Rangemaster/ Mid boost?

[fretbuzz2003]

I finished building my Rangemaster clone. I cut most of the background hiss out by using a battery instead of my power supply.

I was hoping to make something similar to the Keeley Java Boost. His version has a three-way switch that will do the stock treble boost, the full boost, and a mid boost.

By using a three way switch and putting input caps in parallel, I was able to get the treble and full boosts. I'm not sure how to do the mid boost however. Anyone have any ideas on how to get the mid boost?

[Fret Wire]

Here's a previous thread on that:

http://www.diystompboxes.com/sboxforum/viewtopic.php?t=10851&highlight=java+boost

BTW, you had a previous thread on your Rangemaster (hiss). How did you make out?

[fretbuzz2003]

By using a battery instead of my power supply most of the hiss went away.

[fretbuzz2003]

Here's a previous thread on that:

http://www.diystompboxes.com/sboxforum/viewtopic.php?t=10851&highlight=java+boost

I read that thread. There was nothing in it but alot of Keeley bashing. In his schematic, he shows the stock Rangemaster input cap and a three way switch, but nothing on how he does the other boost modes.

[Fret Wire]

Sorry about that, I just dug it out of the archives without reading it. I thought I remembered that they straightened the schematic out. My mistake, no one wants to read another flame thread.

[Oliver]

Hi,

i build a Tubescreamer using a 3Way toggle Switch to change the
Boostrange between Mid/Treble/Bass

I used a Switch ON/OFF/ON
In OFF Position the Range is set to Treble with a 15nF Cap.
In the first ON Position i added a 0,047uF Cap in Parallel for the typical
Tubescreamer MidBoost with slightly cutted out Bassresponse.
In the other ON Position a 0,22uF Cap is added in parallel to the 15nF Cap.

I think, you can do it the same way with other CapValues to switch the
Booster between Treble/Mid/Normal

To use it on an LPB1 i would build it as illustrated

bye
Oliver

[R.G.]

The Rangemaster circuit by itself gives a bass cut plus an overall boost - equal to a treble boost. The stock circuit has a rolloff that starts at about 1kHz and rolls off at a single RC slope of -6db per octave forever towards DC.

If you want to change the turnover point, change the input cap. Doubling it moves the 1kHz rolloff point down to 500Hz. Halving it moves the frequency up to 2kHz.

No amount of tinkering with the input cap will give you a mid boost. For that, you have to roll off treble in addition to bass. It's simpler to do that somewhere other than the input. I personally would put a cap plus a 1M resistor across the output put. Then shorting out the 1M resistor introduces a treble falloff of the pot value and the cap.

With a 10K pot, you get a 2kHz rolloff at C = 1/(2*pi*2kHz*10K) = 7,9nF or 0.0079uF - which is not anything like a standard value. A reasonable sub is a 6.8nF or 0.0068uF or 6800pF (all the same thing) would give you a similar result.

I don't know what Keeley does but this is the simplest way to get a mid boost from that circuit.

[fretbuzz2003]

That makes sense, but I'm not sure how to go about that. Would the cap and resistor be in series similar to a lowpass filter, with the cap soldered to the output pot and the resistor to ground? Which lug of the output pot do I solder the cap to?

Thanks.

[R.G.]

That makes sense, but I'm not sure how to go about that. Would the cap and resistor be in series similar to a lowpass filter, with the cap soldered to the output pot and the resistor to ground? Which lug of the output pot do I solder the cap to?

The output pot acts as a fixed resistor load to the collector of the transistor. The wiper of the pot merely taps off a fraction of the voltage across the whole resistor.

If you put a capacitor in parallel with the ends of the pots (both NON wiper contacts) then you have  simple low pass filter. Frequencies above the RC time constant of the cap and end-to-end pot are cut at -6db per octave.

Note that since one end of the cap goes to the power supply, and that the power supply is effectively shorted to ground for AC signals, that the cap can actually go from the transistor collector to ground and get the same effect.

You might want to switch this cap in and out to turn mid boost on and off. To do that you could open up the end of the cap to ground. That would cause a big pop when you reconnect it as the cap has to re-fill to the correct DC level. You can get around that by putting the ground side of the cap through a 1M resistor and opening/shorting the 1M resistor. That way, the DC level on the cap never changes and you don't get a big pop when you switch it in and out.

[fretbuzz2003]

Great, thanks for the explanation! I'll give that a try.

[fretbuzz2003]

I finally got around to adding the mid boost to my Rangemaster. I wired just like RG suggested. 0.0068uF cap between the collector and the boost pot, the cap in series with a 1M resistor, and the resistor to ground (through a switch). However when I switch the cap in the pedal doesn't sound any different.

I have triple checked my wiring and everything seems to be in order. Any suggestions? Should I try a different value cap?

[Ben N]

I don't recall any indication of any switching going on anywhere besides the input cap in the Java, so I would hazard a guess that his "mid-boost" is really just a treble boost with a lower rolloff--one low enogh to include a lot of what we think of as the midrage--rather like the "mid boost" that folks get in Fender amps by replacing the bright cap with a bigger value.  It's not a true mid-boost, but it may be useful just the same.

Ben