On the dummyload music signals look ok on the scope.
I just do the burst test for reliability after i adjusted the idle current . I heat the amp up by applying bursts every 1/2 second over 10-30 minutes.
The last 8 Rockford oldschool amps i had did not show this behavior. This is the reason why i am confused and think something is wrong.
Should i ignore it?
I just do the burst test for reliability after i adjusted the idle current . I heat the amp up by applying bursts every 1/2 second over 10-30 minutes.
The last 8 Rockford oldschool amps i had did not show this behavior. This is the reason why i am confused and think something is wrong.
Should i ignore it?
To heat the amp up, if you want to confirm that the bias isn't drifting, use music, not a test tone. I used Bass Boy - "Rebel Bass" on a loop for testing amps.
I've never seen any reason (or heard of) using bursts for testing so I don't know what to tell you regarding that method.
I've never seen any reason (or heard of) using bursts for testing so I don't know what to tell you regarding that method.
this burst testing is or was the ihf 202(?) standard.
rockford used this burst method for testing dynamic power to calculate the dynamic headroom.
todays pro audio amps use these bursts instead of continuous tests.
rockford used this burst method for testing dynamic power to calculate the dynamic headroom.
todays pro audio amps use these bursts instead of continuous tests.
Dynamic headroom is useless for car audio amps.
For those getting into repair work, I'd recommend using music for bench/long term testing.
For those getting into repair work, I'd recommend using music for bench/long term testing.
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Hi Perry!
I did more testing with the 1kHz burst.
Now i can say with 100% that the 200 series channel is completely ok. I tested with 2 ohms per channel ( all cycles clean ) and i tested with 1 ohm per channel. ( first 6 cycles clean ( almost 1000 watts and then lowering output like in the pic).
The 300 series channel is doing the same but even with a 2 ohm load it drops power like the 200 channel on 1 ohm.
I said that the amp is acting strange because sometimes its ok and sometimes not.
If i touch Q328 and Q326 with my finger the output signal gets clean immediately.
Should i change them? What do you think?
Why is this the case? i always thought that dynamic headroom makes an amp more musical because it doesnt cut the peaks. Or did you mean useless for
heating the amp up?
I did more testing with the 1kHz burst.
Now i can say with 100% that the 200 series channel is completely ok. I tested with 2 ohms per channel ( all cycles clean ) and i tested with 1 ohm per channel. ( first 6 cycles clean ( almost 1000 watts and then lowering output like in the pic).
The 300 series channel is doing the same but even with a 2 ohm load it drops power like the 200 channel on 1 ohm.
I said that the amp is acting strange because sometimes its ok and sometimes not.
If i touch Q328 and Q326 with my finger the output signal gets clean immediately.
Should i change them? What do you think?
Why is this the case? i always thought that dynamic headroom makes an amp more musical because it doesnt cut the peaks. Or did you mean useless for
heating the amp up?
Did you check the source resistors in the right channel?
Those transistors are in the protection circuit so one of the transistors may be leaky if R364 is within tolerance.
In amps powered by the 50/60Hz mains, there will be a lot of ripple in the rail voltage for amps using simple rectifiers (not switching power supplies). Dynamic power is a cheat to make the amp look more powerful. In car amps, there is no ripple other than from small DCR losses or from a drop in supply voltage.
Those transistors are in the protection circuit so one of the transistors may be leaky if R364 is within tolerance.
In amps powered by the 50/60Hz mains, there will be a lot of ripple in the rail voltage for amps using simple rectifiers (not switching power supplies). Dynamic power is a cheat to make the amp look more powerful. In car amps, there is no ripple other than from small DCR losses or from a drop in supply voltage.
Yes, i changed one of the big source resistors and now they are all ok, i checked them out of circuit.
I agree that dynamic power is a cheat. I tested a 1993 JBL MPA 1100 amp which was rated 1200 watts 4 ohm per channel. With the 20kHz burst it did 2000 watts.
but you will not find this value in the datasheet.
Some people say that their US-made oldschool amps with lower ratings outperformed todays expensive lightweight amps with higher ratings on bass...
I resolder R364 ad check it, thank you so far!!!
I agree that dynamic power is a cheat. I tested a 1993 JBL MPA 1100 amp which was rated 1200 watts 4 ohm per channel. With the 20kHz burst it did 2000 watts.
but you will not find this value in the datasheet.
Some people say that their US-made oldschool amps with lower ratings outperformed todays expensive lightweight amps with higher ratings on bass...
I resolder R364 ad check it, thank you so far!!!
Dear Perry,
i checked R364 and it was ok. So i desoldered Q228 and replaced it with a new one.
The amp is fixed and is behaving like it should, all 20 cycles are clean.
I dont know what repairs have been done to the amp before and Q228 measured fine base to collector and base to emitter but out of circuit i had 0.77V in
diode-check base to collector. A new one had 0.66V
Can you tell me what can cause Q228 to fail? All outputs look good and not replaced
Again, thank you very much for your patience which helps me learning !!!
EDIT: i also replaced Q323 which measured ok, and now i have 20 clean cycles on even lower impedances - crazy what this thing is putting out 🙂
i checked R364 and it was ok. So i desoldered Q228 and replaced it with a new one.
The amp is fixed and is behaving like it should, all 20 cycles are clean.
I dont know what repairs have been done to the amp before and Q228 measured fine base to collector and base to emitter but out of circuit i had 0.77V in
diode-check base to collector. A new one had 0.66V
Can you tell me what can cause Q228 to fail? All outputs look good and not replaced
Again, thank you very much for your patience which helps me learning !!!
EDIT: i also replaced Q323 which measured ok, and now i have 20 clean cycles on even lower impedances - crazy what this thing is putting out 🙂
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For class B or AB amps, technology hasn't changed much in 50 years (more?). The older amps were generally built by those with pride in what they produced. In many instances, the only thing the newer amps are designed for is to make the bean-counters happy.
Q228 could simply be a random failure. The protection circuit isn't generally damaged unless the amp fails in a way that causes all of the source resistors to open.
Q228 could simply be a random failure. The protection circuit isn't generally damaged unless the amp fails in a way that causes all of the source resistors to open.