Red Ranger needs less boost. ideas?

[studiostud]

Hey guys,

So I finished my Red Ranger circuit and I like how it sounds.  The only problem is that it boosts to a ridiculous degree and is far more of a boost that I feel would be useable to me.  So my question is could I do one of two things... are there caps/resistors/trannys that I could swap that would make the boost less?  .... or is there a point in the circuit where I could add a level volume pot and what type and rating of a pot would I use? 

Really what would be nice is to have the center do nothing and have the side toggles do high/low EQ boost without changing the volume... but maybe that's just a different circuit...

Any thoughts?

[MikeH]

You could just add a volume control at the end, to get it closer to unity gain.  I'm not sure what components exactly set the amout of gain, but I think R3 and R4 (tonepad schematic) would be a good place to start.

[studiostud]

I was thinking about an idea... if I can get the gain to unity, I don't necessarily need a controllable volume knob cause the pedal is housed in an enclosure with a couple other circuits, one of them being a microamp booster.  So tell me if this idea sounds kosher... instead of adding a pot, once I find the resistor(s) responsible for the volume boost, could I just replace those resistor(s) with a similar valued trimpot and adjust that until I find unity gain?

[Barcode80]

yes, you can also put the pot in temporarily, adjust it to unity, then measure the resistance between lugs 3 and 2, and that would be the resistor value to put on the output to achieve unity gain.

[slacker]

The red ranger is basically a discrete opamp set up as a non inverting amplifier, If you look at it as though it was an opamp I think it's easier to understand it.
The base of Q1 is the non inverting input the base of Q2 is the inverting input and the collector of Q3 is the output. R7 on the tonepad schematic is between the output and the inverting input and so is like the gain pot on a tube screamer or a rat. Adjusting this sets the volume, if you make it smaller you get less volume and this affects all 3 settings. Unfortunately because it's a non inverting opamp the only way to get unity gain by adjusting R7 is to make it zero ohms, if you do this though you'll get unity gain and a flat frequency response in all 3 settings so that's no good.
R8 also sets the gain though, if you make it bigger you get less gain. If you make it big enough say 1Meg you get virtually unity gain in the middle position, it's really very slightly above unity but not so you'd notice.
I'd try this out before going any further to make sure it works because sometimes discrete opamps don't like being at unity and can act funny.
You then need to tweak the other components to make the bass and treble boost sound the same as before. In the bass setting R8 and R9 are in parallel and if you do the maths you get a combined resistance of 6.2k ish if you replace R9 with a 6k8 resistor that in parallel with 1Meg will be about the same. To get the treble side to sound the same you need to add a 30k resistor (or just use the 27k you removed earlier) from the bottom lug of the left hand switch to where R9 and C5 join. That in parallel with the 1Meg will be virtually the same as the original 27k on it's own.
Of course you can do this and reduce the value of R7 if the bass and treble have too much boost for you.

Hope that makes sense

[studiostud]

wow.  that was quite the description, slacker.  Thanks!  Earlier I traced a large amount of the boost to R7 and so I swapped that out with a pair of single sockets and added a 100K trimpot.  But I see what you meant cause I had to turn it all the way down to achieve unity gain and that killed any change in EQ as well.  I will definitely try your suggestions and see what I come up with.  Thanks for such a detailed response!

Actually, quick question... when you mean the bottom lug of the left hand switch, do you mean the unused lug?  and R9 passes R10 before getting to C5 so should I connect the 27K before or after R10?

[slacker]

Yeah connect one end of the resistor to the unused switch lug, I should of said I was talking about on the schematic when I said bottom left. Then connect the other end to where the 3 resistors (R8, R9 and R10) join C5. On the layout that could be anywhere on the trace with the bottom of those 3 resistors on it.

It's an interesting looking pedal, I'd never really looked at it before, I might have a go at building one You can never have too many boosters

[Barcode80]

i'm confused as to why you would go through the trouble, when a resistor on the output will maintain the frequency boost(s) in the earlier stages while only limiting the volume...