Outboard Amp Project

[n9voc]

Hello, fellow solid state amplifier buffs!

Been awhile since I've posted, and I conceived of an amplifier project – and thought it would interest the members of this forum to see the process of the project from inception, conceptualization, design and final build.

Thus, I started this thread.  I'll be posting to it as the project progresses – with photos, schematics and commentary – I hope that you find it enjoyable as well as informative to "get inside the head" of this builder and player for this project.

As I describe each step, I am aware that there are probably better ways to go about the design, and ways to get "more" out of the design.  However, I am not designing this for production, but rather for performance and ease of build using components on hand as much as possible – in other words, with as little cash outlay as possible and still make a serviceable amplifier.  With those caveats out of the way, here we go!

The Project:

I want to build an amplifier that will be the bottom of a "half stack" configuration with my 3 watt "Classie Lassie" amplifier I built earlier.  I want to be able to add 20 to 30 watts of capability to the "Lassie", and have the amplifier stack look good, like the "Classie Lassie" amplifier does.  (See attached pictures of the "Lassie" below, and further information on this amplifier can be found under my post of "my favorite practice/small group amplifier")

First – The "footprint" of the upper amp (the "Lassie") is 17 inches long by 11 inches wide.  The "footprint" of the amplifier she'll be sitting on must be at least this size, to match in looks.  Height of the bottom (outboard) amplifier will be determined later.

Having worked with and in electronics for the last 30 years, I at times develop a pretty well stocked "junk box". I knew I had a lot of the "basic" parts – resistors, coupling capacitors... etc, but did I have of the "expensive" stuff to keep the cost of this project down in my possession at this time?

I dug into my junk box and came up with the parts shown in the picture below, from left to right I have laid out:

A power transformer pulled form a defunct 150 watt power mixer, dual center tapped secondary with dual primary for configuring to 120V or 240V.

Some "project board", LED's, IEC power connector, a fuse holder, some bridge rectifiers and a good set of filter capacitors for the power supply. The big blue one is 18000 uF at 25VDC rating, computer grade.  The others are either 3300 uF or 4700 uF.

Two FK607 boards (an amplifier module based on the TDA2004/2005 chip),  a couple of TDA2003 amplifier chips, a heat sink, some ¼" jacks, several NE5532 op-amp chips, and cabinet hardware pulled form the aforementioned power mixer.

Speakers:  An 8", 8 ohm 10 W speaker from a JWDavis ceiling fixture, a couple of 5", 6 ohm speakers with big magnets, pulled from a defunct studio monitor set – estimate at least 50 watt capability – and an aluminum plate to mount controls upon.

From this array of parts, an idea of triple PA (one power module per speaker),  op-amp preamp amplifier design suggested itself.

I am now ready to begin conceptionalizing the amplifier, sort of pre-design work based upon the materials at hand.

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