We're talking about the circuit board common point GNDA, usually referred to as "ground".
This is the point where all the power supply capacitors are connected together,
and where the audio input and output "grounds" are connected. This is NOT the
power input utility ground point.
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Thank you rayma.
If I got your advice right, I should then connect the two polarities (the + of one adapter and the - of the other adapter) to that circuit board GND point, right? This doesn't need to be also connected to the metal chassis right?
Actually I now need to find a chassis for this preamp (the original amp chassis is now used to hold the jack connector that now directly goes to the speakers...yes, I'm using the former speakers as a 100W/4-Ohm cabinet). Can I use a wooden enclosure for that? Or it would be better a metal one or am mertattal coating insuide (like a metal foil). What could be then otherwise suitable as a metal enclosure? Any idea?
Best regards
If I got your advice right, I should then connect the two polarities (the + of one adapter and the - of the other adapter) to that circuit board GND point, right? This doesn't need to be also connected to the metal chassis right?
Actually I now need to find a chassis for this preamp (the original amp chassis is now used to hold the jack connector that now directly goes to the speakers...yes, I'm using the former speakers as a 100W/4-Ohm cabinet). Can I use a wooden enclosure for that? Or it would be better a metal one or am mertattal coating insuide (like a metal foil). What could be then otherwise suitable as a metal enclosure? Any idea?
Best regards
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Yes, that's right. The "ground" leads (one + and one -) of the adapters go to the circuit ground.
This is where the two 16V Zener diodes are connected together.
Be careful to connect the remaining leads the correct way, the + to +16V and the - to -16V.
You'll also need to remove the two Zeners from the board, or the adapters will be damaged.
I do want to remind you that it isn't necessary to use the two external power supplies.
Instead you just disconnect the traces from the large filter capacitors to the amplifier circuits,
leaving the connections to the 200 Ohm resistors and the Zener diodes intact. This is simple to do.
Then you will still have functioning +/- 16V supplies built-in, the same as before.
You can use any enclosure for the circuits. Sometimes a metal one helps with noise reduction.
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I'm with Rayma on this one. Just use what you already have. Simply desolder and remove from the circuit board the transistors that attach to the heat sink. You can even leave them on the heat sink, in case you ever want to put the unit back to stock. What ain't there ain't gonna burn up or draw power. Everything else should function like it should.
If you're worried about high voltage, it looks like the only place it is present is inside the white-bordered corner on the circuit board. For easy safety, you can spray paint a couple coats of clear over the bottom of the board on that area. It will be more difficult to repair later, but it won't shock you.
If you're worried about high voltage, it looks like the only place it is present is inside the white-bordered corner on the circuit board. For easy safety, you can spray paint a couple coats of clear over the bottom of the board on that area. It will be more difficult to repair later, but it won't shock you.
The big question which noone has asked yet is this: Does the thing work? It would be a waste to go through all of this trouble if it don't work.
As far as a case, it depends on how you want to use it. Rack mount, stand alone, or part of another combination unit makes lots of difference. Either way, I would either recycle the original faceplate or buy another one. The hole sizing and spacing as well as the lettering and knob scales make a whole lot of difference. The next guy might not like hand scribbled labels and offset holes and such if you get lazy. Exterior fit and finish can make up for a ton of ugly under the skin.
As far as a case, it depends on how you want to use it. Rack mount, stand alone, or part of another combination unit makes lots of difference. Either way, I would either recycle the original faceplate or buy another one. The hole sizing and spacing as well as the lettering and knob scales make a whole lot of difference. The next guy might not like hand scribbled labels and offset holes and such if you get lazy. Exterior fit and finish can make up for a ton of ugly under the skin.
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