How to add a range pot to Madbean Rangemaster?

[FloorIt]

I would like to add a range pot to the Rangemaster in place of the switch.  I have seen posts on how to do this but with pcb's other than Madbean's.  Could someone help me with this?  I'm a newbie, so will need somewhat thorough guidance.  Thanks.

[davent]

If someone would confirm or ex this it would be much appreciated, it's Saturday night...

http://www.madbeanpedals.com/projects/Rangemaster/Rangemaster2014.pdf

Looking at the 2014 doc schematic you need to jumper 1,2,3 together, the TM switch pads on the board. Cut the trace connecting  C1 and C2.

Your guitar IN will be wired to legs 2, 3 of  a 100k pot then to the IN on the board. Leg 1 of the pot is connected to C2 which has a conveniently placed IN pad if you use a non mojo part for C2.

Schematically... from diystompboxes... Out would be junction of 1,2,3 T/M on the MADbean schematic.


The thread.http://www.diystompboxes.com/smfforum/index.php?topic=96308.0;prev_next=next

[FloorIt]

Thanks for your reply.  I don't know enough to be able to comment on this mod.  I'll wait to see what other comments come in.

But one question: I haven't used any Madbean boards yet but he gives this description of their construction: "The site is supported by the sale of PCB products for these projects. These are professionally manufactured with two-layers, solder mask, silk screen".  Are the traces exposed or are they sandwiched between the two layers?  If they are sandwiched, is it possible cut a trace?

[RobA]

Thanks for your reply.  I don't know enough to be able to comment on this mod.  I'll wait to see what other comments come in.

But one question: I haven't used any Madbean boards yet but he gives this description of their construction: "The site is supported by the sale of PCB products for these projects. These are professionally manufactured with two-layers, solder mask, silk screen".  Are the traces exposed or are they sandwiched between the two layers?  If they are sandwiched, is it possible cut a trace?

They aren't exposed, but they aren't sandwiched either. The two layer boards have the traces on the outsides of the top and bottom of the board. The traces are then covered by a thin material. It's easy enough to cut through this material and then cut the trace with a knife of some sort. Pretty much, it's the same as cutting a trace on an etched single sided board.

Edited to clarify: I said the traces are covered. Well, the whole board is covered top and bottom by the thin material. It's not just the traces. It is possible to see where the traces run though and cutting them is easy as I mentioned above.

[FloorIt]

The traces are then covered by a thin material. It's easy enough to cut through this material and then cut the trace with a knife of some sort. Pretty much, it's the same as cutting a trace on an etched single sided board.

Edited to clarify: I said the traces are covered. Well, the whole board is covered top and bottom by the thin material. It's not just the traces. It is possible to see where the traces run though and cutting them is easy as I mentioned above.

Thanks for that info.

[FloorIt]

Would this work?:

[davent]

Beautiful, that is how i envisioned it! A picture is so much easier. I can never decide how best to wire the pot or what type to use, i think i used a 100ka in my last but over at Small Bear he uses a 250kc. Play with that and see how you prefer it set up.

[midwayfair]

Whoa, whoa, whoa, slow down here. There's no need to cut a trace.

Solder two wire to lugs 1 and 2 of a 500KA or 100KA pot (a linear taper would bunch up -- use an audio taper). The pot value doesn't matter a ton; 100K will be a little easier to dial in small chances, while 500K will have a bit more range. Resistance increases as you turn the pot up.

Leave a little extra wire exposed on one of them.

Solder the other ends of those wires to pads 2 and 3 for the toggle. The one with the extra bit of exposed wire goes to pad 2.

Then just bend over the exposed wire into the hole for toggle switch pad 1.

Fill C1 and C2 normally. Do not cut any traces.

The pot will impede signal flow through C2 more as it's turned up; at max, it will sound closer to the original. At lower settings, there will be more bass. If it bothers you that the pot gives you more signal as it's turned down, you can use lugs 2 and 3 of a C taper pot and it will work backwards.

[FloorIt]

Whoa, whoa, whoa, slow down here. There's no need to cut a trace.

Solder two wire to lugs 1 and 2 of a 500KA or 100KA pot (a linear taper would bunch up -- use an audio taper). The pot value doesn't matter a ton; 100K will be a little easier to dial in small chances, while 500K will have a bit more range. Resistance increases as you turn the pot up.

Leave a little extra wire exposed on one of them.

Solder the other ends of those wires to pads 2 and 3 for the toggle. The one with the extra bit of exposed wire goes to pad 2.

Then just bend over the exposed wire into the hole for toggle switch pad 1.

Fill C1 and C2 normally. Do not cut any traces.

The pot will impede signal flow through C2 more as it's turned up; at max, it will sound closer to the original. At lower settings, there will be more bass. If it bothers you that the pot gives you more signal as it's turned down, you can use lugs 2 and 3 of a C taper pot and it will work backwards.

This?:

[midwayfair]

Yes, that's it.

[FloorIt]

Yes, that's it.

Wow, how brilliant and simple!

You said this: "The pot will impede signal flow through C2 more as it's turned up; at max, it will sound closer to the original."

When the pot is turned all the way up will C2 have any affect in the circuit?

What values do you recommend for C1 & C2?  The build doc specifies C1: .005 uF and C2: .022 uF.  Will these get me the full amount of treble as the original (switched) circuit?  I have seen some people call for a lower C1 and higher C2 in order to give more range...

One other thing.  I see that most others are using a linear taper pot for this control.  Can you elaborate on why you recommend an audio taper?

I personally think that Brian should include this mod in the build document.  It seems like a pretty popular mod and it's so easy.

[midwayfair]

You said this: "The pot will impede signal flow through C2 more as it's turned up; at max, it will sound closer to the original."

When the pot is turned all the way up will C2 have any affect in the circuit?

You could calculate the input impedance of the transistor as the two base resistors in parallel, subtract a bit for the transistor, the gain of which is pretty high, and calculate the input's low-pass filter cutoff frequency for both capacitors, and then determine how much signal the new pot allows into the circuit when it forms a voltage divider against the input impedance and permits a varying amount of C2 into the circuit. So if the pot is 100K and the input impedance is about 50K (typical for a Rangemaster), the effect of C2 will be 1/3 as loud as the effect of C1. If the pot is 500K, it would be 1/10.

I know, that's basically word salad. The short answer is "yes," and your ears are a better judge of how much and whether it matters than any calculation I don't feel like doing at the moment.

What values do you recommend for C1 & C2?  The build doc specifies C1: .005 uF and C2: .022 uF.  Will these get me the full amount of treble as the original (switched) circuit?  I have seen some people call for a lower C1 and higher C2 in order to give more range...

Rangemasters work by cutting bass and boosting everything that's left. They also load the guitar pickups, which cuts treble. "The same amount of treble" isn't really meaningful. If you mean will it cut as much bass, then you'd have to lower C1 most likely, perhaps to 3.9nF. But again, use your ears. You might not be able to hear a difference, because it will be a fairly small one. If you absolutely need to know that one setting is the same as the original, use the switch, because no pot will have resistance as high as a switch that disconnects C2.

One other thing.  I see that most others are using a linear taper pot for this control.  Can you elaborate on why you recommend an audio taper?

Because I think it works better. Try both, see which one you like.

[/quote]I personally think that Brian should include this mod in the build document.  It seems like a pretty popular mod and it's so easy.
[/quote]

Brian's PCB is set up so that people can easily create a copy of a classic effect, and the PCB is also designed for beginners. Including too many modifications in the build document could confuse builders, especially because the board isn't really set up for two potentiometers.

[FloorIt]

Brian's PCB is set up so that people can easily create a copy of a classic effect, and the PCB is also designed for beginners. Including too many modifications in the build document could confuse builders, especially because the board isn't really set up for two potentiometers.

Makes sense.

Thanks for all the help on this one!