wiring question: adding a boost circuit to a...boost circuit?

[ppatchmods]

i did a search and didn't really find anything and was wondering if someone could point me in the right direction? i am building a comp & mosfet booster in a box...easy enough. i want to add another boost circuit to the mosfet and eliminate the volume pot of the 2nd boost with a fixed resistor...easy enough. i don't want the 2nd boost to be usable without the 1st boost activated...got my brain hurting. i'm gonna put the 2nd boost(sho) on a toggle and didn't know how to tack it onto the 1st boost(mosfet booster) as part of the same circuit. anybody seen a diagram for something like this? thanks

[.Mike]

This should be pretty easy. Are you using one footswitch for the compressor, and one footswitch for the boosters (plus a toggle for the extra booster)? Or, are you using one footswitch that activates the compressor and one booster, and a toggle to add in the second booster?



Mike

[ppatchmods]

basically what i want to do is toggle in another boost on top of my other boost. 2 footswitches. 1 for comp, 1 for boost. i want to do something like the chili picoso or fulldrive 2(i know the fd2 is a pot extension). if there is an easier way than building another circuit into it, i'm all ears. maybe add another gain stage...not sure how to do this either.

[.Mike]

OK, here's what I drew up. I think it covers what you want to do.

The 3PDTs are the footswitches, and the DPDT is the toggle. The toggle bypasses the SHO.  LEDs, grounding, and input jack power switching is left out. Input jack is on the right.



(Ignore the typo in the drawing-- mosfet, not mostfet... duh.



Mike

[ppatchmods]

thanks a lot mike! my only question is when i flip the toggle does it cut out the mosfet boost or put them in series? i'll give it a try tonight and let you know how it goes. thanks again!

[Mark Hammer]

Um, you DO know that gain is multiplilcative, right?  A gain of 10x, followed by another gain of 10x, is a gain of 100x, not 20x.

You also know, I hope, that there are limits to how much cleangain you can apply when powering with 9v?  If your intent is to get dirt from the pedal fine.  If your intent is to get a superhot clean output and get your dirt from the amp, then you need to think this through again.

[ppatchmods]

thanks mark. my intent was to just add a boost switch similar to the chili picoso (minus the buffer setup). i thought it would be easy to add a gain stage to the mosfet booster and make it switchable...i'm just not there yet obviously. the sho circuit was a plan "b" and i wanted to set the volume with a fixed resistor for just a little more boost. i would prefer not to have another "full" circuit in the box needing 9v. i've been on geofex reading about gain stages, i just don't know how to add that to the mosfet booster.

[dmc777]

OK, here's what I drew up. I think it covers what you want to do.

The 3PDTs are the footswitches, and the DPDT is the toggle. The toggle bypasses the SHO.  LEDs, grounding, and input jack power switching is left out. Input jack is on the right.



(Ignore the typo in the drawing-- mosfet, not mostfet... duh.



Nice. Do you mind showing how the 2 would be wired without the comp? Also, are you planning on running this off 9v?

Mike

[petemoore]

  Mosfet booster gets almost every drop of clean boost to be had out of a 9v circuit.
  There's a control for the gain...
  2xbooster @9v [with mosfet boost in front] will take on a different tonal character.
  Another option [for keeping it 'boost like'] would be to move the headroom limitation more out of the way of the signal swing, on the second stage.
 

[Mark Hammer]

The gain of the MosFet booster is a function of the resistance in series with the 100uf cap.  As that resistance gets smaller, the 100uf cap bypasses the 2k7 resistor more fully.  If a person wanted an easily switchable boost preset, it is a simple matter to have one resistance in series with the 100uf cap, and a second resistance in parallel with that first resistance.  Add the second parallel resistance and the gain suddenly goes up.  Indeed, what I did on mine was have it in circuit all the time, and the "bypass" switch simply selects between a higher resistance in series with the 100uf, and a smaller value preset which is the gain pot.

The gain of the MosFet booster is applied equally across the spectrum, by virtue of the 100uf value bypassing the 2k7 resistor from the lowest frequency on up.  If the 100uf is replaced with a smaller value, such as 4u7, that bypassing of the 2k7 is restricted to higher frequencies.  So, the booster can be reconfigured as a full-range boost, or as some sort of treble boost.  If, say, you had a 4u7 cap and a 100uf cap, and both went to a 5k pot, but the 100uf went to a 1k resistor first, before reaching the 5k pot, the pot would increase the gain for the entire spectrum, but a bit more for the  top end than for the rest.

Because the specific application of gain across the spectrum can be tinkered with, that lets you do things like have two in series, with one of them as a treble boost and the other as a full-range boost.

Something to think about, eh?

[ppatchmods]

thanks mark. i knew there was a simpler way. it surely is a nice sounding boost. will give it a go. thanks

[ppatchmods]

mark, i did what you suggested. i also used a higher value and boosted to the original 2.7k i tried as low as 1k and could not get the circuit to work. got it going with a 10k and a 2.7k. thanks for the help!

[Mark Hammer]

You're welcome.  Sometimes, things don't have to be as complicated as we initially think.  I like when that happens.