Well, like you said, "Now you have no excuse to avoid building it " eheh

This should give a nice weekend project.
Thanks!

Earlier this week I thought about buying a cheap car amp and bridge it, so please tell me how it goes.
You can use this project by Rod Elliot http://sound.westhost.com/project14.htm
Also the October issue from EPE Magazine has a bridging circuit.
Just remember, the speaker impedance will be halved since each channel will see only half. The speaker choice will be critical.
The APX2120 says it gives 90W @ 2 ohms and 60W @ 4 ohms. Im not sure about the speaker level Input, you may need a good preamp?

200 Watts of Maximum Music Power
60W × 2 Into 4 Ohms, 20Hz-20kHz @ < 0.1%THD
90W × 2 Into 2 Ohms, 20Hz-20kHz @ < 0.1%THD
Selectable Bass Boost; 0dB/6dB/12dB @ 50Hz
Adjustable -12db/ Oct. High/Low Pass Crossover, 50Hz-300Hz
Gold Plated Connectors; RCA/Speaker/Power
Speaker Level Input
Dimensions 10 5/8" × 10 7/8" × 2 3/4"

Good luck!

Ok, I got the guilty part. The guitar jack was oxidized and so the ground was disconnected.
The last time I disassembled the guitar I tested continuity with the jack dessoldered and everything checked out fine.
I even disconnected the bridge ground and put a capacitor to see if it helped (I read about it somewhere on the net).
Unfortunatly you theory that I'm the Nuclear Man didn't come true, it would be nice to be a super hero  :tu: but even I admit strange things happen near me. Every time someone calls me to check a computer problem I have a hard time troublechecking the hardware because everything works! I call it the "fear of the doctor" syndrome.  0:)
Electronics on the other hand are still eluding my "powers". Thank god for this forum and for you guys and your precious help.

My guitar is driving me crazy, picking up all kind of interference, mostly 50 hz hummm, every time I touch the strings. Shielding improved it a bit but the humm is still too unconfortable to play. I was thinking on a high pass filter 60 Hz up. What do you think?
What kind of circuit should I build?
Thanks.

I salvage everything I can from old or defective boards. Those relays are quite nice and you can use them to make a soft start for speaker protection or for some other projects.
The chips look like they have been sanded off, so take note of what pins connect to gnd and vcc before you throw away the pcb. It may be though identifying them, unless you can get the schematic for the board. They can be pic, avr, 8051, z80 etc..

A couple of weeks gone by and some more work done. It could have been more advanced but my Ibanex RX played a trick on me... it started humming like crazy every time I touched the strings...The amp was quite silent when unplugged but every time I plugged and touched the guitar... and near my quad core... well it looked my old spectrum loading tapes (load "" ftw  )
I ended up building a little lm386 amp with an opamp pre that is battery powered just to rule out mains interference and that one hummed too so I decided to quit the laziness, and completely stripped my guitar and redid all the wiring. For good measure I shielded all of the inside with conductive paint and aluminum foil.
I am now quite happy, finally its quite silent, except the volume pot that has reached the end of it's life. I've allready ordered some from ebay that should arrive in 2 weeks.
A bit offtopic: I noticed some loaded pickguards from china for like 20€, and I'm tempted to get one. Has anyone ever tried one of those? What looks too good to be true usually is but 3 pickups, 3 pots, 3 pot covers and the pickguard for 20€ is damn tempting... I might even buy it just to build a cigar box guitar!

Thanks Joe If I had to change anything it would be the depth of the cabinet. I made it 30 cm but maybe 20-23cm would make it more standard.
The resistor value, I have no idea how I got  it  I think JMF in the old thread mentioned this configuration but I can't remember what were his values. I ended up on using 3,3k because I had them on my table and it felt like a good idea.
If someone could enlighten us with the math involved?

Actually I think the speaker was from a PA system. I got it for free so it was a good option for me. I can also get some Jensen Alnico 30W for around 50€ (JP10Q). I can't find Weber signatures in Portugal, maybe they are more common in America.
You run them at 40V and many amps? I tested the amp with it's current heatsink for 10 minutes at full power and the heatsink was only barely warm to the touch.
I also have some larger heatsinks salvaged from old PIII, either passive or with fan. If the amp gets too warm I'll put one of those in.

Well, I finnally got some spare time to get back to this. Work has a funny way to ruin all the fun   xP
I got to build my amp, but not without some missaps, as you can see here
I was careless and shorted the output capacitor, instant fireworks... I replaced the TDA2040 with a TDA2050 that I had also bought and the end result is this:

Notice that I still have a 3,5 stereo input jack attached, I used that as input from my Ipod. I connected a 3,3k resistor to the left and right channel and sent it to the input (is that correct or is there a better way?).
The rest of the amp:






I am sorry about the low quality but my camera is at my inlaws and my PDA has a crappy camera.
The cabinet is covered in a tolex like material that I got from a car upholsterer. It's lighter than the one in my fender but it gives a nice look. The faceplate is transparent acrylic but it's not finished, It only has the power switch and the input jack. You can see it in pic nº 4. I will put a sound lever meter (LM3915) with 19 LEDs in the middle and the pots for the preamp.
My largest problem is still the power tranformer. The best thing I have now is a PSU from a HP printer (I believe it was JMF that sugested that one), and it gives 32v and 3,6 A.
The speaker is 10'' 8ohm with unknown watts. The guy I got it from said it should be 120W RMS, but I have no idea. The size of the magnet looks nice so  I don't think the TDA2050 will blow it.

Opinions are welcome

My old posts seem to be misssing, I'll post here my failures and successes when I get home later in the week.
Cheers