FF Axis-Piggy Puzzling

[Nick C.]

I am working on what is a cross of a Miss Piggy and AxisFace. Something happened yesterday that I haven't pinpointed yet. The sustain, even at max fuzz is very poor. Is this pickup loading? Sounds like the guitar running out of gas. Two changes I made which may be the fault, I removed a fixed "smooth" 10k series resistor at the input and have dropped the piggybacking resistors down to 1k and 2k2 to lighten the fuzz. When I bumped them up to 2k2 and 4k7 still the same. I didn't have this when using two 10ks but the fuzz was really hot.

BTW I am using C945 transistors, gain per the datasheet is 50 @ .1ma 200-400 @1ma. Advice?

Nick

[petemoore]

BTW I am using C945 transistors, gain per the datasheet is 50 @ .1ma 200-400 @1ma.
  I guess they're NPN so the data sheet is ok for the  ballparking above^.
  And shows the collector in the middle...
   Advice?
  You can get NPN's in the 70-150hfe range.
  Piggybacking threads about reducing gain for FF use...
  Debugging a FF can sometimes be tricky, see related sticky thread, debugging simply for the sake of determining whether it is actually debugged, or having a second known working FF to compare to helps.
  The symptoms you describe could be a miswired or misbiased circuit.
  How is the output level ?

[Gus]

If I understand the first post

You built it with piggyback transistors at the first transistor location and have a 10k series resistor before the fuzz?
A build without the series 10K at the input should have more gain when direct to the guitar.

2SC945 have a different pinout than a 2n3904 did you get the pinout correct

[Nick C.]

I'm using the c945s cause I got 'em. Would like to use low gainers next time but desided to try piggy backing. Pinouts are correct. My 1st thought was biasing but it's on the money. 4.5v @ Qc2 8.9v supply.

Could it be that the piggy emitter resistors, I'm piggying both Q1 and Q2, are too low. R1=1k R2=2k2 then tried 2k2 and 4k7. I'm trying to get the "Ge like" fuzz I've read about here, but honestly I've never played a Ge FF so I'm not sure what I'm shooting for. What I have gotten easily is a Jimi BOG sound, very saturated compressed long sustain. When I lowered the emitter resistors the sustain went out the window and it feels like loaded or sucking.

[Nick C.]

I took a look at some datasheets for the 2sc945 (I was using a 2pc945 datasheet) and see the gain as 170-210 which is a little lower than the PN100 the Miss Piggy was designed for. Maybe the recommendation for 1k and 2k emitter resisters by Brett are too low for me and I'm loosing too much current. I'll try some larger resistors tonight. Am I on the right track?

[Derringer]

I am working on what is a cross of a Miss Piggy and AxisFace. Something happened yesterday that I haven't pinpointed yet. The sustain, even at max fuzz is very poor. Is this pickup loading? Sounds like the guitar running out of gas. Two changes I made which may be the fault, I removed a fixed "smooth" 10k series resistor at the input and have dropped the piggybacking resistors down to 1k and 2k2 to lighten the fuzz. When I bumped them up to 2k2 and 4k7 still the same. I didn't have this when using two 10ks but the fuzz was really hot.

BTW I am using C945 transistors, gain per the datasheet is 50 @ .1ma 200-400 @1ma. Advice?

Nick

can we see a schem of what you've bilt? what stage is the build? breadboard, perf/strip board?

I was actually thinking about building an axis face with piggy backed Q's in the first position and a normal Q oin the second.

[Nick C.]

It's on the breadboard. It started life as an Axisface with the wrong transistors. I replaced the fuzz and smooth pots with fixed 1k and 10k resistors. It sounded very good more mid range focused. It really knocks the ear bleeding highs and headache inducing bass off. Since my transistors are too hot the fuzz was way over the top. I read about the MissPiggy and thought I'd try piggybacking. I tried just Q1 and it was still too hot.

What I'm finding is that the piggy resistors really need to be dialed in just right for your particular transistors. 10k+10k was too hot, 1k+2k2 was too low. Last night I think I got it just about right with either a 3k3 or 4k7 on Q1 and 4k7 on Q2. Very nice dynamic usable fuzz! The patient breathed.

Interesting to note that with the piggybacked Qs it no longer needs as much filtering of the highs as the Axis, so the 100pf at Q2 is out and the .033uf is optional. The smooth resistor is out too. Also I lowered the 1k2 between the collectors to 470R and I think it got more dynamic. Maybe someone can explain that one. Funny it's more like a tweaked MissPiggy than an Axis now.

[Nick C.]

[Derringer]

Here's a tonebender style circuit I built using 2n3903's (hfe~140) in piggy backed fashion.



I like the soft mod and just left mine adjustable. It really doesn't introduce any noise ... and if you back it all the way off it's not even in the circuit. The soft ability will give you the rolled-off-volume = clean up effect much more dramatically than otherwise if that's your thing. I like having adjust-ability ... different guitars etc

Yes, choosing the correct piggyback resistor is definitely finicky. What I did was set up the trannies on a perfboard and then run leads to my DMM which measures hfe. I used a pot between emitters and just dialed in where I thought it was good. The first time I did it, I shot for hfe's a bit lower than what I ended up with and I just couldn't get the circuit to sound right. It wouldn't pass signal all that well with the lower hfes ... I think they were in the mid 60's or so. I originally had the 3rd Q position piggybacked as well yielding a gain around 100 .. but I tried it with just the one Q in there and it sounded better ... so I left it like that.

And yeah, having that lower hfe definitely tames some of those highs. You can see that the only place I used a B-C cap is on the sole non-piggybacked Q.

470R is what was used in that position in the orignal FF so maybe you just have a vintage ear 

Cool man, looks like you have a fun circuit there. I need to build a FF. It was the first circuit I built but I never bothered to tweak or box it up. I just did it to see if I could. Now look at the mess I've become


Oh .. and something you might want to try ... see what it sounds like if you take the output directly from the collector of Q2 ... between the 10K trim and the collector. It yields less gain.

[petemoore]

  I used an 8pin IC socket for Q1a-b.
  Q1A on the left three lugs [leaving socket pin #4 as extra emitter socket.
  Q1B on the right of the same socket, it's emitter having pin 5 as 'extra' emitter socket.
  Use a pot with a 'plug' [get creative] so that you can try various R values between the transistors emitters.
  Then pick a resistor and install it there [from pin 4 to pin 5, along the bottom of the socket] instead of the pot.
  Makes nice sturdy FF anyway, I used to cut sockets in half, but now look for ways to assign all 8 pins with the socket intact, makes great sense for PiggyFuzz tweeking, both transistors and the pig-resistor are easy to swap.

[Gus]

The .1uf and the 470 form a lowpass filter.  If you had a 1.2K and a .1uf the lowpass filter is set to a lower frequency.  Less highs can make the sound duller.
  Pick your wanted output by the top resistor make the bottom smaller if you make the top bigger to keep the same total that bias like you like.   maybe you find you like a Q2 total collector of 10k then you could have 9.1K and 910 or 8.2 and 1.8K or select the top and adjust the trim
  Then adjust the cap across the top to TASTE.

1/(2 pi RC) will give you an idea of the -3Db point

http://www.diystompboxes.com/pedals/gusFuzzFace.gif

I like a 1K .01uf but it is a taste issue and what amp and guitar

[Nick C.]

You guys got some interesting ideas. I tried Derringer's idea about taking the output straight off the collector. Very cool! More gain not less, clearer more like a distortion less fuzzy. Something I'll have to play with in the future.

8 pin IC sockets seem perfect for piggybacking, thanks Pete.

Gus, I really meant to have a rolloff of 3388hz The AxisFace is 4021hz, giving it a steep mid peak and sounds great at max guitar vol, full fuzz. Rolled off volume sounds better to me brighter so that's why I'm making it switchable.

It's amazing how much you can do with such a simple circuit. The parts are so interactive. After more tweaking this weekend, I'm still not ready to box it up. I'm now liking a .1uf output cap vs the .01uf, but this seems to have effected the fuzz which has me tweaking the piggy emitter resistors again.

I get into these cycles of tweaking a circuit on the breadboard over and over (over 3 weeks on the FF) trying to get some perfect sound with a wide range of tones 'till  I get sick of it and move on to something else. I better stop and just box it up!

[Derringer]

and then when you get sick of the boxed up version ... you can gut it and re-use the housing for something else

Box'em up .. it's good practice