Hey guys, I'm trying to make a big muff with a JFET based input and output stage (and might replace the BJTs for JFETs in the clipping stage), but I'm not sure how to go about it.
I tried breadboarding just the input stage but with a 2n5457 instead of a 2n5088 (or any other BJT), and it didn't work (as i figured), and i only hear my picks attack when I try playing with it. so I'm wondering what I need to change to make it work.
here's the schematic I'm working with right now, but everything is likely gonna change, and I've only breadboarded the input stage.
(https://i.postimg.cc/XpNmpnqR/jfet-muff.png) (https://postimg.cc/XpNmpnqR)
Quote from: snow123 on May 20, 2022, 03:48:24 PM
I tried breadboarding just the input stage but with a 2n5457 instead of a 2n5088 (or any other BJT), and it didn't work (as i figured), and i only hear my picks attack when I try playing with it. so I'm wondering what I need to change to make it work.
Change JFET bias configuration.. :icon_wink:
There was a similar project from Jack Orman, but I can't recall it right now..
Quote from: antonis on May 20, 2022, 03:57:17 PM
Quote from: snow123 on May 20, 2022, 03:48:24 PM
I tried breadboarding just the input stage but with a 2n5457 instead of a 2n5088 (or any other BJT), and it didn't work (as i figured), and i only hear my picks attack when I try playing with it. so I'm wondering what I need to change to make it work.
Change JFET bias configuration.. :icon_wink:
how do i do that though?
Ah snow. The man, the myth, the legend.
Here's a little read on jfet biasing. (https://www.electrical4u.com/biasing-of-junction-field-effect-transistor/#:~:text=Biasing%20of%20JFET%20by%20a,across%20the%20input%20gate%20resistance.)
And welcome back!
Quote from: snow123 on May 20, 2022, 03:58:33 PM
how do i do that though?
May I ask the reason for altering Big Muff In & Out configurations..??
(or am I looking for land in trouble..??) :icon_redface:
Quote from: antonis on May 20, 2022, 04:08:29 PM
Quote from: snow123 on May 20, 2022, 03:58:33 PM
how do i do that though?
May I ask the reason for altering Big Muff In & Out configurations..??
I'm thinking it would give it a different sound. and I just want to experiment with JFETs in a big muff, starting with the input and output stage.
Quote from: snow123 on May 20, 2022, 04:14:27 PM
I'm thinking it would give it a different sound.
May I assure you for the opposite..?? 8)
P.S.
Be aware of oversights when copying schematics,,
(e.g. no ordinary BJT should work with that R20 value..)
AMZ had the fet muff years ago... 4 jfet stages. It sounds great as I recall. Sadly I cannot find a schematic.
Quote from: antonis on May 20, 2022, 04:29:46 PM
P.S.
Be aware of oversights when copying schematics,,
(e.g. no ordinary BJT should work with that R20 value..)
that was actually a typo lol, its supposed to be 100k.
so im assuming i change the value of R2 for it to work? 'cause i believe that resistor is what adjusts the bias for Q1.
Quote from: AdamM on May 20, 2022, 04:30:22 PM
AMZ had the fet muff years ago... 4 jfet stages. It sounds great as I recall. Sadly I cannot find a schematic.
I was curious about this one. Looks like it was pulled years ago.
But they did write a book that snow may very well enjoy! - probably why they pulled their schematics.
https://www.amazon.com/dp/B0749RW4Y6
Quote from: snow123 on May 20, 2022, 04:39:14 PM
so im assuming i change the value of R2 for it to work?
For a BJT, yes.. :icon_wink:
Did you read the link posted by Kevin..??
If yes, we would be happy to answer any possible query originated from there..
Or you're just hoping for a ready-to-race JFET configuration scheme posted by some willing guy..??
JFET gates don't usually need a positive bias voltage - it can be hard enough to get the source voltage high enough to get it biased.
Quote from: antonis on May 20, 2022, 04:52:34 PM
Quote from: snow123 on May 20, 2022, 04:39:14 PM
so im assuming i change the value of R2 for it to work?
Did you read the link posted by Kevin..??
If yes, we would be happy to answer any possible query originated from there..
yes, I did read the link. I guess I'm not entirely sure what JFET biasing circuit in the link would match up best with the input booster I have set up rn.
But my understanding of it so far, is that R4 and R5 would set the biasing, is that correct?
Quote from: snow123 on May 20, 2022, 05:04:55 PM
But my understanding of it so far, is that R4 and R5 would set the biasing, is that correct?
Not quite..
R4 in conjunction with R2 set channel current I
D (current from +9V -> R5 -> Q1 -> R4 -> GND)
R2 serves to set a voltage level at Gate (usually near 0V)..
According to Drain desirable bias voltage and Drain resistor value (which sets stage's output impedance), there is a proper working current (I
D = (9V - V
D) / R5)
That current can be estimated by V
GS /I
D curve, so R4 value is set accordingly (V
S = I
D x R4) and V
GS (absolute value) is V
G - V
S..
Gain of stage roughly is R5/R4 but by shunting R4 to GND via a cap you increase it to
gm x R5..
Let's implement an hypothetical example..
R2 = 1M, R5 = 10k and ID = 450μA for a VGS = -1.75V
VG is 0V (due to practically no current flow through R2 - take it as I say it for the time being)..
For a VGS of -1.75V and ID of 450μA, we need a R4 of 3k9..
(of course, gain only approaches to 2.5 but a R4 by-pass cap might be proved your friend..)
Now you're ready to choose your particular JFET, read its datasheet and make your own Common Source amp.. :icon_wink:
P.S.
In case of weird results after exact implementation of the above said, put the blame on JFET parameters wide spread and not on me... :icon_redface:
Quote from: antonis on May 20, 2022, 05:57:59 PM
Let's implement an hypothetical example..
R2 = 1M, R5 = 10k and ID = 450μA for a VGS = -1.75V
VG is 0V (due to practically no current flow through R2 - take it as I say it for the time being)..
For a VGS of -1.75V and ID of 450μA, we need a R4 of 3k9..
(of course, gain only approaches to 2.5 but a R4 by-pass cap might be proved your friend..)
Now you're ready to choose your particular JFET, read its datasheet and make your own Common Source amp.. :icon_wink:
P.S.
In case of weird results after exact implementation of the above said, put the blame on JFET parameters wide spread and not on me... :icon_redface:
Thank you!
Quote from: snow123 on May 20, 2022, 06:54:57 PM
Thank you!
You're welcome.. :icon_wink:
Just to confuse you a bit more:
It should be easier (IMHO) to implement self-biasing formulas, like I
D = I
DSS (1 - V
GS/V
P)
2, where I
DSS = Drain current for V
GS = 0 (considered device almost maximun current) and V
P = Pinch-off voltage (also found as V
GS(OFF))..
Both the above parameters can be found on datasheets (exhibiting a wide spread, of cource..)
Then you can proceed to proper sizing of Drain (R5) & Source (R4) resistors values for V
DS (Drain - Source voltage) and V
GS (the one contributed in I
D formula) via V
DS = 9V - I
D(R5 + R4) and V
GS = V
G - V
S = 0V - I
DR4..
Good luck..!! :icon_wink:
(a pot, wired as variable resistor, in place of R5 might be your good luck charm..)
If you don't like math, the trendy thing to do is fit a trimmer pot as the drain resistor. Usually, 100k is shown, but to me, 50k should give easier tweaking. Adjust for the best sound although the drain voltage should come out anywhere 3v - 6v.
The gate resistor to 0v basically only sets the input impedance. 1M is usually fitted for guitar input but these distortions often have lower about 100k which tends to make it more mid focused.
The output stage loads the 100k tone pot and that could have a 1M gate resistor but the original BJT is more like 100k I think.
One method not to use a trimmer pot.
(https://i.postimg.cc/F1cbJYLS/20225L00.png) (https://postimg.cc/F1cbJYLS)
Quote from: antonis on May 20, 2022, 04:08:29 PM
.... (or am I looking for land in trouble..??) :icon_redface:
if you need to ask, Antonis ......
i've tried doing similar in the past. it worked, but i really didn't like the sound of the end result. kinda like... a rather shrill and brittle big muff. but hey, wtf do i know? lol
making popcorn. i think i may have the schematic for the 4 fet muff in my archive... that said, imho, may sound better with mosfets than jfets in this circuit.
but ... wtf do i know? lol
i am the president of the he-man jfet hater club ;)
Quote from: pinkjimiphoton on May 21, 2022, 01:48:57 PM
i've tried doing similar in the past. it worked, but i really didn't like the sound of the end result. kinda like... a rather shrill and brittle big muff.
We have a long road ahead till we arrive to Big Muff
Π "input impedance" thing.. :icon_wink:
(@anotherjim hinted something relevant but I'm not sure for OP to the point grasp..)
Quote from: m4268588 on May 21, 2022, 07:45:41 AM
One method not to use a trimmer pot.
(https://i.postimg.cc/F1cbJYLS/20225L00.png) (https://postimg.cc/F1cbJYLS)
Are you ready for a terra-page thread..?? :icon_mrgreen:
Quote from: anotherjim on May 21, 2022, 06:46:02 AM
If you don't like math, the trendy thing to do is fit a trimmer pot as the drain resistor. Usually, 100k is shown, but to me, 50k should give easier tweaking. Adjust for the best sound although the drain voltage should come out anywhere 3v - 6v.
funny you say that, since I was swapping JFETs (and found the the 2n5457 and PF5102 worked best), and replaced R2, R4, and R5 with pots set as variable resistors so I could easily set the biasing for each JFET. but i might try swapping R5 for a 10k trimpot.
Quote from: pinkjimiphoton on May 21, 2022, 01:48:57 PM
i've tried doing similar in the past. it worked, but i really didn't like the sound of the end result. kinda like... a rather shrill and brittle big muff. but hey, wtf do i know? lol
that makes sense, since while i was messing with different biasing and different JFETs (albeit, only in the input stage), i found that some configs would just sound brittle and misbiased, while other configs would be pretty loud and sound somewhat dirty, without sounding too shrill.
how do i do the biasing for Q4?
Quote from: snow123 on May 21, 2022, 06:55:17 PM
how do i do the biasing for Q4?
Exactly the same as Q1.. :icon_wink:
and now the pedal is super quiet.
i finished dialing in the values for R21 and R22, and the values i landed on are 18k for R21, and 33k for R22, aren't those values a bit high for this kind of thing?
If r22 is 33k, then the output impedance will be about 33k. That may be a bit too high, depending on what follows the pedal.
Quote from: pinkjimiphoton on May 21, 2022, 01:48:57 PM
i've tried doing similar in the past. it worked, but i really didn't like the sound of the end result. kinda like... a rather shrill and brittle big muff. but hey, wtf do i know? lol
making popcorn. i think i may have the schematic for the 4 fet muff in my archive... that said, imho, may sound better with mosfets than jfets in this circuit.
but ... wtf do i know? lol
i am the president of the he-man jfet hater club ;)
I'd like to see the schematic of the jfet and mosftet big muff version.
I'm following the topic.
Do you want to share the final schematic once you will satisfied by the result?
I like to see schematics! :P
I used to think of JFET's as ideal components for design but I have run into difficulties caused entirely by a high pinchoff voltage in a Sencore SG165 AM/FM/Stereo generator I have at home. The output stage is a source follower backed up by a Sziklai - style PNP buffer transistor pulling high. The symptom was plenty of positive output drive, almost no negative. The stage is strung between ± 12 VDC rails with a 390 ohm resistor as the output reisistor on the source. The JFET was at the high end of pinchoff so the resistor was normally operating between the -12 rail and the source at +8 volts for a total of 20 volts across the 1/4 watt resistor, so it had 51 mA going through it at a dissipation of 1.02 watts. The resistance had gone from 390 to 2195 ohms, so of course there was little negative drive. I finally used a 390 ohm 2 watt resistor and that restored operation.
This particular JFET was rated for -2 to -8 volts at cutoff and there was no circuitry to compensate for the wide variations. The 2N5457 cutoff varies between -0.5 and -6 volts Vgs which might be OK if you were running from a higher supply voltage but the output stage may not have enough swing if it is at the -6 volt extreme. The input stage proposed by m4268588 would work if you had enough supply voltage but at 9 volts, several different units may sound different because the operating point has too much variation.
I would look at a Darlington configuration for an input and output with high input impedance if you want predictable characteristics with no need for DC feedback to establish bias. You can add a resistor to ground from the first emitter in the Darlington if you want rapid pulldown but a guitar signal may not warrant it - the frequency content may not be high enough.
Quote from: snow123 on May 21, 2022, 07:58:33 PM
and now the pedal is super quiet.
Could you plz post a schematic of both In /Out JFETs configuration..??
Quote from: amptramp on May 22, 2022, 08:27:04 AM
I would look at a Darlington configuration for an input and output with high input impedance if you want predictable characteristics with no need for DC feedback to establish bias. You can add a resistor to ground from the first emitter in the Darlington if you want rapid pulldown
Can't get you Ron..
A first BJT Emitter resistor to GND dominates input impedance (although it helps for first BJT acceptable gain due to elevated Collector current)
IMHO, it should be better to place that resistor between Q1 & Q2 Emitters..
Its value can be estimated by Q2 V
BE and Q1 desirable current while its apparent value should be high enough due to bootstrapping effect..
edit: Now realized about "rapid pulldown effect".. :icon_redface:
Quote from: antonis on May 22, 2022, 08:37:00 AM
Quote from: snow123 on May 21, 2022, 07:58:33 PM
and now the pedal is super quiet.
Could you plz post a schematic of both In /Out JFETs configuration..??
I got that figured out, but here's the schem:
(https://i.postimg.cc/zb6CLjhd/Jmuff.png) (https://postimg.cc/zb6CLjhd)
Quote from: snow123 on May 22, 2022, 03:26:47 PM
I got that figured out, but here's the schem:
(https://i.postimg.cc/zb6CLjhd/Jmuff.png) (https://postimg.cc/zb6CLjhd)
OK.. I presume some other willing guy could take over.. :icon_wink:
P.S.
@snow123: Sorry but I don't need 35 posts, dealing with JFET bias, to come back to 2nd one >Change JFET bias configuration< to feel tosser..
Quote from: antonis on May 22, 2022, 03:41:35 PM
Quote from: snow123 on May 22, 2022, 03:26:47 PM
I got that figured out, but here's the schem:
(https://i.postimg.cc/zb6CLjhd/Jmuff.png) (https://postimg.cc/zb6CLjhd)
OK.. I presume some other willing guy could take over.. :icon_wink:
P.S.
@snow123: Sorry but I don't need 35 posts, dealing with JFET bias, to come back to 2nd one >Change JFET bias configuration< to feel tosser..
wait, the reason i thought the volume issue was fixed, was 'cause im using LEDs as the clipping diodes, and when i go back to 1n914s, the pedal is super quiet. so the issue has not sorted itself out, its just that I'm using loud diodes.
also probably worth noting, is that when i use LEDs, the volume control feels as if I'm using silicon diodes, (like unity is at around 75%, just like my triangle big muff which uses silicon diodes), but when i use silicon diodes, the pedal is still way below unity, even with the volume maxed.
so basically, I was mistaken and thought that the volume issue fixed itself somehow, but i was just using loud diodes to compensate for the loss of volume.
also, when I move the input of the circuit to the output of the tone stage (so my guitar signal is only going through the output stage), the volume is just a little bit higher than unity (with the volume maxed), but when i move the input to the collector of Q3 (so my guitar signal only goes through the tone stage and the output stage), the volume drops MASSIVELY (also with the volume maxed).
and another thing, when I look at JFET boosts in other circuits, they usually have a capacitor in parallel with the resistor at the source of the JFET, so what is the purpose of said capacitor?
Quote from: snow123 on May 22, 2022, 06:43:07 PM
and another thing, when I look at JFET boosts in other circuits, they usually have a capacitor in parallel with the resistor at the source of the JFET, so what is the purpose of said capacitor?
Probably it's to separate the AC gain from the DC bias conditions. I'm no expert in JFET biasing, but I understand the basics.
You need a certain size resistor there to get the correct DC bias, but such a large resistor value reduces the gain. Sticking a cap across it lowers the effective resistance seen by AC signals and thereby increases the effective AC gain without mucking up the DC bias.
HTH
Quote from: ElectricDruid on May 22, 2022, 06:57:41 PM
Quote from: snow123 on May 22, 2022, 06:43:07 PM
and another thing, when I look at JFET boosts in other circuits, they usually have a capacitor in parallel with the resistor at the source of the JFET, so what is the purpose of said capacitor?
Probably it's to separate the AC gain from the DC bias conditions. I'm no expert in JFET biasing, but I understand the basics.
You need a certain size resistor there to get the correct DC bias, but such a large resistor value reduces the gain. Sticking a cap across it lowers the effective resistance seen by AC signals and thereby increases the effective AC gain without mucking up the DC bias.
HTH
I've adjusted the values of R21 and R22, and stuck a 47uf capacitor in parallel with R21, and its fixed the volume issue! but now its a bit too loud, like unity is at around 10 o clock.
Place a resistor (of about the same value of R21) between 47μF cap and R21 and walk in peace (of our mind..)
(11dB gain should be considered adequate for particular recovery stage..)
If it still is loud, increase its value..
If it's quiet, decrease its value..
Quote from: Elijah-Baley on May 22, 2022, 05:32:29 AM
Quote from: pinkjimiphoton on May 21, 2022, 01:48:57 PM
i've tried doing similar in the past. it worked, but i really didn't like the sound of the end result. kinda like... a rather shrill and brittle big muff. but hey, wtf do i know? lol
making popcorn. i think i may have the schematic for the 4 fet muff in my archive... that said, imho, may sound better with mosfets than jfets in this circuit.
but ... wtf do i know? lol
i am the president of the he-man jfet hater club ;)
I'd like to see the schematic of the jfet and mosftet big muff version.
I'm following the topic.
Do you want to share the final schematic once you will satisfied by the result?
I like to see schematics! :P
sorry, when i did that years ago i didn't find it worthy of pursuing, so i never bothered to draw it out or anything.
i just used trimmers to set the biasing. i didn't like the tone of it at all... to get an actually decent distortion it was just too... shrill for my taste. like a big muff with a presence control, kinda, but not in a good or useful way.
i will look to see if i can find jack's schematic in my archive, but i think its only fair to reccomend buying his big muff book instead, its only 5 bux.
and its in the book, if memory serves
Quote from: pinkjimiphoton on May 23, 2022, 01:39:35 PM
i think its only fair to reccomend buying his big muff book instead, its only 5 bux.
Fair enough, Jimi.. :icon_wink:
(regardless book pricing..)
Jack Orman did a JFET Big Muff along time ago. I build this but didn't like the sound.
I remember it used a single diode from drain to gate, where the classic Big Muff uses a reverse pair from collector to base. I was never sure what the purpose of that choice was.
Quote from: antonis on May 23, 2022, 06:21:48 AM
Place a resistor (of about the same value of R21) between 47μF cap and R21 and walk in peace (of our mind..)
(11dB gain should be considered adequate for particular recovery stage..)
If it still is loud, increase its value..
If it's quiet, decrease its value..
just put a 910 ohm resistor there, and it got the volume to where i need it!
And 1 last thing, if I were to put JFETs in place of the BJTs in the clipping stage (Q2 and Q3), would I just do the same thing that I did on Q1, or would I have to do something else?
Quote from: snow123 on May 23, 2022, 10:19:30 PM
if I were to put JFETs in place of the BJTs in the clipping stage (Q2 and Q3), would I just do the same thing that I did on Q1, or would I have to do something else?
To be honest, I didn't get what you did on Q1 but, if it worked for you, simply repeat it..
(https://i.postimg.cc/K42Y6vND/20225L06.png) (https://postimg.cc/K42Y6vND)
I recommend a general method.
(https://i.postimg.cc/2VjS5cgq/20225L07.png) (https://postimg.cc/2VjS5cgq)
Quote from: m4268588 on May 24, 2022, 07:28:34 AM
(https://i.postimg.cc/K42Y6vND/20225L06.png) (https://postimg.cc/K42Y6vND)
You're confusing OP more (if this can be..) and I assure you that it isn't a good thing..!! :icon_wink:
You could just tell him to implement BJT CE amp bias formulas and replace V
BE with V
GS..
I think I'm good now. Thanks for all of the help!!!!
Could you now tell us the outcome of your offbeat(*) JFET implementation..??
(https://i.imgur.com/CeTdCD3.png)
(*) In the mean of losing JFETs high input impedance advantage while also losing BJTs high transconductance one..
Should we expect for some other inovations like biasing BJTs in reverse active mode..?? :icon_wink:
(too bad for JFETs to not be able to experience the above due to their Drain-Source interchangeability..)
P.S.
Absolutely no intention for ironic/sarcastic comments..
Just joking a bit 'cause I found out that it might result into more understanding by OP..
Quote from: antonis on May 25, 2022, 02:45:53 PM
Could you now tell us the outcome of your offbeat(*) JFET implementation..??
(https://i.imgur.com/CeTdCD3.png)
(*) In the mean of losing JFETs high input impedance advantage while also losing BJTs high transconductance one..
Should we expect for some other inovations like biasing BJTs in reverse active mode..?? :icon_wink:
(too bad for JFETs to not be able to experience the above due to their Drain-Source interchangeability..)
P.S.
Absolutely no intention for ironic/sarcastic comments..
Just joking a bit 'cause I found out that it might result into more understanding by OP..
well right now, it sounds great. it's super high gain and fat with the fuzz maxed, but it also seems to turn into more of a light overdrive when you roll back the volume on your guitar, rather than sounding velcro-y and compressed.
(https://i.postimg.cc/w3pXvwRf/j.png) (https://postimg.cc/w3pXvwRf)
snow123 - now that you have given a review of your circuit, someone will want to be building it. so you have to finish the job. go through your circuit diagram over and over and make sure that the values you built are the values you show on the diagram. and measure the voltages on the fets and transistors [at the very least the collector and the drain voltages] on your build, and either include on the dia or in a post with the completed and corrected dia. this will also provide us with a cross-check, so we know you're not pulling any funny business. and now it's your version, you have to give it a name so we all know what people are talking about.
really, it's only fair to Antonis.
Quote from: duck_arse on May 26, 2022, 11:24:28 AM
snow123 - now that you have given a review of your circuit, someone will want to be building it. so you have to finish the job. go through your circuit diagram over and over and make sure that the values you built are the values you show on the diagram. and measure the voltages on the fets and transistors [at the very least the collector and the drain voltages] on your build, and either include on the dia or in a post with the completed and corrected dia. this will also provide us with a cross-check, so we know you're not pulling any funny business. and now it's your version, you have to give it a name so we all know what people are talking about.
really, it's only fair to Antonis.
I changed the schematic up a tiny bit:
(https://i.postimg.cc/06FSpFgT/jmuff.png) (https://postimg.cc/06FSpFgT)
and here's the voltages:
Supply:
9.45v
Q1 (J201):
D: 2.75
S: 0.00
G: 0.47
Q2 (BC550B):
E: 0.05
B: 0.65
C: 4.73
Q3 (BC550B):
E: 0.02
B: 0.61
C: 4.08
Q4 (2N5457):
D: 4.70
S: 2.44
G: 1.64
Quote from: duck_arse on May 26, 2022, 11:24:28 AM
and now it's your version, you have to give it a name so we all know what people are talking about.
well rn its still a work in progress (i still need to figure out the tone stage values, the current values are just a place holder). and i guess ill just call it the JFET muff (I'm not good with naming things lol).
Quote from: snow123 on May 26, 2022, 05:21:22 PM
Q1 (J201):
D: 2.75
S: 0.00
G: 0.47
Are you sure about Q1 as J201 n-channel JFET..??
There was a contest recently for alternatives to build on a muff PCB and I did JFETs all around. Came out great.
https://forum.pedalpcb.com/threads/what-another-contest.10105/page-9
(https://i.postimg.cc/tsDrzvSQ/Fuzzduster-SCH.png) (https://postimg.cc/tsDrzvSQ)
Quote from: antonis on May 26, 2022, 05:57:32 PM
Quote from: snow123 on May 26, 2022, 05:21:22 PM
Q1 (J201):
D: 2.75
S: 0.00
G: 0.47
Are you sure about Q1 as J201 n-channel JFET..??
yes? i'm using SMD j201s that i soldered onto a through hole adapter board
Quote from: jubal81 on May 26, 2022, 08:55:20 PM
There was a contest recently for alternatives to build on a muff PCB and I did JFETs all around. Came out great.
https://forum.pedalpcb.com/threads/what-another-contest.10105/page-9
(https://i.postimg.cc/tsDrzvSQ/Fuzzduster-SCH.png) (https://postimg.cc/tsDrzvSQ)
I'm not sure if snow123 would approve the above JFET "anorthodox" (according to his own standards) bias configurations.. :icon_wink:
Quote from: antonis on May 27, 2022, 05:57:23 AM
Quote from: jubal81 on May 26, 2022, 08:55:20 PM
There was a contest recently for alternatives to build on a muff PCB and I did JFETs all around. Came out great.
https://forum.pedalpcb.com/threads/what-another-contest.10105/page-9
(https://i.postimg.cc/tsDrzvSQ/Fuzzduster-SCH.png) (https://postimg.cc/tsDrzvSQ)
I'm not sure if snow123 would approve the above JFET "anorthodox" (according to his own standards) bias configurations.. :icon_wink:
tbh i just dialed it in to where it sounded best, and didn't measure until afterwards.
Quote from: jubal81 on May 26, 2022, 08:55:20 PM
There was a contest recently for alternatives to build on a muff PCB and I did JFETs all around.
https://i.postimg.cc/tsDrzvSQ/Fuzzduster-SCH.png
As I see that drawing: Q2 Gate has no DC path. If it works it depends on PCB leakage, which is unreliable.
Quote from: PRR on May 27, 2022, 05:33:44 PM
As I see that drawing: Q2 Gate has no DC path.
At a first glance, I saw the same thing, Paul..
But it actually does have via R7, C4 short, Sustain wiper and R6..
Quote from: antonis on May 27, 2022, 05:39:23 PM
Quote from: PRR on May 27, 2022, 05:33:44 PM
As I see that drawing: Q2 Gate has no DC path.
At a first glance, I saw the same thing, Paul..
But it actually does have via R7, C4 short, Sustain wiper and R6..
me counts three.
So, does that make us a crowd..??
P.S.
Finally, snow123 threads DO have "juice"..
Quote from: antonis on May 27, 2022, 05:57:23 AM
Quote from: jubal81 on May 26, 2022, 08:55:20 PM
There was a contest recently for alternatives to build on a muff PCB and I did JFETs all around. Came out great.
https://forum.pedalpcb.com/threads/what-another-contest.10105/page-9
(https://i.postimg.cc/tsDrzvSQ/Fuzzduster-SCH.png) (https://postimg.cc/tsDrzvSQ)
I'm not sure if snow123 would approve the above JFET "anorthodox" (according to his own standards) bias configurations.. :icon_wink:
If it looks weird, it's drawn to be built on a PedalPCB Muff PCB. C4 is a jumper. The treble bypass on the gain control and Q1 bypass cap have to be added extra to the PCB, the orphaned resistors are left empty and the numbering matches the PCB exactly.
also, using J201s for Q2 and Q3 makes it clean up almost like a fuzz face.
To make the J201s work, I connected the sources of Q2 and Q3 to ground, used 5.1k for R10 and R16, and I lowered R7 and R12 to 2.2k to boost the gain a bit.
Quote from: snow123 on May 28, 2022, 05:06:10 PM
To make the J201s work, I connected the sources of Q2 and Q3 to ground, used 5.1k for R10 and R16, and I lowered R7 and R12 to 2.2k to boost the gain a bit.
May I notice that the above aren't in compliance with any schematic posted by you (till now, at least..)..??
What will this new J Muff be called ?
Quote from: Phend on May 28, 2022, 06:03:23 PM
What will this new J Muff be called ?
idk, JFET muff? im bad with naming things lol
Quote from: antonis on May 28, 2022, 05:30:12 PM
Quote from: snow123 on May 28, 2022, 05:06:10 PM
To make the J201s work, I connected the sources of Q2 and Q3 to ground, used 5.1k for R10 and R16, and I lowered R7 and R12 to 2.2k to boost the gain a bit.
May I notice that the above aren't in compliance with any schematic posted by you (till now, at least..)..??
the names are in compliance with the last schem i posted (reply #55), but the values aren't.
I retract my previous comment, about "finished".
Quote from: snow123 on May 29, 2022, 01:05:29 AM
Quote from: Phend on May 28, 2022, 06:03:23 PM
What will this new J Muff be called ?
idk, JFET muff? im bad with naming things lol
Pinchoff Muff would keep everybody guessing.
Mufa Fett.