pedal repair

Maxtone CB Wah Wah Pedal Repair

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George had this wah pedal in his collection but realized one day that it didn’t work.  Could the Unbrokenstring Crew help?

These pedals are common but there is very little literature available on them.  That won’t stop us!

 

On the bottom of the unit, we find this text.

 

And, we find this text.  Not made in PRC (Peoples Republic of China!)

 

The power jack is the older mono 3.5mm jack often seen on period pieces such as this.

 

Peering between the pedal and the base, we see the rack and pinion that runs the potentiometer, and the bypass switch.

 

When we open the unit, we see that the potentiometer has come loose from its mounting fork.  The battery has not leaked.  In fact, it’s still reading nine volts!

 

You can see the fork where the potentiometer mounts.  All of the hardware is present and accounted-for.

 

We have re-mounted the control where it belongs.  This requires some adjustment, as we will see later.

 

From the outside, we can more clearly see the rack and pinion that drives the potentiometer.  Also, the bypass switch is really high.  This needs to be adjusted first so that it switches only when the pedal is all the way down.

 

Here we see the bypass switch is mounted much lower.  When the pedal is pressed downward, we hear a clean ‘click.’  This is an indication that it is adjusted correctly.

 

On the inside of the unit, the jam nut is tightened so that the switch stays in this position.

 

A little bit of petroleum jelly serves as a lubricant for the rack and pinion.  The screw to the right adjusts the mesh ‘pre-load,’ keeping the teeth aligned, yet minimizing the sideways load on the shaft bearing inside the potentiometer.  The gears are ‘slipped’ until the desired portion of the pot shaft rotation is in the correct place (relative to the pedal) to give us proper ‘wah’ action.

 

The actual ‘wah’ circuit is little more than a treble boost/cut circuit.   Now that everything is together, the unit is tested with a guitar and amplifier.  Now that we have confirmed that the portion of the pot rotation is OK for this unit, all the screws are tightened.

 

George said that he installed a new battery, so this one stays.

 

We are all back together and ready to return to the pedal board.

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Ibanez / Stratus TS-9 Clone Pedal Repair

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What do we have here? This pedal is completely custom inside and out.  Who made it?  And why does it not work?  Can the Unbrokenstring Crew decipher this jewel and get it working again?
Matt received this as a gift after a live show, from an appreciative fan.  It has an honored place on his pedal board.

 

Google is of absolutely NO help deciphering any of this text.

 

Very nice circuit board!  This is a Tube Screamer circuit, with several types of LEDs and diodes selectable in the clipping circuit.  Nearly every aspect of the circuit topology is ‘bend-able’ in this pedal.  Very cool!

 

This unit uses a very nice, high-quality Burr Brown operational amplifier chip and precision components throughout.

 

Our principle problem is immediately apparent.  See the broken wire on the output jack?

 

We have another broken wire on the switch.  Solid (unstranded) wire is easy to work with, but is prone to cracking and breaking more quickly than stranded wire.  But solid wire is widely used in the pedal building world.

 

Stratus is a supplier of ‘build your own clone’ pedal kits.  Their catalog confirms that this is a Tube Screamer clone.  Oh, and we found more broken wires.

 

The common ground circuit at the output jack relies on the conductivity of the enclosure.  When the enclosure is painted, as this one is, one can have an intermittent electrical connection.  Here, I’ve removed the jack to scrape some paint and add a toothed lock washer for better connection to the pedal enclosure.

 

This tool is handy to keep jacks from turning while the nut is tightened.  These are designed for hollow-body guitars, but work almost anywhere a quarter-inch jack is found…  for instance, here.

 

I wonder whose cat this is?

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Sovtek Small Stone Pedal Refurb and Update

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The modulation rate control on this wonderful Sovtek Small Stone phaser effect pedal had broken. While the unit is in the shop, could the Unbrokenstring Crew also add a 21st century DC pedal power jack to the unit?

Like a message in a bottle, this pedal has the look and feel of a relic from another planet. Even the switch looks like alien technology.

Removing the top cover reveals a heavy steel plate that holds the major components.  Look at the LED holder!

The control for the phase modulation had disintegrated.  Not much was left holding the shaft in place.

The back side of the modulation control was not out of the ordinary beyond the Cyrillic alphabet. Perhaps it could be rebuilt using parts from another similarly-sized potentiometer.

We have removed the old potentiometer from the circuit.

The tabs on the back cover of the potentiometer can be peeled back in order to disassemble the unit.

Interestingly, the internals of this control are completely different than what we might expect from a domestic control.  This potentiometer is a ‘reverse audio taper’ component.  The Russians achieved this by mounting the resistive element on the opposite side of the main wafer of the control, effectively reversing the direction of the taper.

So, it appears that we need to find a control that is close to the physical size of the old part, so we can reuse the knob.

We are working in millimeters here, in case you are wondering.

An aluminum bushing allows this smaller shaft to fit in the Russian knob.  Perhaps we have another degree of freedom in our search for a proper replacement.

This bushing can be removed…  a good thing that will allow us to do some gun-smithing if we need to do so.

The knob is not quite big enough to allow a quarter-inch shaft to be substituted.

So, we located a reverse audio taper control custom-designed for Neve recording consoles.  Yeah, I got connections.

This part has an appropriately-sized shaft that will permit us to use the original knob.  Good news!

The new control is wired into the circuit in the same manner as the old one.  Teflon spaghetti tubing handles the high-temperature insulation duties here.

These little spacers were rattling around in the enclosure after the circuit board was removed.  Where do these go?

Turns out, they are spacers that go on top of the cast bosses in the bottom of the original box.

The new power jack is mounted and wired into place, along with new steel Switchcraft in and out jacks.

The whole arrangement is now fitted back into the case.

An internal nine volt battery is used for powering this unit for checkout.

We have a winner!  Time to tighten down the screws and button this unit back up.

Here is the top cover with the new control installed.

The case cover is now back on.

The owner wanted to leave no question regarding whose pedal this was.  Mine!!!  Mine!!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

 

Fender Twin Custom Foot Switch Repair

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Matt complained that the reverb function of his amp was erratic when he used the factory foot switch.  Could the Unbrokenstring Crew look it over and find the rat?

Let’s take a tour of the unit.  This one is in excellent shape.  Meet the ‘normal’ channel,’ on the left side.

Effects channel is in the middle.

Everything in this amp works well.  I wonder what the issue is?

Name, rank, and serial number, please!

One thing I really like about this unit is the ON and STANDBY switches sport dust boots.  Good practice to keep these switches trouble-free for years to come!

The foot pedal goes here.  This is a stereo jack, to support two functions.  Is this the problem?

Matt supplied the foot switch.  This looks as if it has never been out of the studio.

Inside the unit, we see cast frame Eminence units.  Very nice!

The tube diagram is as it should be.  I understand that the schematic is the same as the original Blackface Fender, only updated with modern components and largely built upon a printed circuit board.  Nice stuff.

No reverb here!  There is an intermittent within the pedal.

The vibrato section works fine, so we need to investigate the foot switch on the right.

Let’s verify that everything is OK here.  Very clean inside!

Amazingly, the reverb foot switch does not actuate every time it’s pressed.  A new unit is pulled from stock.

Here is the new reverb switch.  Now, the reverb is functional, but there is another source of intermittent operation.

Aha!  At the plug end, the wire insulation has pulled back, allowing the inner conductors to touch the case and each other.  This is a mess!

There are actually three conductors in the factory cable; two are used for switch functionality and the third is the braid, a ‘common’ conductor for both circuits which doubles as a ground shield as well.

Here, I’m carefully pulling one conductor out of the center of the braid while leaving the braid intact.

Here are the three ‘wires’ that we need.

I pulled the braid until it was a solid conductor.  This piece of clear tubing will insulate it from the other wires in case the insulation on the wires pulls away again.

This is the finished termination.  I had to use a big iron on the solder joint to the outer shell, and the insulation is a little worse for wear.  I’ll do better next time.  A tie wrap was added on the exiting cable to help the strain relief do its job.

Everything is back together and works per spec.

Another satisfied customer!

Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

Big Muff Pi Pedal Refurb and Update

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Matt owned this pedal FOREVER and needed to put it to work in the studio for a project.  But, the foot switch had disassembled itself years ago, and the audio jacks were worn out.  This pedal needed an update to the 21st century, adding compatibility with the distributed power in a pedal board.  Could the Unbrokenstring Crew make this happen?

The knobs and controls were in great shape.  Beyond the audio jacks, switching, and power, the unit works great.

With the top cover removed, we see the VERY heavy gauge frame that takes the force from the foot switch.  Yes, stomp boxes get stomped on!  The LED mounting scheme is obviously some Soviet military hardware.

The top view of the circuit board show the ‘in’ and ‘out’ jacks.  The originals are plastic and completely shelled out.

The circuit board is more Soviet military goodness.  Clearly, this board was ‘hand taped’ and not laid out with an automated.CAD program.  I’d call this ‘one step beyond hand wiring.’

Note that all the wiring insulation is white.  This harness started out as ribbon cable, and each wire was pulled out of the ribbon as it was wired to place.

A modern epoxy-sealed foot switch is trial-fitted.  This one is triple-pole double-throw on/off to handle both the required functionality of the old switch and to implement ‘true bypass’ when the effect is deselected.

Here is the user-side of the foot switch.  We need to be sure that the mushroom button is installed as high as possible to simulate the height of the old foot switch.

For those of you who know your ‘one-line’ electrical symbols, you know that these two terminals are ‘no connect.’  What?

These ‘no connect’ terminals are used to mount the current-limiting resistor for the LED.

So the current-limiting resistor is moved to its own spot in the wiring harness.  Yes, that is clear heat shrink tubing.

More ‘one-line’ electrical symbol goodness.  The body of the switch is phenolic.  It is badly cracked and ready to shatter.  Had I been able to find the missing switch hardware, this switch could not be returned to service anyway.

And for those of you who understand the Cyrillic alphabet, this pic’s for you.

The input and output jacks will be desoldered.  The gray plastic is quite brittle after all these years.

Now that they have been removed, we can complete the schematic.  Those jacks have switches in them that need to be analyzed in isolation.  The switching function is not necessarily what Western manufacturers utilize in their jacks.

The printed circuit board is temporarily reinstalled so that we can check the fit of the new jacks.

The new jacks are genuine Amphenol units, professional grade, as they say.

The terminals are bent slightly inward to clear the internals of the pedal.

The stereo jack functions as a power switch, disconnecting the ground to the 9v source when the plug is disconnected.  Both jacks need to be oriented in such a way to minimize mechanical interference with the circuit board.

The original jack escutcheons really dress up the jacks!

All new wiring was made with silver wire with a white Teflon insulation, matching the original SovTek wiring harness.

The new switch is installed.  Unlike the original foot switch, this switch is wired as ‘true bypass’ when the effect is off.

The edge of the circuit board was trimmed away to allow clearance to the body of the new Amphenol jacks.  The trace that was cut is for the sleeve terminal, which is duplicated in the array of remaining pads.

This pic shows the orientation of the notch in the circuit board to the body of the new connector.

A new 9v power jack is added between the two in/out jacks.  This jack is compatible with the ‘Boss’ pedal power “standard” with negative in the middle and 9v on the sleeve.

To reassemble the pedal, the top frame goes on first.

The cover goes on next.  This is beginning to look like a pedal again!

Matt would use the 9v power jack in the studio, but the functionality of the pedal with a 9v battery remains unchanged.

Here is a look at the finished unit, updated with steel jacks and the 9v pedal power capability.  This unit works well!

Thanks for reading all the way through!

CONTACT – David Latchaw EE
281-636-8626