Schematic for Fairchild 664 EQ anyone?

[Allbaldo]

I've tried using the search function, Google, etc, but no luck. Anyone have a schematic for a Fairchild 664 EQ?

Also, I know this unit has a 17db insertion loss. Any suggestions for bringing the level up? Transformer?

Thanks!

 

[ruairioflaherty]

Assuming it's some form of passive EQ a transformer won't be the right solution for the gain.  Although a transformer can provide "free" gain it also performs an impedance transformation which in this case will not be your friend.

I'm guessing this eq will want to see 600 ohms on the input and output.  You could construct a very simple line amp from opamps.

 

[gridcurrent]

It is a peculiar passive eq, nothing at all like the Altec 9061a/Langevin 251a.
Unlike the Art Davis designed units, the 664 must be fed from an  significant source Z and also must be loaded.
From the brochure:
"will accomodate 50 to 600 ohms in, and 50 to 150 ohms out, or 300 to 600 ohms out with a transformer."
If you have a unit, do hope you draw out the circuit.
A few 664's were fitted in the Alan Emmick console at Sunset Sound (Doors, "Light My Fire").

 

[ruffrecords]

Sounds like an interesting EQ. I found one that sold on eBay:

http://www.ebay.com/itm/FAIRCHILD-Robins-664A-equalizer-module-discrete-Gain-stage-664-/260952731211

which says the inductor is a Mil-spec. UTC MM3 8MHY which sort of implies it only has the one inductor.

From here:

http://www.preservationsound.com/wp-content/uploads/2012/02/Fairchild_664_668.jpg

it appears to have plus/minus 10dB HF peaking boost/cut at selectable frequencies of  4, 6, 8, 10 and 15KHz. The LF EQ also has plus/minus 10dB range but is a shelving type at a fixed frequency of 80Hz.

Original price $145

Cheers

Ian

 

[Allbaldo]

From the brochure:
"will accommodate 50 to 600 ohms in, and 50 to 150 ohms out, or 300 to 600 ohms out with a transformer."

This quote from the brochure catches my eye… I have a pile of Triad A67J transformers, which have a 150 Pri/600 Sec. Maybe that could work on the way out?

 

[Allbaldo]

Assuming it's some form of passive EQ a transformer won't be the right solution for the gain.  Although a transformer can provide "free" gain it also performs an impedance transformation which in this case will not be your friend.

I'm guessing this eq will want to see 600 ohms on the input and output.  You could construct a very simple line amp from opamps.

Thanks! I'll look at this too.

 

[mjrippe]

Hmmmm, no mention of it here but member "gridcurrent" just posted the schematic in the Tech Docs section:
http://groupdiy.com/index.php?topic=45705.msg760938#msg760938

Thanks gridcurrent!

Also, check out this editorial from John Klett:
http://www.technicalaudio.com/pdf/Fairchild/Fairchild_Junk_and_Jems_post_edit.pdf