor values specified by Small Bear or the ones in the layout? Are the transistors specified as Q1 and Q2 in the right order? Also some cheaper 9 volt batteries will put out up to 11 volts pushing the bias outta whack, although I think something else might be to blame.

--Brad

[modsquad]

I used the values specified by Small Bear, they were basically the same as the layout.  The battery measures 7.88v.   I am confused by the circuit though, I am assuming the resistors work as a voltage divider.

[modsquad]

Does anyone know if the 2n1305 could be cbe so that I have them in backward?

[Solidhex]

The tab is the emitter, the base will be the offset one in the middle.

--Brad

[petemoore]

Q1
E - .003v
B - .110v
C - .781v

Q2
E - .735v
B - .781
C - 7.88
  I'm not drawing a schematic from layout to tell...looks like it's a Pos Gnd, PNP FF.
  If so, q1E should be Gnd.
  I'm not sure that'd be enough to put Q2C all the way at supply voltage, through a collector resistor...I would test that collector resistor and that V+ isn't sneaking by it somehow.

[modsquad]

Checked and Q1 E is at ground and registering 0v.  It is PNP and appears to follow the original schem for the Arbiter FF exactly:

http://fuzzcentral.ssguitar.com/fuzzface/fuzzfacepnpschematic.gif

All the resistances measure correct, the collector resistor is 8k, C2 is .1uf, R1 is 400k, R2 is 33k, C1 is 2.2, C3 is 20uf, and R4 is 100k

This is such a simple circuit, I just don't get it.   Even the PCB I made and solder points are all clean and no bridges.

[Solidhex]

Yo

  Not sure if its a typo but that 400k resistor should be a 400 ohm. You'll see on the Small bear resistor list the 400 will have an "r" next to it.

--Brad

[modsquad]

Duh, you are correct, its a typo.  It measures 400 ohm. I did do something funky.  I didn't have a 20uf electrolytic so I solderd two 10uf caps in parallel.  They measure 20 uf when I test them though.

[Solidhex]

You know what's weird. I just completed my third fuzz face with the small bear tranny's. They all sound awesome. This last one though I seem to be having a similiar problem. All resistor values are on. I used a 25k pot for the collector resistor and I've checked the voltages with it set to the 10k value as suggested by Steve at Small Bear. I'm getting these voltages with a -9.75 battery

        Emitter   Base   Collector
Q1   0 V       -100mv  -450mv

Q2  -367mv  -445mv  -7.10V

When I turn the pot all the way to max resistance I still can only get the voltage down to -5.25
I must have made the same mistake !

--Brad

[brett]

Hi
in both cases, neither transistor has enough base-emitter voltage to get them conducting.
Maybe check the feedback resistor (100k)?
cheers

[Solidhex]

Yo

  Thanks Brett! I touched up all the solder joints just in case and bingo its working exactly as it should. Sometimes you just can't tell by looking at a solder joint if its cold or not. I'm assuming if you just touch up all your joints you're problem will be solved too Modsquad. Now I just need to figure out why I didn't just do that in the first place?

--thanks again, Brad

[modsquad]

good call.  I swapped out the 100k for another one and bingo we got fuzz.  Thanks for the idea. I had checked everything else.