I have also measured from "-" GND to touching various parts of the copper cages with the other (red) pin of the DMM and it always showed "1". That means none of the copper is conductable right?
From handling the copper foil it is quite firm. It has a glued/sticky side. This one: Copper foil 50mm shielding self-adhesive conductor 1m - Audiophonics. There is no way it could come off the wires. If all something could happen at the cages, but I assume only if there is large heat inside the case. If that happens the glue might party start to melt. However, I don't think there is much heat generated at all, even at loud volume.
Which one is most dangerous from your point of view. The AC-mains-cage, the speakers-out-cage or the DC-mains-wires with copper+heat shrink?
The part with 2 small resistors and 10 Ohm as loads I do not understand. The case is totally assambled again. It is not open anymore. I can measure the case with the DMM to see if I will kill myself touching it. I will do this.
Is there a way to measure output voltage with the case closed? I suppose I can only do that from the PSU-outs directly. I have a cheap DMM that has a 0.5A fuse only. I'm afraid that is quite close to the standby consumption of the board. Im afraid it might blow or something.
The Ma12070 chips are protected against overvoltage. I assume if it gets too much, it will not start or turn itself off shortly after.
I did not notice. I noticed the screws were not turned in with full force. Of course I screw them back in very firmly. If the connectors themselfes would have been fragile, I would have noticed that while I was screwing those screws back in. I did not, so I assume that is okay.
- Copper IS conductive. You don't want it to be a short-circuit to PE. Or from + to -
- I won't speculate what is most dangerous to laymen. To laymen everything is equally dangerous. Sorry, I would not be true to my profession if I would say otherwise.
- Amplifiers are best loaded either with speakers or with a resistor for testing. With speakers the speakers are part of the test and may not survive. The resistors are cheap. Operating amplifiers unloaded is not OK.
- output voltage of the speakers outputs is of course with the casing closed. When amplifiers are broken often a high DC voltage is the consequence and DC kills speakers.
- I often repair stuff. What laymen call "very firmly" often means the thread is gone. Just tighten stuff with only light force (turn till it goes more difficult, then only a quarter turn was the tips of granddads). There is absolutely no need at all to tighten stuff very firmly as it is not a car engine or the like. No mechanical force will be applied in use so stuff won't fall apart. Connectors do need to make contact firmly as it is about lowest contact resistance.
- In hindsight: uncertainty, fear for shock and not enough knowledge are together the most dangerous. Please this is not meant ugly but one should know the basics before working with electric/electronic stuff. If one acts first and thinks later... well I am glad surgeons don't act that way.
- I won't speculate what is most dangerous to laymen. To laymen everything is equally dangerous. Sorry, I would not be true to my profession if I would say otherwise.
- Amplifiers are best loaded either with speakers or with a resistor for testing. With speakers the speakers are part of the test and may not survive. The resistors are cheap. Operating amplifiers unloaded is not OK.
- output voltage of the speakers outputs is of course with the casing closed. When amplifiers are broken often a high DC voltage is the consequence and DC kills speakers.
- I often repair stuff. What laymen call "very firmly" often means the thread is gone. Just tighten stuff with only light force (turn till it goes more difficult, then only a quarter turn was the tips of granddads). There is absolutely no need at all to tighten stuff very firmly as it is not a car engine or the like. No mechanical force will be applied in use so stuff won't fall apart. Connectors do need to make contact firmly as it is about lowest contact resistance.
- In hindsight: uncertainty, fear for shock and not enough knowledge are together the most dangerous. Please this is not meant ugly but one should know the basics before working with electric/electronic stuff. If one acts first and thinks later... well I am glad surgeons don't act that way.
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That would do what exactly? Blow the fuse in my house? Blow the fuse on the PSU? Blow the chip circuit and some other piece on the PCB?
I don't have resistors available. But I will screw it up again and recheck with the eyes of a hawk. In addition I will remove the AC/mains cage. I believe here is the most danger since the highest voltage is being conducted.
Don't they have protectional circuits/fuses against that too?
I make use of your brain for "the knowledge". I understand there can no possible connection emerge from a copper foil touching plastic only. I understand there can be surge currents and so forth so better check that there is enough space to all open conductors. I will open up again and ensure there is at least 2cm space between any copper foil and any open conductor.
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1. All possible.
2. Never use amplifiers unloaded if you don't know they can be used unloaded. So assuming none can be used unloaded is safest = Best practice is to use them with loads.
3. All protection circuits aside... when they are built in and the chip goes kaputt what then? I only trust external protection circuits or, for severe errors, fuses.
4. I am not "the knowledge". The one that is working on unfamiliar terrain better gets experience and does some basic training beforehand. Don't open it again, you have already checked it. Uncertainty is more dangerous than triple checking. 2 cm is extreme and unnecessary.
2. Never use amplifiers unloaded if you don't know they can be used unloaded. So assuming none can be used unloaded is safest = Best practice is to use them with loads.
3. All protection circuits aside... when they are built in and the chip goes kaputt what then? I only trust external protection circuits or, for severe errors, fuses.
4. I am not "the knowledge". The one that is working on unfamiliar terrain better gets experience and does some basic training beforehand. Don't open it again, you have already checked it. Uncertainty is more dangerous than triple checking. 2 cm is extreme and unnecessary.
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Update:
So I opened it up again and checked carefully (without any anxiousness, but diligence). I removes the AC/Mains cage and I removed the speakers-out-cage.
Instead of the speaker-out-cage made of copper foil I came up with an idea. It may be brilliant or foolish. The idea is a new cover in form of:
"Streichholzschachtelunterbodeneinsatz"
It fits perfectly onto the speakers-out-panel. I layed it out with a thin layer of some plastic stuffage foliet to improve noise reduction further. Now as I understand "Streichholzschachtelunterbodeneinsatz" cannot conduct any electricity whatsover, nor can the plastic inlay. Therefore it should be safe. Wouldn't you agree?
Testresult: Success (with a downside)
So I finally got the balls to test it with the lighting match box solution.
Measurement speaker plugs:
All with ears directly to speakers.
Before:
-22db (67%) - white noise/ants crawling from speakers starting
-15db (75%) - white noise/ants crawling intensifies
-10db (85%) - white noise/ants crawling intensifies further (quite noticeable)
-05db (92%) - white noise/ants crawling intensifies further (really noticeable)
-00db (100%) - white noise/ants crawling at maximum
After:
-22db (67%) - Silence
-15db (75%) - Silence
-10db (85%) - A very high frequent whine/humming emerges (very old people probably won't hear this)
-05db (92%) - The high frequent whine/humming intensifies
-00db (100%) - Now it's like those shows where people make drinking glasses "sing" by rubbing them with wet fingers.
I would say that's a success overall. I would never play this amp louder than -10db anyway, so I will hopefully never get to hear it in practice. This gain is despite the fact that the amp is running noticeably higher voltage now (which itself should raise the noise level).
The downside is that my 15V-5V converter does not work anymore, which I used to plug my DAC from the 15V back port. Since I raised the V-output, I assume the DC-out is raised too. Maybe slightly above limits for my converter now.
Hence I cannot plug my DAC right now and cannot play any music. I will buy a cable tomorrow to feed it from a tablet adaptor.
Things to note:
All back panel screws are connected to PE (Schuko green/yellow). All outputs&inputs are connected to PE. The case itself is connected to PE. However, since there is painting on it it isn't connected as long as the painting coat is prestine. If there is a scratch in the case somewhere, the scratch becomes connected to PE. Is this expected?
So I finally got the balls to test it with the lighting match box solution.
Measurement speaker plugs:
- R: 25.6V (measured with DC-V 200m) /before: ~22.5-23.5V *guess by default position of screw knob
- L: 12.1V (is this expected ???)
All with ears directly to speakers.
Before:
-22db (67%) - white noise/ants crawling from speakers starting
-15db (75%) - white noise/ants crawling intensifies
-10db (85%) - white noise/ants crawling intensifies further (quite noticeable)
-05db (92%) - white noise/ants crawling intensifies further (really noticeable)
-00db (100%) - white noise/ants crawling at maximum
After:
-22db (67%) - Silence
-15db (75%) - Silence
-10db (85%) - A very high frequent whine/humming emerges (very old people probably won't hear this)
-05db (92%) - The high frequent whine/humming intensifies
-00db (100%) - Now it's like those shows where people make drinking glasses "sing" by rubbing them with wet fingers.
I would say that's a success overall. I would never play this amp louder than -10db anyway, so I will hopefully never get to hear it in practice. This gain is despite the fact that the amp is running noticeably higher voltage now (which itself should raise the noise level).
The downside is that my 15V-5V converter does not work anymore, which I used to plug my DAC from the 15V back port. Since I raised the V-output, I assume the DC-out is raised too. Maybe slightly above limits for my converter now.
Hence I cannot plug my DAC right now and cannot play any music. I will buy a cable tomorrow to feed it from a tablet adaptor.
Things to note:
All back panel screws are connected to PE (Schuko green/yellow). All outputs&inputs are connected to PE. The case itself is connected to PE. However, since there is painting on it it isn't connected as long as the painting coat is prestine. If there is a scratch in the case somewhere, the scratch becomes connected to PE. Is this expected?
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