Fuzz Face Current Question

[modsquad]

I built the 70's NPN boutique fuzz from http://www.generalguitargadgets.com/pdf/ggg_ff5_sc_b70.pdf.   I have a bunch of BC170s that I was going to use.   So I socketed them and the Fuzz sounds like an overdrive.   I noticed on the datasheet that the average Hfe at Ic = 2mA is between 200 and 450.  At Ic = 10 uA its 120 which is more desirable.  Can I just increase the resistor value into the trimmer to decrease the current or am I way off base.

[modsquad]

Also the Fuzz and Mid control don't seem to do much either.   Kind of disappointed.

[brett]

Hi
The fuzzface already has a low current through Q1 (about 0.1mA IIRC).  That explains the benefits in FFs of using devices that have have low hFE at low Ic (aka a "knee" in hFE). e.g. a medium power device might have hFE of 50 at 0.1mA, and 150 at 100mA.  These are useful in fuzzfaces.

The best way to reduce gain is to build a "piggyback" device.  You can think of it as a "live" transistor "carrying" a "dead" transistor.  For details, use the search function.
cheers

[zyxwyvu]

Also the Fuzz and Mid control don't seem to do much either.   Kind of disappointed.

Looking at the schematic, both ends of the mid pot are connected to +9V, so it shouldn't do anything. It looks like an error in the schematic. The layout seems to be done correctly, though. It has the junction of the 220, 1k and mid pot not connected to +9V. Did you build yours based on that layout, or the schematic?

[modsquad]

I used the layout.  Now I didn't have 1k pots so I took a 1k resister and soldered the ends to 1 and 3 of a 25k pot to get the 1k range.

[mac]

If you want to play with resistors and currents,
http://www.diystompboxes.com/biascalc/
PM if you have some doubts about how to use it.

I haven't see that GGG schem, going to try it.

My Si FF has a couple of 2n2219A (110,117), no gain pot (useless IMHO), variable input resistor and variable input cap. Small pf caps from base to gnd on both Si. Sounds amazing.
My favourites for Si FF are 2n2369a but sometimes they pick up RF interference.
Some options, bd139-10, or any bdxxx low gain, mpsa42, bc140/1-10, 2n3903, 2n2218.

mac

[Dragonfly]

You have a problem with your build....not necessarily "transistor issues".

The "fuzz" and "mid" pots aren't changing much, which is a clue...though the schemo for the mid pot is drawn wrong (plus i wouldn't use a 22uf input cap, as the schemo says...should be 2u2)

Another clue is the low amount of fuzz (more overdrive-like, as you said), especially with higher gain (hfe) transistors.

check your grounds, transistor voltages, etc....this build will put out tons of fuzz if built properly.

[modsquad]

The voltages on the trannies are spot on based on the build document.  I will try and swap out the input cap and see if that's an issue.