Speaker pop on shut off Sanyo JCX2900
- Thread starter curtisw99
- Start date
Bruno Primas
Super Member
I had a 2400KR that "popped" on shutoff. After a recap and changing the bulbs to leds it stopped.
OK, took a look at the schematic and operation is as described above, lamps are not in play.
Yeah a 220ohm will run down the cap (C412) quicker than a 1k item. Also note zener D419, if this has failed short then it will cause pop issues. D419 should cause a power on pop but depends on C412 charge up time.
If you can, monitor the dc voltage at D419 anode (or at D417 anode...) when shutting down the amp.
Diode test D419, try in circuit since looking for a short cathode to anode.
Yeah, it's a fishing trip, looking for how quickly this controlling voltage drops, should drop below D419 zener voltage "instantaneously", need to go back to schematic/D419 zener voltage?
edit 4.7V zener
Consider replacing the 1k with 220ohms.
Interesting observation, would expect the cap to run down quicker if it was tired. Assume cap has not been replaced, I don't see it as suspect faulty/cause of power off pop.
KingBubba
"Too Much Stuff"
I use a very simple action to avoid pops. On shut off, I turn the speakers off first before turning off the amp. When starting, I turn the speaker switches to off first, then turn on the power switch then switching the speakers last. Very simple and it does what is needed. In professional audio, there are devices that automatically do what I just described. It fits in the rack with the rest of the equipment.
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Seems high, would expect 2xVbe(Q431,2) say about 1.2V.
Plz confirm you measured at D419 anode.
0.89V is getting near 2xVbe (Q431,2)
edit consider diode testing Q431 and Q432, in circuit is ok, looking for a c-e or b-e short (these would probably cause p-on pops so unlikely...)
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Have you noticed there is a difference in pop level if for instance the unit is on for 5 minutes compared to for instance only on for 20 seconds?
IF you have that it might be a clue to a capacitor passing along DC somewhere that it is supposed to be blocking DC.
Yes, it appears to lessen the more times I turn it on and off.
Pull the pre-out/main-in jumpers at the rear, do you still get the pop?
?
Q432e 0V
Q432b = Q431e = 0.6V
Q431b = 1.2V
?
So where does the 4.11V on D419 fit, is it anode or cathode
Possibly the pop is caused by an inbalance in the power supply rails, caused by a tired rails cap. Recapping the psu , in this case, should correct the inbalance and the pop. Have you checked psu rails, can measure at case of output transistor taking extreme care not to short to heatsink.
The other approach is the "mute" protection feature (C412, R420) should mute the pop.
4.11V at cathode would be on the low side, zener can't be 4.7V.
Expected cathode voltage is ZenerVoltage + 2xVbe = 4.7? + 2x0.6V = about 6V.
Maybe park this train of thought...
Power off is not a graceful shut down, typically the power amp rails collapse at different rates causing a dc offset and pop. The preamp uses smaller power caps so can collapse quicker, like Warren-Oats pointed out, coupling caps should block some/most of this pop.
Two points, the protect circuit appears to be muting the power amp ok.
Was pop in both channels?
Probable that either preamp coupling caps or power supply caps need replacing.
Will make up a list...
edit
candidates
C566/C666 220/25V
C592/C692 4.7/25V
C917/C918 470/50V
C921/C922 47/35V
C923/C924 47/25V
Most would also replace C591/C691/C551/C661 1/50V with film mks2 1uf/50 or 63V
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