MZ-RH1 hardware volume hack

[Gleb Erty]

Hi, guys!

I've found how to make a relatively simple, but effective volume hack for MZ-RH1 and may be this information can be useful to others, so here is the description. I have no other documentation sources (e.g. separate Sony's chips docs), but the service manual seems to be a sufficient information source for a little reverse engineering.

This device uses a sort of combined DAC/phone amplifier chip with advanced power-saving feature - variable output stage VCC with external control. Normally such control voltage is generated by the PWM-output at the main microcontroller and is used for lowering power stage VCC at low volume levels for battery saving and for low-speed audio muting or fading. According to the service manual, this control voltage reaches 1.5 volt at maximum volume (pin 11 IC301). Embedded voltage regulator in phone amplifier is connected to 3 volt power bus, so we have enough potential for creating a little overdrive.

WARNING: you need VERY GOOD soldering skills (especially with SMD components), a good, clean and thin regulated DC soldering iron for lead-free soldering, a high-temperature neutral flux (RMA-223 or something similar), angle tweezers and a low-temperature (non-lead-free) solder - otherwise you can ruin your expensive and rare unit easily! I cannot take any responsibility for broken units, so proceed only for your own risk! Sure that you will lose your warranty too.

You need a small SMD resistor ~56 kiloohms (often marked as 563); a very thin, high quality isolated wire and (recommended!) a scotch tape with good heat resistance for protecting PCB while soldering and avoid short-circuit with other components. After unit disassembly and removing the PCB shield (3 screws) place the unit with mic and phone jacks in front of you with PCB on top and solder resistor with the wire between two spots on the PCB (see attached image). You can check solder points with service manual - (+) C362 (+3V bus) and R302 (pin 11 IC301). This must be done VERY accurately - no solder joints, no cold soldering - all must be done solid and strong and checked several times!

With this mod we can obtain a HUGE power improvement - +30% output voltage, >50% output power, - and only one drawback: after hack you will hear in phones a short fade-in static at the start of the track if the volume is >70% and the unit previously was in stop or seek mode (sounds like a series of quiet mute clicks) - IMHO this problem is not annoying. Anyway you can later remove resistor and wire.

All research was done in two hours and finished one hour ago. It seems that all other functions working as usual, but I will make some field tests later.

Feel free to ask if you have any questions.