9:00 The input impedance of Q1 (without considering the feedback) can be considered more or less equal to the resistance of the transistor, or "r pi" (r pi= Vt/Ib, or r pi= beta (Hfe)/gm). If "gm" is 0.0088 siemens, and beta of Q1 is 90, the impedance would be 10k (but "beta" is real life is Ic/Ib, it's usually slightly different from the value that the manufacturers give us, because it varies depending on the current and t°. In the real circuit, Z will be sligtly lower due to the feedback effect (100k) and fuzz control 9:35 In this configuration, AV gain can also be calculated as Rc/re* (*dynamic resistance of the emitter; there is no external physical resistance ,only the internal resistance between base and emitter). re = Vt/Ic, or re=1/gm . Again, in the circuit it will be lower due to feedback effect of 100k res.
I just wired this up with some germanium PNP's taken out of an old Japanese radio and it sounds UN-REAL. Thank You! Hot Tip: By switching the positions of the 470 and 8.2K resistors you get a lot more volume!!
This brings back fond memories of buying a bunch of NTE AC128s and plugging each one into my old Radio Shack VM to sort them by HFE and playing with input / output DC blocking cap values. Oh, and if you want a bit less gain you can always bump the feedback resistor to 150K or 200K. 😃
1:27 that's called "split emitter resistance" (It's used a lot when you want a high, but controlled gain; a compromised solution) and helps to stabilize the gain, making "re" (the dinamic, internal base-emitter resistance) less relevant in the circuit. It's the same as setting the fuzz control at 9/10 of the total travel, there is a small resistance between the capacitor and the emitter (that capacitor is feedback path for the AC signal, when the pot is at its maximum, there is only "re" (internal) between Q2 emitter and ground) That's why a "REV LOG" pot in fuzz control is more functional than a linear/log one (you want fine control towards the end of the travel, so you can leave a very small "split emitter resistance" if you want)
Your recommendation on adding a cap to remove oscillation fixed my problem!(Edit note: The extra cap darkened my tone a bit, so I put a resistor on the wiper leg of the fuzz pot. That fixed my problem and left the tone unchanged). I love this video and your others are in my queue. Could you do a fuzz factory analysis? I think it would pair nicely with your fuzz face video. Thank you and please keep it up!
Wow, that's awesome to hear. Glad the vid helped! Maybe I'll take a look at a Fuzz Factory video in the new year. I'm currently focused on designing a handful of circuits.
If you ever wanted to try to make a guitar effect this is the best beginner circuit to try. I made the NPN variant. So get that schematic. Don't worry about silicon vs germanium transistors either. Silicon works just fine. Any small signal transistor ought to do it. You can ballpark the parts in this whole circuit and it should do something. As long as the values you use are kind of close. Really, the more messed up it is the better. Then it'll be extra fuzzy.
I disagree about the FF being a good place to start. It's surprisingly tricky for how few components there are. The circuit is prone to unwanted oscillation, and finding the right transistors can be tricky and tedious. I would recommend an opamp-based booster, or an orverdrive as good candidates for circuits to start with.
@@theandromedacorporation I built a fuzzface and I used whatever random transistors I had lying around and it worked. Perhaps I just got lucky? What impressed me the most was the simplicity of the circuit. There's just not much to a two transistor fuzzface. It's amazing so little can do anything. Some overdrives can be simple. The one I built wasn't. It was all of them in one. I used an authentic vintage JRC4558 in it too. I salvaged a few off an old circuit board. So I know they're the real deal. Although anyone with ears should be able to tell themselves. You can check it out on instructables website, the article is titled, "GM Arts Overdrive Pedal Build"
Good point. If I made money making these videos, I would absolutely spend the extra time doing exactly this. That would be super helpful. To actually hear the effect of potential mods as I suggest them would be fantastic. Maybe on the next one...
Great video! I have a question, where would you put the 3 PDT switch? Does anyone have a schematic with it included? And what is the pinout for the switch, having trouble with this part. Thanks!
In Common emitter configuration the Av (amplification) is equal to the gm = Ic/Vt times the load collector resistance (which I doubt is just 33K since the collector sees also the Rpi of Q2). Usually having an amplification depending from gm is bad since it highly depends on temperature (Vt = KT/q k boltzmann constant T temperature in kelvin q electron charge)
@@qddk9545 "gm" is "transconductance" (it's measured in Siemens) , it's the RATIO between input voltage (at base) /output current (at colector) . In BJT transistors it's an exponential function, that's why you get high numbers . Hfe (or "beta") is a RATIO between the input current at base (Ib) and the output current at colector (Ic). It's not "gain" per se, it's the ratio between those 2 currents. Voltage gain (Av) depends on the circuit design. And here we are calculating voltage gain (voltage comes in (induces a little current into the base) and you translate the output current (Ic) into voltage
As an electronics repair tech being in the business ever since school, i can't say that having positive ground and having mostly pnp transistors in the circuit is rare at all..there are millions of products been made polarized this way during from the early period of transistors to early seventies.. it's just not common these days with silicon semicomductors! ..also one must mention that due to historical reasons we nowadays have stuff kinda reversed..simplified the electron flow goes from negative to positive..😅
On second thought, it might be the case in this sort of circuit because the exception is the rule due to intentional clipping, overdrive and what not. 😂
@@theandromedacorporation I mean, the last filter from my calculations is 3.1 Hz, not 31 Hz. f = 1/(2piRC) = 1/(2pi*500E3*0.1E-6). Also if you could show us how to get to 14 Hz on the first filter I would really appreciate 'cause I'm struggling with that one.
@@danielfc You're right! 3Hz, not 30! It's that damn capacitor conversion from uF to F. I'm always moving the decimal place the wrong amount of digits.
Such a perfect and simple circuit. 1 battery. 1 case. 2 jacks. 2 transistors. 3 caps. (5 with your improved version), 4 resistors.
Please keep these videos up! Absolute gems.
Thank you. That's very nice encouragement. I'm used to the internet being needlessly pedantic and argumentative, so this is a lovely change of pace.
These videos are exactly what i was looking for thank you
9:00 The input impedance of Q1 (without considering the feedback) can be considered more or less equal to the resistance of the transistor, or "r pi" (r pi= Vt/Ib, or r pi= beta (Hfe)/gm). If "gm" is 0.0088 siemens, and beta of Q1 is 90, the impedance would be 10k (but "beta" is real life is Ic/Ib, it's usually slightly different from the value that the manufacturers give us, because it varies depending on the current and t°.
In the real circuit, Z will be sligtly lower due to the feedback effect (100k) and fuzz control
9:35 In this configuration, AV gain can also be calculated as Rc/re* (*dynamic resistance of the emitter; there is no external physical resistance ,only the internal resistance between base and emitter). re = Vt/Ic, or re=1/gm . Again, in the circuit it will be lower due to feedback effect of 100k res.
Thank you! Solid insightful comment on a technical topic without being condescending. It's an internet miracle. You're the best.
I just wired this up with some germanium PNP's taken out of an old Japanese radio and it sounds UN-REAL. Thank You! Hot Tip: By switching the positions of the 470 and 8.2K resistors you get a lot more volume!!
Great video!You explain the circuit thoroughly!Enjoyed the 'exit-music' as well!
Thanks. I tried to get away with a few really sour notes. Glad they weren't completely repulsive. lol
If Bart Simpson was a professor.
"Whoah maan yeah!
This is a capacitor...."
There's a massive problem with your videos. There aren't enough of them.
Thanks! I’m working on it. Tryna post every other Friday.
This brings back fond memories of buying a bunch of NTE AC128s and plugging each one into my old Radio Shack VM to sort them by HFE and playing with input / output DC blocking cap values. Oh, and if you want a bit less gain you can always bump the feedback resistor to 150K or 200K. 😃
1:27 that's called "split emitter resistance" (It's used a lot when you want a high, but controlled gain; a compromised solution) and helps to stabilize the gain, making "re" (the dinamic, internal base-emitter resistance) less relevant in the circuit. It's the same as setting the fuzz control at 9/10 of the total travel, there is a small resistance between the capacitor and the emitter (that capacitor is feedback path for the AC signal, when the pot is at its maximum, there is only "re" (internal) between Q2 emitter and ground) That's why a "REV LOG" pot in fuzz control is more functional than a linear/log one (you want fine control towards the end of the travel, so you can leave a very small "split emitter resistance" if you want)
Good insight! Thanks.
yes man! thanks for that vid :) much love!
Your recommendation on adding a cap to remove oscillation fixed my problem!(Edit note: The extra cap darkened my tone a bit, so I put a resistor on the wiper leg of the fuzz pot. That fixed my problem and left the tone unchanged). I love this video and your others are in my queue. Could you do a fuzz factory analysis? I think it would pair nicely with your fuzz face video. Thank you and please keep it up!
Wow, that's awesome to hear. Glad the vid helped! Maybe I'll take a look at a Fuzz Factory video in the new year. I'm currently focused on designing a handful of circuits.
If you ever wanted to try to make a guitar effect this is the best beginner circuit to try. I made the NPN variant. So get that schematic. Don't worry about silicon vs germanium transistors either. Silicon works just fine. Any small signal transistor ought to do it. You can ballpark the parts in this whole circuit and it should do something. As long as the values you use are kind of close. Really, the more messed up it is the better. Then it'll be extra fuzzy.
I disagree about the FF being a good place to start. It's surprisingly tricky for how few components there are. The circuit is prone to unwanted oscillation, and finding the right transistors can be tricky and tedious. I would recommend an opamp-based booster, or an orverdrive as good candidates for circuits to start with.
@@theandromedacorporation I built a fuzzface and I used whatever random transistors I had lying around and it worked. Perhaps I just got lucky? What impressed me the most was the simplicity of the circuit. There's just not much to a two transistor fuzzface. It's amazing so little can do anything. Some overdrives can be simple. The one I built wasn't. It was all of them in one. I used an authentic vintage JRC4558 in it too. I salvaged a few off an old circuit board. So I know they're the real deal. Although anyone with ears should be able to tell themselves. You can check it out on instructables website, the article is titled, "GM Arts Overdrive Pedal Build"
Would be cool to see the pedal side by side and walkthrough the schematic alongside the pedal. Great info nonetheless.
Gear is expensive
Good point. If I made money making these videos, I would absolutely spend the extra time doing exactly this. That would be super helpful. To actually hear the effect of potential mods as I suggest them would be fantastic. Maybe on the next one...
thank you
why is the Vbe of q1 just 0,2 V ( I expect 0,7V) are those germanium?
Yeah.The original Fuzzface used germanium transistors, but there are plenty of variations out there that use lots of different transistors.
Great video! I have a question, where would you put the 3 PDT switch? Does anyone have a schematic with it included? And what is the pinout for the switch, having trouble with this part. Thanks!
Google "true bypass wiring" and you'll find the answer you're looking for.
Google schmitt trigger !
Can you make a npn fuzz face
Yes! I think the vast majority of modern FF's are made with NPN's, and +9V power. I thought I would start with the original design for this video.
One thing I don´t understand: Q1 has a hfe of 80, but the amplification is over 200, how can that work? BR
In Common emitter configuration the Av (amplification) is equal to the gm = Ic/Vt times the load collector resistance (which I doubt is just 33K since the collector sees also the Rpi of Q2). Usually having an amplification depending from gm is bad since it highly depends on temperature (Vt = KT/q k boltzmann constant T temperature in kelvin q electron charge)
@@shyne_on Maybe I just don´t understand it, but how can you boost a transistor with hfe (amplification factor) to 200?
@@qddk9545 "gm" is "transconductance" (it's measured in Siemens) , it's the RATIO between input voltage (at base) /output current (at colector) . In BJT transistors it's an exponential function, that's why you get high numbers
.
Hfe (or "beta") is a RATIO between the input current at base (Ib) and the output current at colector (Ic). It's not "gain" per se, it's the ratio between those 2 currents.
Voltage gain (Av) depends on the circuit design. And here we are calculating voltage gain (voltage comes in (induces a little current into the base) and you translate the output current (Ic) into voltage
you calculate 14Hz cutoff at the input. What resistance value are you using? This must include the base to emitter of the transistor, yes?
I bet Electrosmash has the math all done out for you to read about. They're great for this type of question.
www.electrosmash.com/fuzz-face
Could you do one on some compression unit starting with the simplest possible. I did subscribe. Don't be difficult. Thank you
"Don't be difficult" lol
As an electronics repair tech being in the business ever since school, i can't say that having positive ground and having mostly pnp transistors in the circuit is rare at all..there are millions of products been made polarized this way during from the early period of transistors to early seventies.. it's just not common these days with silicon semicomductors! ..also one must mention that due to historical reasons we nowadays have stuff kinda reversed..simplified the electron flow goes from negative to positive..😅
I don’t know why…. But given values don’t match up. Appreciate if you could work with real values. Thanks anyway.
On second thought, it might be the case in this sort of circuit because the exception is the rule due to intentional clipping, overdrive and what not. 😂
Which values do you mean specifically? I could've gotten something wrong here. I'm wrong about stuff all the time. Lol
@@theandromedacorporation I mean, the last filter from my calculations is 3.1 Hz, not 31 Hz. f = 1/(2piRC) = 1/(2pi*500E3*0.1E-6). Also if you could show us how to get to 14 Hz on the first filter I would really appreciate 'cause I'm struggling with that one.
@@danielfc You're right! 3Hz, not 30! It's that damn capacitor conversion from uF to F. I'm always moving the decimal place the wrong amount of digits.