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813, 823, 910, 920 NOT 900

Just a note on mjrippe's EQ post above..
The EQ shown is a 900 (Sphere drawing 31217) and not a 920 (Sphere drawing 33916).
While they are both Sphere graphic EQs the pinouts are quite different
as they are different EQs. with different features.

NOTE.. Gain pins left open provides the BST with 15db of gain which is
normal for a Sphere channel fader amp.
 

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Gary, you are correct of course!  I mis-titled that drawing because in the corner it said Sphere 900/20.  Here is a rough copy of the actual 920 schematic from somewhere on the web.
 

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This is the Pinout for the early 18 pin EQs
900 and 803. The extra unmarked pins were for
switching and muting options and are not used
on most EQs.
 

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These are very rare late version of the SPA-62 op amp.  These have been sourced
back to Don McLaughlin of Sphere Electronics.  The going theory is these were made available
to console owners who needed SPA-62 replacements in the days after the end of
console manufacture.

Note... gone are the light bulbs now replaced with diodes.  The tants have all been replaced
with Al electos with the input caps being N.P.
Note that solder mask is used on the pcbs and is  the first use of solder mask I have ever
seen on a Sphere product.

The circuit is basically the same with a few differences in part values and a different
LTP emitter resistor setup using 1% Metal film in a "Y" configuration.

See the Reverse skitz  in the next post.
 

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