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Deleted member 550749
No , only matters the behaviour of capasitor, with heat, frequency, I personally don't like that blue cap, a 50volt NPO CAP or cgo very good, they never change the capacitance with heat, that's why I recommend uđź‘Ť
So let me ask you this one of the 100pf caps tested at 79pf do you think that is enough to cause the amplifier to oscillate??
Hey guys how much dc is acceptable to come from the amp . Cause I just burned the Twitter on my ads speakers I’m really bummed. I’m measuring about 3mv of dc is that a safe range ?
Also the drivers d669 ,d669 and b649 are getting a bit toasty is that normal the output transistors are fine but those drivers are a bit hotter then I’m comfortable with
So it looks like the amp is drawing 100ma at idle with no load connected so is that normal ? I tested that with an inline dc current meter connected to the vcc+
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Deleted member 550749
If offset is 3mv that,s good and Quiescent under 100ma also very good, u burned tweeter? R u connected direct to d amp?? Or use crossover or 4.7uf polypropylene cap
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Deleted member 550749
D669 1watt biasing transistor, I think u need more powerful like D882 or D880 or bd139 or mje340 or 10 to 20 watt to reduce the heat, D669 overheating, not normal
DC offset should not harm a tweeter because the tweeter is usually coupled via a cap in the crossover. High frequency oscillation will burn out a tweeter.
DC offset should ideally be below -/+20 mv dc but historically -/+100mv was considered acceptable. It needs several volts of offset to damage a speaker.
Ok new update the amp basically blow up on me by mistake I connected the output of the amp to the oscilloscope and the entire board fried on the amp both output transistors burned the big 5 w 1ohm resister burned and a 100ohm resister burned at this point it’s not salvageable so I ordered new kits will update you guys on these when they get here . But can someone explain why connecting the amp output to my oscilloscope ground did so much damage ?
If you connected your scope ground lead to the output of the amp then the amp would see a short if the scope was also grounded. Hard to see how that would burn up that 10 ohm in the Zobel network though.
I would recommend you use a DBT (dim bulb tester) next time and wire just one amp up at a time.
I would recommend you use a DBT (dim bulb tester) next time and wire just one amp up at a time.
It didn’t burn the 10ohm it burned the main output transistors it burned the 100ohm resistor the 0.1ohm 5w resistors and some other components that I can’t seem to find that are also showing short . I’m thinking maybe the mains flow back from the wall not sure if it cooked the board !!
A shot in the dark: unless I’m overlooking, I don’t see any low inductance bypass caps on the supply rails.
Guys why should there be a potential difference in the output of the amplifier and the ground on the oscilloscope? There should be no potential . So the problem happened when I by accidentally connected the output of the amplifier to the ground of the oscilloscope the amp popped real loud sent out bunch smoke and that was the end of it . Why should there be a potential between the amp out and the ground on the oscilloscope it just bothers my mind ? I posted a pic of the power supply so you guys can see what I was using !
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Deleted member 550749
The output of the amp has two connections. There is the 'output' from the transistors and the 'ground'. You keep mentioning 'output' and that point will have voltage relative to ground and particularly when signal is present.
Also remember 'ground' is just an arbitrary term. If your PSU ground is connected to mains earth ground and your scope is also mains grounded then you have the possibility to apply a direct short if you touch the scope ground lead to a point with voltage on it (such as the amp output).
If the amp and scope are not mains grounded then they are both 'floating' and the term ground then has a different meaning with it referring to a point of reference for each circuit.
But here is the thing the psu ground was not connected to the house ground when I touched the scopes ground to the positive output of the amplifier boom everything smoked mainly the main output transistor the 0.1ohm 5w resistor and one 100ohm resistor all went poof just because I touched the positive output of the amplifier to the ground on the scope and I say again the ground from the psu was not touching the house ground !!! Why would it short make it make sense .
All I can think then is that what you did provoked some uncontrolled instability. That fits the evidence in post#1 where the 10 ohm in the Zobel network burned.
Only ever connect the scope ground to the power supply ground of the amp (the zero volt line) and use the probe tip to look at the amp output.
Only ever connect the scope ground to the power supply ground of the amp (the zero volt line) and use the probe tip to look at the amp output.