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Thread: Sunn 1200S Restored/Revised amp with new Schematic

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    Sunn 1200S Restored/Revised amp with new Schematic



    This just highlights the end result of a 1200S Restoration project that I began in mid-Nov 2015 and completed in late May 2016. Details are in the 1200S Restoration Project thread found in the Maintenance, Troubleshooting and Repair category. A couple weeks ago, I finally got around to creating a new updated 1200S schematic with the revisions, and have added thiat to this post.

    Click image for larger version. 

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    The above are outside views, after thorough cleaning of the chassis surface, getting all of the crustiness off, as best I could. you'll see all that in the other tread.

    The insides after restoration and upgrades have new supply filters, added a second bias pot so each pair of output tubes have their own bias adjust. Added Hum balance. Revised the previously non-grounding input jacks with a pair of switching transfer jacks (Switchcraft type 13A) and the usual type 12A jacks, so the 'bright' input networks are still there as well as non-filtered inputs, now set up with 0dB and -6dB input levels typical of Fender and other amps. Circuit is in the new schematic

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    The LDR Cell for the Tremolo circuit was moved off of the Tremolo PCB into a mu-metal and brass enclosure and installed between the Volume and Treble pot, moving it's high impedance out of the high hum field of the power supply/power transformer. The single transistor Reverb Return circuit was scrapped, now using a TL071 op amp circuit to mix the reverb tank back in, with the voicing in the Reverb path adjusted to taste. A lot more power supply filtering was added to the half-wave rectifier filter circuit that runs the Tremolo and Reverb circuit from the original.

    I replaced the original Gibbs reverb tank with an Accutronics 4AB3C1A, as the Gibbs was sounding very dark and murky.

    Click image for larger version. 

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    The re-composed and revised 1200S schematic follows.

    Sunn 1200S Guitar Amp-3.pdf

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    Last edited by nevetslab; 11-30-2017 at 12:16 AM.
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