The Korean Squire ‘Blackout Strat’ Build

Matt’s unicorn was to again own a Blackout Strat like the one from his youth.  Could the Unbrokenstring Crew make an equal-or-better unicorn?
The body is a Korean Fender Strat with genuine wear.  The new neck is in superb shape.  This will be the basis for a cool project, particularly since modern parts are available to upgrade this guitar.

 

The neck comes off and will be updated separately.  Say ‘Goodbye’ to the Squire neck plate.

 

The dot inlays in this neck are really spectacular.

 

The pictures do not do justice to the spectacular mother of pearl in this fret board.

 

First, we’ll clean up a couple of handling skuffs that occurred while this project was coming together.

 

Tinted polyurethane, various grades of fine sandpaper, and a buff polish gets us back to where we belong.

 

A set of vintage tuners will be fitted to this head.  Here, we establishing the center line of the tuners.

 

Screws for the tuners will go where the scratches cross.

 

The pin vise is pressed into service to bore the screw holes.

 

This drill bit will be used as a gauge to verify the diameter of the tuner holes in the neck.

 

Sure enough, this neck was pre-drilled for 3/8ths inch bushings.

 

The bushings are fitted tightly into the neck.  This is essential for good tone, as the bushing supports the capstan, which is one end of the support structure that establishes string tension.  If these are loose, your strings won’t work very well.

 

Turning our attention to the body, we find that the ground wire was not properly soldered to the string claw.

 

The interior routes of the body were painted with a conductive paint.  This just won’t do for the Unbrokenstring crew.  This screw ties the conductive paint to the rest of the ground circuit.  We can do better.

 

The output jack is liberated from the stamped ‘football’ socket plate.  We will rework the wiring with heat shrink support in order to support the wires and make it more durable.  And the Unbrokenstring Crew will redo the soldering job, because We Own It if it fails.

 

The neck pocket must be square and clean.  Any debris or finish will interfere with the transfer of mechanical vibrations from the neck.  For maximum sustain, we need to take this pocket down to the bare wood.

 

This side view shows that the corners are square and clean.

 

Copper foil will be used to create the cavity shielding.  We’re starting with the hard stuff, the output jack route.

 

Bottom and sides are done.

 

All of the interior routes are lined with copper.  The seams are tacked together with solder.

 

This is the bottom side of the new pick guard, also made in Korea.  The aluminum foil must go.

 

All of the holes will be de-burred with this tool.

 

We will have a nice flat surface to which the copper foil will adhere without voids.

 

Foiling the pick guard takes just a few minutes!  Again, the seams are tacked together with solder to form a plane.

 

The foil is trimmed away from the edges with an Exacto knife.

 

This build will use these pickups.

 

This set will be a very cool foundation for this instrument.

 

The controls are mounted right to the copper.  True to Fender specs, we are using surgical tubing for pickup springs.

 

The pick guard assembly is done, complete with Orange Drop tone cap.

 

Here is another view.  All that is missing is the output jack wires and the bridge ground wire.

 

Here, the body is going together.  The output jack wiring and bridge ground wire is routed through the body and soldered to the pick guard assembly.

 

This workmanship turned out pretty.  New Old Stuff (NOS) push-back wire insulation is used to complete the vibe.

 

Everything fits!

 

The neck gets a little prep before the strings are installed.

 

Remember the Squire neck plate?  This is the replacement.

 

Meet the strings!

 

This new neck has a new nut, which needs to be slotted and filed.  String spacing is established here.

 

Here, the slots are taken to the proper depth, calculated beforehand.  The stackup of feeler gauge blades establishes the bottom of all of the string slots.  When each file touches the feeler gauge blades, we’re done.

 

The string slot depth is where we want it.  Next is to file off the top of the nut and polish it, which has been shown in other blog posts.  When this is finished, the strings will protrude just above the top of the nut.

 

Now this is beginning to look like a guitar.  This is set up as a ‘hard tail’ so no tremolo bar is needed, but one is supplied.

 

We lost Matt somewhere in the bowels of Guitar Center.

 

This message came into the Unbrokenstring Global Command Center after this guitar made it back to the rehearsal room:

“BTW been meaning to tell you, OUTSTANDING job you did with the recreation of Crow’s Fender Blackout Strat!

     “I think can say, without any hyperbole whatsoever, that just plugged straight into an amp with no tweaking whatsoever, that is the BEST SOUNDING GUITAR I HAVE EVER HEARD IN MY LIFE.

     “Completely outshines even the original Blackout he was trying to unbury.

     “We’re still absolutely dumbstruck by clarity and full tonal range of it. Truly amazing work, sir!

     “Without question, your finest creation to date.”

 

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Ampeg BA115 Bass Amp Falling Apart (Literally)

Back in August of 2017, one of these combo bass amps came through the Unbrokenstring Shop with cracked solder joints, which were probably a result of brittle lead-free (RoHS) solder on the circuit board.  The owner of this Ampeg saw that post and called up the Unbrokenstring Crew to ask if this amp could be fixed as well.  Here we go!

Disassembly and reassembly of the combo amp is exactly the same as was performed on the earlier post.  Here, we are starting this blog post with just the chassis on the bench.

 

Name, Rank, and Serial Number, please!

 

From above, everything appears to be as it should be.  No wires are hanging loose as was seen in the amp serviced in August, 2017.

 

But once the circuit board was removed from the chassis, this rotary switch came loose from the circuit board!

 

As was seen in the other repair, the metallurgy involved with the soldering process was to blame.  In addition, in my opinion, this switch was not the exact part that matches the footprint on the circuit board.  Note that the pins are bent inward to the center of the switch.

 

These pins are plated in gold.  This is a good thing for the component, but gold, in solution with molten solder (yes, the metals mix) makes the resulting solder joint brittle.  Here, some activated rosin flux is added to the gold plated pins to prepare them for a coat of tin-lead (non-RoHS) solder.

 

Tinning is complete.  In this picture, we can see the intentional bending of the legs to match the holes on the circuit board.

 

This is a high quality part, and works well in this application.  However, the manufacturing engineer at SLM was off his/her game that day.

 

Our new solder joints will probably outlast the amplifier.

 

No parts were required for this repair, only labor.  This unit plays 100% now!

See the previous Ampeg 115 post for reassembly.

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Boss DD-20 GigaDelay Pedal Needs Direction

Every function on this pedal works properly.  Except, the user cannot select menu functions without a lot of hassle.  And, the delay time can only be increased, not decreased.  Can the Unbrokenstring Crew decode the mystery and make this unit a little less of a pain in the rear to use again?

The unit turns on and works, but the delay time knob only increments.  This makes it almost impossible to select any function or mode unless the user spins the knob all the way around to wrap back to the beginning of the menu.  And there is, like, three hundred menu items.

 

Everything is accessible from the bottom.  The vertical strips are Velcro hook material, to hold the pedal in place on the pedal board.

 

The black plastic rectangle on the left is a battery box.  On the right is a stack of circuit boards.

 

Removing the circuit boards involves removing the nuts on these jacks.

 

The ribbon cables interconnect the two main circuit boards.

 

The metal piece around the jacks is really part of the noise shielding of the box.

 

We can tip out the bottom board now that the jacks and power adapter jack is free from the rear panel.

 

Interestingly, this little crescent moon-shaped piece is a bushing that makes a small hole out of a large one.  This may have been a design feature for another model of pedal, or, more likely, the result of an engineering change.  Or, my favorite theory, a design screw-up.

 

Back in the early days of electronics, stiffened cardboard was coated with wax to make insulating sheets called ‘fish paper.’  Nowadays, we have synthetic equivalents.  This insulating sheet separates the two circuit boards.

 

To gain access to the top circuit board, we need to remove the control nuts on the top side.  This is the knob for the delay select function.  The knob works fine, the function it performs does not.

 

This plastic bushing covers a larger hole and allows the knob to be recessed below the plane of the top panel.

 

These other controls are more conventional in their mounting scheme.  Those hex drive screws are for looks, and only hold the bezel down on the top of the pedal enclosure.  We don’t have to mess  with them today.

 

At long last, we are able to remove the upper circuit board.

 

We already have a pretty good idea that the rotary encoder for the delay function is not working properly.  To verify that, the unit is partially reassembled for electrical test.  The cardboard is more insulating material to keep everything from shorting out.  Kinda like home-made fish paper.

 

The unit is running and the oscilloscope can tell us if the two phases of signal are coming from the rotary encoder.  The answer is, one phase is missing.  Thus, the rotary encoder can only appear to electrically ‘spin’ in one direction.

 

So, it’s time for the old rotary encoder to come off the circuit board.  A soldering iron will melt the solder and this Solda-Pullit will remove the molten solder.

 

The new rotary encoder is installed, as shown.  This rotary encoder also has a built-in momentary switch that is actuated when the shaft is pushed down towards the circuit board.  Or, in use, when your foot taps the knob while playing.

 

Pretty nice workmanship, wouldn’t you say?

 

Re-assembly is the reverse of dis-assembly.  There are a lot of parts here, so this unit will go back together with the help of all the pictures we took earlier.

 

The insulative sheet goes here.

 

The bottom assembly goes here, with the requisite white cables.  Don’t forget to re-install the little crescent-moon-shaped piece where the connectors poke through the back panel.  I did, the first time.  Oh, yeah, and the metal shield, too.

 

Many of the Boss pedals use this barrel connector for power.  The shell of the pedal housing slide into the slots molded in the connector to firmly hold the power connector in place.  Note that not all barrel connectors have these slots.  If you ever replace a Boss pedal power connector, verify that the replacement part has the slots.

 

This is a little better shot that shows the proper orientation of the shield plate.  The little sharp fingers around the outside edge should point away from the middle of the pedal, so that they can ‘bite’ into the pedal housing.

 

The red and black cable carries power from the internal battery box that we saw in the picture above.

 

The unit is cleaned up and all the knobs reinstalled.  Ready for test!

 

All functions work flawlessly, PLUS the rotary delay time knob both increases and decreases delay time and allows the user to scroll up and down through the menus.  I think we’re done here!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Carvin MTS3200 Amp Head is the Victim of Hurricane Harvey

The Unbrokenstring Crew knew that it would only be a matter of time before gear submerged in Hurricane Harvey’s floods came onto the secondary market, be it CraigsList, OfferUp, or even as used gear at a national retail music chain that I will not name here, but go by the initials “Guitar Center.”.

Who could turn down this awesome piece of gear at a great used-equipment price?  But this guy blow fuses.

 

Carvin is an excellent brand.  Their musical instruments are expertly crafted, and the electronics are top drawer.  And this amp head has three channels!

 

The rear panel of this unit shows all the versatility you could possible ask for in a tube head.

 

The select-able tetrode/pentode bias switch and a ‘cabinet-voiced’ line out signal jack are cool touches.

 

Serial number, for those who are curious.

 

The tube chart is silk-screened right on the chassis.

 

But when we open the unit up and turn it over, we see rust.  Some of the tan residue is rosin solder flux, which is OK.  But at the very top of the picture is a black pit in the end of a socket pin, which has almost entirely rusted away and will require replacement.  Most electrical component leads have a core of iron, which is then tin plated for solder-ability.  If the tin is intact, water is not an issue.  But how many component leads have literally rusted away?  Has this unit been wet?

 

The reverb tank is functional, but shows signs of water exposure.

 

These springs are very hard steel, so they rust and deteriorate very quickly.

 

Confirming our wet theory, the Tolex on the bottom of the case is coming loose.

 

Did I remove those screws and not notice the rust?

 

Looking closely at the hold-down clips for the tubes, they are completely rusted.

 

The steel chassis is coated in white enamel, which is really Top Drawer.  But receding flood waters left mud.

 

Tear-down is in order to assess the condition of the unit.

 

Everything has been wet.

 

This is the component side of the circuit board that holds the power tube sockets.  All this crusty solder flux tells me that the rosin is ‘activated’ with phosphorus, a Good Thing to make good solder joints, but a Bad Thing if it gets wet.

 

The preamp tube sockets show the same reaction with the phosphorus.  This will all need to be cleaned and reworked.  Some of these leads are completely hollow as the iron core has rusted away.  It will be better to replace the sockets.

 

Electrical problems around the circuit board caused the preamp tube on the left to overheat.

A complete overhaul and rebuild of this unit would be necessary to restore functionality and reliability.  Most components should be replaced, including sockets and connectors.  However, the customer purchased this amp because it was in his price range.  The repair quotation was not in his price range.

If you are shopping for gear and see signs of water damage, such as loose Tolex, rusty hardware, or dried dirt where it shouldn’t be, you should consider having a tech go over the equipment to assess the condition and find potential reliability problems before you buy.  Rusty transformer laminations are particularly troublesome, as the rust pierces the insulating coating between laminations and allows eddy currents to flow, potentially overheating the transformer.  Transformers are expensive to replace.

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Epiphone PR-5E Acoustic Gets New Electronics

This wonderful instrument was rescued from an abandoned house.  It sounded good acoustically, so the new owner asked if the Unbrokenstring Crew could repair the electronics and get it playable again?  Let’s get to work!

This instrument is only a few years old, purchased and then cast aside.

 

An online source for specialty guitar parts had a 2018 model of the electronics.  Can we make it work?

 

The mounting scheme uses four screws in the corners.  Cleats will be added to the guitar so that the screws hold.

 

But the REAL advantage of the 2018 electronics is that the enclosure matches the curve of the body.

 

Common wood items such as yard sticks, tongue depressors, popsicle sticks, and paint stirrers are made from birch, the straight-grained ‘poor relation’ to maple.  So the paint department lady at Home Depot gave me this stirrer.

 

Cleats to tightly hold the electronics in the body are fabricated by hand.

 

Next, the cleats are sanded to fit the curve of the body on the inside of the bout.

 

These are ready to trial-fit.  The bevel on the corner, lower-left side, clears an internal brace in the guitar.

 

One shim goes here.  Note the angled pieces, which will catch the screws in the electronics.

 

To protect the finish, low tack painter’s tape is used all around.

 

These clamps will hold the cleats in place as the hide glue sets up.

 

Both cleats are installed and the hide glue is curing.

 

Additional reinforcement is added in the corners to give the screws more material to grip.  These bits will be in compression, so they don’t need to be super-strong, only tough.

 

Before we get too far, we need to do another trial fit.

 

I think we’re going to be good here!

 

I will pre-drill the holes where the screws will be installed.  This should minimize splitting of the small cleats.

 

The actual drilling will be finger-powered, using this pin vise.

 

All four holes are pre-drilled.

 

Yes, I know.  This isn’t terribly interesting.

 

The screws are installed.  Not bad!

 

The jack plate holds the battery and has both 1/4th inch phone plug and balanced XLR connections.  It was temporarily removed to give more access to the interior of the instrument.  The new electronics hook right up to the jack plate.

 

This is a new one on me.  This battery was in the guitar when it came in.  The Golden Thumbs-Up Emoji Award!

 

And, while we’re here, we’ll clean the instrument, string it, and do a setup.

 

The electronics come alive!

 

This is a cool tuner.  The LCD screen has a pointer that swings across its face.

 

Beauty is skin-deep, but what really counts is just below the surface.  This rescued guitar is ready to make music!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

TC Helicon VoiceLive3 Pedal Refurbishment

A lot of capable technology lives in this device.  However, if the musician can’t select a configuration because the big rotary selector knob broke off, then it’s e-waste.  Can the Unbrokenstring Crew bring this pedal back from the dumpster?

Pedals live on the floor, and there is plenty of dust to attest to to the fact that this unit has been working hard exactly where it was born to be.  No harm in cleaning and detailing this unit before we’re through!

 

The main issue here is the broken rotary encoder.  We have the knob, but not the shaft.

 

Time for a quick tour before we begin.  This pedal serves both vocal and instrument duties.  Flexible monitoring options are available, as well as 3.5mm stereo headphones out and line-in capability.

 

Separate paths are maintained through the unit for vocal and instrument signals.  Stereo effects are available.

 

Midi, USB in and out, and a power switch complete the rear panel.  That black rectangle above the USB ports is a cleat to tie off the power cord, to make it a little more difficult to pull the barrel plug out of the power jack.

 

It takes a lot to get into this box.  Let’s start at the bottom.

 

The bottom lid is off.  So far, so good.

 

The footswitches are VERY old school, rugged American made switches, proven reliable since the middle of the century.

 

Let’s remove the sides next.  This bracket on the side panel supports the bottom circuit board.

 

These are the external screws on the sides.

 

These are Torx-head cap screws, giving the device a cachet of ‘tamper-proof-ness’ unless you have the right tools.

 

Next, the rear panel comes off.  More Torx screws.

 

Under the side plates, metal plates support the unit to make a very strong metal box surrounding everything.

 

At last, we can get to the next layer.  The unit is still upside down.

 

I’m documenting where cables go.  This is a front-panel indicator assembly.

 

More cable documentation.  See the Ruffles potato chip?

 

Most of these cables will be marked with a Magic Marker to identify them for reassembly.

 

Next, the front panel is removed.  These knobs pull off.

 

There are no lock nuts under these controls.  Interesting…

 

We have a few more screws to keep track of.  Many of these are a certain length, and shall be returned to the right place.

 

The LCD is tilted back to gain access to a few more Torx cap screws.  Our final objective is in sight!

 

The broken rotary encoder is on the same circuit board as the LCD.  To minimize stress on the circuit board, the old rotary switch is cut away, leaving the individual leads in place.  These individual leads are much easier to de-solder.

 

The holes where the new encoder goes are cleaned and ready to go.

 

This rotary encoder is a special order part.  Not just any component will fit.

 

This is a workmanship check of the solder-side of the rotary encoder.

 

And here is the component side.  Again, not just any part will work here.

 

We can take a break and do the clean-up prior to reassembly.  Compare this with the first picture.  Yes, the LCD window has been cleaned and polished.

 

Reassembly is the reverse of assembly (wow, that’s profound.)  The correct fasteners must be reinstalled at each step.

 

Everything is back where it belongs.  Remember the Ruffles potato chip?  That is actually a dab of adhesive that secures the flat ribbon cable.  A dab of silicone will be added in a moment to secure the ribbon cable again to the same spot.

 

Looking good!  Everything initialized.  The factory reset procedure is complete.

 

Somehow, I thought that this was an appropriate preset screen to display.  I think we’re done!

 

Here is a video showing how the rotary encoder works to change presets and configure the unit into different operating modes.

Support this band! – Fake Believe

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Mackie Thump Active Loudspeakers Need Tweeters

Two active loudspeakers have the same problem – the high-frequency driver has quit.  Does the Unbrokenstring Crew have what it takes to get into these loudspeakers and do the repair?

The enclosures of these units are molded from a very durable plastic material.

 

So are we dancing?

 

The rear panel has a crossover frequency control, equalization, overall volume, and audio inputs.

 

The bottom of the real panel has an input power IEC jack and an on/off switch.

 

The ‘Suggested EQ Settings’ suggests to me that this is a little more consumer than pro.

 

Perhaps we can gain access to what’s wrong by removing the loudspeaker.  These nice Allen-head machine screws hold the loudspeaker frame to the case.

 

With the loudspeaker out of the way, we realize that we cannot really get any tools inside to replace the high frequency driver.  We will need to split the case apart, which is no big deal but at least thirty screws are used!  Let’s get the electric screw driver warmed up and get to work.

 

The first thing to remove is the handles.  This flat-head screw comes out with the aid of a magnet.

 

Inside the handle, a nut falls out when the screw is removed.  I’ve retrieved the nut with a magnet.

 

The nut is held in place in this molded socket.  This may be interesting to reassemble.

 

This one foot long screw driver bit will allow us to reach all of the screws.

 

Some of the screws are long.

 

Some of the screws are shorter.  We make note where they all go.

 

Here is the foot-long screw driver bit at work.

 

There are screws holding the case halves together underneath the plate of the amplifier.  Off it comes!

 

More screws come out.  Glad I got this long bit!

 

The plate that the amplifier is mounted on is gasketed in place with this L-shaped plastic strip on two sides.

 

At last, we are in!  The two sections of the enclosure come apart.

 

And here is the high frequency driver that needs replacement.

 

To completely separate the two halves of the case, this cable to the pilot light can be removed.

 

These drivers are held in place with four screws.

 

Interestingly, the voice coil inside the driver is intact, yet the unit did not work.  This tells us that the voice coil had separated from the diaphragm.

 

The exact replacement, like the original unit, is made in China.

 

The new driver is installed with four screws.

 

All of those screws go back in where they came from.

 

And there are a lot of screws!

 

I used blue tape to keep the nuts captive while the handles were reinstalled.

The handle screws are easily tightened as the nuts are held captive in the plastic socket.

 

Now that the handles are tightened down, the blue tape keeping the nuts in place can be removed.

 

A little originality is necessary to finish the job.

 

At last, these units are ready for testing and return to service!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Intermittent Fender Acoustasonic 150

A fellow musician gave Charles this amp, which was nice gesture.  However, the friend said that it was intermittent.  Could the Unbrokenstring Crew turn this gesture into a reliable amp?

Styled as a unit from the Fender Brownface era, the exterior certainly checks all the boxes for Brownface goodness, with the Correct knobs and silk-screened front panel true to the archetype.  One channel is reserved for an instrument, and the other channel is tailored to vocal performance, including a dual XLR/quarter inch jack for a microphone.

 

No metal shredders allowed.  This unit has a tweeter, and an electronic gain structure that does not distort.  Just the thing for Charles’ acoustic act.  This badge still has the protective plastic in place.

 

The speaker cabinet is sealed.  This polarized connector keeps three pairs of audio signals from the amp going to the correct loudspeaker and tweeter.

 

On the back side, we find the ON/OFF switch and the IEC power socket.  Most of the rear panel is slotted for ventilation.

 

This is a solid state unit, with plenty of pep to be loud.

 

The internal architecture permits stereo operation, as is shown by the FX loop connections.  I did not play around with the USB functionality, but it’s in the manual.  We have bigger fish to fry.

 

Name, rank, and serial number, please.

 

This circuit board holds all the connectors for Line Out and effects loop functionality, as seen on the rear panel.

 

This assembly is an AC to DC power supply on the left, and an efficient Class D audio amplifier on the right.

 

Digital signal processing (DSP) is used to create the reverb and other effects.  The DSP functions are on the mezzanine board on the left.  The thin white cable in the center is the USB cable.  The main printed circuit board handles the clean audio chain and the connections to the front panel controls.  The flat cable on the right brings power from the AC to DC board and sends audio to the amplifier.

A lot of surface-mount components are found in this unit.  Those little cans are electrolytic capacitors; black squares are integrated circuits.  Each of those little black squares does the job of two vacuum tubes.  I feel old and obsolete.

 

The check mark probably means that someone tested this at the factory, I guess.

 

So the audio processing hardware is seen at the top of the picture and the power stuff is at the bottom.

 

The AC wiring comes from the switch directly to the circuit board, where there are filters and a fuse.

 

This power stuff is actually a switching power supply, which efficiently creates the various operating voltages.

 

If you look closely at the gold rings on the circuit board, you will see solder that looks ‘strange.’  It does.  Gold atoms mix into the molten tin/lead alloy while the solder joint is in the liquid state.  The gold makes the solder brittle.

 

The entire circuit board is gold plated.  This plating is among the flattest finishes available for bare circuit boards, perfect for surface mount technology (SMT) components but is a metallurgical compromise for thru-hole components..

 

As you can see, for thru-hole technology components such as these pins sticking through the board, the results of the soldering action can leave something to be desired.  Do you see the holes in the solder joints?

 

Now that those holes are fixed, we can focus on the real source of the intermittent operation.  Do you see that light blue resistor with two red stripes hiding behind the capacitor and the heat sink?

 

That light blue resistor was soldered here.  Or to be more precise, it was soldered there at one time.  The cracked solder joints became intermittent conductors.  Here I have removed the resistor and cleaned away the old solder in preparation for making a new pair of solder joints, free of gold contamination.

 

Another issue with this amp is that someone has been playing with the loudspeakers.

 

This loudspeaker fits the cabinet perfectly, but electrically, it is a 40 ohm (yes, forty ohm) loudspeaker, designed for use in a public address paging system (you know, that mess that you hear at the doctor’s office playing MUZAK, mercifully interrupted by an announcement for someone to call a telephone extension?  Yeah, that.)

 

The Correct part is available.

 

Who would have thought that you could actually replace a bad loudspeaker with a new one of the correct type?

 

Do you like those TV shows where they have a build-up to the ‘Big Reveal’?  I don’t either.

 

Fortunately, we have the correct part and are ready to install it.

 

Once we replace the grille, you will never know the difference.

 

See, I told you that you couldn’t tell the difference.  This unit plays beautiful music and the functionality is solid.

 

Support this musician, winner of a Texas Music Magazine 2018 Album of the Year:  http://www.charlesbryantmusic.com/

 

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

 

Rickenbacker Rick-O-Sound Bass Repair

Craig is a Ric Man.  This beautiful blue bass in only one of his many Rics.  This one has problems with getting both pickups to work.  Could the Unbrokenstring Crew get all this sorted out?

This instrument plays beautifully and has no real discernable setup issues.  However, the wiring seems to be amiss!

 

More than a few of you will have heart palpitations seeing this head stock.

 

Two output jacks allow a mono mix of both pickups as is usually found with most multi-pickup instruments, plus a special “Ric-O-Sound” jack that presents the signals from two pickups as two separated signals, accessible with a stereo cable (TRS.)  This gives the player the ability to run two preamps, two effect loops, two separate amps, etc.

 

Immediately after looking under the pick guard, we find a loose wire.  Poor soldering here.

 

This isn’t even tinned.

 

Here is another broken wire, another ground wire.

 

We have a stack of three inside-tooth lock-washers under each output connector.  Not much spring action available from the teeth of these locking washers, so they don’t really lock.

 

A magnet is the quickest way to clear all this extra hardware out of the control route.

 

This is the stereo jack handling the “Ric-O-Sound” duties.

 

The mono jack handles the single-ended output from this instrument.

 

Soldering workmanship on the switch needs some attention as well.

 

Disconnecting each pickup allows us to do some cleanup in the wiring cavity.  The neck pickup is ohmed-out.  The neck pickup is sometimes called the ‘treble’ pickup.

 

And we do the same with the bridge pickup.  This pickup is also called the ‘bass’ pickup, which seems redundant.

 

Perhaps this soldering was done with plumber’s solder.  It is awfully dull.

 

Another look at the switch.  Not much to brag about here.

 

The ground connection to the control is redone.  Smooth and shiny is the name of the game when soldering.

 

I labelled the controls BV (Bass Volume,) TV (Treble Volume,) BT (Bass Tone,) and TT (Treble Tone.)

 

Now that the controls are identified, we can install the knobs in the Correct location.  Yes, they were in the wrong place.

 

Earlier I pointed out the stack of three inside-tooth lock washers.  Here’s why I mentioned it:

 

When stacked, the teeth have nothing to push against.  The teeth are literally hanging out in space.

 

A flat washer in the middle will provide some ‘resistance’ for all the teeth to press against, thus restoring the action of the lock washers to that of being, er, well, lock washers.

 

The jacks are Imperial measurement and this washer must have been metric.  A little gun-smithing is in order.

 

The output jacks are wired and tightened into their correct locations.

 

Testing shows no output.  It has something to do with this volume pot.  What the hey??

 

This is the hey.  This bit of conductive solder debris was underneath the volume pot, shorting the ‘stapled’ contacts seen in the previous picture to each other, and thus, shorting the output to ground.

 

Together again, and it’s playing in stereo!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Ampeg B2-RE Bass Amp Gets New EQ Potentiometers

Bass players use SERIOUS hardware, and this Ampeg B2-RE is a serious, heavy, high-end bass amp.  So why in the world does Ampeg use those tiny little plastic slide pots for the equalizer controls?  The Unbrokenstring Crew digs in.

Ampeg is a name that needs no introduction nor elaboration.

 

Three of the plastic handles are broken off.

 

A tour of the rear panel shows the cooling fan, the quarter-inch speaker jacks and Neutrik jacks for output power.

 

The preamp and power amp can be separated using these jacks,  An effects loop is nice, and a balanced output for the poor sot in the control room is a nice touch.  The balanced output has a switchable attenuator.

 

A look inside shows a big green circuit board that handles the power amp duties.  This view is dominated by the toroidal power transformer on the right.  The ribbon cable on the left carries power to and signals from the preamp board.

 

And here is the preamp board.  Interesting, the slice potentiometers for the EQ are located on their own circuit board on the left side of this picture.

 

The preamp board needs to come out to get to the slide pots.  This end of the cable comes loose easily.

 

Screws hold the preamp board in place in the chassis.

 

All the knobs come off, as well as the nuts beneath them.

 

The input jack has its own nut and washer.

 

While we’re here, an inspection of the unit reveals a solder joint on the path to failing.  This is an easy fix.

 

The slide potentiometers used by Ampeg are special for a couple of reasons.  One reason is, they have this nice vinyl flap over the slot that helps keep dust out of the internals of the potentiometer.

 

The potentiometer board is held down with these screws and brackets.  This needs to come apart next.

 

The other thing that makes these slide potentiometers special is that they use three legs to attach to the circuit board.

 

Here is the exact part number that needs to be specified when purchasing replacements.

 

A similar part is available from other sources, but if you look closely, the ‘pin-out’ does not match.  The correct part is in the foreground, and the ‘new’ incompatible part is seen in the background, with the ‘1736’ marking, which is probably a date code of year = 2017 week = 36.

 

I was curious if the slider and handle could be removed from the new parts and substituted into the old pots.

 

The interior view of the slide pot.  The black plastic thingie with the fingers, on the left, is the wiper, and the black strip on the right is the resistive element.  The fingers slide along the resistive element to achieve the variable resistor function.

 

Oh, drat.  The sliders are a different thickness.  We won’t be able to use the new parts to repair the old controls.

 

So, a week later, a batch of the new controls come in.  We are going to change them all out.

 

What do you think, folks?  Should I clean up the front panel and remove all these presets?

 

The new parts are installed.

 

The workmanship appears to be pretty good, if I do say so myself!

 

Back on the air, this Ampeg is ready to really rumble through its four hour burn-in!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626