Joe Davisson's Hellfire/Blackfire help needed

[gigimarga]

Hi all!

After I blew my mind trying to bring a Maestro phaser to life, I decided to make a simpler effect.

So, I made a Hellfire (which I understood that's a MOSFET Blackfire) using the schematic http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/hellfire.gif.html?g2_imageViewsIndex=1 and the PCB from here: http://www.aronnelson.com/DIYFiles/up/J_Davisson_-_Blackfire-M.pdf (sorry to upload here, but I can't remember where I took them from...hope not to be a problem...thx to Joe Davisson and to Pablo de Luca!).

And...surprise...it didn't want to work (even I rechecked all the values/solders/pinouts)!!!

My voltages (using a fresh 9V battery) are:

Q1: D=9.00V         G=2.60V         S=0.37V
Q2: D=9.00V         G=0.37V         S=0.00V
Q3: D=9.00V         G=2.60V         S=0.55V
Q4: D=9.00V         G=0.55V         S=0.00V
Q5: D=8.15V         G=2.60V         S=0.19V

The last stage works right, but, even I tested 5 pieces of BS250 for Q4, I can't make the last two stages to work!

Another question is about the 2N5089 (I used BC549C instead) version of Blackfire (
http://www.diystompboxes.com/analogalchemy/sch/blackfire.gif).
It works almost good, but on the collector of the last transistor I obtained only 3.3V, instead of 4.5V as in the previous stages. I replaced the 10k resistor with a trimpot and I biased it to 4.5V, but it sounded worse (less louder and more hiss).

Thx a lot all!

[WGTP]

The obvious issues that you have probably already considered are the Reverse polarity of the circuit and the pin out on the BS250's. Also, in the Northern Hemisphere, as winter and heating is here, dryer air causes more static electricity and Mosfet's can get shocked to death...

With Mosfet's, as Jfet's, sometime the bias has to be tweaked to get the correct voltage. Both the Blackfire and Hellfire sound really cool, (I built a hybrid using a Mosfet stage and a BJT stage) so hang in there until you get it going.  

[gigimarga]

Thx WGTP for your answer!

I respect the reverse polarity (sorry for omitting the minuses from all the voltages posted above).
I also check the pinouts of my BS250s, but here can be a problem: there are 2 reversed pinouts. I tried to check the right one assuming that the internal diode has anode (+) on drain and cathode (-) on source, as opposite in a BS170. Am I wrong or not?

Anyway, which are the correct bias voltages and how to set them (I have no ideea how to do that on MOSFETs)?

On 2N5089 version of Blackfire, how could I bias the last stage?

Thx again!

[petemoore]

  See if you can find out what's different compared to the other Blackfire stage.

[gigimarga]

  See if you can find out what's different compared to the other Blackfire stage.

Thx petermoore, but I didn't understand what you said
Three stages have 2.2M/1M bias resistors on gate, while another 2 stages have no bias resistors (only a 10K resistor from the previous stage).

[WGTP]

Google BS250 and find the brand you have.  The data sheet should show you the pin out.

Q1 & Q2 form a stage and Q3 & Q4 form a stage.  Q5 is a 3rd and different stage (which makes a nice Mosfet Boost by itself, it is the same as the Mosfet stages in the Obsidian).  If I'm not mistaken, you should get around 4.5v at the output of each stage.

[gigimarga]

Google BS250 and find the brand you have.  The data sheet should show you the pin out.

Q1 & Q2 form a stage and Q3 & Q4 form a stage.  Q5 is a 3rd and different stage (which makes a nice Mosfet Boost by itself, it is the same as the Mosfet stages in the Obsidian).  If I'm not mistaken, you should get around 4.5v at the output of each stage.

Judging after the shape (like a trapeze), my BS250 seems to be of this type: http://www.diodes.com/datasheets/BS250P.pdf.
So, they respect the layout above mentioned.
I will test all my BS250 in a MOSFET booster to see if they are working good or not.

Thx all again!

[oldrocker]

Will BS170's work okay in this pedal?

[gigimarga]

Will BS170's work okay in this pedal?

Teoretically it will work, but Joe D. said that it will be more hiss.

[gigimarga]

Nobody has some good voltages?

[gigimarga]

Anyone can tell me how to bias the MOSFETs in this schematic?
I found in an old version of Obsidian that it needs 2.4V on G and 4.5V on D...maybe it will work here

[WGTP]

I'm not sure of the technically correct way to do it, but in the first 2 stages the 15k resister can be adjusted.  In the last stage, the 3.9k or 2.2M. 

[gigimarga]

I'm not sure of the technically correct way to do it, but in the first 2 stages the 15k resister can be adjusted.  In the last stage, the 3.9k or 2.2M. 

Thx a lot WGTP!