so this is the one i PM you about, the heatsink was getting red hot idling, and you were right the current was almost zero,now i have this at around 20mv(closest i could get it with what i had) but it is as cool as a cucumber and sounds great so 2 successes in one night-you dont get those to often.so i think thats my lot repairing for tonight.🙂(this misses wants to watch tv and im in the way )😀
Lol 🙂 and I'm losing track of all the different NAD's you have on the go but pleased to hear you have got another one fixed.
i have 16 all together upstairs 5x3130's, 3x3020b's 3x3240PE 2x3225pe 1x3150 and 1 x marantz PM 200
5 others i have in my living room, 2 i have just fixed,1x 3130 and 1x 3020b
plus 1x 3155 another 2x3130
i only started out with the one, and i became a bit of a bug, but i love it!
good job i have an understanding wife 😉
5 others i have in my living room, 2 i have just fixed,1x 3130 and 1x 3020b
plus 1x 3155 another 2x3130
i only started out with the one, and i became a bit of a bug, but i love it!
good job i have an understanding wife 😉
Yes, it is 🙂
Why not pick one that is essentially OK and use it to experiment on. You could add a speaker relay for example by making your own little circuit on veroboard to add to the amp.
There are other cool things you could play with like adding a DC servo to ensure the output point is always at 0.00 volts. That's a little bit more advanced and would need one opamp but it would all be for learning.
Why not pick one that is essentially OK and use it to experiment on. You could add a speaker relay for example by making your own little circuit on veroboard to add to the amp.
There are other cool things you could play with like adding a DC servo to ensure the output point is always at 0.00 volts. That's a little bit more advanced and would need one opamp but it would all be for learning.
i will do that, but im going to throttle back a little of the practical side(not totally) but I've got behind a bit with the theory a bit so i want to dedicate some real time for that.
I think i know where i need to go now with this subject. Im never going to be a genius with electronics, but i do need to learn more of the theory to at least be able to understand the basics better and then move on to more advanced stuff. I would like to be able to design and build my own quality amplifier, but that is a way off yet. Thanks to yours and other help my knowledge is massive compared to what it was, but i still need to do more of the math bit so i can understand just by looking at a circuit what it should be rather than just relying on practical testing.
I think i know where i need to go now with this subject. Im never going to be a genius with electronics, but i do need to learn more of the theory to at least be able to understand the basics better and then move on to more advanced stuff. I would like to be able to design and build my own quality amplifier, but that is a way off yet. Thanks to yours and other help my knowledge is massive compared to what it was, but i still need to do more of the math bit so i can understand just by looking at a circuit what it should be rather than just relying on practical testing.
Building stuff on your breadboards and also learning basic theory alongside that would teach you a lot. The two go together in many ways. These days you have things like LTspice which can help massively as well.
I shall be doing exactly that.
I do love the practical bit though and that is defiantly my way to go.
I just love repairing electronic stuff.
I do love the practical bit though and that is defiantly my way to go.
I just love repairing electronic stuff.
well that was also short lived.
plugged this in this morning and one channel just does not sound quite right, there is def distortion on one channel, especialy at higher volume
i noticed the Q609 collector voltage is lower on this channel (L) so im gonna work back a bit and see why
plugged this in this morning and one channel just does not sound quite right, there is def distortion on one channel, especialy at higher volume
i noticed the Q609 collector voltage is lower on this channel (L) so im gonna work back a bit and see why
The voltages you measure on Q609 etc are not absolutes and will seem to vary, particularly when you measure using ground as a reference point.
The amplifiers DC offset will alter Q609 voltage for example and so will temperature differences.
What matters is what the bias current is and also that the DC offset is still OK. If those two conditions are met then something else is going on.
The amplifiers DC offset will alter Q609 voltage for example and so will temperature differences.
What matters is what the bias current is and also that the DC offset is still OK. If those two conditions are met then something else is going on.
so im just going to have a look at this one after looking at the other one this morning which is ok now(see the other thread)
the bias keeps going back to zero on this distorted channel, weird(i guess why its distorted)
the bias keeps going back to zero on this distorted channel, weird(i guess why its distorted)
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It sounds a bit of a strange one.
If the bias drops to zero then the distortion does increase but not normally by as much as you might think.
So the low bias in itself might not be the underlying reason for the distortion (assuming its pretty bad) but it is of course a measurable problem related to whatever is going on.
You could (on the good channel) try shorting out the vbe multiplier just to see what zero bias sounds like. That would mean linking collector and emitter of Q610.
Two things to check.
1/ The voltage across C and E of Q609 determines the bias current.
2/ The current flowing in Q609 will partly determine this voltage and so if there is a problem with R647 or R649 going high then that would cause the current to drop and so the voltage across the transistor.
3/ More unlikely would be an issue around Q603. The voltage across R629 (390 ohm) is a direct measure of the current flowing in that whole chain.
4/ An intermittent (dry or fault) driver transistor would cause distortion.
If the bias drops to zero then the distortion does increase but not normally by as much as you might think.
So the low bias in itself might not be the underlying reason for the distortion (assuming its pretty bad) but it is of course a measurable problem related to whatever is going on.
You could (on the good channel) try shorting out the vbe multiplier just to see what zero bias sounds like. That would mean linking collector and emitter of Q610.
Two things to check.
1/ The voltage across C and E of Q609 determines the bias current.
2/ The current flowing in Q609 will partly determine this voltage and so if there is a problem with R647 or R649 going high then that would cause the current to drop and so the voltage across the transistor.
3/ More unlikely would be an issue around Q603. The voltage across R629 (390 ohm) is a direct measure of the current flowing in that whole chain.
4/ An intermittent (dry or fault) driver transistor would cause distortion.
well it had def failed.
when i checked the centre again after trying it this morning i have 21v on the distorted channel so it was just shear luck it didnt blow the speaker up, that is why i went hunting for that one first.
i did take a few of the other transistors out ,test them then put them back in, so it could have been a red herring and 2 probs at the same time, and re soldering the transistors back in may have resolved a joint issue, that unfortunalty i will never know.
when i checked the centre again after trying it this morning i have 21v on the distorted channel so it was just shear luck it didnt blow the speaker up, that is why i went hunting for that one first.
i did take a few of the other transistors out ,test them then put them back in, so it could have been a red herring and 2 probs at the same time, and re soldering the transistors back in may have resolved a joint issue, that unfortunalty i will never know.
