Been a while so I thought I would post an update on this thread, anyway, if you build one of these and it is working properly but sounds slightly off, you can use a multimeter set to say the 20V DC range to check the voltage on transistor Q1's collector, ideally you want to see from about 6.8 to 7.0V on the collector, you can tweak the value of the 3.9k emitter resistor up or down to get the collector voltage within that range, the 68k and 470k base resistors can be left as they are, if you can't get the collector voltage within the range of 6.8 to 7.0V (assuming it's a germanium transistor) it could be that the transistor may be leaky and needs replacing with a better one.
The reason why the transistor is biased with a collector voltage in the range of 6.8 to 7.0V is because that deliberately introduces a small amount of distortion into the sound of the Rangemaster, which is subtle at frequencies below about 1kHz but gradually gets more intense as the signal frequency goes up, this effect is part of the Rangemaster sound.
Note that the collector voltage is going to be negative with respect to ground if a PNP germanium transistor is used.
I think there's a good article in pdf form that you can find on the internet, that explains everything about the Rangemaster, try doing a search for the GEO FX Rangemaster/Austin Treble Booster, definitely a good read for those wanting to know all about the Rangemaster and how it works.
Note 2, you don't necessarily have to use the exact same germanium transistor as specified in the parts list, most small signal germanium transistors will work if they have a gain of at least 75 to 100, and low leakage.
Last edited by DrNomis_44; 17-06-2019 at 02:02 AM.
Reply With Quote