Fuzz Face bias indicator LED?

[Ronsonic]

Just adjust the value of the resistors to dial it in so the LED turns on at the voltage range you select.

[zyxwyvu]

The only thing I would say about having an LED that lights when the voltage is at 4.5 volts is that many guys report that their FF's sound best at a slightly higher voltage (like 4.75, etc.).  At least the LED would tell you when you are at the 4.5v point, and you could still adjust slightly from there, but that points out one advantage of a digital readout, you could adjust to exactly whatever setting you find the best.

Al

If you make R1 or R2 variable in my schematic, you can tune the target voltage. Here is the equation:

Vt = target voltage
Vs = supply voltage
Rv = VR1 in schematic

Vt = Vs*(R2+Rv/2) / (R1+R2+Rv)

This reduces to Vt = Vs/2 if R1=R2.

While we're at it, the voltage range for the LED lighting up is this:

Vtr = target voltage range

Vtr = (Vs*Rv)/(R1+R2+Rv)

[frequencycentral]

You can try a window discriminator circuit like this:



It's based on a circuit on page 669 of the Art of Electronics, with a few modifications for your pedal. Just connect the bias voltage to "IN1", and the LED should light up whenever it's close to 4.5V. VR1 controls the sensitivity. Low resistance = narrow range, High resistance = large range. Make sure to use comparators, not opamps.

I think it would be worth designing a PCB layout for a Ge FF including the circuit above as well as a charge pump for -9v. Sounds like a plan - a Ge FF that will play nice with 9v wall warts and additionally includes a visual indication of bias.

[Morocotopo]

Rick, I already made a PCB, it´s a FF with this bias pot/LED included, and in / out FET buffers from a guy in the net, search "poker face". The thing is that it´s for a negative ground version, should be easy to change it to positive ground, and/or add a -9V charge pump to the thing. I´ll post it later.

[pinkjimiphoton]

http://web.archive.org/web/20030703001207/http://myweb.absa.co.za/g.landry/Smileyface.htm

in case anyone needs this info:

http://web.archive.org/web/20040107004417/http://myweb.absa.co.za/g.landry/Smileyfacesch.pdf

[deadastronaut]

cheers jimi, i'll look into that led mod!!!..cool

[pinkjimiphoton]

cheers, rob, i hope it works out!!

i took my ff apart last nite, the one i always use live. couldn't get the fuzz pot working right, and i figured, since this was one of my first builds, i'd go thru it.

a good thing. it was ALL KINDSA afu!!

i had a 50k trimmer going to the hi side of the 470r resistor. no idea how it worked..worked like a volume control. what did i know...absolutely nothing!! also discovered i had one side of the 100k resistor going to ground, instead of between b and e of q1.

that explained why the fuzz pot never worked out right. duhh. i mean DUH.

fixed that.

i used a proper 10k pot as an adjustable bias control, and put a 3.3k resistor in series with the wiper...now, at minimum settings, it's gated and fuzzy, or you can turn it up into what is almost a very clean compressor. kewl.

still got the nte ac128 "equivalent" ge in q1, a 3906 in q2. did  the britface trick with an 1n34a on q1 to help stabilize it temperature wise.

rewired the switch; i had had it grounding the circuit board, i undid it and made it easier. also had the led wired wrong.. i mean, i'm surprised this thing ever worked!!!!

changed the fuzz pot from 5k to 2k. may do the "hendrix" mods, but i've built a bunch of fuzzfaces using that, and this is bone-stock almost, and to my ear sounds better. i may go to 100k on the output pot, this thing is at unity gain now about 9:00....unity gain used to be around 3:00..

finally, a 100u/1n4001 half wave filter on the power jack.

huge difference.  i MAY have to re-do the power jack filter, cuz i screwed up and soldered in the network backwards, and i'm noticing a bass "ghost note" when i play hard that didn't used to be there. thinking it may be the diode leaking or the cap, cuz did i mention i f'd up and put 'em in backwards?

anyways...my primary fuzzface is now healthy, and i can tweak the bias externally, which for me is easiest. i don't care about it being at 4.5v, i generally set it closer to 6 or 7 volts usually to find the "sweet spot"...i do it by ear. mounted it at the top of the pedal, next to the power jack.

tonite, i'll find out if it worked out right...i used to have to keep a heat gun with me to zap the face with if it got too ornery sounding.

part of that was i had socketed the transistors. not always a good idea, as once you swap a couple transistors around, it tends to get looser than a...
anyways, mounted the tranny's in fresh sockets, tinned those, and got a good fit.

no more crappy fuzz. if it ain't happy, i juice or dejuice until it finds the sweet spot.

next experiment is gonna definitely be one of the other ideas suggested in this thread.

rock on!

[Morocotopo]

...i used to have to keep a heat gun with me to zap the face with if it got too ornery sounding.

I mean...





The things we do.

The things we do!!!

Well, starting by plinking stretched wires over a magnet to make music... I can see why people from the outside tends to look at us as sightly, ermm, crazy.

" Why do you need that old, ugly metal box that costs $1000? Can´t you get a new one? We could buy a new couch!"

I can see you explaining to a policeman "Sir, that´s not a GUN, it´s a HEAT gun, , I need it to heat the Fuzz Face..."

The bias pot/LED is a really useful addition to a Fuzz Face in my opinion.

[R O Tiree]

Well, starting by plinking stretched wires over a magnet to make music...

Some would argue that the term "music" is debatable...

[pinkjimiphoton]

 

well, the external bias pot with the resistor trick i used worked great.. even in creepy weird new england different every 5 minutes weather,
all i had to do was give a quick tweak as the temp fluctuated..

and as an extra added bonus, it lets me dial it from clean almost compressor to blatty nasty filth. may not be for everybody, but it worked for me!

look forward still tho to experimenting a little bit more..i really like the idea of having that led. you can tell what your tone would be by shade of colour.

something about that just makes the ol' pupils dialate, and a sudden desire to sit cross legged on the floor playing bongoes to inna gadda da vida..

yah, the heat gun story is true.. it's actually an embossing tool, looks like a mini blow dryer.

i'd yank out the input jack of the face if it got too "farty" and blast some heat in there for a couple seconds. the face would then stop working.

as the temperature internally approached the external ambient temp, suddenly it would stabilize and sound AWESOME.  until it got too cold.

i did the brit face trick to it, never understood (until now) why it didn't work.

remember i said i had that 100k to ground? well, when i added the diode, i didn't notice that i effectively had it wired so it was diode>100k>ground...so not only did the gain pot not work...

man. the surprising thing is i gigged with it like this for two years, and never noticed the gain pot didn't work. it was always on 10.

that's why it makes me laugh to myself when i see some of the stuff other guys mess up, cuz man, in THAT respect, i can definitley keep up!! lol

anyways, happy to report, my fuzzface is healed, healthy, and sounds great hot OR cold now. the combo of britface mod and external trimmer really did the trick..you can dial in any amount of fuzz down to the resistor.

it may have been discussed in this thread, or may be i am confused...if you use the chip to maintain a constant half voltage, and the led turns orange at half voltage to tell ya you've got it dialed in, the chip will clamp it to where YOU set the sweet spot, correct?

one more dumb question...if using a trimmer as a bias pot (or even a pot, like i did) do you need to tie the unused pot lug to ground? what would be the difference between that and a "sag" pot?

newbe...please don't shoot..

man...hard to get that out and make sense.. sorry.