hi guys! I'm new to this forum, and a new to pedal building in general..
I have made a PNP fuzz face on a breadboard, and I'm trying to get it right before I start soldering - but it doesn't sound good, and the voltages seem off, compared to what I've read.
I'm using an old OC71 Q1 which, when I stick it into my DMM, clocks at 140, I'm guessing that's 140 hFe? I'm not quite sure - and an AC128 reproduction in Q2.. I have two more OC71's, but they both sound worse than the AC128 in Q2
It's very much like this:
(http://fuzzcentral.ssguitar.com/fuzzface/fuzzfacepnpschematic.gif)
except these
250K volume pot instead of 500K
22uF instead of 20uf in the feedback loop
and instead of the 33k going to C of Q1, I tried a 10k (because the voltages on Q1 were quite low, so I tried to compensate)
also, instead of the 8K2, I have a 5k pot wired as a variable resistor, and a 2.2K and 3.3K in series
it does sound better with 10k instead of 33k in it, but still nothing like I imagined.. it doesn't have that sweet velvety fuzz tone that I imagine a germanium fuzz should have, it doesn't clean up very well, and it has this overall farty, spatty quality to it.. It does sound cool when I turn my amp volume(super reverb) up to like 6-7, but at 2-4, it doesn't sound very good at all
I've made sure that I put the transistors in the right way, also tried flipping them around just in case, and got no sound.
Battery = 8.62v
Q1 (with a 10k resistor instead of 33k to C)
C = -0.58
B = -0.11
E = 0
Q2
C = -4.5 (i tinkered with the pot until i hit this)
B = -0.58
E = -0.5
thanks guys
Q1 base voltage is off, it should be similar to Q2 ~ -0.6V.
Quote from: disorder on August 23, 2016, 01:25:42 PM
Q1 base voltage is off, it should be similar to Q2 ~ -0.6V.
thanks man, but how can I change it?
edit, read it wrong.
you can't measure Ge in a voltmeter. There is a technique at geofex or small bear. Where'd you get the Ge?
This might sound silly, but what voltages do you get when you put a 33k instead of 10k?
Make sure Q1 is good, and oriented correctly.
http://www.vintage-radio.com/images/figs/transistor/pinouts.gif
(viewed from underneath transistor)
Quote from: Hemmel on August 23, 2016, 01:44:23 PM
This might sound silly, but what voltages do you get when you put a 33k instead of 10k?
just measured, I got this:
Q1
C = -0.20
B = -0.9
E = 0
Q2
C = -7.33
B = -0.20
E = -0.14
Quote from: blackieNYC on August 23, 2016, 01:44:14 PM
edit, read it wrong.
you can't measure Ge in a voltmeter. There is a technique at geofex or small bear. Where'd you get the Ge?
ah I see.. I got the 3 OC71 on ebay, from this lot http://www.ebay.com/itm/OC71-CV7005-MULLARD-NOS-/260886099837
and the ac128 is new and from banzai I think..
Quote from: disorder on August 23, 2016, 01:50:01 PM
Make sure Q1 is good, and oriented correctly.
http://www.vintage-radio.com/images/figs/transistor/pinouts.gif
(viewed from underneath transistor)
just tried replacing it with another oc71, it changed the voltages a bit, but still way off.. and it's oriented correctly as far as I can tell, I checked the out the pinout before putting it together, but also tried flipping Q1 both ways, and it didn't help
oops, double post
Can you probe the voltage before the 33k or 10k resistor?
Make sure there's -9V there.
Quote from: Hemmel on August 23, 2016, 02:12:43 PM
Can you probe the voltage before the 33k or 10k resistor?
Make sure there's -9V there.
yep, there's -8.something volt, the same as in the battery
Can you also double-check the resistors?
Probe them with your DMM and make sure they are really 33k (or 10k), and also check the 470 Ohm.
While you're there and if your DMM has the capability, check your 2.2µF cap.
Quote from: Hemmel on August 23, 2016, 02:26:09 PM
Can you also double-check the resistors?
Probe them with your DMM and make sure they are really 33k (or 10k), and also check the 470 Ohm.
While you're there and if your DMM has the capability, check your 2.2µF cap.
just checked - 33k is what it's supposed to be and the 470 is amazingly exactly 470 ohm..
and I don't think my DMM can do that, but I'm pretty sure it's good, I had a 1uf in there before, and had the same problem
thanks man!
Welcome artr. You might want to learn how to check Ge trannies gain/leakage current. It has helped me immensely in my Fuzz Face and Tone Bender projects.
I like Steve Daniels' method found here, scroll down to FAQ #24:
http://diy.smallbearelec.com/HowTos/FuzzFaceFAQ/FFFAQ.htm
After you decide whether or not the transistor is leaking too much, you can move forward and have a headstart on which position might it work best in.
There is also a way to determine almost exactly what value resistors to use after you know the gain of your trannies... more on that later, if you want ;)
Good luck!
Quote from: artr on August 23, 2016, 02:07:09 PM
Quote from: Hemmel on August 23, 2016, 01:44:23 PM
This might sound silly, but what voltages do you get when you put a 33k instead of 10k?
just measured, I got this:
Q1
C = -0.20
B = -0.9
E = 0
Q2
C = -7.33
B = -0.20
E = -0.14
Quote from: blackieNYC on August 23, 2016, 01:44:14 PM
edit, read it wrong.
you can't measure Ge in a voltmeter. There is a technique at geofex or small bear. Where'd you get the Ge?
ah I see.. I got the 3 OC71 on ebay, from this lot http://www.ebay.com/itm/OC71-CV7005-MULLARD-NOS-/260886099837
and the ac128 is new and from banzai I think.. Quote from: disorder on August 23, 2016, 01:50:01 PM
Make sure Q1 is good, and oriented correctly.
http://www.vintage-radio.com/images/figs/transistor/pinouts.gif
(viewed from underneath transistor)
just tried replacing it with another oc71, it changed the voltages a bit, but still way off.. and it's oriented correctly as far as I can tell, I checked the out the pinout before putting it together, but also tried flipping Q1 both ways, and it didn't help
Your collector voltages look alright. Q1C measures only a little low, but then again your battery isn't all that fresh.
The base voltage on the other hand is rather high... no idea how that happened.
> Q1 base voltage is off, it should be similar to Q2 ~ -0.6V.
These are Germanium parts. Vbe is likely to be ~0.1V, not the ~0.6V of Silicon.
The 0.5V at Q2 Emitter "is" the Q1 Vbe +plus+ the drop in the 100K base resistor due to Q1 base current. 0.39V drop in 100K is 0.004mA. If "33K" is 10K the collector current is near 0.7mA. This gives hFE like 180, which is high for old GE, but stunningly similar to what his meter told him (and for different test point).
I think it may be working "OK". Guitar impedance, knob settings, and finger-touch may be important. Any circuit will be "harsh" if hit too hard, "cream" may need delicate touch.
Most germaniums do have lower hfes, but some types are higher gain or have a wide range of gains, like OC44s. Some Mullard data books list the hfe spec for these as 40 to 225 - and apparently they meant it. (http://www.ebay.co.uk/itm/1x-NOS-MULLARD-OC44-YELLOW-SLEEVE-GERMANIUM-TRANSISTOR-0C44-for-RADIO-FX-PEDAL-/262540022158?hash=item3d209ad18e%3Ag%3Af24AAOSwqfNXloQA&nma=true&si=2Qom3gMe6u%252FcVXCMNq1iFuOKI1A%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557)
I'd expect OC71s to be lowish gain and have a fair amount of leakage. Unfortunately I have no experience with these metal can military types, but I guess they might have some funky specs?
If it's working alright, it may just need some more swapping around of transistors to find a pair that works well together.
hey guys, thank you so much for the input and the warm welcome!! i really appreciate it
Quote from: Ben Lyman on August 23, 2016, 02:49:59 PM
Welcome artr. You might want to learn how to check Ge trannies gain/leakage current. It has helped me immensely in my Fuzz Face and Tone Bender projects.
I like Steve Daniels' method found here, scroll down to FAQ #24:
http://diy.smallbearelec.com/HowTos/FuzzFaceFAQ/FFFAQ.htm
After you decide whether or not the transistor is leaking too much, you can move forward and have a headstart on which position might it work best in.
There is also a way to determine almost exactly what value resistors to use after you know the gain of your trannies... more on that later, if you want ;)
Good luck!
so I did this exactly (i'm definitely interested in the way of resistor determining btw), and it turned out that the oc71 I was using has these specs :
"leakage current: 455ma
collector current: 2020ma
(2020 - 455) / 8.66 = 181hFe" (which PPR, you calculated exactly right, have no idea how you did it haha amazing)
and the AC128 in there has a leakage of 705 and hfe 290, but luckily, the other two OC71 have better leakage (211 and 166) and gains of 71 and 75! so I put the 71 in Q1 and 75 in Q2, and that definitely seems to have improved the situation of the sound, but now the voltages are:
now powered by a very lively 9.6v ish battery
Q1
C = -0,46
B = -0.09
E = 0
Q2
C = -5.73 (with the bias pot turned all the way down(up? i don't know))
B = -0.46
E = -0.35
does that seem reasonable? what are the standard voltages for a ge fuzz face? i've found a lot of different answers in my googling of this
soundwise - i recorded a clip after putting in the other trannies
https://soundcloud.com/artemr/fuzz (https://soundcloud.com/artemr/fuzz)
I'm interested to hear if this is what a germanium fuzz normally sounds like..
to me it definitely sounds better than before, cleans up well (especially with the voltage high on the collector of Q2, it retains these really nice highs, which get lost a bit when i turn it down), but the problem for me is that I don't know how it's supposed to sound or feel.. so I don't know if I might be missing out on some magic that's still to be found in the cirquit.. it still sounds a bit "squeaky". also, it sounds like crap unless i turn the amp up quite loud, but I've read that this is a thing with germanium stuff. also 2: I need to EQ the amp differently than I usually do, take off some treble and add some bass, otherwise it's very sharp, is this normal as well? a little unpractical, because this is dull when I turn the fuzz off
thanks again for the help
Nice chords and playin!
about the sound, I guess it's a bit different from a FF (though I never heard a real one actually :().
Lacks some sustain I think, and if you can hear chords at maximum gain, then something is wrong.
If it please you, then it's your magic but I bet you can do more than that. Keep searching
Hey, nice playing! I think it sounds about as good as a Ge FF sounds but maybe I'm not to picky. haha. A TB MKII will go more, I think that's the next circuit for you to tackle!
Here's the link to Joe Davisson's "Electronic Math Helper"
http://www.diystompboxes.com/analogalchemy/emh/emh.html
It's not foolproof, but then nothing is when dealing with Germanium.
I think it's still a good idea to use the trimmer, and even mount it on your pedal top for Ge pedals because you will appreciate how quickly you can adjust it when the weather changes
Wow, nice playing! Way better than me (I'm terrible at slide).
I think your FF sounds great. Does it sound like a real one? Well, they were all different, right? I'm sure yours sounds like some of the vintage originals. The one I built is really gainy, and doesn't clean up well. It's just the nature of the transistor pair I used. I had to voice it differently with a (much) smaller input cap to make it a usable sound. Now it's kind of it's own thing, and that's okay I guess. I would like to build another with lower gain that sounds like yours. I'm bookmarking this thread so I can call up the specs you used.
One mod I really like for a FF, maybe you would like to consider it, is a variable resistor at the input. I used a 100KL pot. Turn it to zero and it's out of the circuit for the stock sound, but that resistance comes in really handy when running other pedals in front of the fuzz. If I put my tube screamer or rangemaster in front, I can dial in some pretty cool distortion sounds, but it doesn't work out for me without that added resistance at the FF input.
Quote from: artr on August 23, 2016, 07:49:58 PM
now powered by a very lively 9.6v ish battery
Q1
C = -0,46
B = -0.09
E = 0
Q2
C = -5.73 (with the bias pot turned all the way down(up? i don't know))
B = -0.46
E = -0.35
does that seem reasonable? what are the standard voltages for a ge fuzz face? i've found a lot of different answers in my googling of this
Perfect. You're still well within vintage Fuzz Face territory with your voltages. And more importantly: it sounds good! Congratulations!
I completely forgot about the problems you still have with the circuit:
I guess your amp may be a little too clean with the volume low. The clean sounds a Fuzz Face works well with are rather warm.
As your pedal is still too bright for your setup, try using a 500k volume pot. That should give it a bigger bottom end.
thanks a lot for the compliments and input guys!!! well, i guess i'm going to put it into a box now, looking forward to that
Quote from: Ben Lyman on August 23, 2016, 10:56:18 PM
Hey, nice playing! I think it sounds about as good as a Ge FF sounds but maybe I'm not to picky. haha. A TB MKII will go more, I think that's the next circuit for you to tackle!
Here's the link to Joe Davisson's "Electronic Math Helper"
http://www.diystompboxes.com/analogalchemy/emh/emh.html
It's not foolproof, but then nothing is when dealing with Germanium.
I think it's still a good idea to use the trimmer, and even mount it on your pedal top for Ge pedals because you will appreciate how quickly you can adjust it when the weather changes
checked out the MKII, that's gonna be my next project, especially after i found a clip of jimmy page playing it...
the calculator told me almost exactly the resistor values i have in now, 32.something in the "33k", so that's close enough i guess. and i'm definitely going to have the voltage trimmer in, also for the variation in tone.. i have this huge aluminum knob for it haha
thanks man!
Quote from: thermionix on August 24, 2016, 02:10:39 AM
Wow, nice playing! Way better than me (I'm terrible at slide).
I think your FF sounds great. Does it sound like a real one? Well, they were all different, right? I'm sure yours sounds like some of the vintage originals. The one I built is really gainy, and doesn't clean up well. It's just the nature of the transistor pair I used. I had to voice it differently with a (much) smaller input cap to make it a usable sound. Now it's kind of it's own thing, and that's okay I guess. I would like to build another with lower gain that sounds like yours. I'm bookmarking this thread so I can call up the specs you used.
that's really nice to hear!! i've thought about an input trimmer too, because it seems like all of the fuzz is at the last of the volume knob of the guitar.. so, it could be nice to be able to preset it at a tiny hair lower gain at the input, so I can use it as almost an overdrive without it going to fuuzz
Quote from: Electric Warrior on August 24, 2016, 06:58:42 AM
I completely forgot about the problems you still have with the circuit:
I guess your amp may be a little too clean with the volume low. The clean sounds a Fuzz Face works well with are rather warm.
As your pedal is still too bright for your setup, try using a 500k volume pot. That should give it a bigger bottom end.
yeah, the super reverb i have is soo clean and bright at low volumes, so that's probably why.. i have a 500k actually, i'll give that a try! but it seems like a balance, because right now, it has a beautiful top end when i turn the volume down on the guitar, and i would like to keep that.. thanks man!
i'm going to try it with a strat when i can, all the fuzz sounds i know are strats, i don't have any idea how it should sound with a les paul, which i'm playing now
i just remembered one little thing - the potentiometer that i have instead of "8k2", do i ground the third lug? it makes a pretty big difference in volume when i do
Quote from: artr on August 24, 2016, 09:31:35 AM
i just remembered one little thing - the potentiometer that i have instead of "8k2", do i ground the third lug? it makes a pretty big difference in volume when i do
no, just connect it in series with one outside lug and the wiper, then connect the unused lug to the wiper as well
Quote from: PRR on August 23, 2016, 05:36:46 PM
> Q1 base voltage is off, it should be similar to Q2 ~ -0.6V.
These are Germanium parts. Vbe is likely to be ~0.1V, not the ~0.6V of Silicon.
Ah ha, totally slipped my mind. This reference schematic with dc values threw me off as well, however.
http://www.electrosmash.com/images/tech/fuzz-face/fuzz-face-bias-small.jpg
> This reference schematic
That looks wrong for AC128.
I suspect it is a Silicon plan with "AC128" paste-up.
However 1V at Collector is very odd, Ge or Si.
Maybe silicon with extremely low hfes.
Well, geez, inspired by this thread (and maybe a little boredom) I decided to gut my high-gain FF and rebuild it into a more normal-gain one.
I robbed the lower gain (Hfe ~75) PNP from my Rangemaster build, which I wasn't using much anyway. I moved my existing Q1 (Hfe ~110) into the Q2 spot, and put the rangemaster transistor in as Q1.
All other values I put to stock specs, except the 8.2K is replaced with a 2.7K in series with a 10K trimmer, I kept the 100KL input pot (variable resistor), and I have a 3-way rotary switch that selects different input caps. I used a 2.2uF, .047uF, and .022uF and I'm pretty happy with these values for now.
Going straight in, I prefer the smaller input caps, but with a Tube Screamer in front, I like the 2.2uF. I can really dial in some good tones with that setup. My voltages are very close to the last set artr posted. The pedal cleans up quite nicely now with the guitar volume, where it didn't before. Pretty cool.