GainClown

Making fun of with the clone ...

Part 2: Construction

Last modified: 02-Jun-2003

Construction

For the construction of the amp I used cheap Conrad boxes made of steel. I hate drilling steel, but the boxes were cheap.

All connectors (input, speaker and power) were located at the back side of the amplifier box, the second box would be used for the power supply consisting mainly of a transformer, 4 diodes and two small caps.

At the left side a picture of the GainClown in an early stage.

As you can see, I used an aluminum tube to mount the chips on. The tube is about 1.5mm thick and it will cool sufficiently (unless the LM1875 gets much hotter than the LM3875). As far as the black boxes are concerned: It's a pain to get all connectors in, especially for the power supply where the holes are larger and the IEC320 hole is square.

Anyway, the plumbing of the chassis is now ready, and it's time for adding the guts. I selected following components for this clone:

This a picture of the amp when it was ready. The LM1875 chips are mounted on the central aluminum bar with isolating washers. I did not yet use heatconducting gels etc. so there might be better ways to get the heat off the chips.

The transparent wiring is pure fine silver isolated with PTFE tube. The two black wires are Prefer Microphone cable.

A close view on the Dale resistors. The feedback resistor is soldered below pins 2 and 4 of the chip and is an ordinary metalfilm of 0.6Watt and much smaller than the Dale. Between the two chips is the star ground point. All connections to ground are made to this point (and almost all of them separately to avoid ground loops).

Power Supply

The power supply of the GainClown gives it it's name. The power supply uses exactly the same housing as the amp. At the backside the IEC mains connector is placed, as well as a XLR male chassis.

On the front plate the on/off switch is located and I've chosen a big red one with a lamp inside. After two glasses of wine one can easily understand the association with the clown's nose.. (Well, I could).

For the powersupply I use an old transformer that I received from a friend. It's old, and not a toroidal type so I might replace this one as soon as the amp had time to break in and I like the sound sufficiently.

As for the diodes: I plan to use the same type as I used for the GeenKloon, better types but not exotic. Fortunately I had 4 left over.

Components uses in the GainClown powersupply are the following:

The schema I used for the GainClown powersupply is as follows:

It's OK to use a centertap powersupply should you have one laying around, since we use only one set of diodes (or 1 bridge if you like). Should you want/need to buy a powertransformer yourself then buy for example Amplimo type 58014, 160VA and 2*18V for €37.79 or the 15V in the same series.

Conrad has a ring toroidal 2*18V, 160VA partnr: 518719-44 for €33.75 (2*15V same price)

Clo(w)ne - please make me smile

After a days work it's finished and I can start listening. There are just a few minor details I need to address coming time. The most important being that I have to find a matching knob for the volume control.

But probably I won't open it up until it has got sufficient time to break in. Initial listening makes me feel happy already...

Issues Remaining

First test runs of the GainClown are promising. One of the things that I noticed when running the GainClown for more than two hours on medium sound levels was the temperature rising on the bottom of the amp box. Apparently the aluminum bar was getting quite hot. This might be an indication of oscillation. As such I will have a look at it the coming days.

Maybe it's time to return to the zobel network after all (like I did with the GeenKloon).

© Maarten@Platenspeler.com, April 2003, 2006