Gruntbox - a tentative bass fuzz

[Bernardduur]

Build it.

Liked it.

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



There is no value on the input cap btw.

[Mark Hammer]

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.

[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.

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

[Mark Hammer]

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.

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

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.

[Bernardduur]

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.

[jmusser]

Tone control or no tone control, it still sounded good!

[tesalz]

I'm very interested to build it, particularly because of the harmonics control. The asymetric fuzzing stage might be interesting, too.

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?

[Mark Hammer]

I'm very interested to build it, particularly because of the harmonics control. The asymetric fuzzing stage might be interesting, too.

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.

[tesalz]

thanks!

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..

[j.frad]

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!

[Arvin]

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

[MartyMart]

Hey Arvin, welcome to this great forum
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.

[Gus]

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. 

[seanm]

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.

[Arvin]

Hi guys, thanks for the warm welcome and super quick responses ... this really is a great forum

... 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

[MartyMart]

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
MM.

[Arvin]

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

[Gus]

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. 

[WGTP]

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.   

[aron]

Mark, what is the input cap value and did you use linear or audio taper pots?