Not in the least.
PFC is required to produce a better harmonic spectrum back to the AC power system. It makes a computer power supply look more like a resistive load than the typical capacitor input power supply. Key element is that a PFC is an AC/DC converter.
PFC is not applicable to a DC system. The 14.4V from your battery goes right to the bulk input storage on the SMPS. If you were using an AC source, the PFC circuit would produce this DC voltage at the bulk input. Since you already have DC from the car, there is no need to use a PFC to convert AC into DC.
The SMPS proper then converts the DC into a specified output, say +/- 40V for the amplifier.
PFC is required to produce a better harmonic spectrum back to the AC power system. It makes a computer power supply look more like a resistive load than the typical capacitor input power supply. Key element is that a PFC is an AC/DC converter.
PFC is not applicable to a DC system. The 14.4V from your battery goes right to the bulk input storage on the SMPS. If you were using an AC source, the PFC circuit would produce this DC voltage at the bulk input. Since you already have DC from the car, there is no need to use a PFC to convert AC into DC.
The SMPS proper then converts the DC into a specified output, say +/- 40V for the amplifier.
I have a power supply out of an amp that also has no LC filtering. I've never noticed that it causes any noise issues.
http://i32.tinypic.com/2ik2i5w.jpg
http://i32.tinypic.com/2ik2i5w.jpg
You may be talking apples and oranges here.
An LC filter, applied to "prevent too much high frequency currents from flowing through the power wiring, which is usually quite inductive and prone to produce strong stray fields that contaminate line and speaker signals" would have to be installed close to the battery post, in order to keep said currents out of the long power lead going from battery to the rear of the vehicle. In case you are wondering why you never see any of these LC networks installed at the battery, it's because they are unnecessary. Noise does not couple in a car that way, assuming shielded interconnects. Should you get coupling into speaker wire because you unwisely ran your power wire parallel to it, installing an LC filter anywhere in the system will do nothing to remedy the situation.
Now there are many amps which install LC filters inside the amp, right at the input. The Rockford Punch 45 is an example. The reasons for this are very different, though. The idea is to produce a low impedance source for the internal SMPS. The long power wire, especially at high frequencies, is inductive and results in poor performance of the SMPS. The LC filter isolates the car's system from the SMPS, providing for a low impedance local source suitable to supply the high frequency currents demanded by the SMPS. Most of this is done by the capacitor. The inductor both stores energy to keep the capacitor charged, as well as isolating the car's system from the SMPS in higher frequencies.
Maybe not the best description, but it works.
An LC filter, applied to "prevent too much high frequency currents from flowing through the power wiring, which is usually quite inductive and prone to produce strong stray fields that contaminate line and speaker signals" would have to be installed close to the battery post, in order to keep said currents out of the long power lead going from battery to the rear of the vehicle. In case you are wondering why you never see any of these LC networks installed at the battery, it's because they are unnecessary. Noise does not couple in a car that way, assuming shielded interconnects. Should you get coupling into speaker wire because you unwisely ran your power wire parallel to it, installing an LC filter anywhere in the system will do nothing to remedy the situation.
Now there are many amps which install LC filters inside the amp, right at the input. The Rockford Punch 45 is an example. The reasons for this are very different, though. The idea is to produce a low impedance source for the internal SMPS. The long power wire, especially at high frequencies, is inductive and results in poor performance of the SMPS. The LC filter isolates the car's system from the SMPS, providing for a low impedance local source suitable to supply the high frequency currents demanded by the SMPS. Most of this is done by the capacitor. The inductor both stores energy to keep the capacitor charged, as well as isolating the car's system from the SMPS in higher frequencies.
Maybe not the best description, but it works.
So how much more effective is LC vs. just C?
I have a rather large inductor of unknown value with two 2.5mm wires in parallel. This came from a high current SMPS battery charger. Would there be any benefit to adding this to the input?
http://i31.tinypic.com/1111hxz.jpg
I have a rather large inductor of unknown value with two 2.5mm wires in parallel. This came from a high current SMPS battery charger. Would there be any benefit to adding this to the input?
http://i31.tinypic.com/1111hxz.jpg
I'm not seeing two wires in parallel. I only see two ends of the same wire ?
Regardless, an LC is much more effective than just a C. Can't hurt, I'm sure, though I would place more effort into putting some quality low ESR capacitors in the front end. Adding the L will only improve things, as long as the DC current your amp draws isn't greater than the rating of the inductor (which you don't know, I would guess).
Regardless, an LC is much more effective than just a C. Can't hurt, I'm sure, though I would place more effort into putting some quality low ESR capacitors in the front end. Adding the L will only improve things, as long as the DC current your amp draws isn't greater than the rating of the inductor (which you don't know, I would guess).
An inductor is a series element. Placing it at the battery side or inside the amplifier makes no change at all.
Contrary to what most people think, most of the strong high frequency currents in the 12V power wiring are produced by the own amplifiers when playing loud rather than by the electrical system of the car.
Current consumption waveform is just an amplified and low-pass filtered version of the sum of speaker current waveforms, so it has great potential to induce distortion in signal lines (hello to all those naive installers that like to put together all the wires with cable ties).
BTW: Rockford amps were once great (there were few competitors if any by that time and performance and quality standards were different) but now stuff like MEHSA is the last step in cost reduction, it's the kind of thing that they do when they can't save 10 more cents in the bill of materials while still keeping the product functional. Don't be puzzled if they don't include EMI filters, then again, they don't include fuses either (like in the worst Chinese computer PSU).
Contrary to what most people think, most of the strong high frequency currents in the 12V power wiring are produced by the own amplifiers when playing loud rather than by the electrical system of the car.
Current consumption waveform is just an amplified and low-pass filtered version of the sum of speaker current waveforms, so it has great potential to induce distortion in signal lines (hello to all those naive installers that like to put together all the wires with cable ties).
BTW: Rockford amps were once great (there were few competitors if any by that time and performance and quality standards were different) but now stuff like MEHSA is the last step in cost reduction, it's the kind of thing that they do when they can't save 10 more cents in the bill of materials while still keeping the product functional. Don't be puzzled if they don't include EMI filters, then again, they don't include fuses either (like in the worst Chinese computer PSU).
lumanauw said:
No, it appears more as a resistor than an inductor. 1-2 V seems like quite a bit of voltage drop, though. You sure about your measurements?
Eva said:
I guess we are all entitled to our opinions.
Eva said:
Perhaps you could clarify this statement, because it makes little sense to me. If I inject a 1 kHz sine wave into my amplifier, feeding a speaker or resistive load, the current drawn in the 12V line is DC, nothing else. It will have some high frequency content based on the switching frequency of the SMPS, but not at all related to the audio output of the amplifier. It WILL be related to the POWER output of the amplifier, but it has nothing to do with the audio frequency.
Here we go; one giant series inductor installed. For better or worse.
http://i26.tinypic.com/20rjtc3.jpg
http://i26.tinypic.com/20rjtc3.jpg
zigzagflux said:
The statement about an inductor being a series element is science, not opinion.
The current drawn in the 12V line is a complex waveform that may be described as strong AC with high crest factor on top of some DC. Have you ever tried looking at it witn an oscilloscope?
If you sum all speaker currents, rectify the resulting waveform to make it single ended, apply a 500Hz (or so) lowpass filter, and multiply it by the turns ratio of the PSU transformer of the amplifier, you obtain the current waveform being drawn from the 12V line.
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