Project 5500. Big fun or ....?

[Rob DeFries]

A couple of years ago, a friend of mine came up with an old Pioneer amp. It was a SA-5500II.

"It only hums" he said, "maybe you've got some purpose for it?"
Ofcourse. But then, after I opened it up, I saw the two tiny STK like modules. Pioneers own little crap circuits. I closed it and dumped it in the attick.


Now I have the urge to dive into this amp and see what I can make of it.
So that's what I'm going to do, the next couple of weeks. Bore you all with my Project 5500. It does have a power supply and + and - supply voltage. Oh my oh my, this can become fun!

 

[Rob DeFries]

Well, it's not as much fun as suspected. The amp is a pain to take apart, the main PCB is cheap and moves in every direction like a newspaper and it's wires galore around the transformer.
Since the whole chassis is made out plastic, I really have my doubts if it is worth all the time, to get it going again.
I first had a look if any PA3002 IC's were available. It turned out that I could get one for some $ 10 plus posting..... Nawww, ain't gonna pay a tenner, and probably more for shipping, possible duty and import tax, for an unreliable "pulled" intergrated circuit out of a cheap Pioneer amp.
I have no clue if anybody would pay money for a restored 5500II, in my opinion it's worth 50 bucks, so I might make it worthless by installing something else inside.
And that's what I'm going to do. Gaincloning that thing........

 

[Rob DeFries]

There's + and - 25V handy, from the transformer. That's ideal for the LM3886. I can get these circuits for around $5 each, in the plastic version. Which means no isolating stuff, just some thermal paste.
Best thing is, you can buy them from China, built and all for under 10 Euro's per channel.
One thing is for sure.... this LM is going to be far superior to the PA3002 than expected.

such a kit works 100% good and is cheap. I bought just the PCB's. The rest is always on stock in my shed.

First thing is where to find the PS and the in- and outputs. How to make the PA3002 inactive and redo things if needed.



There's this white and red twisted pair. Red is the +25V and white is -25V. Black is ground and best taken from point 39 on the main PCB. There's also a G on the PCB, that's for the ground wire to the tone PCB ( G --> G).

There's a green and yellow wire, connecting to wirewrap pole 40 and 35 resp. (40 - green - left channel) These go to the + output of the left- and righthand amp. Green to + out left and yellow + output right.
The other two green and yellow wires, from point 32 and 36, are the inputs for the LM3886's. The green goes to the +input of the left unit, yellow to the right. The inputs are capacitor coupled, 4.7uF.

If the holes are drilled and the boards would be connected, it could look like this....


But first we have to undo all the wires and pcb's from the chassis, wires coming from the tone PCB. Otherwise you'll go mad for sure, turning the PCB's....

 

[Rob DeFries]

Take all the big screws out, also the 4 that hold the transformer. Every single board has to be lose. Take all the screws off the front plate, and free all the components. Speaker switches, headphone unit, on/off switch and tone PCB. On the back, undo all the screws from the 120/240V ac connector, the selector switch, the tape- and other RCA board. Undo the screws that hold the phono PCB. Now desolder the wires coming from the tone PCB. Purple (33), black (G), yellow (32), green (36) and brown (34).

 

[moewillis]

seems like a lot of work for a 15wpc unit. especially when you can get the part that drops right back in. cool project though! ill be curious to see how it all turns out

 

[Rob DeFries]

Yeah. I do it just for the fun. And dropping anything in is not possible. The whole mainboard has to come out and needs to be turned around, which means: everything out. So even if I had these PA3002 things, it would still be a pain to get them in.
It's working already, low offset nice sound, but I need more input. Volume open gives me 12 watts, instead off the 35 that should come out.