Author Topic: Bumble Bee Bias  (Read 1771 times)

jkokura

  • Global Moderator
  • Electron Doctor
  • *****
  • Posts: 7647
  • Jacob - SK, Canada
    • View Profile
    • JMK PCBs
Bumble Bee Bias
« on: February 03, 2012, 01:04:20 PM »
Hey dudes,

I'm just struggling to no end with getting this Bumble Bee to bias right. It's crazy how adjusting the knobs on this thing will totally make it go into crazy oscillation, and it's not quite sounding right yet.

Anyone have some bias info on a Bumble Bee they can give me? I need this quick as can be as I'm going away on Monday night and need to have this finished by Monday morn.

Jacob
JMK Pedals - Custom Pedal Creations
JMK PCBs *New Website*
pedal company - youtube - facebook - Used Pedals

dwstanford

  • Solder Ninja
  • ****
  • Posts: 429
  • Danny
    • View Profile
Re: Bumble Bee Bias
« Reply #1 on: February 03, 2012, 01:18:39 PM »
What types of transistors are you using and what are the gains and leakages?  Its been a while since ive done one, but i believe the gains for transistors sounded best as follows.  Q1: 50-70, Q2: 60-80, and Q3: 100-140.  I'll look back through my notes on it, but i think the leakages a less of an issue, but should be around 300 or less.

dwstanford

  • Solder Ninja
  • ****
  • Posts: 429
  • Danny
    • View Profile
Re: Bumble Bee Bias
« Reply #2 on: February 03, 2012, 01:28:43 PM »
after looking at my notes, apparently the leakage is a bit more important.  You dont want transistors with low leakage.  Something in the 300 range for each should be good though.  I experimented with several transistors and settled on Q1: 57, 270. Q2: 72, 360. Q3: 122, 226.  This circuit isnt as picky about gains as some, but anything in that range should work.  The tb sets that small bear sells sound pretty good.

dwstanford

  • Solder Ninja
  • ****
  • Posts: 429
  • Danny
    • View Profile
Re: Bumble Bee Bias
« Reply #3 on: February 03, 2012, 01:48:26 PM »
Yeah, looking back through my notes, you want to get between -4 and -5v on collectors of Q1 and Q2.  Q3 is a bit tricky and you just have to use your ears.  Higher leakage (300+) is better for this transistor to give it more of the gnarlyness associated with the buzzaround.    Depending on the levels of the balance and sustain controls, you should get between 0 and -4v on Q3.  I had to test it out on a breadboard for about a week to get the right sound out of it, but it finally came together and sounded great.

jkokura

  • Global Moderator
  • Electron Doctor
  • *****
  • Posts: 7647
  • Jacob - SK, Canada
    • View Profile
    • JMK PCBs
Re: Bumble Bee Bias
« Reply #4 on: February 03, 2012, 02:28:46 PM »
I got a set of Tonebender trannies from Smallbear. I expect them to fall into the right gain and leakage ranges, but perhaps I should test them. Part of the problem is perhaps that I'm not sure the pinouts are correct. I'm not really finding much info about these transistors actually.

The real issue for me sonically is that trails of this fuzz aren't really very good sounding. I get the massive wall of fuzz sound, but hold a sustained chord or note and after 5 seconds it devolves into this splatty weak signal, not the long sustain of a great tonebender type fuzz. I'm not hearing that in the demos, so I'm wondering what I can do to fix this.

I'm not really a major fuzz guy, so I need guys like you (DW or Paul, or whomever) to help me out.

Jacob
JMK Pedals - Custom Pedal Creations
JMK PCBs *New Website*
pedal company - youtube - facebook - Used Pedals

dwstanford

  • Solder Ninja
  • ****
  • Posts: 429
  • Danny
    • View Profile
Re: Bumble Bee Bias
« Reply #5 on: February 03, 2012, 08:09:21 PM »
Most of the small bear sets are either black glass with red dot on collector or metal can with tab on emitter. 

The fuzz trails are a bias issue.  With even one of the transistors off bias, you will get some weird gating and sputtery nastyness.   I would breadboard it with the transistors and see if you may need to sub some of the resistors to get the proper bias.  If youre getting very different voltages than i listed, make changes as needed.  Having to sub resistors to suit specific transistors is not uncommon on fuzz builds, especially the three transistor ones. 

jkokura

  • Global Moderator
  • Electron Doctor
  • *****
  • Posts: 7647
  • Jacob - SK, Canada
    • View Profile
    • JMK PCBs
Re: Bumble Bee Bias
« Reply #6 on: February 03, 2012, 11:18:03 PM »
Figured out the bias issue. I had two pots switched. 100K and 5K aren't really swappable.

Jacob
JMK Pedals - Custom Pedal Creations
JMK PCBs *New Website*
pedal company - youtube - facebook - Used Pedals

dwstanford

  • Solder Ninja
  • ****
  • Posts: 429
  • Danny
    • View Profile
Re: Bumble Bee Bias
« Reply #7 on: February 03, 2012, 11:35:30 PM »
Woo hoo!