Specific hfe for silicon fuzz faces?

Started by mcasey1, November 25, 2007, 10:46:35 PM

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mcasey1

In fuzz face circuits, is it pretty much standard practice to just grab a few silicon trannies (BC108) and pop them in, not really looking for those 90 hfe-130 hfe values that are typical for a germanium version? 

brett

Those low hFEs for Q1 in a FF determine the input inpedance, and hence the tonal balance, so it helps to keep an eye on them.  Over 100 isn't usually good for Q1, unless you want low loading of your pickup and the extra treble.  The hFE region of 50 to 90 is usually considered more prospective.
cheers
Brett Robinson
Let a hundred flowers bloom, let a hundred schools of thought contend. (Mao Zedong)

yeeshkul

shall i piggyback(+ resistor between emittors) the first one?

petemoore

  8 pin IC socket, left 'column' is Q1'a', right column is Q1'b', from the top socket lugs: collector, base, emitter.
  this leaves the 2 bottom socketlugs.. assigned to the two emitters, allows various value resistors to be stuck across the bottom of the socket, across the two emitters, making it easy to try R values.
  But I've also used a large resistor [leads bent to form plug for socket] with a >20k pot wired across it as a plug in for variable control, then replaced it with a chosen fixed value.
  Should you find a 2XQ1 - R = gain structure you like, the single 8 pin socket can have a bent back matchstick to elmers ~[easy break] glue the transistors down.
  For experimenting with plug in's...also a solid base keeps things sturdy, my preferred method of PBFF building /testing.
  For Q1, [and only 1, Q1] careful choosing of the unit used may fall into a gain you like, sampling various low gain Si's recommended, a great sounding FF can be built using 2 Si transistors [see Fuzzcentral].
  PBing Q1 allows adjustment of the positions Hfe gain, a wider range of transistor types can be made to the low gain which FFQ1 often finds desirable.
  Q2 is a bit easier to choose transistors for, and 110+ hfe transistors work well here. 
  Joe Gagan's Easy Face, which is hybrid FF [Ge / Si], biases ~easily for a FF, reduces Ge finickyness, bias drift and Hfe sorting down to 1 transistor position, makes one fine FF, excellent design, not just easier, for swaps, 8 pin IC assignment to FF board = very stable sockets [2x 8pin IC sockets..for both Q and both DC blocker swappings], bias pot always on Q2 collector  :icon_exclaim: FF tweekboard.
  [see multi-face at ROG.
  GEO technology of the FF is at GEO.
 
Convention creates following, following creates convention.

mcasey1

#4
But for a "traditional" sound of the BC108/109 version of a fuzz face, would it help to go for a low gain Q1 or just pop a BC109 in?  I only ordered two from Steve and I know specific gains cant be requested.  I like the ballpark sound of the silicon version of the Sunface by analogman.  It has a smooth thick tone that is not over-the-top.

http://video.google.com/videoplay?docid=5866223478520696846&q=sunface&total=68&start=0&num=10&so=0&type=search&plindex=1

That is the fuzz face tone I am aiming for.  It doesnt clean up as well as a germanium version, but it is obviously useful with the guitar volume rolled back.  Do you think I would get closer to what I am describing with a low-gain silicon Q1?  I ordered a 2N2369 low gain silicon transistor  as well.  Thanks!

remmelt

Sorry, can't add to the subject, but I love the way that guy in the video starts singing along with his playing. Great sound, too.