I've just finished testing my P101 and everything checks out alright. The only issue I am having is that once the power switch is turned off the amplifier continues to pay music. This goes on for around 30+ seconds without a change is the sound or volume of the music. I'm assuming this is due to the capacitors in the power supply but how can this be stopped.
The power supply was built just for testing the amplifiers so it is only +- 17V. The trafo is connected to two 63V 10,000MFD filter caps and than goes to the amp.
Will this change or even go away once the final supply voltage of +-70V is applied? I will also have 15,000 MFD per rail on the final supply.
Any Ideas?
The power supply was built just for testing the amplifiers so it is only +- 17V. The trafo is connected to two 63V 10,000MFD filter caps and than goes to the amp.
Will this change or even go away once the final supply voltage of +-70V is applied? I will also have 15,000 MFD per rail on the final supply.
Any Ideas?
richie00boy said:
Humm untrue, I use high Value resistors for discharging capacitors all the time. Depending on the rail voltage anywhere from 5K to 20 K per rail, usually 5 or 10 Watt. This is far to high to load up a power supply but will expedite the discharge time.
There are really two issues here; For safety reasons High Value caps should always be discharged given thier capacity to store enormous amounts of energy. As far as muting the sound after power off, the previously mentioned relay or speaker protection circuit will work. I do not like to break the signal path after the output device so I would mute the input signal with a low voltage high quality relay and a 10K resistor.
Regards
Anthony
The bleeder resistor will load the PSU and reduce the switching noise of the rectifier diodes,whenever the amplifier operated with small output power.The peak spike current (diodes conducting only at the peak of a/c waveform) will be somewhat broadened with a bleeder resister.Why add a small switching circuit to put this load whenever the amp output is low.the attack time should be very slow, and disengaged fast, a small relay or Mosfet can be used for switching.
will try to post such a circuit soon....
will try to post such a circuit soon....
There is a short article I saw in EDN that adresses this. First your off-on switch must be DPDT. The "pole" side is conected to the power transformer and one of the Throw sides is connected to the mains. Normally, when in the OFF position the pole/transformer is connected to the unused pair of terminals.
The article you use the normally unsuse terminals to connect the common side of two bleeder resistors thus bleeding off the caps trough two power resistors and the transformer. The resitors are choosen to make this happen a quickly (within reason) as you want.
When the power switch is in the ON position the beeders are open circuit and preserve the full power of the PS.
Although not mentioned, it would seem to me that you want to be absolutely certain that the power switch is "Break before make". I would think this would always be the case in a power switch but who knows . . .
I hope the above is clear. I would give the precise EDN citation but it is buried away in boxes and binders. IfI can turn it up I'll post it.
MODERATORS: I've thought about the saftey of this one as doing anything "creative" with the mains switch should give one pause. However, I can't see a problem if the connections are made correctly. If there is a reason why this is unsafe that has not penetrated my brain, feel free to delete the post.
The article you use the normally unsuse terminals to connect the common side of two bleeder resistors thus bleeding off the caps trough two power resistors and the transformer. The resitors are choosen to make this happen a quickly (within reason) as you want.
When the power switch is in the ON position the beeders are open circuit and preserve the full power of the PS.
Although not mentioned, it would seem to me that you want to be absolutely certain that the power switch is "Break before make". I would think this would always be the case in a power switch but who knows . . .
I hope the above is clear. I would give the precise EDN citation but it is buried away in boxes and binders. IfI can turn it up I'll post it.
MODERATORS: I've thought about the saftey of this one as doing anything "creative" with the mains switch should give one pause. However, I can't see a problem if the connections are made correctly. If there is a reason why this is unsafe that has not penetrated my brain, feel free to delete the post.
Amp plays after power off.
Hi, this can be a problem when you turn off your preamp. If it makes a thump or spike, it will get amplified and be heard in the speakers.
How about a simpler solution: Through the power switch, (seperate low voltage circuit) have a relay short the INPUTS when the power is off! This will keep any spikes,ect. from passing through the amp. If you get instabillity as the power supply droops, You may have to do this on the output to the speakers. I prefer the input as it puts less in line to the speakers and it is completely out of the circuit when on. Best regards, Steve
Hi, this can be a problem when you turn off your preamp. If it makes a thump or spike, it will get amplified and be heard in the speakers.
How about a simpler solution: Through the power switch, (seperate low voltage circuit) have a relay short the INPUTS when the power is off! This will keep any spikes,ect. from passing through the amp. If you get instabillity as the power supply droops, You may have to do this on the output to the speakers. I prefer the input as it puts less in line to the speakers and it is completely out of the circuit when on. Best regards, Steve
Re: Amp plays after power off.
See earlier Post, I suggested the same thing but with a 10K resistor to protect the preamp output.
Regards
Anthony
gearheaddruid said:Hi, this can be a problem when you turn off your preamp. If it makes a thump or spike, it will get amplified and be heard in the speakers.
How about a simpler solution: Through the power switch, (seperate low voltage circuit) have a relay short the INPUTS when the power is off! This will keep any spikes,ect. from passing through the amp. If you get instabillity as the power supply droops, You may have to do this on the output to the speakers. I prefer the input as it puts less in line to the speakers and it is completely out of the circuit when on. Best regards, Steve
See earlier Post, I suggested the same thing but with a 10K resistor to protect the preamp output.
Regards
Anthony
I am interested in this as well. I know all of my other amps do this but it is only noticible if I switch off the power amp while I am still feeding it a signal. Generally I shut down the whole system at one time through a power conditioner so ther is no more signal at the time of power-off.
What size resistors would I need to bleed off 65V rails? Does it just go from the caps to ground? Can it be in the circuit all of the time?
Thanks, Terry
What size resistors would I need to bleed off 65V rails? Does it just go from the caps to ground? Can it be in the circuit all of the time?
Thanks, Terry
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