Monday, February 16, 2015

Jay Turser JTA-Flag 300 - Made In Japan

It said made in Japan
Made in Japan
Their ain't nothing made here in this country anymore
Try the made in Japan, Hong Kong or Singapore
Made in Japan

It had been weeks since I spent any time working on a guitar project.  After trying a few on-board effects circuits for a bass project, I ordered a bunch of semiconductors from a few vendors in the Far East for another circuit.  With some time on my hands waiting for my parts to arrive, I checked in on my son's herd.  Awhile back, we made a trade.  I got his gently used Mitchell Dreadnought and he got my Jay Turser JTA-300 Flag.  After a short conversation, we figured out that the JTA-300 was way overdue for strings.  I also realized there wasn't a battery in the preamp, and remembered that her black plastic heel cover was still in my shed, waiting to be reinstalled.

My son was still pleased with the JTA's action and neck relief, so I figured I could take care of replacing strings, reattaching the heel cover, and replacing the battery within an hour.  I had the heel cover reattached with some gel-type CA adhesive in five minutes.  The restringing was quick and easy, and I put a fresh 9-volt battery in the box.  After that, my one hour estimate quickly fell apart, as I found that the preamp battery-check light was not working.  I brought This Old Guitar back inside to plug her into an amp, and confirmed my suspicions that there was no signal making it to the amp.  Back in the shed, I removed the four screws attaching her preamp to her body, hoping to find something simple like a loose wire.

The first time This Old Guitar was on my bench, I was fortunate enough to find an ARTEC EQ7545 preamp that seemed to fit like it was an OEM replacement.  The cut out in her body was just right, and the holes for the four retention screws lined up perfectly.  Time After Time, fixing This Old Guitar has been full of surprises.  I moved on to a look inside the shielded box.  I traced the power from the battery into the circuit board and verified there was a good connection from the battery to Vin and ground.  It was clear the problem was somewhere else on the board. 

Testing and replacing any of the components that could be shorting the circuit without a diagram and a high-powered magnifying lens was not an option, and I realized this preamp needed to be replaced.  With nothing to lose, I decided to take a look at the underside of the circuit board, learn what I could from it, and possibly scavenge some reusable parts.

Halfway there, I found a huge amount of sawdust between the mounting ring and the slider controls.

I took a few good last looks before reassembling the preamp, putting it aside, and getting online in search of a replacement.

This time around, I thought it would be nice to use an American-built preamp.  Again, the shape, size and location of this preamp mounting hole did not lend itself to anything else I found.  Worse, the eBay vendor I bought from last time no longer existed.  Even worse, ARTEC no longer listed the EQ-7545 model on their website.  But, I did come across a number of vendors, including a particular one in New Jersey with the lowest cost including shipping, that was offering the EQ-7545 and EQ7545-R preamps for less than what I had paid for a EQ-7545 last time.  I was careful to order one listed as EQ-7545, and not the EQ7545-R model, expecting that it would match the listing pictures and be the same as the one I was replacing.  In fact, I remember from the first time around, the description of the EQ-7545 included the word Flat, indicating it was to be installed on the flat part between the lower bout and waist.  So, I was disappointed to find that what I received this time actually was the EQ7545-R.  The differences are subtle but critical.

At this point, the thought of actually finding the EQ-7545 preamp with the flat mounting bezel I needed and waiting for a replacement to ship was unacceptable.  Instead, I decided to swap out the contents of the shielded boxes.  With the removal of a few screws, I was half way there.  In fact, the most complicated part of this swap was exchanging the spring contact sub-assemblies in the battery boxes.  This was necessary since the EQ7545-R circuit is attached to the battery by means of a molded plug instead of straight soldered connections like the EQ7545.  I removed enough of the battery box with my rotary tool to accommodate the plug and snapped the sub-assembly into place.

Assembly of the new working circuit into the old flat mounting bezel went just as easy as taking it out.  With a fresh battery in the box, I was delighted to see the warm glow of the battery-check LED.

I installed the remaining screws, reapplied the controls label, attached the control knobs, and moved on to reinstalling the preamp into her body.

Here she is, ready for another 2 years or 2,000 songs, whichever comes first.

Monday, February 2, 2015

LeSpork Bass Prototype - Unchained

No, I don't ask for permission
This is my chance to fly
Maybe enough ain't enough for you
But it's my turn to try

While researching the two-band passive tone control circuit I put in this bass guitar, I also came across a few articles on Les Paul Vintage wiring.  In short, the idea is to put the volume control before tone control the way Gibson used to do it on some of their early Les Pauls:

There's plenty written on the subject of "vintage" vs. "modern" wiring on many discussion forum sites, including this one:

and even more on other sites, like this one:

I had two reasons for going with a volume-before-tone wiring scheme on this project.  First is that is how it is done in the P-bass stock wiring

Second was convenience, based on the length of the pickup lead wire and the layout of the controls.  So, here is the diagram I ended up using:

After an hour or so with the soldering iron, I had the jack, pickup, and bridge connected to all of the pots, with two pairs of test clips in place of the capacitors C1 and C2.

To make it easier to differentiate between the two tone controls, I used a Fender-type knob for the treble bleed control and a pointer-type knob for the other bass cut control.  After another hour or so, I had the rest of the bass assembled, strung up and tuned, ready for testing.

With the help of my son, we tried playing with it, mixing and matching the caps: 0.0047, 0.0033 and 0.0022uF in the bass control, and 0.047, 0.033 and 0.022uF in the treble control.  We found the 0.0047 did very little that we could hear in the bass control, noticed some effect with the 0.0033, and more of a tonal range with the 0.0022uF.  We heard lots of tonal range with all three choices in the treble control and found the 0.022uF afforded the most amount of brightness.  There's some interesting interaction between the two controls as well.


The guitar amp we played through was likely a limitation to what we can do with this bass.  It will be interesting to hear it through a bass amp, hopefully sometime soon.  My trip to our local Guitar Center and Sam Ash stores in search of a suitable used practice bass amp over the weekend turned up nothing.  We'll see what turns up on Craigslist in my price range.   Now it's time to make her look as good as she sounds.  Next up for this project includes a new color scheme on all of the exposed surfaces, grounding and tidying up all of the wiring in the control cavity, and a custom pick guard.