Fuzzrite Help

[maxra001]

I've just assembled a fuzzrite, sourced parts from PPP and got the board from GGG.  I get the classic no sound when engaged, bypass works fine, so does LED.  I've just built an audio probe, and have started probing but am not exactly sure what to expect from it.  Should I get sound from the input jack and pots or just use it on the board?  I get a crackling sound through the amp when touching most leads on the board.  I aim to go through the schematic with the probe, but again am unclear as to where to start and what to pay attention to. 

Here's the layout:
http://www.generalguitargadgets.com/pdf/ggg_secf_lo_mrfr_si.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

There isn't much crackling going on at the input to the board, 'I' on the diagram.  I opted out of the R11 and didn't use a jumper.  The trannies are 2N3904, oriented as they are shown in the diagram, flat side to the right. 

I'm sorry for the vague descriptions of my problem.  I've put together a Rangemaster and 60's Fuzzface and had no problems to speak of, not like this anyway, so I'm new to debugging and troubleshooting.  It's great to learn about how this stuff works, but sure is frustrating.

Any suggestions or help would be very much appreciated.  Thanks!

[Govmnt_Lacky]

Transistor voltages?

[maxra001]

That's something that I haven't done yet.  I have a multimeter and will have to look up how to test the voltage.  I might not be able to get to it till tomorrow morning.  Can you explain how one can do this, what the settings should be on the multimeter?

[maxra001]

Man, I just blew my lunch hour searching the internet on how to calculate the voltage of a NPN transistor.  Does anyone have a good reference site or can you help me do this?

[Govmnt_Lacky]

1) Look online for a datasheet for the transistors that you used in your build. Just Google the part number form them. This will tell you how the transistors legs are labeled.

2) Go here: http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

3) Follow the steps in the link on Step 2 then re-post with the info here.


Good Luck 

[maxra001]

Excellent.  The pinout is
C
B
E

Which is the way I installed it according to the schematic.  I'll measure voltage and post tomorrow morning.  I really appreciate your help.  Thanks! 

[Electron Tornado]

You will probably want to put R11 in there since it will help reduce popping when you step on the foot switch.

For transistor voltages, there is undoubtedly somewhere on the web that will show you how to measure them. Sorry, I don't have a link.

Using the audio probe is simply a process of checking for a signal at various points along the signal path. Here's a quick and dirty list of  some places to check for a signal. Check them in this order.
1. The point labeled "I" on the PCB
2.  Base of Q1
3.  Collector of Q1
4.  Base of Q2
5.  Collector of Q2
6.  Lugs 1 and 3 of the fuzz pot
7.  Middle lug of the volume pot

Let us know where you lose the signal.

In general (no pun intended), GGG makes decent kits. However, there is a resistor missing in their schematic that is present in the original FuzzRite. In the original, there is a 22k resistor connected to a point between C5 and the fuzz pot and ground. It's an easy mod to add this with a toggle switch, but get the pedal working first. (By the way, the lack of that resistor is not why you're having trouble.)


Hope this helps.

[LucifersTrip]

when using an audio probe, it is much easier to visualize the signal path using a schematic.

note the spots Electron Tornado mentioned.

[maxra001]

Okay, I've done some testing:

Voltages with multimeter set to 20v:

Q1
C = .76
B = .71
E = .00

Q2
C = .55
B = .73
E = .00

Audio Probe Testing:  Again, the results seem kind of subjective as for some connections I can touch the lead with the cap on the probe and get crackling/buzzing, but then touch a part on the ring on the board that puts it in the circuit via the trace and it will go silent.

I - The exposed wire crackles, but will go silent when touching the ring at points.
BQ1 - The lead crackles, but will go silent....
CQ1 -  "   "   "
BQ2 -  "   "   "
CQ2 -  "   "   "
Lugs on Fuzz -  1 strong crackle, 3 faint
Middle lug on Volume pot - strong crackle

Thanks again for all the help!!! 

[Electron Tornado]

What do you mean by "...but then touch a part on the ring on the board that puts it in the circuit via the trace and it will go silent." and  " The exposed wire crackles, but will go silent when touching the ring at points." 

Let's step back  bit. Using the audio probe, what do you get when you check the lug on the foot switch that connects to the pad labeled "I" on the PCB?


By the way, describe your setup when you're testing with the audio probe.

[maxra001]

When touching the audio probe to the lead on the switch coming from 'I' on the board, it crackles a bit then goes silent. 

The setup with the probe is ground lead from the sleeve of the phone jack is hooked up to the ground of the output jack.  The input jack has a cord going to a guitar.  The lead from the tip of the phone jack on the probe has a .1uf cap on it. 

I mean that if you touch the bit of exposed wire between the shielding and the board going into the hole marked 'I', it crackles through the amp as if you were touching the end of a guitar cable that was plugged into an amp without a guitar, but if you touch the ring that this wire is soldered to at 'I', it goes silent.

Sounds as if this wire going from 'I' on the PCB going to the switch is not working at the very least.  Could be the entire switch is not working.  This is the second switch I've used in troubleshooting.

[Electron Tornado]

I doubt it's the switch itself, I doubt even more that a second switch would have the same problem. There's a better chance that you made a mistake wiring the switch, or possibly a wiring mistake elsewhere. Can you post a clear photo of everything so people can see the wiring, as well as a closeup of the switch?

[maxra001]

I am new to posting pics, so if this doesn't work, I apologize.  Here are some pics done from a very basic camera.  I can use something else soon if these don't turn out.

[LucifersTrip]

I fixed the images for you...you need a ".jpg" at the end of each url. most people don't take large enough pics, but...

[LucifersTrip]

Sounds as if this wire going from 'I' on the PCB going to the switch is not working at the very least.  Could be the entire switch is not working.  

a couple quick notes:

1) in the future, it is a good idea to test the circuit before wiring the switch and other offboard stuff. Just connect the jacks, pots & battery with clip leads. Suggested order: breadboard > test circuit > solder to board > test circuit > box it > test circuit

2) I believe ballpark voltages for both transistors are ebc (0, .5, .6-.7)

3) the hfe's  of the original transistors were probably lower than modern 3904's. I've had the best luck with silicon in the 150 hfe range (2SC1815 very cool). With the ge version I've had best luck with Q2 ~ 50-60 hfe. John Lyons also reported good luck with 50 hfe for Q2 in his silicon version of the Orpheum (Fuzzrite variant)

good luck