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Old 17-07-2020, 09:47 PM   #1
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Join Date: Apr 2019
Posts: 3,266
Amp Teardown and Dangers of Buying old 2nd stuff....

Just want to share this and issues we all face when buying 2nd stuff online, esp when they are very old.

Just bought this old amp yesterday..... 20yrs It still good but a hint of distortion at high volume so decide to take it apart. So share some teardown photos.

The preamp circuit board. The layout is high symmetrical since its a stereo amp.

These are OPA604 opamp. 3 of them per channel. Considered old these days and better ones are available. But not sure how it will affect the sound, feel like making a socket and start swapping opamps to play!! Sounds fun!!

The back of the board. Those nichicon caps needs to be replaced. Notice those long metal "poles" on both sides, they are connected to the power section. Hmm... feel like replace them with wires and sheild them.

The power section. Black cylinders are power filtering caps, each is 6800uF. Looks like 0048, needs to be replaced. Again, its high symmetrical in design. Black transistors are Sanken 1860/4886. Its class AB amp. Each pair is rated for 80W and 14A. So, 6 pairs per channel will have lots of power for speakers. Lots of grey resistors, they are ballast resistors. Needed due to running transistors in parallel.

This is the danger of buying 2nd stuffs esp very old ones. Chances are, mods and other stuffs have been done to it. They are 2 vishay Dale 5ohm resistors connected in series soldered across the 10ohm SMD resistor. No idea why. But maybe its to reduce distortion or something. The board has been recapped (poorly done), but power filtering caps wasn't replaced.

The best thing is that you can't really kill these amps. They are just circuit board with bunch of components. So, they all can be replaced. Just take some time and effort. Best of all, components are usually very cheap. Now you know how much $$$ they make from these

Last edited by Clearnfc; 17-07-2020 at 09:49 PM..
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