Fuzz face High end issues

[Fangda]

Hi, I built a fuzz face using this (http://www.geofex.com/Article_Folders/fuzzface/fffram.htm) schematic, but with NTE 158 Ge transistors (apparantly they are the equivilent of AC 128's according to the electronics store guy)... but i have practically NO sustain for my high end...
Does anyone have any ideas on how to fix this problem?  Is it the transistors?

[Zben3129]

Hi, I built a fuzz face using this (http://www.geofex.com/Article_Folders/fuzzface/fffram.htm) schematic, but with NTE 158 Ge transistors (apparantly they are the equivilent of AC 128's according to the electronics store guy)... but i have practically NO sustain for my high end...
Does anyone have any ideas on how to fix this problem?  Is it the transistors?

I'd wait for someone elses (smarter than me  ) opinion, but NTE transistors have been known to be trouble.

Zach

[Fangda]

Dunno, I have a feeling its an issue with the value of the first resistor... when I make it (a lot) lower, my low end entirely dissapears, and my high end actually has some sustain...

[Zben3129]

Hmmm,

well it seems like NTE transistors are basically repackaged stuff that didn't meet specs on an original run by a manufacturer.


But does it have a gated sound? I.E. Chokes out and splutters dies, splattering sound?

Zach

[Fangda]

Hm, the sound is pretty OK, its just that for some reason a) it doesnt seem to have enough gain before the clipping... because it doesnt pick up anything I dont pick fairly hard, harmonics dont exist, and palm muting is total muting... oh yeah, and if I turn the volume pot on my guitar down SLIGHTLY, it picks nothing up... and the high end has no sustain as I said before
Otherwise, it sounds nice and fuzzy....

[brett]

Hi
there's a few possible causes.
If it doesn't sound "splatty" the bias is probably not too bad.  The base of Q1 should sit at about 0.3V DC and the collector of Q2 somewhere between 3 and 6 V DC.

One likely one is that you have high impedance output (pickups and or volume and tone controls).  The FF has very low input impedance, and it is normal for highs to be trimmed.  Higher output impedance of the instrument and the lower hFE of Q1 in your FF both result in more filtering of highs. 
I recommend you use RG Keen's hFE tester for germanium transistors to find out the hFE of Q1.  If it is less than about 40 you will have serious issues with the highs from most guitars (the input impedance will only be about 10k).

good luck and have a nice day

[Fangda]

ugh, as it turns out, the transistors I was using (and I got 3...) NTE 158's are absolute garbage... so now I have a bunch of glorified 5 dollar diodes....
time to go on a hunt for useable transistors....

[brett]

Hi

5 dollar

Really?  You gotta be careful, and try to get good quality, unsorted devices (which usually have 10 to 30% bad ones anyway).
I bought 100 good Ge PNP transistors for OZ$50 (US$40) a while ago.  They're really good.
In twenty years, when such devices are rare as hen's teeth, I'll pull them out and make a bunch of fuzzfaces.
cheers

[petemoore]

  Try measuring the bias voltage of the circuit first, because it sound descriptive of classic FF Ms. bias.
  See debugging instructions.
  Following along with the 'NTE158's are only useful diodes', FF should bias decently if...
  Also see GEO Technology of the Fuzz FAce
 

[Fangda]

yeah apparantly NTE transistors are just roughly grouped factory regects from other manufacturors... so I should have guessed that they would have crap gain and horrid leaking...  Like, honestly... one has like 2 gain... it pretty much functions equally well (meaning not at all) if I wire it backwards (emmitter instead of collector...)