Simple Cheap Compact IC-based High Performance Amp

[Fred]

Que cabron! There's nothing Maori about this whatsoever! :-p I'll let you off for being antipodean to the place Maori are (only recently) from.

PS Maori == Ghetto

[Fred]

My antique 1979 Kenwood KX-550 cassette deck has been disassembled and modified to no longer work, but leave more space for important stuff, and look much the same as it always did. I'll be reusing various panel parts, such as the volume knob, power input, headphone jack and VU meters, etc. The toroidal transformer is mounted and ready for some wiring. I need to suss out a heatsink and a layout for the light-duty parts on the other side of the box. Pics to come.

[Fred]

Parts that I acquired the other day:







200VA (watt) 24V * 2 toroidal transformer, 2 * 40V 22000uF bulk filter caps, and assorted small bits and pieces for the PCBs.

I need a few more bits, eg, fuse holders, and wire, and so on. All in good time.

Fred.

[Fred]

In order:

• Reverse spring to keep the door closed without the damper in place and because there is no point in opening it anymore
• Stripped cassette mechanism and VU meters
• Ugly bit of plastic interfering with my toroid mounting plans
• Rough layout of the big bits with ugly plastic removed

The transformer is now bolted down, however I want to reinforce the bottom panel a bit before it goes live, and also clearance the end even more than I already have.

[Fred]

Component sizes (in mm):

• Output inductors are already specified above with a diagram
• Zobel resistors are 5 diameter with comfortable 21 lead spacing
• 1000uF decouple are 16.2 OD, 0.8 lead dia, 7.3 lead spacing
• 100uF caps (both types) are 8.2 OD, 0.5 lead dia, 3 lead spacing
• 10uF are tantalum and are 4 OD, 0.5 lead dia, 4.9 lead spacing
• Triple decouple ceramics all have 5 lead spacing and 0.5 lead dia, the thickest one is about 2.5, so the three side by side should give a spacing of 5 total centre to centre from 1uF to 0.01uF
• The MKT 1uF caps are a bit under 4.5mm wide, and 7.2 in the lead spacing direction with 0.5 wire dia, and 5 lead spacing. Note that the input DC block "cap" is three of these in parallel. The remaining one is for the Zobel network.
• Resistors are std 1/4 package except for Zobel network resistors
• Diodes are std 1N4007 parts

TODO:

• DONE Find fuse holders, perhaps 2 per module (per rail) too
• DONE Figure out how to connect up the pot from the old Kenwood
• DONE Figure out how to connect up the old switches from the Kenwood for mute/stdby duty
• DONE Reinforce the transformer side with two more bottom-to-side screws
• DONE Clearance the transformer side to avoid damage with vibration (Zapatero?)
• DONE Find a decent heatsink that will fit and work well enough
• DONE Find the schematic for the semi-safe ground lift circuit
• DONE Screw and mounting hole for bridge rectifier
• DONE Speaker posts, completely overlooked this :-)
• DONE Find a new power socket, the Kenwood one is a bit sad...
• DONE Build ground lift circuit and install snubbers to bridge
• DONE Get schematic drawn up
• DONE Bolt down the heatsink securely
• DONE Install new power socket/switch/fuse
• DONE Bolt down both bridge rectifiers
• DONE Wire up all power supply components and test
• Figure out how to mount the filter caps and do it
• Get layout drawn up

I'll keep this post as the TODO post and update it.

Fred.

[Fred]

Today's tiny progress, a brass ("laton") ground bus between the two filter caps:

[Fred]

I had an idea tonight to reinforce the caps relative to each other. Obviously the remaining two terminals must be isolated from each other, however if I put brass bar at 90 degrees to the bridge in the middle, on each of the outer terminals, and go across from one to the other with a stiff bit of plastic, then it'll be braced from the outer two, too. Especially if I pick up the ground with it in the middle too.

So, plastic bar should be less than 19mm wide, but 20mm would be OK too. 10 or 15 would likely be ideal. Thickness wise, it needs to be under 6mm, preferably under 5mm, and then only with countersunk screws and nuts on top. Length wise, at least 86 and at most 102. Colour should be pink... to match my feminine side :-p

[Fred]

The hole in the bridge is 5mm ID, I need a screw :-p

Also, just ordered one of these: http://www.ebay.es/itm/1-piece-Aluminum ... 0818735103

Pic and description don't really match. Who knows what it'll look like. I need 200mm... but i have a hacksaw :-D

Fred.

[Fred]

Ground lift schematic as used in my last amp many many years ago:



Note, this is a standalone thing built using discretes, not on a PCB.

Fred.

[TheRevva]

I hope you don't build it from that schematic... the bridge rectifier will 'let out the smoke' when you power it up if you leave 1 and 3 'connected' like that.
Well, maybe not, since it seems to be missing any form of AC input too...
If you get any volts out of it, you'll be pretty rich in a hurry.
<Grins>