LM3086 Fuzz Face?

[blooze_man]

The LM3086 is a 14 pin dip with 5 NPN transistors with an hfe of about 100. Would a couple of them be a good candidate for a Fuzz Face? The hfe is pretty close to some of the old germaniums.

[deadastronaut]

5 npn's. 2 connected.....so 3 seperate matched npns too very interesting.

just posted to see any answers as i have none...yet!.....curiosity etc...

http://pdf1.alldatasheet.com/datasheet-pdf/view/8838/NSC/LM3086.html

[frequencycentral]

....or a Big Muff?

[petemoore]

  NPN w/gains around 100 looks like good starting point and should make a FF work.
  Since the circuit is flexible, ballpark/low Hfe is a good place to practice hitting.
  ''Should'' works fine before 'it 'does' anything.
  ''Should'' and ''does'' sometimes separate a bit when 'it' begins and 'does' anything...further testing required to comment beyond assumptions.
  Also, a 3 pin adapter socket-jig for DMM Hfe checker to determine the Hfe variance among the individuals of the array to allow assignment of a lower Hfe Q1 than Q2, to get a comparitive of the actual gains.
  Whether Q1 is lower enough Hfe to Q2 might not matter, FF's are pretty forgiving.
  "Racing and rebuilding" 2 FF's was a hobby for a while. It is nice to know what different FF's sound like, but it tends to get extra complicated when this one was here/when/and, the other one was somewhere's else and the bias was X instead of Y and...
  They tend to light up and flame white or sort of blue, if it cleans up at the guitar volume and doesn't mush totally when 8.7'd, tune it for Fuzz definition and Clean up at guitar, not necessarily in that order of priority suggested, it's the in-between 6 and 8.something tones [some would argue it's the FullFuzz with gain preset 110% past 'max] where the FF shines, each ones a bit different and hence tends toward it's preferred setup...when set up ''right'' {IMO, fiddling with Q2cResistor value, and the gain arrangement between input and the gainpot...which is either a dedicated 1k Fuzzface pot [can check with smallbear for that] or takes some kinda 'diddley-fiddlin' since regular 1k is much too touchy in the sweet spot where you need it to 'fine tune' to further tune the gain structure of the input.
  Use of smaller value pot/w stop resistor is one solution...again...fiddley, 200ohm w/some stop resistor that makes the pot/stop R add to about 1k...it varies from FF to FF.
  Say it cleans up at the guitar, now set the gain/guitar volume for sweet fuzz, preset the gain to this setting, use fixed resistors at the input to mimic the R value/sound of the guitar volume pot setting. The input gain can be set to oversaturate the fuzzsound [full-open], or resisted just enough so that the note definition w/fuzz improves [depends on the pickups and the other stuff, all the other stuff.
  Anyway, once it's cleanin' up nice the only other thing is the voicing [which varies the input gain if the HP of input cap value changes much], not a terribly delicate balance once it's in the ballpark for the trix to smooth out.
  I guess it could wire itself right up [wouldn't that be nice] and find it's own fine tone, see Axis Face [fuzzcentral].
 

[soggybag]

I tried making a Super Fuzz out of one of these a few years ago. It didn't work, which I'm sure it's more due to my poor skills. Big Muff, Super Fuzz or Shocktave might all work.

The 3086 has two transistors tied together at the collector. Which may effect your design. This is an arrangement found in many octave effects. Figure you could build a Fuzz with three transistors and use the co-joined pair for an octave effect on the end.

There is a tremolo based on this chip in Stompboxology. All five transistors are used as a VCA with a few extra parts.

[JDoyle]

The 3086 has two transistors tied together at the collector.

They are tied at the emitter, not the collector, so as to facilitate a matched pair for a differential amplifier.

All of the transistors will be as matched as one can get because they are all grown at the same time, so one really only needs to measure the hFE of one of them to know the hFE of all of them.

Regards,

Jay Doyle

[soggybag]

Oops, you are correct, two of the transistors share a one pin for their emitters.

If I recall all of the transistors are about 100 hfe. So they are not nigh gain. Might be good a for an Si Fuzz Face. Use the extra transistors for an octave up or tone control. 

[petemoore]

  The 3086 has two transistors tied together at the collector.
  So...it'd work for a common emitter project where all stages are emitter grounded.
  I'm trying to think of one, then one that'd do well with low Hfe transistors.
  Perhaps some kind of feedback between emitters tied through resistor to ground in an effort to control gain, or some other configuration w/all emitters common and grounded.

[soggybag]

There is a very interesting looking tremolo in Stompboxology that uses the 3086 configured as a VCA.

http://www.moosapotamus.net/IDEAS/stompboxology/Vol13No2/Page_14.gif

[PRR]

3086 is useful for a few things, is out of production.

If you need 5 transistors, buy 5 transistors.

Save (or sell) the 3086 for those few things which "NEED" the five matched transistors.

[soggybag]

I can't think of any guitar stuff that uses this chip. Though it seemed to popular with the analog synth crowd, if memory serves.

[diydave]

breadboard, and have fun.
If it's no good, you could still use (or sell) the chip for something else. 

[blooze_man]

Yeah...I guess I should buy one so I can try it out

[JDoyle]

3086 is useful for a few things, is out of production.

True, but the 3046 (better matching) isn't. Nor is the 3083 is my memory serves...

[R.G.]

There was one boutique repro of the big muff that used a transistor array chip (the term for these collections of matched transistors) to implement the entire circuit.

I suspect that it was done to be obscure, as there is no need for matching in that circuit.

The SuperFuzz circuit does need one matched pair if it's available, in the octave generation section, although it can be done satisfactorily by hand matching or a variable offset trimpot.

[mac]

Kay Fuzztone F1, you need just a diode.   

mac

[soggybag]

Good idea! Use the extra transistor as a gain recovery after the tone control.

[petemoore]

There was one boutique repro of the big muff that used a transistor array chip (the term for these collections of matched transistors) to implement the entire circuit.
  I Can't recall the part # of the chip, IIRC 14 pin chip w/ a set of four transistors suitable for BMP circuit, made for tidy PCB and fewer parts.

[Dragonfly]

I kicked around the idea of using a CA3086 transistor array to build a SF or a Kay F1 a few years back, but never got around to it....should work ok though.

[roseblood11]

I think the 3086 is really a perfect fit for a Super Fuzz clone.
I remember that someone at "the other  f o r u m" mentioned that The Edge/U2 uses such a custom made pedal.
But  it´s not easy to find that chip...
Should be possible to find another usable transistor array that is still in production.