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Author Topic: Dolby 361 Schematics anyone?  (Read 6383 times)

Offline stellavox

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Dolby 361 Schematics anyone?
« on: February 09, 2010, 07:33:20 AM »
I'm working on a pair of Dolby 361's ("A" type encoder/decoders) for a project member.  Anyone have schematics for these that I can borrow or get a copy of.  Don't need the Cat 22 card info, just the input output form these to the "outside world"

THANKS

Charles

Offline ironbut

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Re: Dolby 361 Schematics anyone?
« Reply #1 on: February 09, 2010, 12:24:47 PM »
Hey Charles,

I don't have the schematics but if you have any particular questions, I might be able to answer them. PM me if that's the case.
I also have the email address of someone who certainly will have the schematics and just about any spare parts you might need.
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Offline newmedia

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Re: Dolby 361 Schematics anyone?
« Reply #2 on: February 09, 2010, 04:40:06 PM »
Charles:

I have the Model 361 Instruction Manual -- which has Section 9 (Interface circuit description) and Section 11 (Interface servicing) -- with various drawings but nothing that resembles a real schematic for the chassis.

Lots of I/O signal paths, however.  Glad to send you the PDF if you'd like.

Mark Stahlman
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Offline stellavox

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Re: Dolby 361 Miscellaneous info
« Reply #3 on: March 07, 2010, 01:09:48 PM »
Just finished "converting" two of these mono units to unbalanced operation.  Bypassed both the input and output transformers.  As the units will be used for playing master dubs of differing levels and would be fed from a fixed level (Cello) tape preamp,  I added a front-panel-mounted input level control (to replace the little screwdriver-adjust-10 turn-internal jobbie).

After putting them both back together I measured levels "on the bench".  With the new input level control set fully clockwise, the minimum input level needed to get the Dolby calibration tone to read up to the "dot" on the meter (on the front panel of the 361) was -8dB.  0dB came in around 10 o'clock on the input pot.  Note that if you try to feed a 361 from a Seduction tape preamp, it may not have enough gain to drive the meter to Dolby level.  Set the 361 output level to +3dB, which should match the inputs of most any preamps/line stages yet preserve plenty of headroom.

Sounds fine, although I don't have any Dolby A tapes that I would categorize as "A" grade.

Next up is the same "conversion" to the original Dolby A unit (can't remember the model number).  The owner of both is kindly letting me keep everything for a while to compare the "sound" of each.

Charles

Offline stellavox

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Re: Dolby A301
« Reply #4 on: March 25, 2010, 05:37:45 AM »
Also finished converting another one of these last night (to unbalanced I/O) - bypassed the transformers and added two 20K input level adjust pots on the front.  With the pots full CW, the minimum level needed to get the Dolby calibration tone to read up to the "dot" on the meter was -7 or so dB.  Corresponding output level with Dolby input level in was +3dB  - identical to the 361.

Now that both units are done, I hope to listen and compare them over the next week.  Will let you'se know any findings.

Charles