Archive for the ‘DIY Guitar Amplifier Projects’ Category

Here is a new project I’m quite excited about.  It has been in the design and chassis fabrication stages for a little while already but I now have some pictures worth sharing.  This is one my most ambitious gear constructions yet!  It’s a Vox AC-30 clone.  Okay so that’s nothing revolutionary, but what makes this one a little more special than most AC-30 clones is that it has a smaller footprint.

The basic design requirements for this project were to 1) replicate the Vox AC-30 brilliant channel circuit (Marshall/Korg/TBX or Jennings/JMI as desired…Note that it’s easy to do one or the other with a few component changes) 2) Use hand wiring as the construction method (i.e. turret boards for easy repair) and 3)  Try to keep some “vintage” flavor to the overall look of the amp, even though it’s not specifically a replica of a particular version of the AC-30.

Since the vibrato/tremolo channel is not included this allows some saving of space used for the overall footprint.  I used a mostly traditional 1960s Vox type chassis design, where there is a separate preamp and power amp chassis, which are then bolted together. However, I added some extra flanges for added rigidity. Here is the preamp/main panel chassis:

AC30 Preamp Chassis 1

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And here is the chassis for the power amp section:

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The two parts get bolted together, and then a back panel (with ventilation slots) is also screwed on:

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The back panel will hold the speaker output jacks and an IEC connector for use with an AC power cord. You can see that I already started inserting some parts (mains switch and fuse holder) to check the fit…stay tuned for more updates as I wire this baby up!

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Building amps tends to become a bit addictive, and I’m particularly fond of the 5e3 circuit.  It’s very simple to put together, yet supplies great tone.  The amp is also very lightweight compared to some.  My first 5e3 DIY project was based around a kit.   Nothing wrong with that – it’s a quick way to get something up and running.  However, my friend Pierre and I decided to design a 5e3 circuit board from the ground up using turretboard construction instead of the traditional eyelets.  We also didn’t want to make “replica” of the old Fender board or other existing layouts but instead came up with a new layout of our own inspired the ideas of Merlin Blencowe and Doug Hoffman.

Here’s a look at the turretboard before being populated with parts:

5e3 Turretboard

 

After glueing on the face frame and rounding the corners with a 3/8″ radius cove bit, the cabinet looks like so:

One the amplifier chassis was finished, it needed a cabinet of some kind…  While there are plenty of places to buy cabinets for these amps, I thought it would be fun to build one.  The originals were constructed of box-jointed pine, so I planned to do the same.  Some plans for a Tweed Deluxe cabinet have been posted on a few guitar-related forums:

5e3 Cabinet SHEET1

5e3 Cabinet SHEET2

5e3 Cabinet SHEET3

I didn’t plan on following these plans exactly, but rather used them as a I guide for overall dimensions, etc.  As in the drawings t I used 1/2″ dovetail/box joint template for the top and side pieces:

The box-joint joinery was created with a Porter-Cable dovetail jig:

After all the pieces were cut and routed  the cabinet was dry-fit  for a test, and then finally glued together.  Once the glue was dry the cabinet was sanded in order to smoother out the joints.

Here are a couple of pics of the completed chassis from the outside.  Transformers are by Heyboer.  Tubes are JJ Tesla, except for the 12AY7 and rectifier, which are Electro-Harmonix.

 

So far I have tested the amp out with a Celestion G12-80 8-Ohm speaker.  I’m loving the sounds of it.  Compared to my Vox AC30TBX, it’s cleaner on the low settings, with crisp highs, more bottom end, and less mid-range emphasis.  This amp can get very loud. It’s not an AC30 but it’s also nowhere near as heavy to carry.  Even at only 18 Watts, I’ve used it in a few small club gigs and wasn’t able to turn it up over 3 without dirty looks from the sound crew.

The kit instructions call for cutting off the little anti-rotation nibs on the potentiometers, then inserting them into the chassis holes.  However, I like to keep them on as they prevent the  pots from moving if a nut should work loose.  Since the chassis does not have corresponding holes (and I didn’t want to drill it), my solution was to make up a little aluminum plate like so:

This also works as a nice template that allows everything in that part of the circuit to be pre-wired befpre dropping it into the chassis.  The original Fender amps had brass grounding plates, but in this case, the aluminum plate is not for soldering to.  It’s just there to prevent the pot cases from spinning.

Once the pots we inserted into the chassis, it was then time to insert the circuit board into the chassis and wire it into the rest of the amp.

 

Here are some shots of wiring up the old-school style eyelet board (front and back):

I made a few component changes from the stock Trinity kit parts:  Sprague Atom filter caps, Sozo Bluemolded caps (which are supposed to replicate the Astrons used in old Fenders), a few metal film resitors, and I also replaced the 5W Xicon cathode resistor with an Ohmite “Brown Devil.”   I also used stranded teflon-coated wire for signal wiring as I find it easier to work with compared to the fairly bulky solid vinyl coated wire the kit shipped with.