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DIY Stompboxes => Building your own stompbox => Topic started by: Mark Hammer on July 30, 2005, 09:48:32 PM

Title: Gruntbox - a tentative bass fuzz
Post by: Mark Hammer on July 30, 2005, 09:48:32 PM
People have asked for bass-oriented fuzzes, so I figured I 'd take a shot at one.  The tentative result can be seen here: http://img.photobucket.com/albums/v474/mhammer/Gruntbox.gif

I say "tentative" because it is essentially an untested theory-based design on paper.  I'm perfing it tonight once the football game is over.  If it sounds okay, I'll try and whip up some sound samples and post a schem+sounds package at my website.

The premise is that a bass fuzz wants a clean bottom and some lower-order harmonics.  Too much sizzle and the bass loses its role and place in the ensemble.  Bass is allowed to sound "angry", but it still has to generally keep its cool if playing behind others.  So, what I've done is split the signal into a clean and fuzz channel, with the fuzz channel strategically filtered and mixed back in with the clean.  The schem provides a great deal of technical info, a sort of circuit walkthrough in a schem.

The clean channel has a gain of 10 applied and can be full bandwidth or be rolled off.  I used the SWTC (Stupidly wonderful tone control) as a variable lowpass filter for the clean channel.  The output volume control allows this to be attenuated for effect/bypass level-matching.

The ultra-low stuff from the bass is filtered out before fuzzing, as well as filtered out between stages.  Essentially 80% of the fundamental you hear will come from the clean channel.  The corner frequencies are sheer guesses.  Once I perf and test with my bass I'll know if they're suitable or not.  The basic design may hold but component value changes may be needed.

The quad op-amp (LM324/TL074 pinout shown) is used entirely in inverting mode.  In order to assure the harmonics are in phase with the fundamentals, the fuzz chennel inverts then re-inverts.  Just for the hell of it I figured I'd split the clipping over two stages, as a kind of "affordable experiment" (i.e., tried out something different where it couldn't hurt).  One half-cycle is clipped in one stage and the other half cycle is clipped in the subsequent stage.  The diode is oriented the same way because the signal is inverted.

The cascaded gains of 10 and 22 give a total gain of 220 at the first clipping stage.  This is multiplied again by 10.  Because the one half-cycle is clipped by the first diode, I wouldn't consider the total gain applied to be exactly equivalent to 2200.  That being said, by the time the other half cycle hits the second diode, it's hot enough.  Normally, that much gain would get you over-the-top fuzz.  However, with the bottom significantly cut, I'm betting that the resulting signal is just hot enough

The two clipping stages restrict the high end significantly such that mostly lower order harmonics are generated.  The highpass filtering after the Harmonics Level control should result in that control introducing mostly a gurgly edge to the bass tone.....or at least that's the hope.

There are only three controls, but quite a bit of flexibility in those three controls.  The Clean Tone and Harmonics level controls allow you to dial where the mids and highs come from.  Because there is greater sensitivity to the fuzz signal than the clean signal at the mixing stage, rolling off the clean tone and goosing the harmonics should get you a nice bark.  Alternatively, you can shut off the harmonics, roll the tone control up to full treble and use the unit as a clean booster if you feel like it.  The rolloffs at both the input and output stages shuld help to keep hiss at a minimum.

Once again, this is a hypothetical circuit, to be verified by a build.  It should "work", but whether it sounds as intended using the component values shown is another thing.  Even if it sounds as intended, this will not sound all that hot for guitar.  But that's fine, guitarists have enough fuzzes of their own I should think.  Bass players need a little TLC too.

I kind of like the way the schem is done, and encourage others to include similar sorts of information in the future.  It wil be very helpful for newbies, and those trying to jog their thinking.
Title: Gruntbox - a tentative bass fuzz
Post by: moosapotamus on July 31, 2005, 12:24:24 AM
Very cool, Mark... one for the bass players, oh yeah! 8)

I'll be very interested to see/hear how your design turns out, for several reasons... one, I play bass... two, I'm coincidentally toying with another bass fuzz idea too, based on the blue clipper circuit.

My design goals for bass fuss have been slightly different. IMO, the clean blend has to be there, but the rest is wide open to individual preferences.

Personally, I've never been able to get a lot of use out of a tone control on the clean side. Others may like it alot, and that's totally cool. I guess I can see how it could be useful. But, to me it feels more natural to have the bottom stay in the same place with the fuzz washing into the upper registers when you step on the switch. 460 to 10k is quite a wide range for your lowpass filter. I'm curious to hear how that works out.

I'm not trying to roll off any high end at all from the fuzz. I'm trying to get as much treble content into (and out of) the fuzz side as possible. It's suprising how much the clean signal can fill in. I also like the sound of a really grinding, screetching, buzzing fuzz blended into the clean signal at a really low level.

Another reason for not rolling off any high end in the fuzz is that the majority of bass amps & cabs already do quite a bit of that already. I would say that EQ is crucial to getting a great bass fuzz sound, but more from the perspective of boosting certain frequencies instead of cutting or rolling off... But, that's just my theory. :wink:

The main criticisim I have of the majority of bass fuzz pedals I've heard is that they sound tame... they just don't get really fuzzy enough for my tastes, especially in a live setting. So, my current theory is that having more treble content in the fuzz will make it cut through a bass cab with 15" speakers much mo better... maybe. Anyway...

Cool scheme. Interested to hear how the proto sounds.

Thanks
~ Charlie
Title: Gruntbox - a tentative bass fuzz
Post by: Gabriel Simoes on July 31, 2005, 01:37:59 AM
Nice idea mark!
The project looks superb, let's see how it sounds ...
I will try to put it all on a protoboard and tweek the component values to see how it gets ..

In my opinion it only lacks volume controls for both channels ... since sometimes I like to use the fuzz just on the top end ... and in a lower volume, just to make the bass sound more agressive, but with the same punch of the clean ... I hope you understand what I'm saying, my english is not that good, ... and right now I'm really asleep hehehe
I think the tone control on the clean signal is good, sometimes you just dont want to mix the high end of the clean signal with the fuzz signal ... versatility! ... so... if you dont want it .... roll it all the way and let the signal flow as there was no tone control there ...
I just didnt get why using 2 stages for clipping, just to make it a little assimetrical because of the difference in the in the gain ?
Lets see how this project will go ... right now I'm not that genius but I'm happy that in 2 months I can understand a lot of things from the project .... maybe in some time I will understand everything hehehe .... dreaming ....
It's time for the bass players to show that 6 strings are not really necessary for anything ..... well guitar players ... maybe to play alain caron fusion songs hehehe :D
Gabriel
Title: Gruntbox - a tentative bass fuzz
Post by: Mark Hammer on July 31, 2005, 02:02:50 AM
Well, I finished it, and it works pretty much as planned.  My bass sounds a little bit more like a tenor saxophone.  Of course, I don't sound like either a bass player OR a saxophone player, but that's another story! :lol:

I need to change a few resistor and cap values to provide better balance between straight and fuzz.  Right now, moving the harmonic level control up just a tiny bit drowns out the straight signal.  I want to include that possibility, but not until the harmonics level control is up about 3/4 of the way or more.  I also need to try it out with a 12" speaker tomorrow - an 8" speaker may not wake up the family, but it doesn't wake up the bass either.  In general, though, the gain of the clipping stages and the filtering seems to work just right.

Why two clipping stages?  Because if I used one non-inverting stage that would be 3 op-amps.  I went with a quad op-amp for layout purposes and am glad I did.  The pinout made things easy - it's not often I whip up a perf project in one night and it works just like that.  Since I had 4 op-amps to work with, I used two inverting stages.  By inverting twice that made the fuzz in phase with the clean signal at the mixing stage.

But you are right.  I *could* have used one inverting stage and done all my clipping with a back-to-back pair of diodes, then simply used another inverting stage as a unity-gain buffer to reverse phase before mixing.  I just wanted to solve my phase problems while tinkering with something else.  And you are right.  This does introduce some asymmetrical clipping.

Listening to it (and sound clips will follow tomorrow when I have it tuned just right), it occurred to me that it would be great to combine this with an envelope controlled filter.  In this scheme, the input stage would feed the mixer with clean signal, the fuzz channel, and a rectifier stage to drive a filter on the fuzz path.  The reason why I mention this is because bass doesn't normally have a lot of harmonic content so there isn't much to filter.  As well, sweeping a bandpass filter robs the bottom.  If one has a parallel fuzz channel that could be independently filtered, you'd get to keep the bottom and at the same time have something to filter.  As you well know, having a harmonically rich signal always makes filters sound like they are working harder.
Title: Gruntbox - a tentative bass fuzz
Post by: Gabriel Simoes on July 31, 2005, 09:41:17 AM
Hey ..... so you are almost reaching a kind of bass synth / fuzz in the same pedal! hehehe and in a much simpler schematic than most synths hehehe ....
I hope you get the values balanced pretty soon, and if it's not a problem I hope I can find a pcb of perf layout of it too, because thats my biggest problem right now, I'm worse than bad drawing pcbs ....
But about the volumes, do the 2 channels sound balanced or there's a need to use individual volume controls ?
Title: Gruntbox - a tentative bass fuzz
Post by: Fret Wire on July 31, 2005, 10:19:24 AM
I'd be curious to hear the clips. I've got an EB-O, but don't take it seriously, just fool around a little. One of my favorite dirty bass sounds is Cream's live version of "Sitting on top of the World" off the "Goodbye" album. Especially during the intro. Check out that specific cut if you never had. Jack Bruce using an EB-O with Marshalls. I'd like to emulate that at home. :)
Title: Gruntbox - a tentative bass fuzz
Post by: Mark Hammer on July 31, 2005, 11:09:14 AM
Quote from: Gabriel Simoes
Hey ..... so you are almost reaching a kind of bass synth / fuzz in the same pedal! hehehe and in a much simpler schematic than most synths hehehe ....

Well, I wouldn't call the suggested circuit a "synth", but if it worked as intended it would give a more usable autowah sound, even if your bass pickups are dull sounding and your strings old.  Lying in bed last night, I realized that since there is a gain of 220 at that point I could simply run a diode from the output of the first clipping stage and I'd have a decent envelope signal level to drive a filter stage like the Dr. Q filter.  That would only require one more op-amp.  

Alternatively, since the fuzz channel signal is so hot, maybe the absolutely bonehead simple thing to do is to stick a fixed resistor after the harmonics level control, parallel it with one half of an optoisolator, run a cap to ground for a variable lowpass filter of the harmonics, and use the LED half of the optoisolator as the diode from clipping stage 1.  How's that for simple?  I may try that later today.
Quote
I hope you get the values balanced pretty soon, and if it's not a problem I hope I can find a pcb of perf layout of it too, because thats my biggest problem right now, I'm worse than bad drawing pcbs ....

Actually, I find the circuit ridiculously easy to perf.  Unless you have no perfboard, just go straight to perf and don't even bother with a PCB.  Most of the caps are small values, so between that and the vertically-mounted resistors and diodes, it's a snap.  The use of inverting op-amps makes it easier still - fewer components to tinker with and having all '+' inputs facing each other simplifies wiring up the Vref.  I'll post a picture of my perfboard (front and back) with the soundclips when it's "done".
Quote
But about the volumes, do the 2 channels sound balanced or there's a need to use individual volume controls ?

I left the clean channel fixed in terms of level.  Because there is an overall gain in the circuit from the input stage, it is a simple matter of using the output level and harmonics level controls to get more clean than fuzz and more fuzz than clean at levels above bypass.  Although, I suppose one could always set up the output stage like a mixer with two level controls, and skip the master volume.  Personally, I think the setup I used is easier to use, but that's a matter of opinion rather than any absolute.
Title: Gruntbox - a tentative bass fuzz
Post by: rocket on July 31, 2005, 02:21:01 PM
I think the input impedance is a little low ( it's only 10k as the opamp is inverting)
Title: Gruntbox - a tentative bass fuzz
Post by: Bernardduur on July 31, 2005, 05:25:50 PM
I would like to hear this one; am now happy with my bazz fuss, but am always looking for something better.
Title: Gruntbox - a tentative bass fuzz
Post by: jmusser on August 01, 2005, 01:47:49 AM
OK Mark, I may as well ask this question, because someone will, will there be some mod notes with this circuit to adapt it to guitar, or is this circuit so geared for bass, that it wouldn't make a decent guitar pedal? I know I've read in the Anderton book, that there were mods you could make to his bass fuss that would make it usable for guitar.
Title: Gruntbox - a tentative bass fuzz
Post by: puretube on August 01, 2005, 04:54:36 AM
8)  jogging here...  :)
Title: Gruntbox - a tentative bass fuzz
Post by: Mark Hammer on August 01, 2005, 08:21:18 AM
Quote from: jmusser
OK Mark, I may as well ask this question, because someone will, will there be some mod notes with this circuit to adapt it to guitar, or is this circuit so geared for bass, that it wouldn't make a decent guitar pedal? I know I've read in the Anderton book, that there were mods you could make to his bass fuss that would make it usable for guitar.


Nope.  This is pure 100% bass content.  Bass players deserve something that is theirs and theirs alone.

On the other hand...... :wink: ......it strikes me that the little sidechain with two consecutive op-amps handling clipping of each halfwave is an interesting idea that maybe folks should play with.  We keep blathering on about symmetrical and asymmetrical clipping here, but tend to do so by applying the SAME gain to an imbalanced pair of diodes.  Splitting the clipping across two stages with disparate gains is another way to tackle asymmetry.
Title: Gruntbox - a tentative bass fuzz
Post by: Bernardduur on August 01, 2005, 09:42:13 AM
Good answer!
Title: Gruntbox - a tentative bass fuzz
Post by: robotboy on August 01, 2005, 10:16:06 AM
Sounds awesome. I can't wait to hear a clip. I have a few bass player friends who keep nagging me to build them a pedal, and this might be just what they've been looking for.
Title: Gruntbox - a tentative bass fuzz
Post by: Mark Hammer on August 01, 2005, 10:59:58 AM
Unfortunately, I won't be able to supply them (soundclips) until much later today, and perhaps not until tomorrow, but the nearest comparison I can think of is the tone that Larry Graham gets in the old Sly and the Family Stone nugget "Dance to the Music" during the little solo showcase in the middle.
Title: Gruntbox - a tentative bass fuzz
Post by: Bernardduur on August 01, 2005, 02:44:46 PM
That is one cool sound, I must agree..... I once searched to get this sound.... I'll try to build it also tomorrow.
Title: Gruntbox - a tentative bass fuzz
Post by: Mark Hammer on August 01, 2005, 03:04:12 PM
If you do, make the following changes:

1) Change the cap on the second clipping stage from 1nf to 1n5 or 1n8.  That will provide better tonal balance in the harmonics.

2) Insert a 68k fixed resistor between the output of the 2nd clipping stage and the input of the Harmonics-Level pot.  That will attenuate the harmonics signal a bit and make more of the pot's range usable.  You will still be able to get more fuzz than clean, but will be able to dial in a broader range of subtle sounds as well.
Title: Gruntbox - a tentative bass fuzz
Post by: Mark Hammer on August 01, 2005, 08:51:39 PM
Okay.  Mods done.  Soundfile posted to hammer.ampage.org

The zipfile contains the soundfile and revised schem.  Nothing terribly impressive in the playing but the tone is clearly illustrated.

Make a point of looking at the waveform if you have a chance.  This is nicely asymmetrical clipping and it works extremely well in this context.  Clipping that "knows its place" and politely bows out before it obscures things.
Title: Gruntbox - a tentative bass fuzz
Post by: soggybag on August 01, 2005, 09:05:19 PM
Can not download the file thee is a permissions problem.
Title: Gruntbox - a tentative bass fuzz
Post by: Mark Hammer on August 01, 2005, 09:32:57 PM
Fixed.  Sorry about that.
Title: Gruntbox - a tentative bass fuzz
Post by: Bernardduur on August 02, 2005, 06:24:46 AM
Build it.

Liked it.

But it can't replace my Bazz Fuss (+ 12 stage voicing)....



There is no value on the input cap btw.
Title: Gruntbox - a tentative bass fuzz
Post by: Mark Hammer on August 02, 2005, 09:29:37 AM
Glad you liked it.  Thanks for telling me about the missing cap value.  I'll fix that later tonight.

12-stage voicing?  Now you've made me curious.
Title: Gruntbox - a tentative bass fuzz
Post by: moosapotamus on August 02, 2005, 09:49:24 AM
Audio clips sound great, Mark. I'll bet a lot of bass players would find this to be a really useful fuzz. Seems to have some similarities to the brassmaster. In fact, if you compared block diagrams, I think the circuits would look pretty similar, too. Yours is a bit less complex, tho. 8)

How does the low pass filter on the clean side sound blended with the harmonics/fuzz side? Does it sound useful over it's whole range?

~ Charlie
Title: Gruntbox - a tentative bass fuzz
Post by: Mark Hammer on August 02, 2005, 10:55:51 AM
Quote from: moosapotamus
Audio clips sound great, Mark. I'll bet a lot of bass players would find this to be a really useful fuzz. Seems to have some similarities to the brassmaster. In fact, if you compared block diagrams, I think the circuits would look pretty similar, too. Yours is a bit less complex, tho. 8)


...and you don't have to buy a transformer either. :D

Quote
How does the low pass filter on the clean side sound blended with the harmonics/fuzz side? Does it sound useful over it's whole range?

~ Charlie


Thanks, Charlie.  Here, I have to confess some embarrassment. :oops: I don't know what difference the tone control makes because I installed a bad pot whose wiper makes no contact (...but, but, they were 50 cents each; how could I resist?).  I have to dig up my bin of better pots tonight and replace it.  That move may well end up changing a few details about the clean channel.

As for similarities to other devices, take a peek at the Anderton Octave-Doubling Fuzz sometime, and I think you'll end up mumbling "Why that little sneak!".  Although the kind of 2nd channel tone he aims for in that circuit is evidently different, it's the same basic idea: take one basic tone and blend in another.

I like the fact that it sounds nicely farty, but not fuzzy.  Years ago I learned some valuable lessons in a band context about keeping the frequency ranges of the various instruments (harmonics included) as distinct as possible.  That's one of the reasons why the Fender Rhodes was such a popular instrument - it didn't clash with anything - and one of the reasons why so many bands will have one guitarist using a single-coil instrument and another using a thicker humbucker tone - the complementarity of tones.
Title: Gruntbox - a tentative bass fuzz
Post by: Bernardduur on August 02, 2005, 12:25:41 PM
That 12 stage one is a rotary 12 selector switch so I can switch to different diode / resistor values.

From Ge to Si to different numbers of them to resistors (nice touch). I also added a paralooper so I can dial in some clean sound. Finally I added both an input as output volume pot (so I can attenuate the incoming signal).

It can get a bit rough (to speaker cone schredding sounds) but usually it sounds very good.
Title: Gruntbox - a tentative bass fuzz
Post by: jmusser on August 02, 2005, 02:08:21 PM
Tone control or no tone control, it still sounded good!
Title: Gruntbox - a tentative bass fuzz
Post by: tesalz on September 06, 2005, 09:49:36 AM
I'm very interested to build it, particularly because of the harmonics control. The asymetric fuzzing stage might be interesting, too.

Quote from: Mark Hammer
Glad you liked it.  Thanks for telling me about the missing cap value.  I'll fix that later tonight.

So which value to take for that cap?
Title: Gruntbox - a tentative bass fuzz
Post by: Mark Hammer on September 06, 2005, 09:54:24 AM
Quote from: tesalz
I'm very interested to build it, particularly because of the harmonics control. The asymetric fuzzing stage might be interesting, too.

Quote from: Mark Hammer
Glad you liked it.  Thanks for telling me about the missing cap value.  I'll fix that later tonight.

So which value to take for that cap?


1uf will do fine for any application here.

The degree of asymmetry can be toyed with by varying the gain of the two stages.  For reasons I don't understand, the page can not be accessed at the moment.  Completely out of my control.
Title: Gruntbox - a tentative bass fuzz
Post by: tesalz on September 06, 2005, 10:51:21 AM
thanks!
Quote from: Mark Hammer
For reasons I don't understand, the page can not be accessed at the moment.  Completely out of my control.

fortuneatly I downloaded the file yesterday..
Title: Gruntbox - a tentative bass fuzz
Post by: j.frad on September 06, 2005, 04:10:59 PM
hope it will work again soon, I came too late for that file! Damn!

Hey do you guys think it could be turned into something similar to de Hartke Bass Attack? that pedal it basically the same thing with a bit of compression and a 3 band eq and a brightener (might work with the one posted a few weeks back?) , the harmonic control is not too bad to add some flavour and that pedal can take any dull sounding bass and make it shake some real bass! real hartke punch!
Just a thought...

cant wait to hear the clips...

edit: ok it's not really the same thing, just that harmonic knob made me think of that pedal which really impressed me!
Title: Re: Gruntbox - a tentative bass fuzz
Post by: Arvin on June 03, 2007, 07:04:13 AM
Hi all,

This is my first post although I've been lurking in the shadows as a 'guest' for a few weeks now. I've learned a lot and have finally put iron to solder and built myself a Gruntbox for my Bass.  I'm really pleased with it although it's still a bit of a 'lash-up' as I haven't debugged it or put it in a proper box etc. As you've guessed, I'm new to building effects pedals and everything audio related although I do have experience of building and repairing electronic devices so I'm not starting from zero.

I have a couple of questions for those of you who are way ahead of me here;

1. What value works best for the input cap? There's nothing marked on the schematic. I've used a 0.1uf but I suspect this value is too low.

2. The 'Clean Tone' control seems to have no effect. I've checked the wiring etc. and I think its fine. Does this control produce a very subtle effect that I'm missing or should I go back and re-check everything?

3. Finally, there's a lot of crackle and 'noise' when the effect is switched in. Will this clear when the effect is 'boxed' in a metal case or is there anything I can/should do now to sort it out. I'm using old jack sockets and pots for the moment as I had them in my junk box. Would new ones help?

Thanks upfront for any responses.

Arvin
Title: Re: Gruntbox - a tentative bass fuzz
Post by: MartyMart on June 03, 2007, 10:28:41 AM
Hey Arvin, welcome to this great forum :D
Input cap for bass I use either 0.22uf/0.33uf/0.47uf  all should be fine.
I've had problems when recycling old pots, probably not worth it when new alpha's
are less than 1 each, jack sockets should be fine and "boxed up" would normally fix
any earth hum problems ( open jacks earthed to the metal box and from circuit ground )

MM.
Title: Re: Gruntbox - a tentative bass fuzz
Post by: Gus on June 03, 2007, 10:37:37 AM
I don't know if anyone noted the input stage and how differnt things "feeding" it might change the sound.

The input being an inverting type with a 10K to the - node might change more that people want using the effect at different parts of the chain.

What am I posting about?  How many ff after wha problem posts have people made over the years.  This input stage has some of the same problems/coolness of a FF

With a passive bass to the input the mess of the bass (inductances, resistors, caps network) is part of the feedback EQ network just like a FF.

 The input gain will be the feedback R(100K) divided by the 10K + the bass RLC that times -1 because it is an inverting amp.  The bass RLC should cause an EQ because the BASS RLC changes with frequency.  So different basses should have different EQs P,J ,PJ etc...

So maybe part of the coolness might go away with an active bass or using this effect after another effect or buffer ........... OR one might want to drop the input 10K more to make the bass cause more EQ 2.2K of 4.7K etc when using with a passive bass. 

Title: Re: Gruntbox - a tentative bass fuzz
Post by: seanm on June 03, 2007, 01:24:48 PM
2. The 'Clean Tone' control seems to have no effect. I've checked the wiring etc. and I think its fine. Does this control produce a very subtle effect that I'm missing or should I go back and re-check everything?

Wow, I had forgotten about the Gruntbox. I also found the clean tone control didn't make a difference. I replaced the 470R, 10k pot, 4.7k , and the .033uF to ground with a 15k resistor. Or just replace the 10k pot with a 10k resistor if you have everything soldered up.
Title: Re: Gruntbox - a tentative bass fuzz
Post by: Arvin on June 03, 2007, 04:06:29 PM
Hi guys, thanks for the warm welcome and super quick responses ... this really is a great forum :icon_biggrin:

... jack sockets should be fine and "boxed up" would normally fix any earth hum problems ( open jacks earthed to the metal box and from circuit ground )

MM.

Marty, sorry for being slow here but do you mean that when there's no jack plug in the jack socket the input should be grounded to both the metal case AND the circuit ground?
Should the metal case normally be connected to the circuit ground in any effect that I build?


... maybe part of the coolness might go away with an active bass or using this effect after another effect or buffer ........... OR one might want to drop the input 10K more to make the bass cause more EQ 2.2K of 4.7K etc when using with a passive bass. 

Gus, Thanks for the advice, although I have to admit you lost me pretty early on. My bass is an active bass (Ernie Ball Musicman Stingray) so I'll try placing another effect in line before the Gruntbox to buffer it and see what happens. I may even play with the value of the 10k input resistor. Hey, it's all part of the fun!



Wow, I had forgotten about the Gruntbox. I also found the clean tone control didn't make a difference. I replaced the 470R, 10k pot, 4.7k , and the .033uF to ground with a 15k resistor. Or just replace the 10k pot with a 10k resistor if you have everything soldered up.


Sean, Glad it's not just me then ;) I think I'll take your advice and just replace the whole lot with a 15k resistor.

Thanks all
rgds
Colin
Title: Re: Gruntbox - a tentative bass fuzz
Post by: MartyMart on June 03, 2007, 05:47:05 PM
Marty, sorry for being slow here but do you mean that when there's no jack plug in the jack socket the input should be grounded to both the metal case AND the circuit ground?
Should the metal case normally be connected to the circuit ground in any effect that I build?


There are a number of ways to wire "ground" - the more complex ones apply when building a PSU
or higher voltage device such as a valve amp etc, but for general 9v "stompers" I have a ground rail
on the circuit, which I connect with wire to both in and out jack's ground point - sleeve of the jacks.
In and out from circuit/switch go to the tip of the jack socket and for power switching, your negative
battery lead connects to the stereo input socket's "ring", so power only flows when a jack is inserted
into the input jack - just like most commercial pedals.
The Jack sockets will have their ground "sleeve" connected when screwed to a metal enclosure, which
provides a good large ground plane and should keep noise down.
Search for more on this or see the DIY FAQ above :D
MM.
Title: Re: Gruntbox - a tentative bass fuzz
Post by: Arvin on June 04, 2007, 04:38:27 PM
Thanks again Marty, that's cleared things up. I'll have to get the Gruntbox modified and housed properly and then we'll see how it goes from there.

Cheers
Colin
Title: Re: Gruntbox - a tentative bass fuzz
Post by: Gus on July 27, 2007, 01:15:38 PM
I was looking at the schematic again and noted something.

The 2nd clipping stage is wired like a old  stereo trick for using opamps like the TL072.  With a +- 15volt supply one might see a 5.6k or CC diode or... from the output to the - supply this device bypasses the PNP output transistor in the opamp and kind of makes it a NPN SE people sometimes call it making the output stage Class A.

YOUR schematic has the 10k harmonic level wire to ground so it is kind of doing the same thing if you use a TL07x

I would try a .01uf to .047uf  for the .1uf between the input opamp and the first 1/2 clipper more mid "bark" and less clipped lows

With a cab having 15" or 18" speakers one might not want the low pass filters to be set were you have them.

I need to take some inductance readings of P and J basses.  The resistance can be measure with a DMM for a P take the reading from tip and ring of a cable plugged in the bass.  Take readings at vol set to 0, 1/2 and 100%

Draw a few  schematics  of a bass wiring (I would use a P to start)  with the vol set at 0%, 50% and 100% and connect them to your input. 

Title: Re: Gruntbox - a tentative bass fuzz
Post by: WGTP on August 09, 2008, 03:17:50 PM
http://runoffgroove.com/ubescreamer.html

http://www.diystompboxes.com/smfforum/index.php?topic=48815.msg362915#msg362915

With 4 inverting stages, this might be a good candidate for conversion to a CMOS 4049 as done with the examples above.  Also note the direct signal path in parallel with the distortion path in the ubescreamer.   :icon_cool:
Title: Re: Gruntbox - a tentative bass fuzz
Post by: aron on February 20, 2009, 05:44:18 PM
Mark, what is the input cap value and did you use linear or audio taper pots?
Title: Re: Gruntbox - a tentative bass fuzz
Post by: Mark Hammer on February 20, 2009, 06:30:46 PM
I wish I could tell you.  The prototype is in the hands of a guy who just moved to Israel, and I don't have any drawings other than what is posted.  The tone pot was linear, and the two other pots were log.  Sorry. :icon_redface:
Title: Re: Gruntbox - a tentative bass fuzz
Post by: bytedog on October 01, 2009, 04:45:37 AM
Vero or PCB anyone?
Title: Re: Gruntbox - a tentative bass fuzz
Post by: mr.adambeck on October 01, 2009, 01:15:37 PM
Any sound-clips of this one?  The bassist in my band/my fiance, is always looking for good bass pedals!
Title: Re: Gruntbox - a tentative bass fuzz
Post by: spaceace76 on February 13, 2010, 01:03:24 PM
what opamp is used in the gruntbox? haven't seen it mentioned anywhere
Title: Re: Gruntbox - a tentative bass fuzz
Post by: geertjacobs on February 14, 2010, 04:53:18 AM
From post #1:
Quote
The quad op-amp (LM324/TL074 pinout shown) is used entirely in inverting mode.
Title: Re: Gruntbox - a tentative bass fuzz
Post by: spaceace76 on February 14, 2010, 06:19:13 AM
ah of course, right in front of me the whole time! now that you've pointed it out though, it's impossible to miss. thanks!
Title: Re: Gruntbox - a tentative bass fuzz
Post by: mothercruncher on May 28, 2011, 05:01:45 AM
Hi all,

Has this, rather excellent sounding, project withered on the vine now?
Having begun to play bass recently, I'm a bit fed up of adapting pedals I've built to also work on bass and think the little fella deserves something specific  :)

Did anyone ever make up a vero layout for this?
Title: Re: Gruntbox - a tentative bass fuzz
Post by: johnk on July 23, 2013, 03:09:28 PM
being a bass player since 1967 and liking the concept of this circuit, I drew up a vero of it and built it last night. it works as specified, and I sincerely mean no offense,  but it's just not what I look for in a bass fuzz at all.
the (fizzy) fuzz is completely separate from the clean signal and there's no 'cohesiveness' between the fuzz and clean tones whatsoever (I guess that was the intention). the clean tone control does almost nothing (probably could use a larger cap value).
personally, I think it would be a lot better if the amount/gain of distortion was adjustable, possibly had its own tone control, and had a fuller range to it.  the pre-set amount of fuzz just sits on top of the clean signal and all you get to do is blend it in.
if anyone would like a copy of my vero for it, just ask and i'll post it.

Title: Re: Gruntbox - a tentative bass fuzz
Post by: Mark Hammer on July 23, 2013, 03:28:42 PM
Absolutely no offense taken.  It was an experiment, and I fully understand that it is easier to arrive at a mutually agreed-upon list of toppings for a single extra-large pizza for 12 than it is to arrive at a distortion that makes even a quarter of potential users happy.  Personally, I think the drawing is actually better than the tone, and the only reason people keep attempting it is because there just aren't that many distortions out there that declare themselves explicitly for bass.

hack away, and if there are elemtns you want to custom tailor, feel free to pop me a note and we'll conspire.
Title: Re: Gruntbox - a tentative bass fuzz
Post by: Bill Mountain on July 23, 2013, 04:04:59 PM
being a bass player since 1967 and liking the concept of this circuit, I drew up a vero of it and built it last night. it works as specified, and I sincerely mean no offense,  but it's just not what I look for in a bass fuzz at all.
the (fizzy) fuzz is completely separate from the clean signal and there's no 'cohesiveness' between the fuzz and clean tones whatsoever (I guess that was the intention). the clean tone control does almost nothing (probably could use a larger cap value).
personally, I think it would be a lot better if the amount/gain of distortion was adjustable, possibly had its own tone control, and had a fuller range to it.  the pre-set amount of fuzz just sits on top of the clean signal and all you get to do is blend it in.
if anyone would like a copy of my vero for it, just ask and i'll post it.



Great to see you here John.  This is FatherofFires from talkbass.

And for those who don't know.  This guy is a building machine:

http://johnkvintageguitars.homestead.com/Overdrive-Pedals.html

And a huge inspiration.
Title: Re: Gruntbox - a tentative bass fuzz
Post by: bluebunny on July 23, 2013, 04:37:18 PM
Great to see you here John.  This is FatherofFires from talkbass.

And for those who don't know.  This guy is a building machine:

(http://johnkvintageguitars.homestead.com/Effects/114pedals-1000.jpg)   Wow!    :icon_eek:

Welcome, John!
Title: Re: Gruntbox - a tentative bass fuzz
Post by: johnk on July 23, 2013, 05:23:46 PM
thanks guys.
and thanks Mark for posting the schematic.
I'll probably experiment with the circuit to see if I can get it where I want it, but I need to finish up a couple other pedals soon.
IMO, it definitely has potential.
Title: Re: Gruntbox - a tentative bass fuzz
Post by: Mark Hammer on July 23, 2013, 06:22:26 PM
thanks guys.
and thanks Mark for posting the schematic.
I'll probably experiment with the circuit to see if I can get it where I want it, but I need to finish up a couple other pedals soon.
IMO, it definitely has potential.
Did you mean "a couple" or a couple dozen? :icon_mrgreen:
Title: Re: Gruntbox - a tentative bass fuzz
Post by: ashcat_lt on July 23, 2013, 11:47:09 PM
My experience with a pedal very similar to this is that it really benefits from compression on the clean side.  The distorted side has no dynamics whatsoever, and that's why it seems to ride on top of the clean tone.  I put an effects loop going into each side, but we've ended up just sticking the comp in front of the pedal itself.  Subtly different effect from in the loop, but it works better for our situation.

Then it can take some fiddling.  I had to do some silly things to balance the gain, voice the distortion, voice the LPF on the clean side, and get the blend pot to offer a useable sweep.

I agree that it would be more flexible with more knobs, but there are a lot of good tones in mine, from a subtle "bass expansion" type thing that adds just enough first octave to help the bass translate on small, bass-deficient systems, to a pretty nasty buzz saw thing.  I had Les Claypool's bi-amped system in mind when I built it, and there's definitely a little bit of Pork Soda in those two knobs.

I guess I'm not trying to hijack this thread, just trying to defend the basic premise.  It can work.  I don't have a schematic to show you.  It's three buffers (one with a little gain), a wide open Rat, and a whole bunch of half-assed, dimly remembered hacks dreamed up in simulation and then "perfected" on the breadboard.  If I had it to do again I might try to put a compressor inside the thing, but I highly recommend the loops.  Put a wah on the distorted side, or a phaser, maybe a delay...

Edit - rather than double post, since there have been no replies.

Reading that other thread re: adding dynamics I had the idea that we could maybe do the opposite of what I suggested above and add some expansion to the distorted side so that it follows the clean a little better.  But then, if you just used a more "transparent" circuit for the distortion...

Honestly, though, if you're actually looking for ultimate flexibility you'd be better off just building a Buff N Blend or other splitter/mixer/looper thing.  That's really all this thing is.
Title: Re: Gruntbox - a tentative bass fuzz
Post by: carlosjofernandez on January 20, 2016, 11:56:33 PM
Hi !, I have built this fuzz and have made a PCB. This pedal sounds nice and smooth, ideal for funky bassists.  The tone control makes almost nothing, nevertheless that is ok.
Here you are: https://mega.nz/#!TYBGXBga!gwbFQNR6FDhhkYmFqI5b3ZUrqnNIa83l3eeQS__-_3A (https://mega.nz/#!TYBGXBga!gwbFQNR6FDhhkYmFqI5b3ZUrqnNIa83l3eeQS__-_3A)