guitarist looking for clean boost with treble boost

[runmikeyrun]

he doesn't want a distortion, but a clean boost with emphasis in the "10-12khz" as he put it so it can hit his preamp harder.  Thoughts?  The simpler the better, and i'm trying to avoid finicky ge circuits...

thanks

[petemoore]

  All are like dogs, more similar than different.
  What's different is how hard the preamp actually likes getting hit.
  Hit the preamp generally equates to hit everything after the preamp too.
  So hit it with something strong and see if you really want something stronger to hit it with.
  If you have 12v handy, grab a transistor, find a schematic for gain stage, whip something up.
  If you have a booster sitting around there that'll give you an idea of what signal boost level above unity the amp likes to recieve and output, at least with 'that' guitar.

[oliphaunt]

Sounds like a stock SHO or Sparkle Boost to me.

[runmikeyrun]

I should have put he plays a V with an Engl tube rack pre.

[darron]

well, if you do it the way of the old rangemaster then to make the treble boost you just need to have the input cap switchable to something smaller. you can apply that to anything.

[Mark Hammer]

Simplest thing is to just make yourself a JFET gain stage or op-amp gain stage, and set the gain a little higher for that frequency range.  That strategy is used in the Proco Rat, but we'll ratchet down the gain a bit to make it work for us.

Consider the MXR Micro-amp: http://www.generalguitargadgets.com/pdf/ggg_mamp_sc.pdf

The gain is set here by the ratio of R4+R5+R6 to R5+R6.  When R5  is set to zero ohms, the gain is essentially 58k7/2k7 or 21.7.  Upper and lower bounds of the where the gain is applied are set by C2 and C3, respectively.  C2 "rolls off treble" around 60khz, which is principally for electronic stability not for tone-shaping purposes.  C3 rolls off bass at 12.5hz at maximum gain and under 1hz at minimum gain.

Let's say we apply the Rat strategy, and add a second "ground leg" in parallel with C3/R6/R5, using components we will label Ra and Ca.  We'll assume R5 is set to minimum value (so maximum gain).  If Ra = 2k2 and Ca = .01uf, that path would increase the gain of content above 7.2khz from 21.7 to 26.4.

Let's increase the contrast.  We'll eliminate R5, and change R6 to 3k3.  That will set the ciorcuit to a default gain of 17.6 across the entire passband.  Keeping our added Ra/Ca network, we still get the added boost for content above 7.2khz.  A 26.4 vs 17.6 gain factor should make the upper content more noticeable.  T'wer I, I'd increase C2 to 150-220pf just to keep that extra top-end in check, so it doesn't become objectionable.

But wait!  We've set the gain to a default value.  What if that is not the volume you want to use all the time?  Simple.  Make R10 a 10k log pot instead of a fixed resistor.  That will let you vary the output level.

Why or how is this different from something like a Dallas Rangemaster?  Well, for starters, it isn't intended to distort on its own.  Additionally, the unit is intended to be flat below a certain point and add boost above a certain point, rather than rein in everything beliow a certain frequency range, as the Rangemaster (and workalikes) do.

You can feel free to play with the component values to attain different degrees of boost and different "inflection points".

[runmikeyrun]

My God Mark, i do believe you've hit the nail on the head.  I've printed all this and the MXR schemo out and will be putting something together for him....  thanks a ton dude!

[runmikeyrun]

jammed it together tonight on perf... i only had a 741 not the recommended TL061.  Sounds pretty good, gets a little distorted when the strings are hit hard but might not ever notice it with all the other gain.

I wired the 10k pot in as a variable resistor vs. a volume pot since the schematic had the 10k to ground.  Doesn't really control the gain at all, just volume.  Or should i put in the R5 500k pot on the original schematic?

I added the parallel leg to ground, and connected at the -input.  I didn't notice a whole lot of difference connected vs unconnected.... should it be that subtle?  What is a good way to boost the gain in that upper register?  I'm not sure which component will actually boost that top end gain, my guess is Ra and to decrease it from 2k2 to maybe 1k or lower?

Thanks in advance, this is a fun little circuit to play with.

[sevenisthenumber]

ROG Omega.... Nuff said.

[Brymus]

I love my Omega for driving a tube amps input stage into saturation.
But He asked for a CLEAN boost and the Omega adds a noticable amount of distortion to the signal.

Yeah thanx Mark I might try this too for the same reasons.

[Mark Hammer]

Pleased that you were able to try it out so quickly.  Do consider a TL071 instead of a TL061.  When you're boosting treble you don't want a hissier op-amp!

The suggestion to omit the gain-control was because the perceptibility of treble boost depends on maintaining a certain balance between how much gain is applied to the whole signal and how much is applied to only part of it.  If you do want to play with the gain, then I would suggest replacing the 56k resistor in the feedback loop with a 22k fixed resistor in series with a 50k pot.  That will govern the gain for both things at the same time, without disturbing their balance too much.  It may also be the case that the default gain I've provided earlier is too much so this will let you turn the gain down for a (potentially) cleaner output.  Naturally, you will have to turn up the volume pot to compensate.

Alternatively, one could use a dual op-amp, with one stage to provide the staggered gain, at a lower general gain level, and a second stage to simply boost the result of that by some overall factor, keeping the stagger constant.  Just keep in mind that gain is multiplicative, so if you had the default whole-bandwidth gain set to 10x, and the treble-only gain set to 15X, you would likely not want to add more than a max gain of 4x to the second stage.

[runmikeyrun]

what i ended up doing today (before your reply mark) was subbing r6 with a 10k pot (connected to a 2k2 so it wouldn't go to 0 ohms) so i could adjust the amount of gain in the lower frequency section.  Worked like a charm- increase the resistance and the gain of that section goes down, so the treble section starts to take over.  I tried lowering Ra in the treble section and it didn't do anything to boost the highs. 

I'm currently gimping along with a 741 because it's all i had, but plan on picking up a TL071 tomorrow.  I don't know how much that's going to change things but whatever, opamps are cheap.  I've got the basics nailed down though, because the treble is what he wants boosted in the end.

Thanks again for your help!! 

[Gus]

Or you could look in schematics and the gallery

http://www.diystompboxes.com/pedals/gusOverdrive.gif

One transistor, gain is controlled to limit clipping, has a built in boost and lowpass and a bootstrapped input.  One could adjust the eq and midboost with some math.  BJT design for repeatability. Put it in your sims use a 1meg load(tube preamp etc input resistance) on the output

If you want a variable HP filter look at this
http://www.aronnelson.com/gallery/main.php/v/gus/plus.GIF.html?g2_imageViewsIndex=1

[morcey2]

ROG Omega.... Nuff said.

+1


But.   Does he really mean the "10-12khz range"?  The highest note on a 24-fret guitar tuned normally is ~1.3khz.  Does he have something against the dogs in his neighborhood?  And most guitar speakers have a pretty steep roll-off starting at about 4-5khz.

Matt