Transformer Hardware Modifications

(DISCLAIMER:  Executing these could void the warranty ... I'll have to look into that. - JF)

Also:  If you' don't have any soldering experience, get a friend or technician to help you.

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In this page:
Mute Circuit Adjustment
External Speaker Jack for 112
(bottom)

Accessing the circuit boards on the Transformer

The chassis must be removed to do this. I don't have a 212 to look at, so I will describe the procedure for the 112. The 212 should be very similar.

First, lay the amp on its face. There are two large screws on the top, just behind the handle and toward the edges (on the tolex, not the plastic corners.) Remove these. Next remove the power cord restraint clip (inside the cabinet) and the power cord. Next, remove the three screws that go through the chassis lip up into the cabinet (above the back panel jacks). You should now be able to remove the chassis from the cabinet.

NOTE:  Try to avoid touching any big capacitors (cylindrical) near the power input. They could hold enough charge to pack a nice wallop.

Place the chassis on a workbench or table with the knobs facing you.

Mute Circuit Adjustment

The Transformer's mute circuit is designed to cut the preamp signal if the line voltage drops below a certain threshold. The stock amp will start cutting signal around 112 VAC, which is too high. I've had volume drops (similar to a hard tremolo) when the line voltage drops due to long extension cords shared with PA or bass, etc. No problems since making the mod.

The modification involves removing a single surface mount resistor (68-ohm, labeled "680"), thereby lowering the mute threshold to around 102 VAC. It resides on the main preamp board - roughly behind the pre gain knob.

Use the following pictures as a guide:

Before
 Before (zoomed)
 After (zoomed)


External Speaker Jack for 112

The 112 plays nicely by itself, but the cabinet and speaker can sometimes leave you wanting some more volume and/or beef when playing loud. Substituting an external cab for the internal speaker can yield great results. Since the headphone jack on the 112 is not speaker simulated, it's not that useful. I decided to convert mine to an external speaker jack that disconnects the internal speaker. This allows the amp to be a very nice little combo, or a "head" unit when bringing another cab for more oomph. It's pretty small, and lighter than a lot of heads, so why not? I use mine with a Wiggy 212 or a Carvin split stack. (With the Wiggy cab, I have to use a Y speaker cable with the cab in stereo mode to get 4-ohms. I just leave the cable in the back of the amp.)

NOTE:  The lack of a regular external speaker jack is due to the amp being 4-ohm with a 4-ohm speaker. The impedance can't be dropped any lower. This is the same reason this mod lets the jack continue to disconnect the speaker.

The modification involves shorting two resistors with (somewhat thick) wire, removing a capacitor (optional), and pulling back or removing one of the connectors on the headphone jack (the ring connector - making it a mono TS jack).

Use the following pictures as a guide:



Before
 Jack mod
 After

I just snapped the capacitor out of there from the top. Yeah, I could have removed the board and taken it out nicely, but why? I'm not converting it back to a psuedo-headphone jack, so there. I also pulled up the middle connector of the jack. I could have changed it to a real TS jack, but again .... why?

Other pics:

    Schematic section
    Layout section

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