No matched pairs necessary (or even SLIGHTLY useful) in this power supply.
Plus not only will matched pairs cost you MORE, but NTE is the LAST resort for parts, and have a huge markup for the repackaging and remarking that makes other manufacturer's transistors into NTE's.
I choose the zetexes for many reasons, but their current handling capability and heat dissipation, especially while still delivering oodles of gain at lower currents, results in their being minimally stressed, even when the circuits they are feeding are misbehaving.
One of the possibilities I have been considering is that the power supply transistors have been operating at the top end of their stress tolerance for a long time and just aren't up to it in certain conditions.
As for that shorting allegedly at the relay, if you wish, you could check out the actual wiring at the relay to see if this is done, or is it just something drawn by some idiot apprentice draftsman. When I saw it in the schematic I immediately looked for the relay's PC board location to figure out what was going on by examining the foil pattern... no such luck, it's hardwired.
Monitoring with headphones is fine, plus the 150 ohm resistors it has in series with the headphones will limit the currents. Personally I have a few sets of old computer speakers that I use as low level sacrificial loads. If they pop, oh well, I was originally going to toss them anyway... but the computer speakers connected through a headphone plug would be unbeatable....
If the amp misbehaves, with no speaker load connected, there is no way anything can be damaged. Particularily on the outside, on the inside there are some rare conditions that the new c2682Y's pretty much eliminated, i.e. BOTH outputs turning on full at the same time, push-push as opposed to push-pull. The 150 ohms of the headphone resistors is insignificant to the output's capability.
IF the outputs are misbehaving, you should hear some sort of POP. This is why I suggested a voltmeter monitoring the output, WHILE it is in protection, if you can catch it, turn off the volume and look at the dc voltage at the output.
Like I said, it will be most interesting if the protection triggers with the protection circuit's inputs disconnected.
The HOT side disconnected wires from the amp must be insulated from each other, while 5 & 6 inputs at the board can be shorted together, as well as the 7 & 8 inputs, and the 1 & 3 inputs grounded, do all these if you want to be absolutely sure about eliminating any possible external influences. The impedances of these circuits are low enough that stray signals will most likely NOT affect things, but this way we are SURE...
Plus not only will matched pairs cost you MORE, but NTE is the LAST resort for parts, and have a huge markup for the repackaging and remarking that makes other manufacturer's transistors into NTE's.
I choose the zetexes for many reasons, but their current handling capability and heat dissipation, especially while still delivering oodles of gain at lower currents, results in their being minimally stressed, even when the circuits they are feeding are misbehaving.
One of the possibilities I have been considering is that the power supply transistors have been operating at the top end of their stress tolerance for a long time and just aren't up to it in certain conditions.
As for that shorting allegedly at the relay, if you wish, you could check out the actual wiring at the relay to see if this is done, or is it just something drawn by some idiot apprentice draftsman. When I saw it in the schematic I immediately looked for the relay's PC board location to figure out what was going on by examining the foil pattern... no such luck, it's hardwired.
Monitoring with headphones is fine, plus the 150 ohm resistors it has in series with the headphones will limit the currents. Personally I have a few sets of old computer speakers that I use as low level sacrificial loads. If they pop, oh well, I was originally going to toss them anyway... but the computer speakers connected through a headphone plug would be unbeatable....
If the amp misbehaves, with no speaker load connected, there is no way anything can be damaged. Particularily on the outside, on the inside there are some rare conditions that the new c2682Y's pretty much eliminated, i.e. BOTH outputs turning on full at the same time, push-push as opposed to push-pull. The 150 ohms of the headphone resistors is insignificant to the output's capability.
IF the outputs are misbehaving, you should hear some sort of POP. This is why I suggested a voltmeter monitoring the output, WHILE it is in protection, if you can catch it, turn off the volume and look at the dc voltage at the output.
Like I said, it will be most interesting if the protection triggers with the protection circuit's inputs disconnected.
The HOT side disconnected wires from the amp must be insulated from each other, while 5 & 6 inputs at the board can be shorted together, as well as the 7 & 8 inputs, and the 1 & 3 inputs grounded, do all these if you want to be absolutely sure about eliminating any possible external influences. The impedances of these circuits are low enough that stray signals will most likely NOT affect things, but this way we are SURE...
