posted
Hey I was wondering if it would be possible to crack open a car audio amp, take out the 12V transformer, and swap one in for 120V, so the amp could be run in a house on 120V, without having to get a power supply to run it down to 12V. Just a thought I had.
-------------------- 1994 Ford F-250 7.3L Powerstroke Diesel Super Cab Long Bed 33" Mud Terrains Yeah, it's big, and yeah, it's got balls. Posts: 876 | From: Decatur, IN | Registered: Apr 2002
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the components in the amp are not designed to handle the higher voltage...
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--------------------------------- Loud...it's when you can see the ground move, it's when you have to force yourself to breath, it's when the rest of the world ceases to exist. Posts: 4136 | From: Denver, CO | Registered: Sep 1999
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posted
The power supply in a DC car amp is nothing like an AC power supply in a home amp, see in the car you start with low voltage dc (12 volts) and have to go into a step up transformer and a switching power supply to convert low voltage dc to higher internal working voltages, then this becomes high voltage ac by the power supply, this has to go through a bridge rectifier to convert the high voltage ac back to high voltage dc (+/- dc), then this goes through a capacitor bank that filters out any left over ac from the power supply and gives a more pure +/- dc voltage to the output transistors to work, the capacitor bank also stores some reserve power. This voltage then goes to the appropriate outputs, in a class ab amp you have p (NPN) channel and n (PNP) channel devices (positive and negative)they have to run on positive or negative dc voltage, one transistor makes the upper half of the musical waveform and the other makes the lower half. these two halfs of the waveform are combined back toghether at the output of the positive and negative output transistors usually through an emmitter (buffer) resistor. Then this completed siganl is sent to your speakers. In a home amp, you do not have to have a switching power supply since you are starting with ac voltage, you have to go through a ac transformer not a dc transformer and step the ac voltage up or down to get the proper voltage, then it is rectified just as in the car amp, but the home amp has no switching transitors and other things used in a car amps power supply, so just changing a transformer will not work, SORRY!
-------------------- For the Love of Music Posts: 87 | From: pearl,ms,usa | Registered: May 1999
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posted
Yes, it could be done, but it needs more work than just replacing the transformer. Me and my friend have done this, and it worked just perfectly.
You must measure secondary output voltages of original SMPS power supply. Then, choose appropriate transformer, so that rectified and filtered DC voltage is about equal the voltage you just measured. Remember, unloaded voltage is higher than loaded. That is because filter capacitors charge themselves to peak output voltage, so filtered output is about 1.412 times AC RMS voltage. You must take care about smaller voltages also (for line level circuits) +-15 VDC or something like that, if they are not generated from "big" voltages. So you must bypass original SMPS altogether.
Bottom line is that this is kind of operation you shouldn't be doing unless you are fully confident what you are doing..
Regards, Janne
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posted
Really, it would be easier to show how to do it, than explain..
I think that answers are not conflicting.
This is because above negative answers dealt with just replacing the transformer in SMPS (=Switch Mode Power Supply). That is not possible, since SMPS switches (usually MOSFET's in car audio amplifiers) are not designed such high voltages, they are low voltage types. 120 VAC rectified to DC would mean that there would be 170 volts DC in SMPS primary, what is normally powered from 14 volts or so.
Also, amplifier casing would become live, because in car there is no need to completely (that means that in mains powered equipment, isolation barrier in power supply can take several kilovolts before breakdown between secondary and primary) isolate SMPS primary from secondary, in electrical safety sense.
Only reasonable and much more easier way to do this would be (and what I explained above) is to build new DC power supply from ordinary AC transformer, rectifier bridge and filter capacitors. Original power supply would remain unused.
Regards, Janne
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posted
Hey thanks alot- I am still a little unsure of this- I was thinking about buyin a big car amp like a D2, and changing the power supply to work with 120V, but how much current would it draw? I guess I just have to do some reading up and get educated on power supplies, then try it.
-------------------- 1994 Ford F-250 7.3L Powerstroke Diesel Super Cab Long Bed 33" Mud Terrains Yeah, it's big, and yeah, it's got balls. Posts: 876 | From: Decatur, IN | Registered: Apr 2002
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posted
An amp like a D2 will only draw about 30 amps at 120V. This is still alot of current for a house. You would need to use a dedicated circuit to run the amp.
To run the amp at 120v ac, you're forced to convert it to 14vdc. This involves the steps mnetioneed above. Get a transformer, then rectify it and finally filter. A power supply of this size is going to be fairly expensive. It might be better to consider a very powerful home amp. Or maybe some pro equipment.
Last ditch effort is use several good batteries in parallel to power the amp at 12 v. You will lose a bit of power from the amp, as well as need to recharge the batteries.
Posts: 768 | From: Ottawa, On, Canada | Registered: May 2000
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posted
Hey that's just what I was gonna ask- if running some batteries paralleled with a battery charger on them would work and how many I would need. Would a 20A or so power supply charge the batts, or would it mess up cuz it's not a charger. j/w
-------------------- 1994 Ford F-250 7.3L Powerstroke Diesel Super Cab Long Bed 33" Mud Terrains Yeah, it's big, and yeah, it's got balls. Posts: 876 | From: Decatur, IN | Registered: Apr 2002
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quote:Originally posted by emu: To run the amp at 120v ac, you're forced to convert it to 14vdc.
Not necessarily, if you open up the amplifier and bypass original internal switch mode power supply. This would eliminate losses produced by it. This was the point by asauer, I believe. Additional advantage of this approach is considerably smaller current draw from transformer, hence losses in rectifier are also reduced.
Transformer power rating in VA's should be at least equal the total power rating of the amplifier. That should suffice, in normal use.
Regards, Janne
-------------------- For box/port calculations, try these:
posted
Yes Janne, that's what I was getting at is to completely bypass the stock power supply and run it via 120V converted down...and soundrew- that's no fun lol
-------------------- 1994 Ford F-250 7.3L Powerstroke Diesel Super Cab Long Bed 33" Mud Terrains Yeah, it's big, and yeah, it's got balls. Posts: 876 | From: Decatur, IN | Registered: Apr 2002
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posted
To bypass the power supply and apply your own, you'll need access to schematics for the amp. You'll also need to build a new power supply.
I hope you have time and money to kill. Or else, stick with a car battery as a apower supply.
Posts: 768 | From: Ottawa, On, Canada | Registered: May 2000
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posted
as stated in earlier post but may have not been specific enough, you just can't pull one dc switching transformer out and replace it with a ac transformer, the WHOLE circuit is different, they are correct you would have to redesign the whole power supply in the amp, it would be much easier and cheaper to A) run a ac to dc convert in your home for the amp if this is what you are dead set on doing, or buy a true hoome amp. Modifying circuitry to this level should be left to professionals to do, but it can be done.
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