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My DIY amplifiers


The 4100       

        The 400 watt amp has four P3A amplifier modules using ON Semi MJ15003/4 power transistors. They have proven to be very reliable and are very neutral sounding. it puts out 100 watts RMS per channel (four channels) at 4 ohms or 60 watts at 8 ohms.

 Here are some pictures of the insides:

Here is the inside looking from the front.



Rear view....



and the top view.




did you notice the fan? it blows air out. air enters through the sides and straight into the heatsinks.
(from top left to top right, when looking at the top veiw picture of my amp)
18v 1A transformer for muting circuit, fan and crossover; single PCB for fan speed controller, 7812 regulator, time delay relay, and P05; 4.1kHz and 112Hz linkwitz riley crossovers.
P3A's are on the sides of the case, one channel attached per heatsink.
the fuses are on the same PCB with the capacitors. muting relays are on the top of the heatsinks.
the front panel LED is red at turn on when outputs are still muted and turns blue when in normal condition.
as you can see, I'm using a snubber network on both 288VA transformers.
speaker protection will be added and installed behind the gain controls (the space beside the transformers.)
RCA jacks of the crossovers are all independent so I just use RCA cables to link inputs and outputs to achieve a lot of different system configurations.
jacks are for; input, HP and LP for 112Hz; input, HP and LP for 4.1kHz
and below them are the inputs for the 4 P3A's.
I used only carbon film resistors but the noise is still totally inaudible. (except for a slight hum.)
the star ground return are made on the foil side of the capacitor banks.


The 2250

        The 500 watt amp is a two channel amp. It was originally a pre-built module but it came with no specs whatsoever so I hooked it up to my speakers and it kept blowing up. I then made several modifications to it and now it is still playing hard. It puts out 250 watts RMS per channel at 4 ohms or 125 watts RMS @ 8 ohms.


This is the front of the amp.



The rear....



and the top.


the fan configuration is the same but this amp operates in class-B so it has a little bit higher distortion than I wanted but the modifications I did made it inaudible.

        update: a few weeks ago, I did an upgrade to the 2250, adding a Vbe multiplier similar to Rod's P3A amp, distortion got lower but at the expense of higher dissipation at standby.



The 2400

        This amp has been with me for several months. after the recent event where the output stages blew up (luckily, I have DC protection. my subs are safe.) I added an additional pair of output stages per channel so now I have 16 MOSFETs in the amp.

        Note: these pictures are showing the older pictures of the amp before I "blew" it up. I will be posting the more recent pics while it was disassembled showing how I mounted the additional output stages.


The torroid transformer is from Hongkong (while I was there for a few days) and they said it was locally made there. it is only a 500VA unit with 48-0-48V secondaries but I have no trouble with it.  I have eight 10,000uF caps for all the amps and each has 20,000uF of capacitance per amp rail. The pots I used are Alps (blue ones, don't know the model).


Here is the rear panel showing the gold plated connectors (first amp that I used gold plated ones!). If you can see well enough, you can see how the air flows throughout the chassis ventilating the heatsinks. All my amps have the fans blowing out the rear panel. 

(the circuit board with those pots on the upper left hand corner of the pic is Rod's P27 guitar preamp. I have two, one for guitar and another for bass.)


Here is the top view of the amp. Using a torroid does give you more room to work in.


Here is an additional pic of the amp from the side.


Updates to my 2400

Here are some pics of it disassembled while I was servicing it. this was the old chassis layout which is slightly different from the new one. you'll see in a moment.....

The top half. which contains the amp boards, heatsinks, fans, and controls.


The bottom half which contains the PSU and DC protection.


A view of the additional output pairs. The lone TO-220 transistor mounted in the middle is the temp sensor.


The recent pics with the new chassis layout. and still messy. my 0V star earth point is the big blob of solder in the middle of the black wire between the caps. (there are two)


The top view, so you can see the chassis layout more clearly.


and the toroid I used in the amp. this pic was taken in the hotel when I had just bought it in hongkong.




And this is my 2100

        The simplest of all my amps. It uses two P3A boards, 225VA toroid, four 6800uF caps and two bridges. (separate caps and bridges for each amp) The volume pot is only a garden variety carbon pot since that is all I have in the parts bin. This was completed in just a short time because I needed a stereo system in my workshop ASAP! (hard to work without music, you know. )

Front of the amp, very simple. Just a volume knob, a power switch and a blue power on LED.


Here is the rear panel. Just a pair of gold RCA connectors, spring terminals for the speaker connection and a fused IEC mains connector. The holes for the RCA connectors were originally there so I just enlarged it a bit for the connectors to fit. It was a big pain in the a** drilling holes inn the back panel. That is a 2mm think STEEL SHEET!


     The top view shows the layout of the components inside the case. The case is originally from a brushless DC motor controller found in a junk shop. The front panel was replaced with a plywood one which is much much easier to make holes into. The heatsink also came originally from the chassis, notice the positioning of the output devices? I didn't want to drill more holes to the heatsink and besides, it's already tapped.  The little bunch of components on the right side of the heatsink is a temperature controller for the fan (also came with the case) which seems to do nothing but run the fan at low speed. the fan is 12V and I have 35V supplies, how did I run it? simple, use a 10 watt 220ohm resistor in series with the fan (near the main filter caps, just under the green wires.) gives about 11V. You might be wondering why the PCB's are slanted. simple, I was too lazy to rim it to fit on the case and instead slanted it. makes it easy to reach the bias pots too.


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