Hipster Fuzz - Fart-y Sound Troubleshooting

[Ammalato]

Hi everyone, I completed a hipster fuzz build recently. And while I was able to bias Q2 up around 4.5 V between the test pad and ground, I am getting strange sounds from the pedal. I installed some BC183's (Q1 272 hfe
Q2 288) I am attaching a video and some images to help diagnose. Basically the pedal sounds farty and almost like an under biased fuzz pedal, even though I've confirmed that the collector of Q2 is 4.5 V. The boost and bias trimpot's internally have affect on the overall sound but never get me to replace that is acceptable for a face face

I'm curious if something is wrong with the board components, or if I botched the switch wiring (they appear to match up with the build guide though)

[Ammalato]

...

[Ammalato]

...

[midwayfair]

Post the voltages on all pins of the transistors, and also on both sides of R4

[Ammalato]

Post the voltages on all pins of the transistors, and also on both sides of R4

With Power Supply: @ 9.38VDC
Q1:
C: 1.297v
B: .577v
E: .000v

Q2:
C: 4.49v
B: 1.299v
E:.693v

R4: 9.34v on one side, 9.04v on the other

[Bio77]

Are your transistors in backwards?  They don't match the screen on the board, but that might be right depending on what you used.

[Ammalato]

Are your transistors in backwards?  They don't match the screen on the board, but that might be right depending on what you used.

So, I thought the same thing because I noticed that the flat side of the transistors as screen printed on the pcb are opposite of how I have the transistors oriented.  However, the PCB also has each pad labeled "C" "B" and "E"  and I used that when orienting the BC183 transistors I used which have a CBE pin out. Now it's possible the pcb is labeled incorrectly?

Here's the pcb image from the project page. If you check the pin out of a BC183 it looks like the screen print on the pcb might actually be wrong.
https://www.madbeanpedals.com/projects/_folders/1590A/images/Hipster.jpg

[madbean]

The silk screen is correct. The standard CBE orientation is used here similar to the pinout on the 2n3904, 2n5088 etc. Most of the BC183 have an EBC orientation so reversing them from the silk screen drawing would be correct. However there are some that have an ECB pinout, too.

Any info on where you got your transistors? Is there a datasheet for the particular ones you bought provided by the vendor?

[Ammalato]

The silk screen is correct. The standard CBE orientation is used here similar to the pinout on the 2n3904, 2n5088 etc. Most of the BC183 have an EBC orientation so reversing them from the silk screen drawing would be correct. However there are some that have an ECB pinout, too.

Any info on where you got your transistors? Is there a datasheet for the particular ones you bought provided by the vendor?

I can confirm that this pin out is correct for the transistors I used. I've used this batch in other builds and had measured the transistors for gain prior to installing them.
http://www.el-component.com/bipolar-transistors/bc183

If the transistors are orientated correctly I'll have to look elsewhere to identify the problem. Do the parts all seem to be in the right order / polarity? Does the switch appear wired correctly?

Does anyone have gut shots of a successful build. I haven't found any for this current revision of the circuit (2019)

[madbean]

Your resistor values look correct. But, what have you got in C3? There are film caps in pF values but that looks rather large for 47pF.

[Ammalato]

Your resistor values look correct. But, what have you got in C3? There are film caps in pF values but that looks rather large for 47pF.

A ha! See attached photo.  It's a 473J / 50v Capacitor.  .047uf / 47nf.  I suppose that's the WRONG value since that appears to translate to 47000pF if I'm reading this correctly?

[madbean]

Correct, that is a 47nF. Remove that cap and the problem will hopefully go away. That cap is a mod for a bit of high end fizz reduction. It's not required but can be helpful to tame noise at max fuzz settings.

[Ammalato]

EUREKA! The C3 Cap was the wrong value.  I removed it, and everything is now working as it should. Big thank you to Brian, and everyone on this forum...I knew I could save myself some grief here. 

FWIW -  I find that I like my BC183's in this fuzz biased a little hot (~5vdc) with the boost maxed.