How to modify the Orange Pedal Baby 100 for direct power amp input — bypassing the preamp section for use with a modeler?
It is really simple, the following drawing clearly illustrates the basic concept:
One of the speaker jacks is repurposed as a power amp input.
Inserting a plug into this jack will disconnect the preamp and route the signal directly to the power amp, bypassing all front-panel controls. This effectively turns the unit into a clean, linear analog power amplifier—where all parameters, including volume, are controlled from the modeler.
As a bonus, this also eliminates the tonal coloration and distortion typically introduced by the preamp section. While these characteristics are often desirable, they’re not always a great match for modern modelers.
The sensitivity for full output with this new input is +4.5 dBu, i.e., approximately 1.3 VRMS. Input impedance is about 32 kΩ, and the DC-blocking capacitor at the power amp input forms a first-order high-pass filter with a cutoff frequency of approximately 10 Hz when driven by a low-impedance source. The input circuit also forms a first-order low-pass filter with a cutoff frequency slightly above 100 kHz. The power amp’s voltage gain is +30 dB.
Most modern modelers should have no trouble driving the input to full output power. For example, the Neural DSP Quad Cortex delivers a nominal maximum output level of +9.5 dBu from its TRS outputs when used unbalanced.
The schematic above already covers the electronic side in detail.
Mechanical implementation notes will follow.
Full article coming later… stay tuned!
We’ve already received quite a few questions about this—even before publishing the full article! 🙂
Below are the original questions along with our answers:
Q: What is the main reason for cutting off the preamp section?
A: The preamp section slightly colors the tone—even with a flat EQ—due to mild distortion from the JFET stages and some dynamic range compression from its “tube-like-ish” design. While many users prefer this character, especially in traditional setups, we personally find that a more linear response works better with modelers. To our ears, the mod sounds more transparent. That said, your mileage (or kilometreage) may vary.
Q: If I can achieve a flat response with the EQ on the Pedal Baby, there should be minimal impact on the sound, right?
A: Yes and no—see the previous answer.
Q: Do you recommend it with my Hotone Ampero Stage II?
A: We don’t have personal experience with the Hotone Ampero Stage II, so we can’t say for certain. That said, we’d expect it to work well with the mod. The only way to find out is to try it—if you do, please let us know how it goes!
Q: If I do this mod (if I understand correctly), I need to sacrifice one output and convert it into an input (which is not a problem since I only use one output). In this case, if I still want to use the preamp with the front input on the Pedal Baby, will that still work even when the mod is applied?
A: Yes, that was one of the main reasons for doing the mod this way. It’s designed so that the Pedal Baby functions normally—with the preamp active—when you use the front input. Plugging into the repurposed rear jack bypasses the preamp, so you can switch between them just by moving the cable.
Q: Can I switch the cable between the front input and the modified input on the back whenever I want, so that the preamp works when using the front input and is bypassed when using the back input?
A: Absolutely! See the previous answer.
Q: If there is no volume control on the Pedal Baby, will that cause it to make more noise, since gain and volume will only be applied from the modeller?
A: No, the mod won’t introduce any additional noise. The power amp section in the Pedal Baby is always running at full voltage gain in the original design, and this mod doesn’t change that. You’ll just need to lower the output level of your modeler (or whatever device is last in your signal chain) when using the rear input—otherwise, it’s going to be loud.
Q: Since signal from modded input can flow back to preamp. Is there any chance preamp board gets damaged? Should i install switch between preamp and modded input switch?
A: Normalled jacks, like the one in question, work so that the contacts marked with the letter N in the picture (TN, RN, SN) disconnect from the main signal path (the contacts that connect to the plug) when a plug is inserted into the jack. The arrow in the picture represents the switching contact that disconnects. So: the preamp output gets disconnected in that case, and there is no risk of damage. That’s the whole point of a switched (normalled) jack.
Here are a few pics of the final setup:
