DBX 786 Schematic Request

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glorymorris

Well-known member
Joined
Apr 30, 2009
Messages
55
I've checked the groupdiy account and searched all over, but I can't find DBX 786 schematics. DBX tightly controls their intellectual property, so it's no surprise. If anyone here has schematics, please let me know.
 
Hello,

I´m also trying to find the dbx786 schematics or service manual. I´ve just bought one in very good shape, but I'd like to adjust it properly. I´ve also checked the documents page but no luck.

On the board there are two trimmers, one labeled "p4 meter ref.", wich I suppose is for Vu adjustment, and "p2 20HZ THD", maybe to adjust the harmonic distortion (i've tried that feeding a 1khz signal, but seems to have no impact on the measured out THD).

Any info will be highly appreciated.

Thanks in advance and best regards.
 
Hello and welcome aboard!

1KHz THD is supposed to be about 0.002%... Your measuring equipment is reliable that low?
At any rate, p2 is meant to adjust distortion at 20Hz, not 1K. this white paper seems to confirm it https://dbxpro.com/en/product_documents/786wppdf

"Most equipment that incorporates a transformer in the output stage will have a fair amount of distortion at high levels and low frequencies. The 786 uses a patented circuit in conjunction with a proprietary oversized output transformer, designed by Jensen, which overcomes these distortion problems."

So I guess you should inject 20Hz, scope the output, and see what effect p2 have on the waveform.
 
Hello mad.ax and thanks for your quick response! And also greetings to everyone at the forum.

Yes indeed, I'm going to try it with a 20Hz signal. I don't know why I assumed that the adjustment was to be made with a 1khz signal, as in many of my other audio equipment, because the trimmer is labeled clearly!

Thanks a lot again, and if anyone has the schematics, just let me know!
 
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