repair

Peavey 1810 Bass Enclosure Crossover Doesn’t (Crossover)

by

Most of what you see in this post works well. However, a crossover network inside the speaker cabinet doesn’t work at all. Could the Unbrokenstring Crew sort out a solution that would put this cabinet back to work?
Here is some file old hardware from the 1980s.  This cabinet has an eighteen inch subwoofer underneath two ten inch loudspeakers.

 

Behind this panel is found a crossover network that routes the input signal to the proper destinations.  The crossover automatically routes the really low frequency stuff to the 18 inch loudspeaker and the rest is routed to the ten inch loudspeakers.  Or, you can specify which signal goes to which driver using the BI-AMP jacks.

 

The sheet metal screws hold this circuit board in place.  An inductor plugs into the pins in the center of the picture.

 

The input jacks are seen in this view.  The capacitor is part of the crossover network, and has been replaced.  As this is in a high powered audio network, the electrolytic capacitor is a non-polarized variety.

 

We can examine the circuit side of the printed circuit board to figure out the schematic for this assembly.

 

This inductor is cooked.  Unfortunately, this part is no longer available.

 

An examination of the inductor may give us some clues that we could possibly use to fix it and use it again.

 

This component can take the place of three different inductors, thus the three wires.  Any two wires yield a different inductance.  Unfortunately, the insulation is thoroughly cooked.  No salvaging this guy.

 

The functions of each ‘net’ on this circuit board is labelled with a felt tip marker.

 

For this particular model of crossover, the inductor wires we need to use are indicated by this inductor symbol.

 

This is an inexpensive crossover kit, with similar specifications.  We can harvest this inductor for use in the crossover.

 

Here are a few details, listed on the end of the box.

 

This inductor is has a laminated bar core.

 

We can remove this inductor from the circuit board and use it in the Peavey circuit.

 

The back side of the donor network is covered with some self-adhesive foam rubber.

 

The foam sticks really well!  But now we have access to the solder joints that need to be unsoldered.

 

The mechanical mounting scheme is VERY robust for this heavy part.  We can use all of this in the Peavey circuit.

 

These white plastic caps are handy to hold the mounting nut and to insulate the exposed iron core.

 

We will use the original circuit board as a template for finding and marking places to drill new mounting holes in the Peavey circuit board.  We can search around for a practical mounting location.

 

The mounting holes are marked.  Away We Go!

 

One end of the inductor is electrically wired here.

 

The other end of the inductor is wired here.

 

We will make lock the threads of the mounting screws with this stuff.

 

The thread locking compound is thin enough to seep into the threaded fasteners and lock them.

 

Now, we can reassemble the crossover network assembly.

 

The original inductor was mounted in the foreground.  This doesn’t look to tacky, does it?

 

One last look before it disappears into the enclosure.

 

The panel is ready for reassembly into the enclosure.

 

No.  Wait.  We need a new gasket between the I/O panel and the cabinet enclosure.  This self-adhesive foam strip material is just the ticket for this application.  Note the mitered corners.  Because I’m OCD like that.

 

Holes for the mounting screws are cleared with the Exacto knife.

 

OK, NOW is one last look at this assembly.  The wire pairs go to the loudspeakers in the cabinet.

 

This system is pretty awesome.  Everything tests out at full power.  Life Is Good!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Mackie 808S Powered Mixer Blows A Fuse

by

This powered mixer lives two lives; During the week, it rides quietly in the back of the sound van; When the weekend comes, it works hard as the sound system on the main stage for outdoor festivals. After years of incredibly reliable service, the unit just stopped. And it already had a date on the main stage at The Lonestar Rally in Galveston for the following weekend.  Could the Unbrokenstring Crew see what happened and bring this unit back to life?

This unit was cold and lifeless on the bench.  But where is the main AC line fuse?  We need to get inside.

 

Mackie is top of the line name brand, nearly ubiquitous is the sound reinforcement industry and in recording studios.

 

Name, rank, and serial number, please.

 

These screws hold the front panel in place.  The lock washers are captive.

 

We note that some of the machine screws are a different length.  This is noted in the notebook.

 

The screws in the back of the enclosure have large fender washers around them.  We note this, too.

 

The front panel is free.  Ah, but we are just getting started.

 

A large ground cable and a smaller white signal cable is seen in this view.  These are taped to the side to get them out of the way.

 

At the other edge of the front panel is this relatively fragile flat cable.  This requires special care as these are easy to damage and pinch.

 

Next, the power section of the unit is removed from the case.

 

This is what it takes to handle 600 watts per channel of audio power.

 

And here at last, at the very back corner, is the AC line fuse.  This fuse has fatigued over the years and finally opened.

 

The actual fusing element inside most cartridge fuses is a soft metal strip, suspended at each end.  They can fatigue and fail open, even under normal use.  I believe that this is what happened here.  The green tool is a real fuse installer.  Because I’m OCD like that.

 

There appear to be no other problems with this unit.  All the screws going back into the right places for testing.

 

 

So we tested the unit with a little Lennie Kravitz.

 

This unit has operated at full power for four hours, as do all of the finished repairs at The Unbrokenstring Shop.  I am deaf.

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

 

Peavey Artist Combo Amp Refurb

by

This Peavey Artist combo amp was WAY too distorted to suit even the most extreme metal head. Could the Unbrokenstring Crew look into this and put this unit back into service?
First, a tour.  You can have two channels, or a mix of the two ‘Automix’ inputs.  This was a ‘thing’ back in the day.

 

The other controls are straight-forward.

 

The standby switch is in the front, whereas the AC power on is in the back.  Actually, I like this because if both power switches are in the back, half the time I switch the wrong one.

 

The AC line duties are all squared away on this side.  The City Of Los Angeles has their own version of UL.  That’s the yellow and red sticker.

 

The right hand side of the rear chassis has the ins and outs for this amp.

 

These are all Peavey-branded tubes.  They are all in good shape and will stay in this amp for now.

 

So we put a clean sine wave in, and this is what we get out.  The positive power supply is weak.

 

An overall gut shot shows power on the left, preamp on the right, and power amp on the bottom.

 

These capacitors have begun to swell and push the seals outwards.

 

We have signs of overheating.  These resistors handle power distribution and are somehow related to our problems.

 

The other power supply has a cooked resistor as well.

 

Here I am just documenting all the plugs and wires so I can get them back in the same place.

 

These capacitors are also bulging and will be replaced.

 

Time to remove the power supply board and work it over.

 

This circuit board holds the tube sockets.  We have an intermittent short to ground under this assembly.

 

At first I thought that the short was under the tip terminals of these jacks, but that was not the case.

 

I am going to pull this assembly out and look it over as well.  The blue, red, and brown wires are high voltage.

 

The blue capacitor in the upper right is the ‘death cap.’  If it shorts, 115vac is connected to the chassis.  Not good if you ever touch the amplifier.  Fatal if you touch the amplifier with one hand and grab a microphone with the other hand.

 

This circuit board is supported by the tube sockets.  All four sockets will be unsoldered.

 

Out this guy comes.

 

Here is our short circuit.  These are component leads from parts installed on top of the circuit board and soldered from the top.  I guess if the excess length is out of sight, then it is out of mind.

 

Here are some of the parts on the top side.  I don’t think these were replaced in the field, but rather it came from the factory with the untrimmed leads.  Sloppy.

 

However, wires that are too long are easier to deal with than wires that are too short.

 

I am cleaning up the bits of crap in the bottom of the chassis, using some sticky tape as a way to capture the crap.

 

I have installed new bleeder resistors and new capacitors on this assembly.  That big blue resistor is a high voltage dropping resistor.  This part is fine and will not be replaced.  However, those are not made anymore, and I have some of the last remaining stock of the OEM resistor.  You’re welcome.

 

Everything gets trimmed and cleaned up before reassembly.

 

The power supply board has new caps everywhere.

 

The Ty-Wrap was my idea.  These big parts need some mechanical support, but I’m not big on lots of hot glue.

 

The original power resistors were way out of spec, so these new parts are higher wattage to take the abuse.

 

These caps on the preamp board were replaced.

 

As was this guy.

 

These were the overheated resistors that we saw earlier.

These new resistors are actually more robust than the parts they replaced.  And they are flame-proof.

 

We are back on the air!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Gibson Les Paul De-ghetto-izing and Rewiring

by

Quyen found this 2013 Les Paul Custom Lite on Craigslist, and purchased it from a church musician.  The instrument was everything he wanted, except the controls were not the traditional Les Paul controls that he was familiar with.  Could the Unbrokenstring Crew make the control configuration a little less ‘ghetto’?  Let’s see what we can do!

This instrument is really top-drawer.  Bound neck and headstock, gold hardware, totally pimped out!  The body is thinner, partially hollow, and the back of the instrument is contoured to feel a little more comfortable.

 

Here’s the rub.  The coil splitting duties are performed by this mini-toggle switch, which takes the place of the second tone control.  The owner wanted the ergonomics of the Custom Lite instrument but with two tone controls.

 

The control cavity is under this plate.

 

To simulate single coils, one side of each pickup coil is grounded.  The ground wire has yellow insulation.

 

With one tone control to rule them all, this little blue capacitor and the control under it is the whole tone circuit.

 

This pic just documents the bridge ground wire.  None of this needs to be altered.

 

If you compare this control cavity with other Les Pauls, you can see that it is much shallower, because the body is thinner.  Otherwise, it is not hard to visualize a two-volume, two-tone setup here.

 

To preserve the ability to go single-coil, a tone control with a push-pull pot is evaluated.  Here, a drawing is made of the actual cross-section of the guitar body at the instrument cavity, and the exact dimensions of the push-pull pot is recorded in the notebook.  Making this modification fit properly will require some careful gun-smithing.

 

The center of the hole where the mini-toggle switch originally lived is in the correct location for the second tone control.  Here, a stepped bit is used to carefully enlarge the bore in the body to accommodate the push-pull pot.

 

The inside of the hole is cleaned up a bit with the stepped bit.  The loose wires are taped out of the way and the finish on the guitar is protected with blue low-tack painters’ tape.

 

The bare maple exposed by the stepped bit is refinished with some appropriate stuff.

 

Pushing on the felt tip of the pen dispenses black lacquer.  This step is not entirely necessary, because none of this will be visible, but there is no sense in leaving bare wood exposed to Houston humidity.  And I’m OCD.

 

The threaded portion of the push-pull pot is long enough to work in a Les Paul body.  However, the switch portion is nearly too long to fit under the control cover.  Likewise, we will use another nut to get the control knob height to match the height of the other three knobs.  We have some fiddlin’ ahead of us.

 

The three bent leads on the potentiometer were bent a little more to keep them away from the edge of the spot-faced recess in the body.  You can see this by comparing this picture to the previous one.

 

This tang provides mechanical support for those instances when this particular switch is used on a printed circuit board.  But, it extends past the end of the switch.  So, it has to go.

 

The tang is gone.  The two fingers that hold the end of the switch housing in place were pressed down.  This is about as compact as I can make this assembly.

 

The paint is dry!

 

The switched potentiometer is mounted, and the height of the shaft is adjusted so that, when the knob is installed, it will appear at the same height as the rest of them.

 

The owner wanted the vintage ’50s wiring for this instrument.  Already, we are about 3/4ths there.

 

This horrible solder joint was almost certainly done at the factory.  I can’t let this go out of the shop like this!

 

These orange 0.022uF caps are just the thing to match the 50’s wiring esthetic.

 

To tie the switched potentiometer body to common ground, I am soldering the ground wire to the interface between the pot and the switch.  That is a weak place that can use all the support it can get.  Just looking at the long haul, folks.

 

The yellow ground wire is added, and the original switched wires from the pickup windings were transferred to this switch.

 

Now this looks more like a 50’s Les Paul wiring cavity.  No circuit boards here!  The cavity cover fits without interference.

 

More OCD-ness.  The output jack stuck out too far.  These washers were redistributed and a nut added inside.  I feel better now.

 

Does this look factory?  Mission accomplished.

 

This Cragislist instrument is a real winner!

 

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Crate Vintage Club 50 Amp Repair

by

St. Louis Music produced this handsome tube-based Crate amp. Robin said that this unit is ready for some service.

I just love the blonde Tolex and clean appearance of this unit!

The front panel reveals that this is a single input, two channel unit.  The clean channel sports conventional treble and bass controls.  Bringing the effects loop to the front panel is a nice touch!  This jack is stereo, for in/out with one jack.

The gain channel has separate gain and volume controls, and a mid-tone control.

The foot switch is wired in parallel with the channel select switch seen above.  Note the separate controls for reverb for each channel!

These loudspeakers are original and still in great shape.

Taking a tour of the bottom of the chassis, this unit has an attached line cord.  The power transformer is affixed at an angle, as seen on the left.  The grey wires go to and from the reverb tank.

Five minutes of visual inspection is worth thirty minutes of troubleshooting.  Can you see the problem?

To remove the chassis, we need to unsolder the cables to the reverb tank.  I marked this one so that it can be reinstalled in the proper place on the circuit board.
The loudspeakers are wired in parallel.  This pic documents the wiring colors.

The chassis is now free of the cabinet.  A quad of EL84 tubes serve as the class AB push-pull output circuit.

The preamp tubes, in the foreground, and all 12AX7s.

Removing the brackets on the output tubes is a little gnarly, though.  This screw will be replaced.

Silicone foam cushions the envelope of the tube from  the stresses of vibration and thermal expansion.

To do any soldering on the main circuit board, all the controls need to be disassembled.  Marshall knobs, anyone?

We have three jacks to disassemble in order to liberate the electronics.

The primary and secondary wiring is easily disconnected from the circuit board, as shown here.

One more chance: Do you see any electrical issues?

We have the main circuit board well in hand.

Some glue was used to support the large mechanical parts.  This stuff needs to be chipped away.

Here, we are checking the caps in-circuit with the Heathkit capacitance checker, just to verify that they are toast.

My only criticism of this amp (and others) is that the tube sockets are directly attached to the circuit board.  The thermal expansion is more than the average solder joint can stand.  Wire those sockets by hand; don’t mount on a PCB!

Here we are with new capacitors.  All of the solder joints have been inspected and reworked as required.

With the unit disassembled, this is a good time to clean up and polish that gorgeous front panel.

The wrong sized fuse was installed.  The Unbrokenstring has a complete stock of fuses, for such a moment as this.

Remember the broken screw?  Here, we are drilling and tapping the chassis for a new screw.

The blue masking tape was deployed on the inside of the chassis to catch all the metal shavings.

The screw fix worked!  As we knew it would.

The reverb tank wires are fished back through the hole in the chassis and refastened.

Everything has been reinstalled and we are ready to test.

This cover conceals the bottom of the amplifier chassis.  The amp was a little noisy.  Could some shielding help?

Aluminum foil tape is added to the cover.  This will be electrically in contact with the chassis of the amplifier.

Aluminum shielding goodness at its finest!  This is all on the inside, so no one but you will ever know that it’s there.

This Crate is very versatile – the clean channel is almost hifi quality, while the gain channel is a vast territory of sonic goodness to explore.  And LOUD!  Pick one of these up if you find one.

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626