All about Tubes, Tube Circuits, Tube Gear
Showing posts with label Power Supply. Show all posts
Showing posts with label Power Supply. Show all posts

Monday, June 18, 2012

Ultralinear Guitar Amp (10): Transformers, Grommet!




Transformers, Grommet!

 


 Yes, whenever you mount transformers to a chassis, always have plenty of rubber grommets to protect the wiring insulation from abrasion, cuts, and short-circuiting!  Especially with high voltage stuff.


First Transformer goes on the Chassis!  Output tranny at one end, and power supply trannies and chokes at the other.  Orientation aint so critical with this incredibly long chassis.


 I always seem to be short of lock-washers.  Ideally locknuts would be even better, but hey, we'll be using what is on hand for this economy build.  When you run out of washers, you can always use nail-polish to fix nuts from loosening, that are never supposed to come off again.  Transformers are one of those parts that should never die!


The second (Power/HV) Tranny goes in the corner.
Here my son is drilling the holes for the massive choke (larger than the Power Tranny!).  We had to check for clearance with the speakers in the Fender cab.



After this quick training exercise, my son is now a professional Grommeter!
It first seems impossible to stuff correct-size grommets into the hole, And in the past I've even cut them to assist in tucking them in.  But the best tool for this is simply a medium flat-head screwdriver.  You have to watch it, so that the rubber isn't penetrated or torn, since that defeats the whole (hole) purpose of protecting the wires from contact with sharp metal edges, and also providing electrical insulation.


Power Plug Innovations:

Next we want to get the power chord installed.  But here, instead of the usual fixed line, we want the new 'computer-plug' style.  There are several good reasons to go this route:

(1)  If the chord is damaged, its an easy replacement, without tools!

(2)  You can change the length of the power cord, if you want to add a longer one!

(3)  There is built-in powerline filtering in most of these units, which is pretty essential these days with tons of digital broadcast noise all around, (cells, internet etc.) and all kinds of equipment piggy-backing on powerlines (local transmission of security, LANS, even audio!).



 But alas, there's a snag!  How do you cut a square/rectangular hole with ordinary tools?  Sure, of course you can make four or more holes with your drill, dig out the jigsaw and cut out the extra metal, and finish up with some various sized metal files; all a lot of annoying and boring work, which is also time-consuming.

Or you can graduate to

The Nibbler!

When I found out about this tool, I fell in love!   It does just what they call it, It nibbles out sheetmetal of almost any thickness or type, and its easy and fast.
Of course the metal handle isn't the most comfortable, but you can either wear a glove, tape on some rubber padding or apply insulating sheaths from a pair of pliers, or just MAN UP and cut the hole!  Usually for one or two holes, you don't need to do much except mark out the size and nibble away!




To get started, you just drill a 3/8" or larger pilot hole to work the tool in to where it can start chopping.  Be sure to use cutting oil to protect the sharpness of your Nibbler tool, which is going to become your favorite tool for cutting perfect rectangular shapes, refitting new parts which are the wrong size, etc.


Here the son gets an instructional hands-on in Nibbling 101.   Soon the AC socket will be ready for power!


A final nostalgic look at today's accomplishments.  Time to rest.
I don't want to tucker the boy out.



A few more internals, like caps, a bridge and a power-switch and fuse, and we'll be ready to wire up and test the output stage!

For that, all we need is a good tube-pedal (like one we built earlier) to drive the splitter, Output stage and transformer!   Lets rock!


Thursday, June 14, 2012

Guitar Pedal Power Supply




Project Goals:

To design and build a reliable, high quality, heavy duty power supply
in a small size that can power 10 – 20 typical guitar pedals,
replacing 9 volt batteries and/or multiple wall-warts.

This would substitute for a typical $150.00 commercial unit,
available at music stores or on the internet.

Circuit Design:

A transformer-based supply was chosen, to reliably deliver the current and power required, rather than a lighter but less reliable and/or noisier 'switching supply'. The simplicity of the design, coupled with independent regulators will make a low-maintenance unit that delivers clean D.C. Power and very low noise. (See circuit diagram).

Full-wave rectification with de-rated parts and a wide safety margin for voltages and current was chosen, since consistency of voltage is needed, while the number of guitar-pedals and their power-needs will vary greatly and be out of the control of the designer. The unit must perform consistently under a wide variety of loads.

Important:  Each Regulator was mounted on a small heatsink to allow it to operate at high current values.

Guitar pedals range in current-draw from as little as 10 mA to as high as 100 mA.

Using a daisy-chain cable to connect them in parallel,
means the currents will simply add up.
Each regulator can handle a maximum of less than 1 Amp,
so load each branch accordingly.

Examples: (actual measured current draw)
Distortion + (BOSS) - 10 mA
Chorus Factory 7 (Digitech) - 90 mA
Main Squeeze (Digitech) - 80 mA
Accoustic Simulator (BOSS) - 20 mA
Noise Reducer (Behringer) - 30 mA
Ultra Temolo/Pan (Behringer) - 15 mA
Reverb RV600 (Behringer) - 90 mA
Digital Delay DD400 (Behringer) - 95 mA

Dual branches were chosen, to lessen the load on each branch, and further isolate various pedals from each other, when connected.
Also, in case of part-failure, one branch alone can easily drive at least 10 typical guitar-pedals so that the unit can continue in use until one branch can be repaired.

Long A.C. Mains chord and power-lines were chosen, to allow a physical distance of up to 3 feet from pedal area and/or signal cables, and to allow convenient connection to A.C. Supplies located anywhere on stage.

An indicator light was added to reveal power-on condition.
A heavy metal box which can endure abuse was also chosen, to support the weight of the transformer and protect circuitry.