Korg TA78 Filter Chip Info

[Vsat]

Hi Listers,
At least one of Korg's old diode-based filter circuits (in the Korg-770, possibly also the Synthepedal) uses a diode array or diode bridge chip called the TA78 - this is probably a very old Toshiba part. I have some chips labelled TA78 here - but they are 12-pin SIPs, with staggered pins. Anyone know if this is the same part?  
Cheers, Mike

[Dan N]

My Roland SH-1000 uses 4 of these. Five NPN transistors with a shared emitter. Kind of looks more like it's being used for buffering or driving in the presets switching circuit? They are sips with staggered pins.

Here are a few in action:

http://users.rio.com/senorris/junk/pg07matrix.gif

P.S. The Korg Synthhepedal is all transistors and 2 vactrols. High and low pass filters controlled by envelope or footpedal.

[Vsat]

Thanks for the reply Dan! I looked at the schematic you posted but it shows TA57 and TA58 rather than TA78 (?). However, someone from the sdiy list also emailed and  also said it was a 5-transistor array with common emitter... either diodes or transistors would match up with my meter readings..  5 separate diodes with a common n-type substrate (which presumably would need to be connected to the most positive point in the circuit for isolation) , or 5 NPN... take your choice. Unless it's a different chip, Korg used this to build a diode bridge which was used as the tuning element in a Sallen-Key filter.. also as a diode-bridge based VCA. They later used the CA3019 diode array for the filter and VCA in the MS-50. The Korg 770 schematics are on the net (I think at the Swedish SAS site).
Regards, Mike

[Dan N]

Sorry Mike! Somehow I got the wrong number! I have the 770 pdf and see the guys you mean. Also see how you might think they would be in the synthe pedal.

The TA-78s in the 770 schematic look like 3 4 pin units. Or, maybe 1 12 pin?

Sure don't know.

[Vsat]

Dan,
I was expecting the TA78 to be something like a "TO-5 can with 4 or 5 leads"... or even a "TO-5 bridge rectifier with good matching specs"      but a 12-pin SIP is a bit of a surprise. CA3086 and similar have been used to make diode bridges for this kind of filter, so it is probably reasonable that Korg used the TA78.

Ever heard of the TX-429D that Korg used in some pedals? From the schematics (phaser, parametric equalizer) it appears to be a MOSFET.
Regards, Mike