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voice coming trough my power suppy only with the amp on

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  #1  
Old 01-05-2012, 10:21 PM
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Default voice coming trough my power suppy only with the amp on


ok this is my second post on this issue. i had a power supply that was just able to handle my dx 400 on medium power, 35 amps or so. when i keyed up and started talking it sounded like my voice was coming through the power supply, weird shit huh! i mean loud as hell to. my buddy suggested to put a 3.5 fared capacitor in line with it. like my maybe not enough power or something. holy shit! i worked like a charm! i had my old lady whistle into the mike and i held my ear against the power supply and couldnt hear a thing. hooray!!!! like i said when you whistle into the mike without the capacitor you can hear your voice in the power supply just like a distorted talk back. ive never heard someone using a car stereo big ass 3.5 fared cap with a volt meter in a ham shack before. so anyway a coulple of guys suggested my power supply is to small and get a bigger one. cant argue that, hell you need atleast a 50 amp supply to run that amp, 4 pill dx400. not a 35 amp supply. so i just got a mfj 75 amp switching, mfj-4275mv power supply. up to 16 volts and all that happy shit. guess what? as soon as i got it hooked up i set the amp on med power with a 2 watt input which would give me a 100 watt dead key and up to 300 watt swing and what ya know my voice is coming trough the power suppy again or vibrating trough what ever you want call it. what the hell is going on here? im running a hr-2510, turner plus 3 mike, 75 amp mfj-4275 switching power supply, texas star dx-400 amp with 100ft of cable xperts rg213 coax and a maco 5/8 wave antenna thats 35 ft up in the air. im pushing 2 watts into the amp also. put the 3.5 capacitor on it and its fine. leave it out and you can hear your voice vibrate through the power suppy loud as hell. every word you say like a fucked up talk back. how is this? i didnt know power supplys had speakers in them. its not the amp or my radio. i also tried ferrite beads, made it worse. checked grounds and the whole nine. the likely hood of someone figuring this one out is slim. guess im gonna have to run a 3.5 fared capacitor like a filter after my power supply then to the amp. why does the cap solve the problem totally? is it severe ocillation and how can i stop it? i also noticed on high power i have backwards amprege


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Old 01-05-2012, 10:47 PM
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Sounds like 'Common Mode Current' or 'CMC' problems to me.
Its like RF feedback.
What is happening can be changed; but you are going to need to jump thru some hoops to get there.

Improperly grounded equipment, need for ferrite on wires and coax, and even an 'ugly balun'/RF choke will be things to look into.

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Last edited by Robb; 01-05-2012 at 11:07 PM.

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Old 01-06-2012, 06:29 AM
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Quote:
i didnt know power supplys had speakers in them
Most of them do not, I agree with Rob, RF is getting back into the supply somewhere and by putting the big cap inline you are filtering it out.

Any Modifications done to the 2510?
If the limiter is disabled or modified and not properly adjusted along with the Amplified Mic may be contributing to the problem.
What happens if you push in the "mic gain" button in on the radio or reduce the mic gain on the turner?
The Amp meter going back on high power I would also say could be a sign that RF is getting back into the supply.
What voltage are you running?
Anything over about 14.8 volts into a Texas Star Amp will lead to Failure, they do not tolerate over-volting at all and will increase the chance that the signal is getting dirty coming out of the amp.
After that, as you have already said, just keep going over the whole system, grounds, the Choke that Rob talks about will help if CMC`s ( common mode currents , this is RF that is flowing on the outside of the coax) are letting stuff get back into the supply.


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Old 01-06-2012, 07:23 AM
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Sounds like RF is causing the transformer windings to vibrate and reproduce the audio. I am surprised a huge 3.5 FARAD cap cures it as electrolytic caps do not respond to RF very well. Smaller disc caps are better for RF bypassing. I would bet that a couple 0.01 microfarad disc caps across the power supply output and from the transformer secondary to ground would cure the issue as well at much less expense and bulk. Throw a toroid core on the AC cord just inside the case and that should block anything coming in on the power cord.
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Old 06-01-2012, 06:19 PM
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patent the set-up as a novel new speaker

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Old 06-03-2012, 10:39 PM
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What the big amount of capacity is doing is more regulation of the output voltage under load current demands.
Here is the way it works.
With the big cap in place, the power peaks are being fed out of the stored capacitor current and helping the supply to be more stable in output by not allowing the internal regulation to swing so wide trying to adjust output vs load.
If this is allowed, the transformer could react to current changes at an 'audio' rate you are able to hear.
The use of big caps in automotive audio systems is for the same purposes when a very large audio amplifier is used and especially during base notes of high power content when the power cables, alternator and battery cannot hold up to the needed current requirements.
Actually some alternator voltage regulators were never designed to control output at varying audio rates.
This is why they are available.
.
If you check with a voltmeter on the output with no cap in place you may see the voltage droop or swing with modulation from the current being drawn.
These are all indications of too small leads, supply defficiecies in regulation and ability to track current demands "at an audio rate" etc.
Using the big cap largely aleviates or reduces many of the problems.
It can also be some RF getting back into the supply and upsetting regulation.
3.5 F does not always shunt RF frequencies well due to the large inductance that may be inherent in it's design, so smaller values are often needed in along with the large value.
Also be awhere that with the big cap accross the power supply that on inital powerup it can/will act like a dead short accross the supply before being charged up.
Sometimes this trips the fuse, the circuit breaker or the Crow Bar circuit or whatever over current protection the supply has.
The proper way is to have a push button switch pressed to put a current limiting resistor in series with the big cap for a second or two the let the cap connect to the supply, begin to take a charge, then connect with out the resistance in series with the cap..
Good luck.

Last edited by KM3F; 06-03-2012 at 10:50 PM.

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Old 06-04-2012, 05:43 AM
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don't turn the amp on

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Old 06-04-2012, 08:00 AM
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I have heard of toasters talking..but never power supplies.

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