Project "Phoenix"

HITACHI CASSETTE DECK D-2200M

During my modifications with new BIAS generator and HXPRO circuit I realized that manual tuning of the BIAS would be possible using support of VU display. That simple method was used in many high class Cassette Recorders with big accuracy for many years.

Originally Hitachi D-2200M used the same method with support of microprocessor, enabling to perform the tape test automatically by pressing just "ATRS" and "START" button. My manual test tape method sets Left channel VU display for proper recording level at 1000 Hz internal test generator and Right channel VU display for 14000 Hz. Those indications should be equal for proper tape calibration. All manual adjustments are made by BIAS Potentiometer and independent Record Level Pots. My TTL logic "Processor" sets the deck to Test Recording mode automatically after deck is set to REC PAUSE mode and "TEST" button is pressed. The VU display peak hold mode should be disabled during the test.

During my final tuning process of my circuit, the VU display chip suddenly just blued up. Unbelievable lack of luck or maybe that dammed bad ghost was in this machine.

I should call exorcist before I started to work with this deck. Only thing left to do, to "kill that bad ghost" or dump that machine to the garbage. I put so many hours to rebuild this machine so I decide to kill that ghost myself.

Project NEW VU Display

I decided to make my own VU display driver for this large VFD display. I had to solve a few problems creating new driver board for this VFD display. The original VU display has logarithmic scale with 18 elements per channel. The most available IC logarithmic display driver LM3915 has only 10 elements and has to be cascading with another chip.

To achieve proper scaling on VU VFD Display logarithmic driver LM3915 was cascading with linear LM3914. The Display calibration was made with micro Pot's visible on top layer of my display board.

Top view of my VU Display Board

Bottom view of VU Display Board

The Display Board made from many IC components replacing one big integrated chip is working good like old chip, with few new options useful for Test BIAS Tape Tune up.

The new board increased power consumption from Power Supply that was necessary to do something with it , to prevent constant overheating of power supply and causing excessive hum noise when power line voltage was dropping in my area in summer time.

I had to make a new stronger Power Supply for this machine.