2N3906 as Q1 and Q2 for Easy Face

[Mugshot]

quick question guys: after building a couple of Silicon FFaces, i am raring to build the EZ face adapted for positive supply as per the Tonepad project file. i understand the 2N3906 is silicon, and Q1 should be germanium. any reason why another 2N3906 wouldnt fit as transistor for Q1? i know both trannies are PNP. does it necessarily need to be germanium?


and yes, i did try reading some earlier stuff, but.. 

[petemoore]

  FF works if everythings 'right', then works differently if everything is 'just so', also, the tone and ability to clean up varies among FF's.
  "Adapted to''...? early FF's were all PNP / POS Gnd., I believe all the Tonepad FF project schematics are verified to work.
  Socket the transistors !
  Trimpot, makes great variable resistor to bias the circuit as Q2CResistor, but I've used 4k7 + 10k linear pot and that makes for 'smooth dialing' between 4k7 and 14k7.
  Make the feedback resistor easy to re-value [or otherwise modify..make the legs on top of the board a bit long, then you can put say 2 x 100k there, to try out a 50k feedback resistor.
  The sockets and trimpot are ~must-haves for finding the 'right' transistors..

[Derringer]

2n3906 in Q1 will work fine.

It just won't sound exactly like the vaunted low-gain germanium.

The only real restriction here is that if you use the positive ground scheme, then you must use PNP transistors. PNP's other than the 2n3906 will work as well.

[Ben N]

If you are building an all-silicon FF, why make it +-gnd at all?

[Mugshot]

thanks for the replies guys 

now some points (i forgot to include when i posted the thread, sorry hehe):

1. isnt 2N2906 silicon a PNP transistor?

2. i meant this layout from tonepad, http://www.tonepad.com/getFile.asp?id=36 for the EZ Face layout.

3. since the circuit has a pregain control, im thinking it no longer has the clean up properties akin to Fuzz FAces(?) and therefore may sit anywhere in the chain, even after buffers;

4. im building this with a negative ground/positive supply like most of my pedals, for convenience. the Tonepad layout specifies also that this can run on the usual Boss-style power supply;

[Ben N]

Right, so, if you want it to be + supply, - ground, then why make it with PNP transistors, when there is an NPN equivalent, the 2N3904?

[Mugshot]

Right, so, if you want it to be + supply, - ground, then why make it with PNP transistors, when there is an NPN equivalent, the 2N3904?

the layout as i see it already uses a positive supply, but transistors are PNP (Q2 is 2N3906 which i think is PNP). i have built a Tonebender MK2 using PNP germaniums before that was powered using a positive supply-negative ground like most pedals.


as for NPN transistors (silicon), i dont think i can just solder them in with that layout unless i flip the circuit(?)

[Mugshot]

2n3906 in Q1 will work fine.

It just won't sound exactly like the vaunted low-gain germanium.

The only real restriction here is that if you use the positive ground scheme, then you must use PNP transistors. PNP's other than the 2n3906 will work as well.

from what i see in the layout, the circuit is set to run on + supply/negative ground like most pedals. idk. what gives?

[Ben N]

OK, I see, Francisco already flipped the circuit, which originally used a positive ground supply, as is standard for PNP devices. Just be aware that some people have had difficulty with unexplained oscillations and such in V+ powered PNP design adaptations. Here, the point of using PNP is to take advantage of the greater availability (mojo?) of PNP germanium transistors, while the sili Q1 made the design easier to tweak. Once you are going all silicon, what you basically have is a silicon FF, which is, if anything, easier to do with NPN trannies and V+. But if you are already committed to that layout, then good luck with it, just be aware of the risks, and the fact that making Q2 silicon kind of defeats the point.

[Mugshot]

OK, I see, Francisco already flipped the circuit, which originally used a positive ground supply, as is standard for PNP devices. Just be aware that some people have had difficulty with unexplained oscillations and such in V+ powered PNP design adaptations. Here, the point of using PNP is to take advantage of the greater availability (mojo?) of PNP germanium transistors, while the sili Q1 made the design easier to tweak. Once you are going all silicon, what you basically have is a silicon FF, which is, if anything, easier to do with NPN trannies and V+. But if you are already committed to that layout, then good luck with it, just be aware of the risks, and the fact that making Q2 silicon kind of defeats the point.

you hit the nail Ben! thanks! exactly the explanation i was rooting for! 

actually i have a penchant for tonepad's layouts (small and accommodates mount in feature for pots), while GGG's is easier for modding. im really interested in using the layout but i guess i just have to trace the schematic to know what connects to what.

im equally interested in the pregain mod implemented for this circuit. another question: do you think this will still have the FF's clean up magic? because that is really magical. 

[Ben N]

Sorry, never built one so I can't say. However, I would think the low gain of a classic FF is part of that equation, so if you were going to use a silicon in Q2, you might want to find one with a lower hfe than your typical 2N3906. I'm not familiar with low-hfe PNP silicon types. (For a low-hfe NPN silicon FF variant, check out Jack Orman's YAFF article at AMZ.) Another way to do this might be to piggyback a couple of 3906s together. You can find out more abouit piggybacking by making a search here.

[drewl]

Since I have a bunch of 3906's I tried them in fuzz builds and yeah, they work but they just don't sound too good.
Try searching through some old electronic junk you may have like old radios or CB's etc.
I've found some real good sounding silicone transistors in old stuff....especially old multi-meters.

[petemoore]

  2n3906 is like a PNP version of the 2n3904.
  These are medium gain transistors [usually >200hfe], as such they make for high gain FF, and may not exhibit the same HG tone as lower gain transistors [especially for Q1 position] would, and cleanup at the guitar volume will tend to be less.
  I would use the 3906's for the high gain high gain tone, and try other [lower gain] transistors as search-time produces them.