Help Out Someone Stumped on their First Project

[L0ki]

So after spending alot of time reading on this site, and Beavis Audio, I decided to try my hand at building a pedal.  I decided to build the Bazz Fuss fuzz pedal because it seemed like a very simple circuit and all the parts could be bought at Radio Shack.  I used the following schematic that I found on this forum to build the pedal.



I couldn't find the recommended MSPA13 transistor at Radio Shack, but I could find a 2N3904 tansistor (as recommended by http://www.home-wrecker.com/bazz.html ).

So Ive got everything put into my breadboard and soldered up the volume pot and in and out jacks; hooked it up to my bass, turned the amp on and all I get is a loud buzz; I am fairly certain I have the volume knob wired right, as I can turn it down and the signal will fade from loud buzz to silence, so Im thinking the error is somewhere in the actual circuit.  Since I am such a newbie I dont really know what to do as far as trouble shooting.  Ive tried flipping around the transistor (incase I had it in backwards) it didnt seem to do anything.

Here's a quick mockup of the breadboard layout Im using, comparing it to the layout above I can't figure out what the problem is.




Any help you guys can give me would be very much appreciated.

Thanks!

[Hupla]

I cant spot anything you have done wrong really? maybe some one else can, but have you tried a different transistor? also are the pinouts of the 2n3904 the same as themspa13?

[petemoore]

  Loud buzz...check grounds, clip DMM to a ground, black lead, set it so it beeps when leads touch, test that every other ground on schematic...beeeps.
  Jacks...anything with a ground mark.

[L0ki]

  Loud buzz...check grounds, clip DMM to a ground, black lead, set it so it beeps when leads touch, test that every other ground on schematic...beeeps.
  Jacks...anything with a ground mark.

Just did as you instructed, all grounds (the jacks, lug 1 of the volume pot, and the emitter of the transistor) tested positive for continuity.

I cant spot anything you have done wrong really? maybe some one else can, but have you tried a different transistor? also are the pinouts of the 2n3904 the same as themspa13?

Im not entirely sure what you mean by the pinouts of the 2n3904 being the same as the transistor in the pcb layout I followed.  Can you elaborate?



Also, if this helps,  if I crank the volume on my amp I can hear my bass's signal under all the buzz but only just barely.

[Hupla]

  Loud buzz...check grounds, clip DMM to a ground, black lead, set it so it beeps when leads touch, test that every other ground on schematic...beeeps.
  Jacks...anything with a ground mark.

Just did as you instructed, all grounds (the jacks, lug 1 of the volume pot, and the emitter of the transistor) tested positive for continuity.

I cant spot anything you have done wrong really? maybe some one else can, but have you tried a different transistor? also are the pinouts of the 2n3904 the same as themspa13?

Im not entirely sure what you mean by the pinouts of the 2n3904 being the same as the transistor in the pcb layout I followed.  Can you elaborate?



Also, if this helps,  if I crank the volume on my amp I can hear my bass's signal under all the buzz but only just barely.

I reckon they are the same pin out but you said you used 2n3904 instead of the mspa13. I was just wondering if they both had the pins in the same order.

Also do you have any other transistors you can try instead to see if there is something wrong with that one you are using?

[Kearns892]

A couple suggestions
1. Are you sure you have correctly Identified  the tips and sleeves and not switched them?
2. Triple check the pinout of your transistor by googling the data sheet for the specific part number
3. The only schematic of the bazz fuss listed on homewrecker that doesn't use a darlington type transistor (similar to the one you purchased) is the first which also uses a higher value resistor 100k ohm as opposed to the 10k you are using. Try upping the value of the resistor.
4. It sounds like you have the pot right, but if nothing else works you may want to try the circuit with out the pot. Simply move the lead from lug 3 to the output jack and your circuit will be on max volume (or buzz  if you're unlucky)

[L0ki]

The only schematic of the bazz fuss listed on homewrecker that doesn't use a darlington type transistor (similar to the one you purchased) is the first which also uses a higher value resistor 100k ohm as opposed to the 10k you are using. Try upping the value of the resistor.

I am now thinking this is the solution, I didnt have a 100k resistor sitting around, but had a pack of 5-10k's.  So I wired them in series and voila, fuzz.  I am so embarrased now that one little resistor was what hung me up.  But I guess thats why I do mechanical engineering, and not electrical 

Thanks so much for your help guys.

[L0ki]

Well now Ive got a new question.  The circuit works great so far, but only if I run it off a battery, when I hook it up to my onespot power supply (with a battery snap adaptor) I just get a really loud ground hum.  Could this be because of the simplified way I have the jacks wired to the circuit? Would wiring it up truebypass with a 3pdt switch solve the problem?

[newfish]

Are we talking about the breadboard version?  If we are, you *can* expect a fair amount of background noise on a breadboard build.

Think of your jumpers / wires going backwards and forwards as aerials picking up whatever they can.

Steel / Aluminium cases provide excellent shielding from this.

Is your Onespot powering *just* this pedal?  Youmay find that the noise dies down if it's powering two or more devices.

Another tip you could do (and use as standard on any subsequent builds) would be a 100uF capacitor between your positive and negative rails.

This is in parallel to your circuit, so any two points on your breadboard (like the two spare next to the transistor's 'C' on your diagram) would be good - observing polarity of course (negative stripe on cap goes to negative rail).

This one cap. provides an extra bit of smoothing on your pedal's power supply.

Hope these suggestions help.

Cheers.