My Fender Passport PD-250 makes a popping sound through the speakers when I turn it off. I am not sure why this is happening. Any help would be greatly appreciated.
Thanks
Tom S.
Thanks
Tom S.
If that pop happens exactly when the switch turned off, it may be the switch contacts.
Try this: plug the amp into a switched power strip. With the strip off, turn on the amp.
Now turn on the power strip. After a couple of minutes, see if the pop happens
when the strip is turned off (don't touch the amp's switch).
If there's no pop, you may need a new amp switch, or a snubber across the switch contacts.
Hi rayma,
Yes, I think you've got it.
Maybe a better way to deal with that is to use a varistor across the transformer primary. This will clamp the voltage and prevent burning the switch contacts. I used to use the 130 VAC ones, today with increasing AC voltages you might want to go with a 150 VAC model.
-Chris
Yes, I think you've got it.
Maybe a better way to deal with that is to use a varistor across the transformer primary. This will clamp the voltage and prevent burning the switch contacts. I used to use the 130 VAC ones, today with increasing AC voltages you might want to go with a 150 VAC model.
-Chris
Years ago, I installed a large audio system in a customer's home.
It included a Hafler power amp with a light-up power switch.
Their little boy immediately took to flipping it on and off, over and over.
After a couple of weeks, it went bad and welded the contacts closed, permanently on.
I decided it was for the best, and left it that way.
the "pop" happens after the switch is turned off like a capacitor is discharging through the outputs to the speakers
Ok, then has this always been the case, or has it recently started?
Is it more of a "thump" or a "pop"?
if the speakers are plugged into the send outputs I don't hear the pop only when they are plugged into the main outputs. I have a service manual for it but all it says is that the jfet's are supposed to control the "popping" and mute the speaker output upon power off.
More like a squealing sound through the speakers.
has done it ever since I changed to the output decoupling capacitors that connect the filter circuit from the mixer to the output section of the amp. PM me and I will provide the service manual since it is too big to upload to this forum.
Thanks
Tom
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It could be oscillating as the supply voltage decreases. Maybe that's normal,
and why they had the muting. Did it always do this?
Hi Tom,
It sounds like that's what is going on then. So it goes pop, then oscillates as the volume drops?
What did you change the coupling caps from and to? Are they in exactly the same place as the old ones? This can be very important depending on design.
Why did you change the coupling caps?
-Chris
It sounds like that's what is going on then. So it goes pop, then oscillates as the volume drops?
What did you change the coupling caps from and to? Are they in exactly the same place as the old ones? This can be very important depending on design.
Why did you change the coupling caps?
-Chris
And the plot thickens. Go back to the old ones and see if it's ok then.
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The "send" outputs are line level outputs, not meant for speakers.
Is this really a problem? Or just something you notice? ANy power supply collapse noises are not going to hurt the speakers.
The JFET muting circuit is simply a power amp input shunt, so it will only stop pops and thumps from the preamp circuits. It will have no effect on the power amp circuitry as it powers down.
here is the service manual for the PD250D, for anyone who wants it.
http://bmamps.com/Schematics/fender/Passport_PD-250_Service_Manual.pdf
Page 25 is the powr amp schematic.
Is this really a problem? Or just something you notice? ANy power supply collapse noises are not going to hurt the speakers.
The JFET muting circuit is simply a power amp input shunt, so it will only stop pops and thumps from the preamp circuits. It will have no effect on the power amp circuitry as it powers down.
here is the service manual for the PD250D, for anyone who wants it.
http://bmamps.com/Schematics/fender/Passport_PD-250_Service_Manual.pdf
Page 25 is the powr amp schematic.
C211 and C225 according to the manual are supposed to be 1000uF 16V AE caps, what was installed were as follows:
C211 1200uF 63V (2)
C225 1200uF 63V (2)
C211 1200uF 63V (2)
C225 1200uF 63V (2)
So, they are a little larger than spec, but they are just filter caps, so that hurts nothing. And you can always use higher voltage caps than necessary.
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