RF 1001bd turn-on pop - diyAudio
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Old 26th September 2007, 05:02 PM   #1
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Question RF 1001bd turn-on pop

Is it normal for this amp or is it a frequent defect of these amps? Is there any effective way to minimize it?
I never had a new RF 500bd, 1000bd, but all used ones I had were experiencing this turn-on pop. Current 1001bd on my bench works great, but turn-on spike in output is so significant, that damaged outputs or a sub is just a question of time Thank you!
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Old 26th September 2007, 05:56 PM   #2
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That's not normal. Does it pop as soon as the power supply begins oscillating or does it pop at the same time the protect light goes off?

Is there any DC offset on the output before or after the pop?
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Old 26th September 2007, 06:13 PM   #3
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Quote:
Originally posted by Perry Babin
That's not normal. Does it pop as soon as the power supply begins oscillating or does it pop at the same time the protect light goes off?

Is there any DC offset on the output before or after the pop?

Thank you for reply, Perry!
It seems to be it's popping almost immediately as soon as turn-on signal applied, when power supply starts. Also protect light never goes out completely - it just become very, very dim. It isn't getting a lot brighter on turn-on too - just slightly.
Pop happens almost immediately, but after it there is no DC offset on output.
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Old 26th September 2007, 06:32 PM   #4
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There are two opto-couplers. The op-amps connected to the opto-couplers are supposed to be muted with a DC input. This DC signal passes through an SMD diode very near the op-amp. Make sure the DC signal on the anode of the diodes is going high at turn on (on both diodes) and then dropping to -10v.

If it's not dropping, it could be that U21 has failed.
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Old 26th September 2007, 06:55 PM   #5
Flyin11 is offline Flyin11  United States
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It might just the way the amp is...I was told a long time ago about the turn on and off pops of amps. My Precision Power amp has always done this ever since I purchased it back in 94. I use to have a MTX amp before it got stolen, and it didn't pop when you turned it on. This one does though and I was just told that it was the way the amp was. Maybe someone else could shed more light on the subject? That's what I was told by a audio dealer though. The way you are describing it though, it sounds like yours is A LOT louder when your turn yours on though...

I too would like to see maybe if there is any way to kind of defeat the sound of it when you turn your system on?
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Old 27th September 2007, 01:09 AM   #6
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Thank you! I am closer !!!

New, interesting findings:

Replaced U21, it was bad; after that amp stuck muted... After some trace-tracing / measuring lifted up diode D30. Amp started to work normally - on turn-on it illuminates protect light, then it goes out and sound plays just fine No turn-on pop

Still have no idea what's going on

Quote:
Originally posted by Perry Babin
There are two opto-couplers. The op-amps connected to the opto-couplers are supposed to be muted with a DC input. This DC signal passes through an SMD diode very near the op-amp. Make sure the DC signal on the anode of the diodes is going high at turn on (on both diodes) and then dropping to -10v.

If it's not dropping, it could be that U21 has failed.
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Old 27th September 2007, 01:56 AM   #7
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I don't have an amp here so you'll have to check and confirm the following.

D30 is parallel to R15 and the anode of the diode is connected to the positive terminal of the 10uf capacitor.

R17 appears to go to ground. The capacitor is used for a turn on delay. The diode is likely there to provide a quick discharge of the cap so the amp will mute when the remote is removed. I wouldn't think the diode would prevent the amp from powering up normally. If the above information is accurate, an open diode would prevent the amp from muting quickly when remote voltage was removed. A shorted diode would prevent the amp from having a mute delay when the amp is being powered up.

Double-check the solder connections on u21. If they're OK, check D30. If it's OK, solder it back into the circuit.

When you apply remote voltage to the amp, measure the voltage on the positive terminal of the capacitor. It should come up slowly. As it reaches 5v, the amp should come out of muting. When you remove remote voltage, the voltage on the cap should drop quickly.
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Old 28th September 2007, 04:04 AM   #8
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You are absolutely right describing this schematic even without an amp U21 soldered perfect. With removed D30 voltage on C51 is climbs to 6V and amp is out of mute; with D30 soldered back - voltage stays at 0.7V and amp is always muted Diode is fine. After turn-on signal is removed, voltage drops very quickly on C51 (without D30).
This was previously pretty much over-abused amp with all power supply FET's blown (but no damage to audio section), if it can make any sense.
Thank you again!
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Old 28th September 2007, 04:35 AM   #9
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From what I can see, I don't think the diode can cause that. Neither terminal of the diode goes to ground. That's the only way it could prevent the cap from charging.

Are you sure that there isn't a conductor of some sort under the diode that conducts when it's soldered down to the board?

If you don't see anything conductive but there's a lot of flux, clean the area with solvent and solder the diode back down.
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Old 2nd October 2007, 08:01 PM   #10
Flyin11 is offline Flyin11  United States
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I might want to stop mine from having turn on and turn off pops so I was wondering is there something externally that can be used or done for it? I don't know anything about the inside of a amp and I'm not going to open it up or anything...If nothing can be done by like a external switch or something then I'll just deal with it as I have for the past 13 years but just wondering...Thanks
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