Build a Blackfire Overdrive

[Oliver]

Hi,

i just build a Blackfire Overdrive and tested it some minutes ago.
Gread Sound for me !!!!
There is one Thing that lets me ask a question here...

At the Maximum Gain there is a little sizzle in the Sound, just like in a
FuzzFace when Gain turned up to max, but not as much.
I used all parts as in the Schematic ( http://www.joefus.com/pedals/images/blackfire.gif ), only the GainPot i used a 500K Audio, because i didn't had an 1M one.

Is there a way to tweak for a good high End sound?

thanx for suggestions !!

Oliver

[petemoore]

You can 'build' a pot that'll get 1 meg Resistance by adding resistance's' to the lugs... but will have limited range [500k should be enough to tune the gain to your liking, I leave gain knobs pretty much set...'?']
 Just got the Jaxx for my Blackfire's Red on Blackburst painted box !!!
 3PDT Blue w/ bypass indicator...beautiful !!

[maarten]

The 500K pot should be no problem I think; if you change it to 1M, probably your problem, might increase somewhat. Remember that the Blackfire is a high gain pedal, so some distortion probably can not be avoided. Also the type of guitar you use, might have some impact, e.g your pickups may be more efficient than Joe D.'s, or your action might be lower (distance between strings and pickups), which would give a stronger inputsignal than the Blackfire was designed for.

Anyhow, you seem to bevery pleased with this project, so why don't you restrain yourself to just turning up the gain to 9? (I build the pedal myself -including the first version-, and I must say that I am very pleased with it. However,  when I turn up the gain to the max, it is too much for me in most situations - so I just don't do it.

Joe, thanks again!

By the way, I just used the very ordinary BC547C, which have good availability here in Europe, I think. I must add that the suffix is very important here: whether you use a BC 107, 108, 109 or BC 547, 548, 549  or 550 is less important than the suffix A, B or C. Suffix A stands for a gain of 125 - 260; suffix B for 240 -500; suffix C for a gain of 450 - 900. The difference between numbers has to do with  a) supply voltages (lowest numbers like BC 107 accept only 20 volts; BC547 45 volts, BC 548 30 volts: nothing to worry about, when you are building a 9V pedal); and b) the differences have to do with what is called in my data-books "border-frequency" - this is a very literal translation, maybe it is called "max. frequency" in English. Anyway, this seems to be approximately  50 MHz for older types, and something like 150 or 300 MHz for more recent types. Therefore, I don't think we to bother with this difference either, when looking at effects for guitar. So the only thing to worry about with European transistors, is the gain: and this will be revealed by the suffix, not the transitor type-number itself! The only other thing (but this is not in my databooks) of importance is the noise-factor of the transistor. BC 550 is recommended for low noise (that is why I usually use this type), but either BC548 or BC549 also should be low noise, I think.

Maarten de Huu

[Joe Davisson]

That's right, my pickups are fairly weak, being HS3's and a humbucker-crammed-into-a-single type thing with a medium output. There's something about those HS3's despite the low output... I used to like high-gain pickups but I now like to get the extra gain with pedals. So there's a good chance it can be overloaded.

I don't think the 500k pot will matter either, it may increase treble a tad. If you need more gain/bass response lower the 470k resistor (in parallel w/470pf) to say 330k. Not too low, though.

The final inverting stage can be used to shape the tone a bit, mainly by placing a small value cap from base to ground. (Like 470 - 1000pf). This can help tame the high end -- it seems to be better to shape the tone after the distortion part.

If the gain is too high, you can adjust the 470k/470pf split to something like 2.2M/100pf, etc. Glad you got it working.  :mrgreen:

-Joe

[brett]

Hey Joe (pun intended),
I'm in the middle of building a BlackFire - it's such an interesting looking circuit.  But how and why does it work?  The secret seems to be in the biasing transistor and 10k resistors - the gain transistor setup seems much the same as in 101 other circuits.  

The base current into Q1 must be very small (a couple of uA, I suppose), and the voltage is going to be on the low side, too (about 1.5V).  Presumably it can't swing too close to the ground rail, so there's only room for a half to 1 V swing on the low side.  So does this make it clip asymettrically?  

But what's the 10k resistor going into the base do?  The emitter-follower before it doesn't mind if the next stage has low impedance, so I presume it's not to increase impedance.  Does much voltage drop occur across this resistor?  Is it there to lose some gain?  If so, wouldn't you get the same effect without it and reducing the 10uF bypass caps?  

Sorry about all of the questions, but I know just enough to be intrigued, but not enough to work out what is happening in this circuit.

Thanks for any advice.

[Oliver]

The 500K pot should be no problem I think; if you change it to 1M, probably your problem, might increase somewhat. Remember that the Blackfire is a high gain pedal, so some distortion probably can not be avoided. Also the type of guitar you use, might have some impact, e.g your pickups may be more efficient than Joe D.'s, or your action might be lower (distance between strings and pickups), which would give a stronger inputsignal than the Blackfire was designed for.

Anyhow, you seem to bevery pleased with this project, so why don't you restrain yourself to just turning up the gain to 9? (I build the pedal myself -including the first version-, and I must say that I am very pleased with it. However,  when I turn up the gain to the max, it is too much for me in most situations - so I just don't do it.

Joe, thanks again!

By the way, I just used the very ordinary BC547C, which have good availability here in Europe, I think. I must add that the suffix is very important here: whether you use a BC 107, 108, 109 or BC 547, 548, 549  or 550 is less important than the suffix A, B or C. Suffix A stands for a gain of 125 - 260; suffix B for 240 -500; suffix C for a gain of 450 - 900. The difference between numbers has to do with  a) supply voltages (lowest numbers like BC 107 accept only 20 volts; BC547 45 volts, BC 548 30 volts: nothing to worry about, when you are building a 9V pedal); and b) the differences have to do with what is called in my data-books "border-frequency" - this is a very literal translation, maybe it is called "max. frequency" in English. Anyway, this seems to be approximately  50 MHz for older types, and something like 150 or 300 MHz for more recent types. Therefore, I don't think we to bother with this difference either, when looking at effects for guitar. So the only thing to worry about with European transistors, is the gain: and this will be revealed by the suffix, not the transitor type-number itself! The only other thing (but this is not in my databooks) of importance is the noise-factor of the transistor. BC 550 is recommended for low noise (that is why I usually use this type), but either BC548 or BC549 also should be low noise, I think.

Maarten de Huu

Hi Maarten,

thanx for your reply - and even the others too !!  

I used BC549C (didn't measure the hfe out) - they have a Gain between
450 and 600.
I use a Strat with handwound SingleCoils - they come like the Fender TexasSpecial.
With my Epiphone SG (Stock PUs) it sounds a better, because there is no
HUM and the overall sound is more bassy.

My favorite Gainset is about 7 to 8 from 10 - goooooood!

There is one other thing, that makes me ask  :?:
The Output Level seems to be not very high.
Can the last Stage be tuned for higher Output by keeping the
Soundquality like it is?
I shorted the last Stage to test and got a huge step up in the Volume.
I only have a littleGem at home to test my Stuff and it was driven into
a bad sound.
I dont understand how to tune the last Stage for more Volume..
Can anybody explain (Joe??)

thanx
Oliver

[Oliver]

That's right, my pickups are fairly weak, being HS3's and a humbucker-crammed-into-a-single type thing with a medium output. There's something about those HS3's despite the low output... I used to like high-gain pickups but I now like to get the extra gain with pedals. So there's a good chance it can be overloaded.

I don't think the 500k pot will matter either, it may increase treble a tad. If you need more gain/bass response lower the 470k resistor (in parallel w/470pf) to say 330k. Not too low, though.

The final inverting stage can be used to shape the tone a bit, mainly by placing a small value cap from base to ground. (Like 470 - 1000pf). This can help tame the high end -- it seems to be better to shape the tone after the distortion part.

If the gain is too high, you can adjust the 470k/470pf split to something like 2.2M/100pf, etc. Glad you got it working.  :mrgreen:

-Joe

Hi Joe,

thanx for the Informations !

i was wondering - it worked just after it was build...

at the Final Stage i will add a HighEnd shape for tonetweak
in the Middle Stage the 470K Resistor looks good for a 250K Pot
in Series with a 300 or 330K Resistor for the Bassresponse, or
switchable (Fat Switch?)

Good Circuit !!!!

I just asked in a reply, but - is the 1M Resistor before the last Stage
for the possible max. Output Level?

than you !

Oliver

[Joe Davisson]

I put up the wrong schematc. This is the right circuit:
http://www.joefus.com/pedals/images/blackfire.gif

Lowering the 1M resistor will raise the output. I had that set too low in that version. Probably 220k - 470k is right. Or 100k to keep it even. Sorry 'bout that, but the difference is not significant if you already built it.

-

Unverified Theory:
Q1 corrects the input impedance, which on a regular transistor stage is somewhat lower. This makes it more sensitive to the guitar. The input impedance of an emitter-follower like this can be approximated by the bias resistors' values in parallel, roughly 820k in the Blackfire.

The input signal is copied onto the output at a current level set by the 100k resistor. Q2's bias current is held consant. This basically turns Q2 into a voltage-controlled device. Any current sucked away by Q2 is replaced by Q1.

Transistor operating speed is dependent in part on input current. (Higher currents result in higher switching speed.) By keeping the input current low but constant, Q2 will react to voltage changes slower. Lowering that 100k resistor (to increase the current level) will raise the switching speed and amount of hard-clipping considerably.

The frequency response and gain are still too high, and the 10k series resistor takes care of that. I don't know what other effects it may have. I guess there is enough asymmetry in the soft-clipping to make it sound more tube-like.

Can anyone verifiy any of this?

Using a FET or MOSFET as Q1 doesn't seem to improve the sound. So the sound comes from Q2 -- an ordinary transistor???

Hehehe.

-Joe

[Oliver]

I put up the wrong schematc. This is the right circuit:
http://www.joefus.com/pedals/images/blackfire.gif

Lowering the 1M resistor will raise the output. I had that set too low in that version. Probably 220k - 470k is right. Or 100k to keep it even. Sorry 'bout that, but the difference is not significant if you already built it.

-

Unverified Theory:
Q1 corrects the input impedance, which on a regular transistor stage is somewhat lower. This makes it more sensitive to the guitar. The input impedance of an emitter-follower like this can be approximated by the bias resistors' values in parallel, roughly 820k in the Blackfire.

The input signal is copied onto the output at a current level set by the 100k resistor. Q2's bias current is held consant. This basically turns Q2 into a voltage-controlled device. Any current sucked away by Q2 is replaced by Q1.

Transistor operating speed is dependent in part on input current. (Higher currents result in higher switching speed.) By keeping the input current low but constant, Q2 will react to voltage changes slower. Lowering that 100k resistor (to increase the current level) will raise the switching speed and amount of hard-clipping considerably.

The frequency response and gain are still too high, and the 10k series resistor takes care of that. I don't know what other effects it may have. I guess there is enough asymmetry in the soft-clipping to make it sound more tube-like.

Can anyone verifiy any of this?

Using a FET or MOSFET as Q1 doesn't seem to improve the sound. So the sound comes from Q2 -- an ordinary transistor???

Hehehe.

-Joe

Hi Joe,

thank you for the corrections !!

I played around and bridged the Last Stage with a cable jumper just between the 0,1uF Cap and the 1M Resi. directly to the Output(Volume)Pot.
The Output was amazing!!!
I Will add a TrimPot to adjust the possible OutputLevel to my taste.

The sound ist really good !!

Good Work Joe!

bye and Thanxx

Oliver

[RDV]

I finally got my Blackfire de-buuged(cold solder joint), and boy is it gnarley!! Joe: if you're still checking this topic, I'd like to know what type of E.Q. you'd recommend for this as I don't think it's gonna work with the Marshall with this much treble.

Regards

RDV

[Joe Davisson]

A basic tone control should work fine. I made one with a Marshall-type 3-band EQ that works well, too. Or try a small cap from Q5's base to ground, say 470-1000pf

-Joe

[RDV]

A basic tone control should work fine. I made one with a Marshall-type 3-band EQ that works well, too. Or try a small cap from Q5's base to ground, say 470-1000pf

-Joe

Thanks much Joe! I've been using a slightly modded Obsidian(transistor) for quite a while with excellent results. I love the way guys who want to look at your pedals so they can cop your tone look at mine and just keep on going :twisted:, cause they don't have a clue. None of them ask for me to make em' one though strangely enough :shock: One of your fuzzes and a good clean booster is all anyone really needs to gig.

Regards

RDV

[brett]

thanks for the answers to my "how does it work?" questions.

[Oliver]

Hi once more  

i played a bit around with the Blackfire and finally changed some little
things:

Removed the 470K Resistor (parallel to the 470p Cap)
and added a 300KResistor with a 470KPot in Series for a
FAT Control.
Than i added a simple ToneControl (TS Like) with an 100K Pot
from Signal (before the last Stage) and a 0,1uF Cap in Series to
Ground. That steals some Output, but there is so much Level and
Gain left, that it doesn't matter.

I have pretty much fun with both of my guitars...
Using an Epiphone SG it comes with a good rock crunch and
the Strat makes it sounding like a very useful BluesOverdrive when
using about 1/3 Gain.

BlackFire ON!!

Oliver