In this video, I do a review of the Caline CP-81. It is an upgraded version to their CP-24 Ten band EQ. Both are clones of the MXR M108S 10 Band EQ, a very solid pedal. The solution for the noise happens at 7:14 if you want to skip to that.
I contacted Caline about this issue and they sent me the schematic to the CP-81, and with that discovered the voltage problem and how to fix it. At the time of recording this video Caline told me their engineers were actively addressing this issue. It helps when you send the manufacturer compelling video proof of the problem. :-) They are not endorsing or compensating me for this video. They have provided me great customer service with sending the schematic. Hopefully they will have a more permanent fix in the near future. For now, this video provides a great inexpensive work around.
The highlights:
- Both the MXR and CP-81 have the SAME Quad Op-amp chips running them! The circuit design is similar in both
- The Caline is advertised to run at 9 Volts only. You CAN run it at 18 volts, but there is no benefit.
- ****The Caline has a special "step-up" converter that takes the incoming 9 volts and makes 18 volts internally to run the PCB. There is no need to feed it 18 volts. the MXR pedal does NOT have this
- There is a design flaw with this voltage circuitry in that it causes a very high noise floor despite the similar circuit designs in both pedals. Running ~9.0-9.1VDC the Caline is very noisy. Running it at 18 volts makes it WORSE!
The MXR claims to have noise suppression circuitry, well this Caline pedal does too. It is normally a few capacitors added to the output stage to bleed off the high frequencies so the noise is less. Output stages of both pedals have similar designs.The step up converter is the cause of the noise floor problem.
HOW TO FIX THE NOISE: I have a power supply that outputs 9.1VDC no load. Using a buck converter, I drop the voltage from the PSU down to exactly 8.5VDC. Notice the drastic reduction in the noise floor. Output 1 of the 10 band eq plugged into the input of a Peavey Basic 112. Pre-Gain set to 4, and volume set to 3.
Input Voltage Resistor: www.amazon.com/dp/B06WP5FJV9
Barrel Tip Adapters:
www.amazon.com/Power-Connecto...
***I used a buck converter in the video, and mentioned I would use a smaller form factor converter, however that converter required a higher voltage than 9 volts to regulate down to 8.5vdc, unlike the one I had used for testing which could be inputed 9 volts and output 8.5V. The less expensive and simpler way to achieve 9V to 8.5V is to use a variable series load resistor. Others have suggested using a rectifier diode which has about a 0.5V voltage drop, however not every pedal PSU is created equally and the tolerances are too small to use a common diode unfortunately. With the multi turn resistor mentioned above, you can dial in the voltage exactly.
www.amazon.com/Caline-CP-81-G...
www.calinemusic.com/products/e...
Op-Amp Datasheet:
www.mouser.com/datasheet/2/30...