What's Your Favorite Boost and Cut design

[Bill Mountain]

I've been thinking of building a pedal that would have a single knob that boosts and cuts.  There are countless ways to do this.

I'm having a hard time deciding between:

1. Buffer -> Volume Pot-> Boost
2. Boost -> Volume Pot
3. Boost -> Inverting opamp with boost/cut pot in feed back loop.
4. Gain stage where pot boosts in one direction and puts signal to ground in another (Similar to Klon or some amps I've seen)
5. Boost -> Volume Pot -> Boost
6. Something I haven't though of yet...
7. Bluesbreaker with no clipping diodes and bigger caps.
8. Etc.

I've come up with more ideas but I can't remember them all at the moment.  My design goals are: Simplicity, High Input Z, and phase coherent.  Some of my ideas are out of phase but I could always add another gain stage or active inverting eq circuit but that destroys my goal of simplicity.

The desire for simplicity is based mostly on an abundance of small chunks of vero board and a few empty two knob enclosures.  The second knob could be a simple eq circuit or switch caps etc.

Basically I need to cut one of my basses and boost 2 of my other basses in order to have similar volumes.  Most boost pedals start at unity.  I'd like to start at -20 or -30dB and go up to about +20dB.

Anyone has any good ideas?

[Bill Mountain]

Here is a simplified schematic of my favorite idea.  I took this idea from a SS Ampeg schematic:



I breadboarded it and the pot was noisy no matter what I did and I felt like I was having headroom issues because at some points in the knob's rotation the opamp was boosting while the signal was being turned down on the back end.

Basically it's wasn't as smooth a transition as I was hoping for.

Note:  I'm pretty sure these weren't the values I used.  I just put this together to show how it worked.

I believe the 470k was something closer to 22k on my breadboard so the opamp itself wouldn't have much boost.

[digi2t]

Not quite sure if I`m wrapping my head around your predicament properly, but would something like a TC Electronics Integrated Preamp help you?

I did one on vero recently, the report is here;

http://www.diystompboxes.com/smfforum/index.php?topic=105455.0

[Bill Mountain]

Sorry, I had hoped to make it clear.  I'm looking for a simple design that boosts and cuts with a single knob.

[digi2t]

No need to apologize Bill, I`m usually the one on the «thick end of the stick»

The TCE preamp could do both, I suppose. The volume knob, turned down to 0, does kill your signal. From there, I found that I can adjust it to be above, or below unity. With sufficient supply voltage (more headroom), it provides a really nice clean boost. The EQ section could be omitted.

[The French connection]

http://www.muzique.com/news/frequency-booster/
http://www.diystompboxes.com/smfforum/index.php?topic=77739.0
http://www.diystompboxes.com/smfforum/index.php?topic=101427.0

[GibsonGM]

Re. feedback, oscillation and whatnot, I had much more luck with this one than the one posted above.   http://www.diyguitarist.com/PDF_Files/FreqBooster.pdf

It uses a dual opamp, slightly more parts count, but IMO was more stable.  Can't say why the one above didn't cut it for me; if that one causes someone grief, you could try Paul's instead.   (?)

[PRR]

If you are clipping AND need high impedance, only #1 works.

[Gus]

Like PRR posted only #1 works from your list
Something small could be a dual opamp based circuit
one volume control
two noninverting stages
An opamp buffer or maybe X2 gain first stage, 1meg input resistance.  You did not define high input z
volume control
2nd gain stage X 10 gain for the first stage input buffer
OR
2nd stage X 5 gain for the X2 gain first stage

[Bill Mountain]

http://www.muzique.com/news/frequency-booster/
http://www.diystompboxes.com/smfforum/index.php?topic=77739.0
http://www.diystompboxes.com/smfforum/index.php?topic=101427.0

Maybe I'm missing something but isn't this an EQ circuit?

[Bill Mountain]

If you are clipping AND need high impedance, only #1 works.

That's what I was thinking.

[Bill Mountain]

Like PRR posted only #1 works from your list
Something small could be a dual opamp based circuit
one volume control
two noninverting stages
An opamp buffer or maybe X2 gain first stage, 1meg input resistance.  You did not define high input z
volume control
2nd gain stage X 10 gain for the first stage input buffer
OR
2nd stage X 5 gain for the X2 gain first stage

I guess a dual opamp takes up as much space as a single.  I could maybe make the buffer switchable between buffer and 10dB boost or something.

I could also use the buffer for a buffered bypass which I prefer.  I guess that seems like the most logical way to go.

[PRR]

> desire for simplicity

If you are serious: build pads for your too-hot axes so they match the others.