Fender AcoustaSonic Pro Combo Amp Refurb

My customer found another wonderful old amp in the pawn shop.  Could we refurbish this unit to its former glory?

The unit worked, but the grille cloth was dry-rotted. We also need to do something about the broken push buttons.  The stereo preamp assembly lives on the left side of the faceplate, and an effects processor is found on the right side.  This amplifier is an early attempt at what is called an ‘acoustic amplifier’ these days, suitable for voice and acoustic instruments.

Made in U.S.A!

Does anyone know about the ‘PATENT PENDING’ sticker that was added to the rear panel?

The badges on the front of the unit were in excellent shape.

Tiny #2 screws hold the Fender badge in place.

We need to replace the grille cloth.  The badges shall be returned to their correct positions.

The rectangular badge is pretty easy to measure.

The Fender logo, however, is a little more complicated in shape.

Fortunately, we just need to be ‘close’ and the screw holes in the baffle underneath will assure correct positioning.

Velcro loops were stapled to the corners of the grille.

These loops will need to be restored to their correct position after the grille cloth is replaced.

Here you can see the position of the Velcro hooks.  As an aside, this is a sealed cabinet unit.  All the wiring in the speaker cabinet is done through the loudspeaker holes.

To hold the new cloth in place, we will use similarly-sized staples.

This grille cloth pattern is vintage, and is called ‘wheat’ in the catalog.

We picked up a couple yards of the new wheat material from an Internet supplier.  The color match is nearly perfect.

The new grille cloth is stretched and stapled onto the original baffle.

Sure enough, the screw holes in the baffle enabled us to properly locate the Fender logo.

Likewise, we got the rectangular badge back where it belonged.  The blue handled tool is a tapered punch.

We’re done here!  This will be set aside for now.

The internals were removed from the amp.  This front panel is a mess, with nicotine and finger oil everywhere.

A little Gibson guitar polish cuts through the crud and cleans everything up.

The broken push button switch is problematic.  I salvaged some pieces from other switches, but they weren’t quite perfect.

New switches were ordered.  These are dimensionally and electrically identical, and fit the PC board perfectly.

Here are the new switches going onto the PC board.  These select four preset effects when pushed.

The controls on the left were all cleaned and lubricated.

The effects processor PC assembly is installed on the right side of the faceplate.

There are lots of different hardware pieces used to attach these assemblies to the amplifier chassis.  A socket finger-tightens a nut which holds the effects processor in place.

This is a view of the back of the face plate.  This style of electronics is SO very 1970s!

The loudspeaker and tweeter cables pass through the bottom of the chassis.

The hole to the right is where the loudspeaker and tweeter cables pass into the bottom cabinet.

I removed the loudspeakers and tweeter to clean up the cabinet.  This is a Motorola tweeter.  The speaker wiring is completed from the front, as this cabinet is a sealed, un-vented cabinet.

So, we pass the cable into the bottom section of the box.  When the wiring is squared away, this hole will be filled with RTV to re-seal the cabinet.

The chassis is complete.  These big screws hold the chassis in the amp cabinet.

The customer wanted a foot switch.  A four-button foot switch was the original Fender accessory.  However, those are rare.  This three-button foot switch will work well enough for the customer to select three of the four presets from the effects processor.  These switches are wired in parallel with those buttons we replaced earlier.

The original wiring was intended to control a synthesizer.  Out it comes!

Everything is cleaned up and desoldered.  The momentary switches were just right for this application.

The bottom of the switch box will be modified for a DIN5 connector, which is compatible with the original amplifier foot switch connector on the back of the amp.

Here is everything running.  This is a pretty nice unit, which represented the state of the art in acoustic amps in its day.

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE