Biasing a Bazz Fuss

Started by mac, November 20, 2007, 11:53:34 AM

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mac

For all those BF lovers.

If you look at v1 (single transistor) and v2 (darlington transistor) schems you may notice that the collector resistor goes from 100k in v1 to 10k in v2. That is, Rc depends on hFE a lot. Higher gain -> lower resistor.

My advice is to use a 100-250k pot at the collector and find the optimal bias. It is an easy task. Just set the amp and BF volume loud enough to hear background noise. Tweak the pot until noise is at its max level. You may hear some crackle near the sweet spot, a kind of Rangemaster volume pot noise. If you biased a Fuzz Face before you know what I'm talking about.
At the same time you may lower the guitar volume and softly pick open strings. Near the optimal point  notes will sound more defined and louder.

mac

mac@mac-pc:~$ sudo apt install ECC83 EL84

GibsonGM

Are you saying that biasing the BF this way will allow clean-up with the volume knob?  I've been wanting that for a while....
  • SUPPORTER
MXR Dist +, TS9/808, Easyvibe, Big Muff Pi, Blues Breaker, Guv'nor.  MOSFace, MOS Boost,  BJT boosts - LPB-2, buffers, Phuncgnosis, FF, Orange Sunshine & others, Bazz Fuss, Tonemender, Little Gem, Orange Squeezer, Ruby Tuby, filters, octaves, trems...

ambulancevoice

Open Your Mouth, Heres Your Money

stopstopsmile

I never thought you needed to bias it, just build it as is. 

ambulancevoice

yeah, but re biasing it can like, yield new (if not better) sounds (most of the time)
Open Your Mouth, Heres Your Money

nordine

good call,

ina fuzz i think there's 2 things that rule the overall sound: Filtering and Bias

Bias alters lot of the character of a fuzz pedal, so thats why there's a genre called "misbiased 60's fuzz", known by their constipated sound... having a pot there, you can have gradients

GibsonGM

I like my Orange Sunshine; I used a 5k pot on the collector of Q2 to dial in some Strawberry Alarm Clock, lol.   Sometime I'll revisit the Bazz, it's a nice circuit...I just didn't like that it wouldn't clean up when you rolled the vol. back.
  • SUPPORTER
MXR Dist +, TS9/808, Easyvibe, Big Muff Pi, Blues Breaker, Guv'nor.  MOSFace, MOS Boost,  BJT boosts - LPB-2, buffers, Phuncgnosis, FF, Orange Sunshine & others, Bazz Fuss, Tonemender, Little Gem, Orange Squeezer, Ruby Tuby, filters, octaves, trems...

mac

QuoteI never thought you needed to bias it, just build it as is. 

Don't get me wrong, if you build it as it is, with the specified parts, 2n5088 or a darlington, it sounds good. But with some tweaking it may sound a little better, imho.
Think of a Gaussian Bell Function. At a given point the diode and base current are the optimal for a given transistor. Have to figure it out why it is so.

QuoteAre you saying that biasing the BF this way will allow clean-up with the volume knob?  I've been wanting that for a while....

If you mean the guitar volume the answer is no. It still sounds a little dark when you lower the vol knob, maybe an input impedance issue.
A gain pot of about 10k at the emiter and a big bypass cap works a lot better.

Quotetry it and see

+1

mac

mac@mac-pc:~$ sudo apt install ECC83 EL84