Dallas Rangemaster
Similarly to Brian May who uses his Deacy amp with a treble booster in front, I wanted to build something similar that can be used with my germanium radios converted into guitar amps. All those amplifier circuits in radios are designed to amplify wider range of frequencies and they expect lower impedance signal at the input, so plugging the guitar straight into the amplifier may not be ideal. As soon as you roll down the volume on guitar from 10 to 9, output volume drops significantly, because of the higher impedance of pickups. Having some sort of a treble booster at the front helps shape the sound of the guitar and reduces issues with impedance mismatch. I chose Rangemaster because it’s a legendary circuit and I have a bunch of germanium transistors that I could try and pick the one I like the most.
Circuit
The circuit is very simple, but effective. It can pump out a respectable 24db boost in higher frequencies and push the amplifier into overdrive. Two components are crucial for the effect – input capacitor and transistor. Input capacitor forms a high pass filter and depending on the value it will let more or less of middle and lower frequencies.It’s best to experiment and find the right value for the particular guitar and or amp, but I found that anything above 22nF makes it less of a treble booster and more of a full range booster. Feel free to experiment with wider range of capacitance, but I recommend starting with values between 5nF and 15nF. The transistor should be a PNP Germanium (or even silicon). It affects boost level, but also the sound. Rangemaster is not a squeaky clean booster, it will overdrive when pushed hard and transistor will affect the character of overdrive. R.G. Keen from GeoFex.com wrote a great article dissecting the Rangemaster circuit. He recommends a low-leakage Germanium transistors with gains between 75 and 100. In addition to the choice of resistor by gain, we also need to worry about the bias. According to R.G. Keen, the best sounds can be had with collector voltage around -7V.
Mods
For more versatility, input capacitor can be omitted from the circuit board and placed on a switch, so we can have switchable capacitor values. One of many ways to accomplish this uses an ON-OFF-ON toggle switch with 5nF capacitor across the middle lugs. It’s always in the circuit. Outer lugs can have two capacitors that can be switched in parallel with the existing 5nF capacitor. Diagram below shows a setup that allows switching between 5nF, 10nF and 15nF capacitors for a wide range of sounds.
Layout
I drew a simple perfboard layout that can be used on 1×1″ protoboards that have 81 holes. It’s drawn with a trimmer for bias, although I put a fixed resistor in there and experimented with several transistors until I found the one that biases perfectly. Also, there’s room if you want to install sockets in parallel with input cap to add more capacitance and shift the frequency response curve to the left.
Build
Being simple circuits, most boosters can be squeezed onto small boards, so I used one those awesome little 1×1″ proto boards with 3-per-pad plated-through holes. It’s very sturdy and easy to work with and I love using them for simple builds like this. I started from Dallas Rangemaster schematic and changed a few things – added socket in parallel with the input capacitor so I can add more capacitance and change the low-end/midrange response of the booster, replaced 47uF emitter capacitor with 22uF solid electrolytic (shouldn’t affect the sound, even 22uF is plenty), replaced the 10nF output capacitor with 22nF (there’s another input capacitor at the amp input, so I didn’t want to cut too much bass by having two capacitors in series).
As always, I used transistor socket to allow playing with different types of transistors and tried pretty much everything I had unfortunately, no OC44). The one I liked the most was GT308V that came out of the bin labeled 100-110hfe and gives a perfect collector voltage of -7V with stock biasing resistors.
![Deep Purple - Lazy [Guitar Cover]](https://i.ytimg.com/vi/7ZyjTZgM2DY/default.jpg "Deep Purple - Lazy [Guitar Cover]")
I have an excellent mod the gives of fuller body crunch on the pick attacks and a sustain with more personality.
You will need a 250k audio taper potentiometer, a SPDT switch, and a 41 mHenry inductor. Although any 41mH will work, ideally source one from an organ supplier who has old Thomas Organ TDK inductors. I’ve been an organ collector for 25 years so I have many values and 41 is the magic number. 43 mH is too high. I’ve used it with a dozen different transistors. Probably 40mH is fine.
The mod. DRAW OUT THIS ON PAPER. Super simple mod. I call it the “Induction Bias” mod.
Solder one side of the inductor to the (E) emitter on the transistor. Solder a wire from the other side of the inductor to the switch. Solder another wire to the other switch terminal and solder the other end of the wire to terminal 1 on the 250k pot. Solder terminals 2 and 3 of the pot to the chassis ground (regardless of whether you are using PNP or NPN transistors). This is a ground/ on-off mod so you can make a simple 2-terminal make/break foot switch to kick the mod in and out.
Using the effect. Turn the pot to max. It will cut out your signal at max. Now slowly turn the pot back until you hear what sounds like voltage starvation break up. Note, when it’s set to your satisfaction it won’t sound starved, although you can have those elements. Now very very carefully play a steady open string(s) palm mute and find the sweet spot in your sound. It will be locked in where you leave it. I recommend the stomp switch bypass.
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GREAT HACK: Ever think about a Treble booster or Fuzz pedal with several transistor and capacitor values in one pedal? Here is the key to that coming to fruition. In fact my single inductor mod works great on my 9 Rangemasters in one pedal!
If you can find a DATA DOC (brand) DATA SWITCH box ,serial port A/B or A/B/C/D etc switch box. Contained in the brushed aluminum box is an industrial grade ceramic 9position/ 6 pole rotary switch! That 6 output terminals and 9 x 6 input terminals. 60 easy to solder to open oval terminals. The serial port wires are plug on ends, so once unplugged you’re looking at a brand new switch. So why do they use a 9 position switch and only use a couple positions? Don’t know, but even A/B boxes use them.
My 9 different transistors and 9 varieties of input caps only use 4 of the 6 terminals since the base and one input cap legs share a terminal. The leaves 2 spare terminals for anything. Even an LED indicator for each position. Although the switch positions are exactly in the positions of a clock. Position 5 looks like 5 O’clock…
Just wondering the the blue point indicate on the board there the bias is?
The 3 blue points are legs of the bias trimmer.
I actually had an original Rangemaster treble booster, which I used in my rig in the 70s. Unfortunately, as I wasn’t using it I gave it away. (Yes I know!) I would like another one but know buffer all about building electronic pedals. You said that this was a relatively simple circuit, I was wondering if this would be a good one to start off with(?)
Many thanks!
Absolutely, boost or fuzz are great first pedal candidates.
Thanks for publishing this!
I am making a tagboard range master and want to do the input cap switch (slightly simpler on-on between a 5 and 10nf) and was wondering – do I need to run a ground wire from the switch? Or will it be okay as your image suggests – just wires running from and to the board?
Thanks again for posting this!
It should be fine to run some wires, just keep them nice and tidy.
Monsieur Bancijka,
Si’l vous-plaite, où est l’affichage LED sur votre schéma?
Merci beaucoup,
Josh
LED and bypass switch are not shown, they are standard true-bypass circuit together with the LED current-limiting resistor.
I don’t see the LED anywhere on your schematic….. was that an afterthought that didn’t get included in your recao?
Not an afterthought, LED is part of the bypass circuit that is not shown on the schematic for simplicity.
Why have you included a second 47mf cap with a 1meg resistor, when my treble booster kit only has one?
I cannot possibly know why your kit has one. The second one filters input DC voltage when using a 9V adapter. If you use batteries you might not need it.
Thanks for the tip, I don’t know why the kit didn’t come with the second cap in the first place! – Finally got mine working after a few attempts, (now where’s that resistor I left out…….)
When sourcing components such as capacitors, should the ‘max voltage’ just be >9v? Does it matter if the max voltage is much higher than that, e.g. 50v?
Thanks for this awesome project.
Yeah, any will do. However, higher voltage rating means bigger capacitor (and costs more), so it’s usually impractical to go to high across the board.
Hi Bancika! congratulations and thank you so much for this content:) I was wondering, how do you deal with the -9v power? do you require a specific power supply? thank you so much in advance
Thanks for the comment, Guido. There are few ways you can get -9V:
* 9V battery with – used as -9V and + used as ground (that’s what I do)
* use isolated pedal power supply and then flip the polarity +9V
* use +9V from any power supply and then use MAX1044 or similar charge pump circuit to get it to bipolar +-9V and then use the -9V from there, ignoring the +9V tap.
I just wanted to say thank you for taking the time posting all your “hobby projects” here on your website. I’ve been trying to gather information in amp building/modding and pedal building/modding for months hoping to teach myself or learn from people such as yourself. I can’t begin to tell you how grateful I am to have found your website. Many of your projects are exactly the same ones I’ve been interested in learning about and hopefully building myself someday. Also, it’s very cool that you respond to people’s comments and questions. Thank you
You are very welcome. This site stands as my thanks to the online community that has taught me everything I know.
Yeah removing the 9V battery and power it by the jack cable directmy plugged into the amp .
If this not possible, can you tell me where I need to solder the black cable of the battery. There’s no indication for that on the schematic
Thanks
Hello,
First let me tell you that is a really good job !
You have to sell ’em !
And by the way I wanted to see if I can remove the 9volts battery of the system and at the output directly solder a Jack cable that directly going to the amp and if that gonna be function .
Thanks a lot if you answer to that 😁
what do you mean remove the 9V battery? what would you use to power it?
Nice but, did you have a sound sample to hear what it sounds like ? And I found a oc44n does it will works ?
Thanks for your time and attention.
Hi
with those old transistors you really have to try and see as they are all over the place with the specs. Gain and leakage may or may not be good enough. Ideally, try a handful of transistors and pick the one you like.
Cheers
Ho i didn’t know that !
Nut I searched on internet for schematic but yours is very different from all others that I found .
I didn’t know if it will function :/ .
You said earlier that you changed a lot of things . So i’m not very sure :/ .
Have sound sample for me please ?
Thanks for reading this message.
And by the way can you answer to that please?
I modified the picture of the schematic to see if that can be possible
https://prnt.sc/nj211m
Nice job, do you sell these units by chance. I am interested.
Thanks, Craig
thanks for the comment. Unfortunately, I don’t have time and resources to turn this hobby into a business. I only build for myself and sometimes sell stuff that I get bored with to make room for new builds 🙂
cheers