Rocktron Nitro repair and mods

This is the "Nitro" booster pedal by Rocktron. It's a pretty basic booster effect with a gain/boost control and a DPDT On/Bypass switch. The pedal uses a dual OpAmp to amplify the guitar pickup signal. It stays clean with low output pickups but active pickups could make this pedal sound overdriven at high boost levels.

http://www.thomann.de/gb/rocktron_guitar_and_bass_effects.html?partner_id=73786

This particular pedal came in with a broken gain control and it produced no sound at all. I opened up the metal housing and found out that the level pot has kicked its back. So, I replaced this pot with a Korean-made A500K one. The pedal was still mute, so I had to replace the OpAmp as well. The on board chip is a NE5532. Since this is not a distortion pedal, I tried a TL072 on. The sonic result was about the same. You could use high spec chips to see some tonal difference. Just make sure to place an 8-pin IC base on the PCB to try different OpAmps without having to use the soldering iron all the time.
Then, I noticed that the pedal was cutting out some times. So I re-soldered the DPDT switch to make sure there are no loose connections. I also replaced the LM7805 regulator just to be sure. Then, I did a solder re-flow on the solder side of the PCB to ensure no soldering joints are cracked. This pedal took a beating, that's why all these steps were necessary...

Notes: There is a large LM7805 voltage regulator that lights up the large red LED. Check this regulator for overheating issues.

Here is the Schematic diagram of the Nitro Booster pedal (open in new tab to enlarge):

Suggested MODs:

(OD) Overdrive pedal mod
One could easily turn this booster pedal into a mild distortion/OD pedal. You could just solder a set of 1N4001 or similar diodes and Leds back to back in parallel with C7 capacitor for an OD effect.
The output level will drop a bit but you'll get an OD/Dist sound. The boost pot will become the Gain pot of the OD pedal. The level could be controlled via a second pot. The 2nd "level" pot can be an A100K or a A250K one and it would replace the R15 resistor. See the following schematic for more!
Moreover, placing a switch in series with the diodes/leds will give you 2 effect modes: clean boost(stock sound) or distortion effect.
BTW, a couple of Red and/or Green Leds will give this modified pedal more clean headroom and output level while two 1N4001 diodes back to back will produce a more distorted signal.
Here's the modified schematic for the Nitro overdrive pedal: (open in new tab)

More gain
For extra boost, replace the boost pot with a A1M one. This will double the gain of the pedal and could make it sound a bit like a mild overdrive pedal with its level pot set to max.
Lowering the value of R11=100K to 47K or less will also increase the gain.

Less bass
To reduce unwanted bass response, replace the C2 = 10uF capacitor with a 100nF one. You could use 1uF / 16V or even 22nF capacitors in this place. Higher capacitance = more bass. I would prefer a 100nF cap for guitar use.

Bass guitar use
If you use this pedal with a bass guitar, replace the C10 capacitor with a 10uF/16V one, rated at 16Volts. C10 cuts-off low frequencies when the pedal is On. Replacing C10 with a 10uF cap, will make up for the low end loss.

More output level
If you want more output level without increasing the overdrive/gain of this pedal, just replace the R15 = 100K resistor with a 220K up to a 1M one. Higher resistance value of R15 = more output .

Less treble
To reduce high frequencies and treble, replace the C7=10pF capacitor with 22pF up to a 1000pF=1nF. Higher capacitance of C7 = less treble.  47pF would be a good value for a mild treble cut.

Led too bright?
Just replace R6=1k with a 1/2Watts rated, 1.2K or 1.5K resistor. This will reduce led brightness a bit. You could also replace the red led for a different color one. Just buy an Led of the same size and be careful not to swap the Anode and Cathode legs of the new led.
Here is an interesting pic that will help you identify LED pins:

Here are a few pictures of the actual pedal:

Cheers,
Thanos