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Replace SID 8580 by SID 6581

Project: Replace new SID by old SID
Target : C64 (new board)
Time   : 10 min (20 min with switch)
Cost   : 1-2 US$
Use    : Possibility of using old SID in new boards (for sound
         quality reasons or substitute for defective unit)


Replace Z-diode CR7 (9.1V or 10V) with a 12V type.


The new SID 8580 requires only 9V as opposed to the old SID 6581 which needed 12V. Since the 9V are generated by a Z-diode, we can simply replace the diode with a 12V type.
Exchanging the capacitors to obtain the 'original' sound seems to be useless, the 6581 does not seem to change its sound characteristics on varying the capacitors, at least we could not hear any differences. If you had different experiences, mail me.
Note: If I find the time, I will do some more experiments with the capacitors later.



  1. Pull off all cables, then open case.
  2. Search for diode CR7 on the right side of the keyboard connector.
  3. Replace it with the 12V type. Pay attention to the polarity of the diode; simply solder the new one so that the cathode ring (black) points to the same direction.
  4. If you want to switch (more easily) between old and new SID, solder the old diode in parallel to the new diode, but via a jumper placed onto a Vector board.
  5. Check the sound with the SID 6581 inserted (and with the 8580, if you performed step 4).
  6. Close case again.
ALWAYS be sure to select the right combination of SID and Z-voltage!! (6581: 12V, 8580: 9V)

Possible failures

Updated: September 30th, 1997
Created: February 3rd, 1997
Status : Verified

Site copyright © 1997 by Marc-Jano Knopp
This document is part of MJK's Commodore 64 & LCD Page
Brought back to life by Peter Schepers, Dec 10, 2005 because I really liked this site!