Monday, September 26, 2011

Aikido Pre-Amp Project - Part 3

In the previous article, I've came to the following layout.
Commercial amplifiers does has similar form dimension, I will use Pioneer A400  foot print which is 16 1/2" x 12" (420x305mm) as a rough guide.
Layout is not strictly a 2D affair, in the real world, we have 3-dimensions to play with. We can stack irons on each other if I have a magnetic shield between them hence, I'll place the filament transformer under the aluminium plate & have the choke directly above of it without adverse effects.

That leads to Ver.2
We get a huge space at the bottom left corner, plenty of real estate for future additions.

It struck me that if we put the PCB & all the iron is 2 different casing & we get separate PSU arrangement!

 But I don't fell comfortable with that huge void in the PCB casing so one thing lead to another, another layout appears...

Here are the other views
I go for a 100mm height chassis for now but 80mm will be the bare minimum for any reasonable working space within the chassis.

All these work just to  obtain the dimensions require for chassis preparation, be it off the shelf or custom made. Do you feel why I always end up with chassis-less amp???  LOL!!!

I started with all the intention to produce a 3D model of the chassis, unfortunately, getting to this stage has eaten up over 24 man hours. Since I've got all the dimension required to start construction,  I'll have to take a short cut & skip the whole 3D modeling exercise... :(

A description of the 3D chassis instead... :(

PSU Chassis
The mains tranny and the filament tranny will be on top of the PSU chassis & the choke under the filament tranny separated by the chassis top panel. They are space up lavishly.

The void between the two are filled by the filtering circuit component within the casing.

The IEC socket will be on the back panel  since all commercial amps has the
On/Off switch on the front panel, I'll follow suit even though I feel like an idiot routing the wire loop from back to front & back again... also... I can use relay & implement remote activation but I don't have one in my junk pile... Lets just keep it simple...

PCB Chassis
The PCB mounted on the bottom of the top panel to keep them away from dust & most importantly exposure to any form of interference.
The tubes protrude through the 4 holes on the top panel for best possible ventilation. I choose to have the tube orientated as such for it is farthest possible from the PSU exposed irons.
Filament wire layout can make or break any tube circuit... they are very high on my priority list. Tug into the chassis corners & away from any signal wire, even if you have to detour. The twisted wire will be travelling along the bottom of the chassis as shown & go vertically into the +H & -H terminals on the PCB.
The signal in & out terminals are on the back panel as shown... Detailing the hole dimension will have to wait... 
The selector & volume pot will be located just beside the signal input terminals at the back panel. they are linked to the front panel via separate connecting rods. This is important as the raw input signal is weak, susceptible to noise corruption. The extra wire length will act as antenna to invite noise. For extra protection, tug the wire into the top corner (top & side panel).

Finally! We come to the point where there are enough numbers to proceed with chassis preparation.
Go find ready made chassis of in close proximity of 142x293x100mm & 120x293x100mm & start drilling.

Fabicate from these developement drawings.


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