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Author Topic: Need advice in modifying Little Rebel's tone control  (Read 12890 times)

newbiediy

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Need advice in modifying Little Rebel's tone control
« on: August 09, 2012, 10:31:43 PM »
My friend said Little Rebel's tone control is too subtle. Can anyone explain what topology it is and suggest modifications? I just can't figure it out with my limited knowledge. xP

Having read Temuuk's book (great job Temuuk!), I am trying to change the tone control to active FMV. I also use the remaining op-amp as active low pass filter to cut high freqs. This IS my first attempt in modifying / designing an amp. Please point out any mistakes as I tend to copy & paste schematic fragments and glue them altogether. :duh
Any comments and suggestions are welcome.
Sorry for my bad English. We say "laik dis" instead of "like this" in Facebook. :P

Roly

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Re: Need advice in modifying Little Rebel's tone control
« Reply #1 on: August 10, 2012, 09:41:31 AM »
"Subtle" eh.  And unique too - don't recall ever seeing anything quite like that before; all their own work I'd say.

As you can see the treble and middle come before the master volume, and the bass control after, so a simple conversion to some from of Fender/Marshall/Vox type passive isn't really practical.

In fact given how little there is in it you may be better off building something similar from the ground up using the tonestack you want.

What you could try playing around with is making the existing controls a bit less subtle.  You can't model this in Duncan's Tone Stack Calculator since it isn't any of the common arrangements, but you could model it in LTSpice or Tina-TI (both free).

Really, the question you have to answer first is "what do you want?", more bass, more treble, more control range?  Then we can have a look at which components to change in value that might give you what you want.

You should also remember that whatever speaker and enclosure you are using will have a pretty major effect on the end sound.

HTH
If you say theory and practice don't agree you haven't applied enough theory.

J M Fahey

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Re: Need advice in modifying Little Rebel's tone control
« Reply #2 on: August 10, 2012, 10:48:11 AM »
It's not subtle at all, and it's not your typical FM tonestack either.
It's a tone control specially developed by Marshall for their distortion pedals and attending their particular needs.
The Little Rebel designer didn't actually do much "design" , if any, just copied and pasted.
It's basically a ripoff of the Marshall "Guv'nor" family pedals,

with a bass boost added (since it will typically drive very small speakers) , straight driving a flat LM386 amp.
A FMV tone stack will probably sound buzzy (that's why the other one was developed).
So if you find it "dull" .... well, it's its character.
If you want to homebuild an amp, go for, say, a Valvestate 10.
KILLER little amp

And same complexity or simpler than the Little Rebel

newbiediy

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Re: Need advice in modifying Little Rebel's tone control
« Reply #3 on: August 11, 2012, 06:18:36 AM »

Really, the question you have to answer first is "what do you want?", more bass, more treble, more control range?  Then we can have a look at which components to change in value that might give you what you want.


I think my friend meant more control range. He also said lack of bass. Can you suggest value changes? Actually what I want is to learn more about this unique tone stack. :)


It's basically a ripoff of the Marshall "Guv'nor" family pedals,
with a bass boost added (since it will typically drive very small speakers) , straight driving a flat LM386 amp.
A FMV tone stack will probably sound buzzy (that's why the other one was developed).


I have compared the two, and indeed they are identical from input to clipping diodes. But I'm still confused about the bass control. I haven't seen anything similar to it. Can you give me some more explanation about it? So I can learn more about these things. <3)


A FMV tone stack will probably sound buzzy (that's why the other one was developed).


Buzzy means too much treble? Will the active filter help?


If you want to homebuild an amp, go for, say, a Valvestate 10.
KILLER little amp


Yes, it's already in my list. I'm not sure about the supply voltage. Is it +/- 18V?

Thank you so much for the answers. :dbtu: :dbtu:
Sorry for my bad English. We say "laik dis" instead of "like this" in Facebook. :P

J M Fahey

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Re: Need advice in modifying Little Rebel's tone control
« Reply #4 on: August 11, 2012, 01:52:48 PM »
But I'm still confused about the bass control. I haven't seen anything similar to it. Can you give me some more explanation about it? So I can learn more about these things. <3)

Buzzy means too much treble? Will the active filter help?

Yes, it's already in my list. I'm not sure about the supply voltage. Is it +/- 18V?

1) that strange "dull" Marshall tone control was developed because distortion pedals are meant to be used before a guitar amp, which typically has gobs of treble,
Buzzy means not only highs (which are fine) but "ugly" highs.
The same sound as putting a piece of paper on a hair comb and blowing into it to imitate a harmonica/trumpet/sax, o what you hear of a mosquito flying at night when you are trying to sleep or what has been described as "angry bees inside a tin can" or more graphically as "icepicks in your ear".
As you see, all "ugly" sounds.
Now, if you send that distortion pedal straight into a flat power amp , which has *no* treble boost, the same design sounds dull and *appears* to have poor range.
Mind you, that same pedal into a Marshall amp is killer!!!
This is another, more "normal" version of the same family, the Shredmaster.
It has a more normal looking tone stack ... until you see the values have been totally edited, in a gross way.
The bass net, 68K/.022 is now 6K8/.022 so it has shifted up 10X !!!!
TONS of low mids (to add "body")
And the treble net, 500pF/220K now is .022/22K (shifted down 4X) to provide mid/high mids instead of highs, to avoid emphasizing "buzz".

So as you see, pedals are good used as intended, but not so good as preamps, because the requirements are different.
That's why I (heresy !!!) suggest straight copying a commercial *amplifier*.
Mind you, you can build the Valvestate 10 preamp and drive an LM386 if you wish !!!
But, since you get into it, with a little more complexity you can have the full amp.
As of the +/- 18V or whatever, just look at the TDA2030 datasheets and use what they suggest.
The "standard" values, not the absolute maximum ones.
I suggest you build a wooden base, with an aluminum front panel full of holes, so you can mount jacks, switches, pots, Leds, etc. and double face tape a protoboard to it, so you can easily experiment and try new ideas.
Good luck.
PS: and that "humble" Valvestate 10, driving a good 12" speaker (not the puny cheap original 6" or 8") will make your hair rise. ;)
« Last Edit: August 11, 2012, 01:57:46 PM by J M Fahey »

J M Fahey

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Re: Need advice in modifying Little Rebel's tone control
« Reply #5 on: August 11, 2012, 08:06:40 PM »
For you to see (and hear) what a little SS amp can do, as far as distortion is concerned, our friend ONEBALDBLOKE , who writes here too, has posted a You Tube video where he *seems* to be playimg through a wall of Marshalls.
Truth is, told by himself, that that would be uncontrollable: too much volume/power/feedback , so he actually played *live* into a little Squier ... which was backstage, sitting on a roadcase, and miked into the PA system.
Yes, the PA system had quite a few thousand Watts.
Listen and enjoy:
http://youtu.be/3QEjiJ56Zac
and please comment later what you think.
The full thread is
http://www.ssguitar.com/index.php?topic=2560

And in case you didn't notice, they are Australians ;)

newbiediy

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Re: Need advice in modifying Little Rebel's tone control
« Reply #6 on: August 12, 2012, 02:59:50 AM »
Thanks Fahey for the great explanations. I learn much from them.
 I've tried to simulate Little Rebel's tone stack as Roly suggested. (It's my first time with these softwares btw.) Yes, it has weird freq response.

I'll go for valvestate 10 then. Btw (maybe a silly idea) if I want to run the preamp from single power supply, say 12V, how to do it? Just as simple as connecting some bias resistors to op-amps?
Sorry for my bad English. We say "laik dis" instead of "like this" in Facebook. :P

J M Fahey

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Re: Need advice in modifying Little Rebel's tone control
« Reply #7 on: August 12, 2012, 03:09:01 PM »
It can be done, of course, but I fear it will introduce new variables into what we are trying to keep very simple.
And in any near future, if you go for any TDA20xx (except for the almost obsolete TDA2003) you will use split (+/-) supplies for it anyway, useful also for the preamp.
Only justification would be if you tried to make a pedal out of it ... but then just use a pedal distortion schematic which already has that single supply capacity built in.

newbiediy

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Re: Need advice in modifying Little Rebel's tone control
« Reply #8 on: August 17, 2012, 04:25:00 AM »
It can be done, of course, but I fear it will introduce new variables into what we are trying to keep very simple.

Oops I didn't think of that. I guess I will upset the low pass and high pass filters and such. :P

It's basically a ripoff of the Marshall "Guv'nor" family pedals,
http://www.freeinfosociety.com/electronics/schematics/audio/pictures/marshallguvnor.gif
with a bass boost added (since it will typically drive very small speakers) , straight driving a flat LM386 amp.

Btw Fahey, when I looked at Little Rebel and Guvnor, I realized that they're virtually identical. The difference is that in Little Rebel the bass control is made "fixed" with 1k5 and 100k resistors, and it uses (as you mentioned) a variable bass boost instead. :o

So here's my mod:
  • Replace 1k5 and 100k resistors with a 100k pot and use it as bass control.
  • Replace the 1M bass pot with a jumper. Or better yet, rename it to "depth" or "bottom" control, I think it's more appropriate. But my front panel is too small and crowded, so I just jumper it.

Viola... The tone control now have better and more "normal" freq response, especially bass freqs. :dbtu: <3)

Thanks for pointing out. :dbtu: :dbtu:
Sorry for my bad English. We say "laik dis" instead of "like this" in Facebook. :P

newbiediy

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« Last Edit: August 17, 2012, 04:59:31 AM by newbiediy »
Sorry for my bad English. We say "laik dis" instead of "like this" in Facebook. :P