Arp Quartet cheap?

Scott Gravenhorst chordman at
Thu Nov 4 20:41:14 CET 1999

Wow, what nostalgia...  I built a 4 voice synth with a 50240 years
ago.  I still have 2 of the chips.  If I remember correctly I think the
ratios provide at least 1 cent accuracy.  It was a very simple synth,
but it was 4 voice polyphonic.  The synth computer was a SWTPC 6800
system and I wrote a sequencer in assembler for a TRS-80 color computer 
that sent it's commands via serial port to the 6800.  What memories.
The synth electronics never made it past solderless breadboard, but
the damn thing worked and worked well.

Harry Bissell <harrybissell at> wrote:
>Its no secret whats inside the top octave generator... its just digital dividers
>that have the 12th root of 2 relationship to each other. If anyone has the data
>sheet it will tell what the division ratios are... A PLA FPGA etc could do this, or
>even good old CMOS logic. An 8 bit divider would give acceptable accuracy in most
>cases... more bits are better.
>Somewhere in the junk drawer I have an old paper that has some best fit ratios. I
>could find it... interest ????
>:^) Harry
>patchell wrote:
>>     Somewhere in my junk box I should have one of those suckers.  If somebody
>> needs one to restore an old piece of equipment, I could see if I could find it.
>> I have no idea what condition it might be in, or even if I could find it.
>>     -Jim
>> WeAreAs1 at wrote:
>> > Rory McDonald wrote:
>> >
>> > <<There is an Arp Quartet on eBay (not mine, I just noticed it), not working
>> >
>> > (no sound output, but everything else looks ok-opamp?) -could be a bargain
>> >
>> > for a DIY'er.>>
>> >
>> > ...or it could wind up as another white elephant in the attic, if its top
>> > octave divider chip has gone bad.  As far as I know, these chips are not
>> > available anywhere anymore.  They are a common point of failure in string
>> > ensembles.  If anyone knows where they can be purchased, please let the list
>> > know.  (Mostek 50240 and variations thereof)
>> >
>> > Michael Bacich
>> --
>> -----------------------------------------------------------------
>> Visit:
>> -----------------------------------------------------------------

-- Scott Gravenhorst	                | Linux Rex, Linux Vobiscum
-- FatMan:     | RedWebMail by RedStarWare
-- NonFatMan:
-- Al Gore: I'm the father of the internet.

More information about the Synth-diy mailing list