Let's build a Treble Booster
Step by step guide on how to build your own germanium treble booster.
Let's build a Germanium Treble Booster
Step 1: Choose a suitable germanium transistor
The original Dallas Rangemaster Treble Boosters used either OC44 or OC71 germanium transistors. It's good to use these transistor models if they are available. However, the characteristics of the transistor are more important than the actual model number. Information is available on the internet about suitable replacement options. One of the websites I use to determine replace ment options is this:https://www.radiomuseum.org/tubes/tube_oc44.html
Before buying a transistor always look at the data sheet. There are three important parameters when choosing a transistor for a treble booster:
- the general voltage that the transistor operates at. This is marked UCE or UCB and in the case of the OC44 is 15V. Somewhere up to 32V should be okay. Don't use power transistors!
- the current gain or amplification factor known as HFE or Beta. For the treble booster circuit an HFE over 55 is great. However, keep in mind that going with a higher HFE means it will amplify noise more as well, so it can be noisier. This is not the only factor determining noise but it is one of the factors.
- the current leakage marked as Ic. This should be as low as possible for this circuit. In general anything over 0.3mA is useless. For a treble booster stay under 0.1mA.
For this build a Tungsram OC1044 is used that has an HFE of 92 and virtually no current leakage as show below.
Step 2: Testing the transistor in a test circuit
The next step is to test the transistor in a treble booster circuit. Use a breadboard to create the circuit from the schematic. Here are two websites that have information about classic circuits:
-Electrosmash - Dallas Rangemaster
With the treble booster circuit bias is achieved when voltage reading on the collector of the transistor is around -7V. In my experience it is better to go lower than higher, so keep this voltage between -6.5 and 7V. To achieve this replace the 68K with a trimmer. In some extremely rare cases the 3.9K resistor may need to be tinkered with too. Generally, though the circuit is fine as is.
Here is my measurement of the collector of the transistor in the test circuit:
When testing the transistor it is also important to listen to the sound of the output. Some transistors have excessive noise even if the above parameters are perfect. The circuit does have some inherent noise, but if the transistor is faulty the noise will be excessive to the point that it overpowers the sound of the unit.
Step 3: Build the final circuit
Use a Vero board or point to point method to create the circuit. The circuit is simple enough not to need a printed circuit board (PCB). Generally, there's no need to use higher wattage resistors and higher voltage capacitors but it does look better and again the cost difference is minimal.
Step 4: Wire up
The enclosure will probably be the most expensive element of the pedal. Painting a pedal deserves its own chapter. In order to have a durable pedal it is better to either buy one already powder coated or have it powder coated professionally. Once painted drill the enclosure and wire up the switch, the LED (not needed, just a nice to have) and the input/output. The unit can be powered by a 9V battery and the battery will "last forever" especially if there's no LED indicator and the input jack is wired up so that unplugging the input jack cuts the power to the circuit.
Step 5: Rock on!
Put the knobs on and close the enclosure and you are ready to go!