Rocktek PHR-01 phaser

[Yazoo]

I am trying to repair this pedal. I've recapped it and it works fine with a battery. However, when I power it with a power adapter the led is very dim and it does not phase. Voltages on the opamps are around 5.3v. It uses a 270R resistor and diode in series, similar to what is shown in the schematic for another Rocktek pedal I found. The actual schematic for the PHR-01 I found on the web does not show these! Is it dropping the voltage across that resistor and is this a problem with the pedal design or is something else faulty in the circuit do you think?

[Rob Strand]

Pedals with that type of DC jack circuit require unregulated 9V adaptors which actually produce 12VDC under light loads.   The same circuit is used by the older Boss ACA pedals.   More modern pedals use 9V regulated supplies like Boss's PSA pedals.

There's many different ways to deal with powering these older pedals but you can't really get them to work 100% reliably with both unregulated and regulated power.

The simplest mod is to replace the 270R/390ohm resistor with say 10 ohm.   You could replace the diode with a Schottky diode. The diode provides reverse voltage protection so if you remove it you might need to add a parallel type protection which isn't such a great idea these days.


It's certainly possible your pedal has other problems.  For debugging your problem you might be best sticking with a 12V regulated or 9V unregulated supply as the resistor is providing current limiting in case of a fault.

The estimated current from the pedal is,

I = (9-0.7-5.3)/270 = 11 mA

Which seems quite reasonable and perhaps not indicative of a fault, in which case you need to sort out the power supply.

[Yazoo]

Thanks, I'll try reducing the resistor size.