Modifying a Music Hall Cruise Control PSU

[ronenash]

Hi all,

I have a Music Hall Cruise Control turntable PSU which I am trying to modify to work with 50hz turntable motor and pulley vs. the 60hz it is setup for now. I have the schematic but cannot really get my mind on how to modify it to output a 50hz signal. I have attached the schematic in hope that someone on the forum can assist me with the modification.

Any help will be greatly appreciated.
Thanks,
ronenash

 

[kevinkr]

Simplest approach might be to try a 10MHz crystal, but no idea whether that would work or not.

Edit: My bad, see Pyramid's post below and ignore this one.

 

[ronenash]

Seems like a long shot but it might work. Maybe someone else has done something like this before and can chip in.

 

[Pyramid]

I think I would go in the other direction: Replace the crystal with 13.5 MHz.

The CC uses freqs of 44.444Hz and 60Hz for 33/45 RPM, using the large spindle on the pulley. Changing the xtal to 10 MHz will make the freqs 37.037Hz and 50Hz. The motor and/or the output transformer will not like this.

If you make the xtal 13.5 MHz, the freqs will be 50Hz and 67.5Hz for 33/45 and you can use the small spindle on the pulley.

 

[ronenash]

Hi Pyramid,

Thank you for your insight. Are your sure that changing the crystal will change the output frequency? I am not sure what processing is done within the processing unit.

ronenash

 

[Pyramid]

Yes, the CC uses PWM to generate the sinewave. If you change the clock frequency, everything will be scaled by a proportionate amount. 50Hz/44.4444=1.125x12 MHz=13.5 MHz

I thought you had a Falcon on your Classic?

 

[ronenash]

I do have a falcon on my Classic. I am going to use the CC on my Transcriptors Hydraulic reference which has a 50hz pulley.

Thank you for sharing your knowledge.

Ronenash