Blackfire 2 Beta

[Joe Davisson]

Here it is:
http://www.joefus.com/pedals/images/bf2beta.gif

Did I invent that method of hooking up the input transistor? Sounds good so far...forgot to test the gain control but it's probably okay.

Boring stuff:
I got the idea after reading this (long) explanation of transistors:
http://amasci.com/amateur/transis.html
The notion of two depletion regions was new to me, and led me to the idea that the transistor will conduct signals in reverse as long as the bias voltage requirement is satisfied. It worked, so I tried it in the circuit.

The transistors seem to be extremely sensitive in this configuration, like the way MOSFET's will pick up every little noise. Hmmm...

-Joe

[Ansil]

looks cool man

[aron]

You are a genius. It looks very interesting!

[Zero the hero]

so cool, SO COOL!!!!!
I would have much more free time to build every single project posted in this forum....
Will reverse conduction works with j-fet and mos-fet junctions too? Is there something similar out there?

[smoguzbenjamin]

Zero, I don't need more spare time, I need more money!

[Chris R]

ahhhh.. i havn't even made the first one yet ;p

[rocket]

Joe, I suspect that the 4m7 restitors contribute to the noise.
there is a high voltage drop on this transistors that generates noise.
I don't quite understand how  biasing work in the BF2, but in the first version it would be easy the generate the biasing voltage with a seperate divider and filter it with cap ("noise less biasing").
You then go from the generate (relativly low impedance) voltage to each point where you need biasing. As there is no or low current (and voltage) at the biasing resistor  you'll have less noise.

V+
|
|
R1
|_______   Vbias   <connect your biasing restors here
|.....|
R2...C1
|.....|
|.....|
V-....V-

ignore the dots (.)

[Joe Davisson]

Thanks for the idea, I'll try it out. (Would just using metal-films work as well?)

-Joe

[rocket]

There are different kinds of noise that parts produce.
I am refering to noise that is proportional to the value of the resistor and the dc current trough it. It doesn't matter of which material the resistor is.
Carbon resistors add a different kind of noise on top of that.
Noise is produced by different physical properties of materials.
Some "noises" are due to defects (imperfections) in the material, others are produced even by perfect components.
Some of these noise sources can be fought by choosing the right
components like low noise transistors and metal film resitstors, others by careful cricuit design like noiseless biasing.
however i am not an expert in audio circuit design (or ciruit design in general) and can't tell how much noise is produced by which source.

i am sure that there are sources in the net that give more in depth explanations.

writing all this it comes to my mind, that a reversed CB juntion of a bipolar transistor is often used as NOISE SOURCE.  It might be just what happens in BF2.

I hope I didn't generate more confusion than clarity with my posting and I hope that others have some useful comments.

[rocket]

here is a link showing a noise source with a reversed transistor:
http://www.cryogenius.com/hardware/rng/

this one show the noise source of the roland tr808.
http://machines.hyperreal.org/manufacturers/Roland/TR-808/schematics/TR808_4.TIF

both use reversed BE junction not as I stated reversed CB junctions.

[Marcos - Munky]

Cool, Joe. Thanks for another effect.

[Joe Davisson]

It's probably the first transistor/resistors. Thanks for the help. I guess I'll count my blessings, since the pedal sounds especially good (for me anyway).  I tried to make a sample but it sounded crappy, will try again sometime...

-Joe

[Mike Nichting]

Joe, does the pedal sound good??  How much noise is there??

Mike Nichting

[Joe Davisson]

Darker sounding, with a "harder-hitting" punch to it when playing loud. Sounds very tube-like, and great through my trusty old Fender solid-state amp's clean channel. I would say the noise is tolerable, but it's there, so I wanted to make sure I mentioned it.

The design is probably finalized. I may try to work on the noise some more, but it's not so bad that I care that much... You can raise the gain a bit by lowering the last 470k down to say 220k or 100k. Changing the 470k/470pf to 2.2M/100pf will lower the gain..

-Joe

[Mike Nichting]

Thanks Joe~!!!
I will give it a build :-)

Mike N.