Hey, all
I'm trying to make a fuzz for a bassist friend. I really like Mark Hammer's Gruntbox but seems like I'm not ready yet for that fine tuning. I searched about buffing and blending between clean signal and a simple fuzz path using op-amp like ROG Splitter and Blend; I got trouble to make the whole thing right but I'm glad the buffer worked fine, since I'm dealing with 072 for the first time. So I got this on breadboard, sounds ok for me although I don't know the benefits from a buffer before the Electra. From the beggining I wanted to put a simple tone control (SWTC or BMP tone stage) and don't want to waste the other side of the chip. How would you finalize this? Take the output of Electra back to the pin 6 (inverting) and tailor the tone around it? Tone control before the distortion? After all stages? Between stages? I appreciate any suggestions, do's and don'ts because I got to a point tired messing with this idea and will be nice to learn a bit about opamp inverting, non-inverting, phase, frequency response.
Thanks
(https://i.postimg.cc/476pF4qv/ESQUEMATICO.png) (https://postimg.cc/476pF4qv)
Ok, I have a more concrete ask for help on this.
I can't make the other side of the chip to work.
I took the Electra output to the inverting pin 6 (thought that would be a good idea to get the signal in phase again);
calculated a gain of 4 then go to the BMP tone stage.
No output, although the tone pot is aparently doing his job on the noise floor.
What I am missing?
I took pin 5 both to ground (0V) and virtual ground (4,5V) but nothing change.
PS.: The schematic now shows the power section.
(https://i.postimg.cc/bG3Nqch1/ESQUEMATICO-TONE.png) (https://postimg.cc/bG3Nqch1)
Place a resistor (10k or so)* between Q1 Collector and 104 cap..
(it is needed when hard clipping diode pair is ON)..
Disconnect TL072 +5 pin (non-iverting input) from GND and connect it to Vref..
Connect a big electro cap (10μF or bigger) between 2nd op-amp output (pin 7) and 27k/472 junction..
(*) It should have minor impact on Electra stage gain due to 4M7/10k ratio primary role on gain..
P.S.
It should also be a good idea to move 100nF cap (104) between diode pair uppper side and 4k7 resistor..
(just to roll-off DC gain to unity)
Should the gain pot, 100kB, be wired up as a variable resistor this way, rather than a divider? I would think that the lower end would go to ground without the wiper connecting to it.
Thks Antonis!
All right it's working through the second opamp, the tone works fine, but when I stick the diodes to ground..no sound.
Quote from: antonis on May 24, 2021, 04:09:31 PM
Place a resistor (10k or so)* between Q1 Collector and 104 cap..
(it is needed when hard clipping diode pair is ON)..
Indeed, no change, but I can only tell because I bypassed the opamp-tone when following yours instruction step by step.
Quote from: antonis on May 24, 2021, 04:09:31 PM
Disconnect TL072 +5 pin (non-iverting input) from GND and connect it to Vref..
Quote from: antonis on May 24, 2021, 04:09:31 PM
Connect a big electro cap (10μF or bigger) between 2nd op-amp output (pin 7) and 27k/472 junction..
Did it.
Quote from: antonis on May 24, 2021, 04:09:31 PM
It should also be a good idea to move 100nF cap (104) between diode pair uppper side and 4k7 resistor..
So, I moved the cap after the diodes and before 4k7 resistor. No sound when diodes engaged
Quote from: GibsonGM on May 24, 2021, 05:14:51 PM
Should the gain pot, 100kB, be wired up as a variable resistor this way, rather than a divider? I would think that the lower end would go to ground without the wiper connecting to it.
Ok, gonna try, won't hurt.
Quote from: GibsonGM on May 24, 2021, 05:14:51 PM
Should the gain pot, 100kB, be wired up as a variable resistor this way, rather than a divider? I would think that the lower end would go to ground without the wiper connecting to it.
Ok, Mike. If I connect this way you suggested, when the gain is min, the sound is gone. So, I'll left the lug 1 floating instead.
It should have "weird" gain responce, Sir.. :icon_wink:
Q1 stage gain is considered the 4M7/(10k + Gain pot) ratio..
(roughly like NFB inverting op-amp with far less than infinite open loop gain..)
Pot wiper is connected to - almost- AC GND (TL072 pin 1) so by connecting pot lower lug to GND counteracts on gain by splitting the Base incoming signal..
e.g.
With pot set at 50%, as it is, gain is 4M7/(10k +50k)..
// , with lug 1 grounded, gain is the same but for a signal of 50k * (50k + 10k + hFE*re) / 50k + (50k + 10k + hFE*re) amplitude..
Quote from: Guerrilha Music on May 24, 2021, 05:22:10 PM
No sound when diodes engaged
Shorted diode pair or false switch placement..??
Quote from: antonis on May 24, 2021, 05:36:15 PM
It should have "weird" gain responce, Sir.. :icon_wink:
Q1 stage gain is considered the 4M7/(10k + Gain pot) ratio..
(roughly like NFB inverting op-amp with far less than infinite open loop gain..)
Pot wiper is connected to - almost- AC GND (TL072 pin 1) so by connecting pot lower lug to GND counteracts on gain by splitting the Base incoming signal..
e.g.
With pot set at 50%, as it is, gain is 4M7/(10k +50k)..
// , with lug 1 grounded, gain is the same but for a signal of 50k * (50k + 10k + hFE*re) / 50k + (50k + 10k + hFE*re) amplitude..
Ok, gonna keep it for later studies. :icon_lol:
I thought that it was a simple pre-gain..but seems to complicate all around. The gain pot itself makes more sense with diodes on, so it may be placed on a better location, but I liked how it acts when Electra is boosting clean and dirty too.
Quote from: antonis on May 24, 2021, 05:43:21 PM
Shorted diode pair or false switch placement..??
I don't think so because, I'm switching manually on the breadboard; and if I take the output from the Electra to volume out, the switching goes ok. (volume drop, sound distorts).
(https://i.postimg.cc/4mkr2cR2/ESQUEMATICO-TONE.png) (https://postimg.cc/4mkr2cR2)
I see Antonis, it is 'unusual' in that sense. I would move the gain pot to the emitter of Q1 - although it may be just fine as it is!
Generally I see this without a buffer in front of it, which helps with issues of weak input signal. In this case, that may well not cause any issues.
Quote from: GibsonGM on May 24, 2021, 08:05:41 PM
I would move the gain pot to the emitter of Q1
You're free to do so, Sir but it shouldn't be a "Gain" pot anymore..
(Q1 Emitter is AC grounded so pot should act as bias trimmer..)
https://i.stack.imgur.com/8hKP8.png (https://i.stack.imgur.com/8hKP8.png)
Quote from: antonis on May 25, 2021, 06:13:40 AM
Quote from: GibsonGM on May 24, 2021, 08:05:41 PM
I would move the gain pot to the emitter of Q1
You're free to do so, Sir but it shouldn't be a "Gain" pot anymore..
(Q1 Emitter is AC grounded so pot should act as bias trimmer..)
No?? It works when I do it with triodes :) And does not shift the bias. A single pot would of course change bias!
(http://i.imgur.com/dx7coUm.png) (https://imgur.com/dx7coUm)
:icon_lol: :icon_lol: :icon_lol:
You didn't mention "is series with Emitter bypass cap" Sir, did you..?? :icon_wink:
P.S.
It should work fine for a CE amplifier with single resistor or voltage divider bias..
Here, stage gain is a combination of open loop gain (RCollector / REmitter) and closed loop one (RFeedback / RIN)
i.e. Aclosed = Aopen / (1 + Aopen * Feedback) results into Aclosed = 1 / Feedback only for Aopen very high..
Q1 Aopen definately can't be considered as very hign so the Aclosed is partially dependent on (and not totally idependent of) Aopen, hence "Gain pot" setting, as per your suggestion, can't "directly" respond in gain setting..
Quote from: antonis on May 24, 2021, 04:09:31 PM
Place a resistor (10k or so)* between Q1 Collector and 104 cap..
(it is needed when hard clipping diode pair is ON)..
It should also be a good idea to move 100nF cap (104) between diode pair uppper side and 4k7 resistor..
(just to roll-off DC gain to unity)
Ok, by unity you mean 4,68 (22K/4.7K), right?
Also, what makes 10k (between Q1 Collector and 104 cap) necessary here, but not un-necessary on Electra by itself?
Quote from: antonis on May 24, 2021, 05:43:21 PM
Shorted diode pair or false switch placement..??
What if I tell you that the diode switch works only if I take the output directly from the 10K resistor (bypassing the cap)?? :o
I was about to give up and use only one side, but with the tone control and distortion, the volume must be at maximun.
I tried again to use other side.
So here is where I am:
INPUT > INVERTING (6) > ELECTRA > NON-INVERTING (3) > TONE > OUT
I tried switching this order every manner you imagine.
Gonna update the schematic.
Quote from: Guerrilha Music on May 25, 2021, 11:39:08 AM
Ok, by unity you mean 4,68 (22K/4.7K), right?
Not actually.. :icon_wink:
By unity I mean unity (X1) 'cause a cap in the gain branch of NFB loop (in series with 4k7 resistor) acts as "open" circuit for DC, hence TL072 inverting configuration works as a DC unity gain amp..
No DC current flows through 4k7 resistor, hence no voltage dividing effect from 22k/4.7k, hence DC Vout = DC Vin, hence Vout/Vin = 1..
Quote from: Guerrilha Music on May 25, 2021, 11:39:08 AM
Also, what makes 10k (between Q1 Collector and 104 cap) necessary here, but not un-necessary on Electra by itself?
Just different points of view..
Diodes to GND severely load Q1 Collector by dominating its current sourcing capability.. This
might be welcome from distortion viewpoint but it shouldn't be "incorporated" into hard clipping effect..
Oh, I see.
How would you come with an arragement to make a gain of 4?
My intention was to compensate the tone control loss before it.
Well, maybe switching order have messed up things, I ended with some very strong synth fuzz putting EQ before opamp non-inverting; although the switching diodes shut the sound off in every arragement.
I got lost here, nevermind
:icon_biggrin: :icon_biggrin: :icon_biggrin: :icon_biggrin:
Obviously, you didn't get me.. :icon_wink: :icon_wink:
(my teaching skills suck..) :icon_redface:
Signal (AC) gain indeed is 4.68 (22k/4.7k)..
(AC finds its way to GND through cap where DC doesn't)..!! :icon_wink:
DC gain is rolled-off to unity for various reasons, the most significnat here been not saturating output due to DC gain..
For bi-polar supply ideal op-amp, biased at GND (0 Volts), high DC gain shouldn't be a problem 'cause many times zero equals zero..
(for real world op-amp, DC offset should multiplied by gain but could easily further "isolated" via an output cap..)
Here, a DC gain of 4.68 means that amp output has to produce 4.68 X 4.5V (non-inverting bias level) hence permanently hitting power supply rails (saturated)..
Ok, sorry, didn't get that AC/DC thing.
So, if the diodes were between opamp and capacitor, the DC will take a way through the diode and the DC gain will be differente than unit?
So, for whatever AC gain (buffer, 4x, 10x, etc) I'm setting an opamp, I must set it for unity DC gain?
Yes.. :icon_wink:
(strictly speaking, at one diode forward voltage drop above GND..)
&
Yes.. :icon_wink:
(except for buffer 'cause it's inherently set to unity..)
P.S.
First one stands for hard clipping configuration with diode pair connected to circuit GND..
There is a similar arrangement with diode pair connected to Vbias, which also represents AC ground due to filter cap.. In such an arrangement, filter cap blocks DC but it "leaks" to GND through voltage divider lower resistor so DC gain is then set by the ratio of feedback resistor and gain + lower divider ones..
I was not able to understand and resolve the diode switching issue, my time has come and so I decided to try to use them to distort on the feedback loop of the inverting amp.
It worked, switching manually on the breadboard. I tested with two pairs of diodes. I wanted to use also without diodes (as a clean boost).
Is it possible to use a spdt (on/off/on) for that, like diodes to ground on hard clipping?
tks
(https://i.postimg.cc/NyqdPHZm/ESQUEMATICO-FINAL.png) (https://postimg.cc/NyqdPHZm)
PS. I decided to leave the tone stack out since the midiscoop of BMP tone control was not good for the bass.
On/off/on should work. But I think you need a double pole. One pair goes to the Opamp +input, the other goes to Vref.
If ithat second pair went to ground, one diode would be conducting when the opamp is "idling" at mid voltage. The other would never turn on (never get below 0.)
Or you put that pair after the 4.7uf capacitor; there they can go to ground. I think the second way is more conventional. I haven't seen the other way done.
Quote from: idy on June 18, 2021, 12:39:48 AM
On/off/on should work. But I think you need a double pole. One pair goes to the Opamp +input, the other goes to Vref.
If ithat second pair went to ground, one diode would be conducting when the opamp is "idling" at mid voltage. The other would never turn on (never get below 0.)
Or you put that pair after the 4.7uf capacitor; there they can go to ground. I think the second way is more conventional. I haven't seen the other way done.
no you don't need a double pole
Garagaman is clipping like in a tube screamer, but with an inverting stage, somewhat like a blues breaker, this gives hard clipping! nice
you can just use a no/off/on switch to chose between the diode pairs.
you can take out the 101 capacitor in the feedback loop of the first opamp since its shorted anyways, and after the transistor gain stage you have 2 resistors and a cap in series, you can leave out one of the resistors and replace the other with a 15k
cheers
Tks for the tips, Ian.
About the clipping switch I found this:
(https://i.postimg.cc/4Y0q70Zp/18-0.jpg) (https://postimg.cc/4Y0q70Zp)
Will work? If so, what value the C7 cap should be to not affect the tone?
The higher the C7 value the more "transparent" the clipping effect..
(the less the stage gain in diode bypass mode forn on-ON-on switch, which isn't the case here..) :icon_wink:
100nF to 1μF should be fine..
(check for Big Muff Π various versions..)
Quote from: Gargaman on June 18, 2021, 07:07:51 AM
Tks for the tips, Ian.
About the clipping switch I found this:
(https://i.postimg.cc/4Y0q70Zp/18-0.jpg) (https://postimg.cc/4Y0q70Zp)
Will work? If so, what value the C7 cap should be to not affect the tone?
that connection from the output of the gain stage to the middle lug would kill all gain, making it silent in your case, that should be left open.
the rest looks fine
cheers
Tks.
Quote from: iainpunk on June 18, 2021, 11:44:20 AM
Quote from: Gargaman on June 18, 2021, 07:07:51 AM
Tks for the tips, Ian.
About the clipping switch I found this:
(https://i.postimg.cc/4Y0q70Zp/18-0.jpg) (https://postimg.cc/4Y0q70Zp)
Will work? If so, what value the C7 cap should be to not affect the tone?
that connection from the output of the gain stage to the middle lug would kill all gain, making it silent in your case, that should be left open.
the rest looks fine
cheers
With C7 where it is?
If so, when switch to the side 1 or 3, the cap will be series with a diode pair.
In the middle position, diodes and cap bypassed?
Right?
I'm having trouble to incorporate this to layout.
Just to make it clear, I have an ON OFF ON switch.
(https://i.postimg.cc/Hj24hdRq/BASS-FUZZ.png) (https://postimg.cc/Hj24hdRq)
PS. Values on the layout may not be updated. For the cap we're talking about, I'm going with the values suggested by @antonis
Quote from: iainpunk on June 18, 2021, 06:10:52 AM
..and after the transistor gain stage you have 2 resistors and a cap in series, you can leave out one of the resistors and replace the other with a 15k
won't this mess with the setup gain of the inverting?
Quote from: antonis on May 25, 2021, 04:09:56 PM
Signal (AC) gain indeed is 4.68 (22k/4.7k)..
Maybe just taking the 10k out, since Antonis suggested it when there was diodes to ground on there?
Quote from: Gargaman on June 18, 2021, 12:19:32 PM
Just to make it clear, I have an ON OFF ON switch.
I'm not able to post a schematic for the moment but you just haver to wire one leg of C7 to pin 6 (inverting input) and the other leg to switch middle lug..
Each of switch outer lug should be wired on Ge or Si diode pair respectively..
P.S.
It will also work with a SPDT ON-ON switch.. :icon_wink:
Working on it now, wish me luck.
Tks.
(https://i.postimg.cc/K4bT6kRs/BASS-FUZZ-ERROR.png) (https://postimg.cc/K4bT6kRs)
"Expect there to be 'serious design flaws..." :icon_lol:
Quote from: Gargaman on June 18, 2021, 12:19:32 PM
Tks.
Quote from: iainpunk on June 18, 2021, 11:44:20 AM
Quote from: Gargaman on June 18, 2021, 07:07:51 AM
Tks for the tips, Ian.
About the clipping switch I found this:
(https://i.postimg.cc/4Y0q70Zp/18-0.jpg) (https://postimg.cc/4Y0q70Zp)
Will work? If so, what value the C7 cap should be to not affect the tone?
that connection from the output of the gain stage to the middle lug would kill all gain, making it silent in your case, that should be left open.
the rest looks fine
cheers
With C7 where it is?
If so, when switch to the side 1 or 3, the cap will be series with a diode pair.
In the middle position, diodes and cap bypassed?
Right?
yes, right!
having that cap there in series prevents lower notes form getting clipped, this makes it less fuzzy and gives a bit more 'clean' bass, while still having distorted mids /higher notes, i recommend playing with that cap's value (or even adding a switch for more cap options!)
you can actually leave it out if you so desire, but for the original where you took it from its there to block DC, which isn't necessary with an opamp feedback loop im 95% of all cases
cheers
Made the board with the layout above, put it in a box, no sound. (not rocking before boxing damnation) :icon_evil:
Bypass fine, led is (was) on when engaged. Voltages on the chip seems to be fine. Checked for shorts on pots.
Started to track the signal with audio probe and was going inside pin 3 but not coming through pin 1)
Meanwhile the led burnt.
Gonna take it out from the box and check for shorts on the board.
EDIT: Man, what a dumb. The layout don't have the feedback loop of the buffer and since I remove the little cap as suggested by Iainpunk, it's open. Gonna fix.
That's it!
Thanks for the tips.
how does it sound? is it as bass friendly as you hoped?
cheers
Sounds ok.
This friend of mine asked a month ago if my fuzz face clone would sound good on bass. I tested and sounded bad. I sent him some Bazz Fuzz samples and he said was too much distorted and point me a Cream video as example of the sound he wanted. I searched Jack Bruce used Marshall amps so I gave a try to a Marshall Guvnor that I was screcthing. Bad idea. Sounded no good. Then I ended at this Electra sandwiched into a tl072.
He liked more the germamiun diodes pair distortion on low and high notes. The other pair is a led and a silicon but in the end clipping was very subtle than when I was breadboarding and planned. EDIT: I see why. I.didn't breadboard the cap (C7), maybe it made less distorted. On the breadboard it was very noticeable.
For my taset it loose brightness a bit when distorted.
One issue is that popping is occuring when engaged, despite it has the 1M5 resistor at the input. Maybe another cap is causing the pop?
Thanks again, mate
EDIT: the pop is much loudet at clean mode and Led+silicon mode; doenst pop on germaniun, at leaat not audible.
FWIW, the fairfield barbershop works really nicely on bass for that low/medium chugalugging overdriven bass amp vibe.
(https://1.bp.blogspot.com/-AJGKZJ3ahuY/YBPLrPhdFQI/AAAAAAAAEDk/4cXsKLZEV787hARMPKpPE39puhhzT1qxACLcBGAsYHQ/s1003/Fairfield%2BCircuitry%2BBarbershop%2BMillenium.png)