Adding Boost circuit to OD circuit - Where in the circuit does it go?

[BuddyPrince]

I'm beginning to understand a little more about building circuits and have a couple of novice questions.

I've built an OD circuit that I like, but I want to be able to blend in clean tone.  I built a simple clean boost circuit that I want to add in to the mix.

Here's what I'm going for and my thoughts.  Am I on the right track?  What do I need to do differently?

1. Wire the input to Boost into non-inverting input of op amp - I want the boost to be getting the same dry signal that the op amp gets.
2. Do I need a low pass filter to attenuate hiss from the boosted clean signal? Is that best put after the boost?
3. Lug 2 on the OD volume knob goes to the 3PDT switch. Can I wire the boost volume knob lug to directly to lug 2 on the OD volume?

Here's a diagram of what I'm thinking.

[garcho]

It's certainly easy enough to implement but in order to help we'll need a schematic of your overdrive.

1. Wire the input to Boost into non-inverting input of op amp - I want the boost to be getting the same dry signal that the op amp gets.

when it comes to inverting or non-inverting inputs on op amps, outside of how the op amp is being used of course, what matters most is when the dry and wet signals get blended together again at the output; inverted and noninverted signals theoretically cancel each other out, practically they cause weird sonic issues that usually result in sound nobody likes or wants or finds useful. what happens at inputs doesn't matter in this regard as long as you take care of it at a later stage.

2. Do I need a low pass filter to attenuate hiss from the boosted clean signal? Is that best put after the boost?

nope. why would there be hiss? boosted clean signal should be exactly that, especially from an op amp (you're using a TL072?).

3. Lug 2 on the OD volume knob goes to the 3PDT switch. Can I wire the boost volume knob lug to directly to lug 2 on the OD volume?

draw a schematic so we know for sure what you're doing

[BuddyPrince]

Thanks for your reply Garcho.

EDIT: Seems as though this thread has been sufficiently hijacked below.  I'll take my thread elsewhere.

[Mark Hammer]

Some commercial pedal-makers have finally seen the light and incorporate boosters that can be positioned before OR after the OD circuit, with a toggle.  Both are useful and musically vald.  They just have different impacts.

[slashandburn]

incorporate boosters that can be positioned before OR after the OD circuit, with a toggle.

Sorry to hijack this thread. Ive though about how such arrangements would work but switch wiring confuses me at the best of times. If we box up two pedals together like this, how straight forward is it to implement an "order" switch?

Can someone explain like I'm 5? Are we talking just a 2pdt/3pdt and some clever wiring arrangement or would it require some something more in terms of switching circuitry?

[vigilante397]

Are we talking just a 2pdt/3pdt and some clever wiring arrangement

Yes. Now finish your vegetables or no dessert.

DPDT will do just fine.

[Plexi]

I agree with Mark.
But, the only position switch I know y using a 4pdt.
Is ther any other way?

[Plexi]

I would like to add, in some way it depends -what and -with what you will boost.
As my experience, for example:
- Big Muff's accept very well the LPB kind booster before, with lower in/out caps to add more highs and rise the eq.
- Some Ods combine great with booster based on the Electra, in special the clean Od's. It add some nice grit and compresion to them. Like the Amp11 with the Cot50.
-Some distortions works great with some Mosfet boosters after them. That way both compress and add some grit. Like in the Box of Rock (Distotron and then SHO).
In the opposite way, they are unusable and very noisy ...

Sent from my Moto G (5S) Plus using Tapatalk

[Mark Hammer]

Order-flipping can be done with a 3PDT toggle.  With a toggle, one doesn't need a 4th set of contacts to actuate a status LED, since the position of the toggle handlecan be used to indicate "who's on first".

Some feel compelled to use a stompswitch for order-flipping, but quite honestly I have yet to run into anyone who needs to be able to swap order on the fly.  Moreover, sticking a boost after an OD results in a volume-level jump.  If the goal is to hit the boost and gofrom a softer to louder OD level, that's great.  But if both are on and you hit the order-swap switch, you'd need to adjust the volume when using OD->boost.  That's why few need to use the order-swap on the fly.  And it's why a 3PDT toggle is perfect for the job.

[Steben]

If switching between output level settings is needed, why not passive with two volume pots (either in series or parallel)?
Pre-boost is the same: even then you can switch between two pots (as in fulldrive etc)

[antonis]

boosters that can be positioned before OR after the OD circuit.... Both are useful and musically vald...

I'm waiting for Sir Mike's statement concerning "BEFORE"... 

[Mark Hammer]

Both any OD and any boost would have their own level control.  But where the OD puts a ceiling on what the amplified signal could be, and the volume pot for the OD sets how much of that gets through, the ceiling for the boost is essentially set by the supply voltage and "swing" of the boost stage. 

So, or example, if the OD were a Tube Screamer, the maximum signal level is set by the back-to-back diode pair at around +/-550mv.  The gain can be cranked to whatever you want, but the level has a hard ceiling on it.  If boost is inserted before the OD, it's equivalent to simply turning up the gain on the OD...but the ceiling imposed on the OD level remains in place.  If the boost is inserted after the OD,then the effect is equivalent to cranking the output of the OD.

The point is that if one had the intention of stomping on a switch to flip the order - obviously with both circuits on - on the fly, you'd need one heckuva stompswitch to adjust/change presets to maintain the same volume.  It can be done (and probably more reliably if done using e-switching), but again, I dont know how often anyone would need it. 

The more sensible approach is two stompswitches, one for full pedal bypass, and the other for boost, and an order-flip toggle.  The full bypass always gets you OD or not.  You can add boost on top of that with the second stomp, and the toggle sets whether the boost comes first or second.  If second, then kicking the boost on will raise the overall level.  If first, the the level may rise a little bit but the intensity of the overdrive will increase.  AFAIC, that's pretty much all 99% of players would want.

[garcho]

EDIT: Seems as though this thread has been sufficiently hijacked below.  I'll take my thread elsewhere.

It happens, just hijack it back.

[GibsonGM]

boosters that can be positioned before OR after the OD circuit.... Both are useful and musically vald...

I'm waiting for Sir Mike's statement concerning "BEFORE"... 

Never before.  Never.  Please.    AFTER, into something with the headroom to not distort much at all, itself. Just a bit, for punch.

Well, if you like a completely square-wave fuzz sound with no touch sensitivity, ok, put it before.....even better, if it were done to a Tube Screamer, then you'd have all that boosted mid, like a goose going through a blender!   Might as well just put 2 distortion pedals together. 

(ok, I know some people do that, and they like it.  I don't know WHY they like it...unless they run them at VERY LOW levels of distortion/boost?  But then - why do it at all?  Why not use a multi-stage FET preamp and take control over your sound?  Box of Rock mentioned above is exactly that).   It seems a total waste, to me, to go to the trouble of putting a boost before that you can only use some small amount of before it sounds like garbage.   

To each their own!  You can't really argue the point, it's like arguing about preamp distortion vs. power amp...there is no right answer.   We're ALL boosting before our amps, after all!

[Plexi]

The only way that I think (almost) always work, is to use a LPB/electra boost with fixed output volumen, and use gain knob as 'boost' (Emiter to ground resistence).

[Mark Hammer]

I never said it was better before  , only that it did something musically useful and valid.  Quite frankly, one could say that there is more need to go from a mild overdrive for rhythm to a harder over drive for solos, than to go for a thick overdrive for rhythm to a louder thick overdrive for solos. 

Virtues and vices of either order aside, the OP was interested in being able to flip the order.  And whether aperson uses the one order more than the other, I still maintain that an unobtrusive 3PDT toggle is all one needs to do so.

[GibsonGM]

Yep. ^^^   

Whatever gets someone the sound that they want is musically useful and valid.

If you use (many varieties of) tube amps, you can increase volume AND gain at the same time by simply 'clean' boosting for your leads...like, Slash levels of distortion.   Just one more approach out of about ten that people use     It came from having no sound person and thus 'missing' solos, or from having incompetence at the board and too loud or too quiet leads.  Works mic'd or un-mic'd.   

You gotta have the headroom to do it, though.   

[antonis]

like a goose going through a blender!

I admire your strictly sientific terms, Sir.. 
(Plz, define THD level..)