Users of the Audio Control LC7i, LC6i or other active Line Out Converters

For those who have chosen to keep the factory HU when upgrading the sound system, I have seen no mention of maintaining a proper load on the HU. This is an issue you might want to consider. I will try to explain why. No, I am not a vendor or pushing a particular manufacturer.

In today’s modern factory systems more and more class D amplifier technology is being designed into HU’s. This technology can mute, distort or emit damaging frequencies into your new after-market audio equipment when the factory speakers are removed and replaced with an improper load. And it is possible to damage the HU if it is not properly loaded. I don’t know if the factory HU’s are in fact class D designs but it is likely. Knowing the cost of our HU’s I sure don’t want to have to replace one. Some non-active LOC’s come with load resistors built in which helps to alleviate this but active LOC’s and EQ’s usually do not. But there is a solution for this. It’s called a Zobel Network and is a combination of capacitors, resistors and inductors. It is placed between the speaker leads of the head unit and the input of LOC’s, EQ’s and amplifiers with speaker level inputs. It functions as a load generator and signal stabilizer for the factory HU to ensure the best possible audio. A Zobel Network can be very complicated to design on your own but fortunately they can be purchased ready to install. I used the Audio Control version (AC-LGD) from Sonic Electronix. They can be found on ebay and Amazon as well. A package consists of 2 units (one for front and one for rear) and comes equipped with the same 4 screw connectors as is on the LC7i, LC6i etc and will plug directly into the LOC. For instance, unplug the front speaker connector from the LOC, plug the AC-LGD into the LOC then plug the front speakers into the AC-LGD input. Same for the rear speakers. Yes, they are a little pricey but if nothing else they are cheap insurance for the HU and amp. For more info go to Audio Control's website and look up AC-LGD.

 

I have edited the above post for clarity.

 

When I read pricey in your first post I was thinking more than $25. Not pricey to me. I thought I read somewhere that our HUs are Class D but not sure where. Taco Tunes does not seem to think this is a problem. I am still on the fence on what amp to use in mine. I like the Taco Tunes because they don't require a LOC. On the other hand if I was putting in a sound processor I would probably not do Taco Tunes due to added cost of shipping, harness, and taxes. Rockville amps seem to get real good reviews but you know the saying. You get what you pay for. I am trying to find some real world comparisons between the Taco Tunes and other amps in same price range.

 

Not trying to be a jerk here but your post is extremely misleading. Class D amplifier technology has nothing to do with a factory head unit requiring a load which would typically be on the line from the speaker itself. When an LOC is used you are putting the LOC in line before the speaker and the load (required or not) may or may not be there depending on the LOC used. The worst case scenario of "Burning up your aftermarket amp" would not happen immediately (huge puff of smoke and all). The amp would more than likely go into thermal cutoff numerous times before "burning up" which would give any logical user a clue something is amiss and needs to be looked at.

The question I have is why was there no warning and/or nod in this direction when query's were sent to Audiocontrol by numerous people with "white noise" issues, hissing, etc which could very well be attributed to an overpower situation from the head unit to the LOC. The configuration video I have in my build post describes using the LOC to turn down the power until the hiss/white noise is no longer present which would make me think you are cutting down the over driven signal.


http://www.audiocontrol.com/knowled...ut-resistor-load-speaker-outputs-factory-amp/

Q: Do your line converters put a resistor load on the speaker outputs of my factory amp?

A: None of our line converters or processors put a resistance on the outputs of the factory system/amp.
A lot of newer vehicles factory systems MUST see a resistance on the outputs in order to work properly.
If they don’t see a resistance, there are a number of different ways the system may react.
The most common is that it will not output any signal at all. Or, it may output distorted signals, or will send random noise to specific channels. The worst case scenario is that the amp will see no resistance at all and it will just send all of its power out all at once, which typically results in burning up your after market amp.
The work around for this is to put resistors on the inputs of the line converter.

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Class D
Often erroneously referred to as “digital amplification”, Class D amplifiers represent the zenith of amplifier efficiency, with rates in excess of 90% being achieved in the real world. First things first: why is it referred to Class D if "digital amplification" is a misnomer? It was simply the next letter in the alphabet, with Class C being utilized in non-audio applications. More importantly, how is 90%+ efficiency possible? While all the amplifier classes previously mentioned have one or more output devices active all the time, even when the amplifier is effectively idle, Class D amplifiers rapidly switch the output devices between the off and on state; as an example, Class T designs, which are an implementation of Class D designed by Tripath as opposed to a formal class, utilize switching rates on the order of 50MHz. The output devices are typically controlled by pulse width modulation: square waves of varying widths are produced by a modulator, which represents the analog signal to be reproduced. By tightly controlling the output devices in this way, efficiency of 100% is theoretically possible (although obviously not achievable in the real world).



Example of a full bridge Class D circuit (left; sourced from sound.westhost.com), and the IQ M300 Class D amplifier, a pint sized 300W wonder (right).


Delving deeper into the world of Class D you’ll also find mention of analog and digital controlled amplifiers. Analog-controlled Class D amplifiers have an analog input signal and an analog control system, usually with some degree of feedback error correction present. On the other hand, digitally controlled Class D amplifiers utilize digitally generated control that switches a power stage with no error control (those that do have an error control can be shown to be topologically equivalent to an analog-controlled class D with a DAC in front). Overall, it’s worth noting that analog controlled Class D tends to have a performance advantage over its digital counterpart, as they generally offer lower output impedance and an improved distortion profile.

Next, there is the (not so) small matter of the output filter: this is generally an L-C circuit (inductor & capacitor) placed between the amplifier and the speakers in order to mitigate the noise associated with Class D operation. The filter is of considerable importance: shoddy design can compromise efficiency, reliability, and audio quality. In addition, feedback after the output filter has benefits. While designs that do not utilize feedback at this stage can have their response tuned to a particular impedance, when such amplifiers are presented with a complex load (i.e. a real world loudspeaker as opposed to a resistor), frequency response can vary considerably depending on the loudspeaker load it sees. Feedback stabilizes this issue, ensuring a smooth response into complex loads.

Ultimately, the complexity of Class D has its rewards: efficiency, and as a good consequence, less weight. As relatively little energy is wasted as heat, much less heat sinking is required. Ratcheting that up a notch, many Class D amplifiers are used in conjunction with switch mode power supplies (SMPS). Like the output stage, the power supply itself can be rapidly switched on and off to regulate voltage, leading to further gains in efficiency and the ability to shed weight relatively to traditional analog / linear power supplies. Taken together, it’s possible for even high powered Class D amplifiers to weigh only a few pounds. The disadvantage of SMPS power supplies over traditional linear supplies is the former typically don't have much dynamic headroom. Our limited testing of Class D amps with linear supplies vs SMPS supplies have shown this to be true where two comparably rated power amps both delivered rated power, but the one with the linear supply was able to produce higher dynamic power levels. Still SMPS designs are becoming more commonplace now, and you can expect to see more high powered, next generation Class D amplifiers employing them.

 

Well.........what to say here??
Last time I looked at Sonic Electronix the AC-LGD pack was $29.00 which might seem expensive to some folks especially since these are small units. Since I know and understand the importance of impedance matching I offered this suggestion for the reasons stated. Even $29.00 is not much compared to the price of a good amp and a set of good speakers. A cheap system can perform as well as an expensive one if all of it's components are properly matched. There may not be any problem with not using anything between the HU and amp. I don't know if our HU's are class D. I don't know of any problems being reported on this forum about hooking HU's and amps directly together. But I do know a well matched system performs better and will last longer than one that is not.
My system is all Pioneer. Their speakers are known for excellent music reproduction. I have 6x9 4 way fronts, 6.5 3 way rears. Replaced the dash side speakers with 3.5 2 way full range, removed the center speaker. Front sides are powered by the HU. All others powered with Pioneer 9605 5 channel connected through the AC-LGD's and LC7i with a 10" sub in a custom enclosure. Amp is under passenger seat with a ********* mounting plate and connector harness. Not sure what you want to spend but my total investment is about $650. No, I couldn't compete with it but it is a kick butt system for the dollars. By the way, you don't need a LOC to hook up any amp with speaker level inputs. But you will need a LOC of some kind to get your sub channel.
So where am I coming from? I am a retired electrical/electronics engineer and almost became an acoustic engineer since I like working with audio. I have installed many systems in my own vehicles and building my own speaker boxes and home systems. I love music and was involved in music as a drummer....hence..styx.

 

The taco tunes amps are nothing special. Most amplifiers have speaker level inputs. thats all you need to check for if you aren't going to do a loc.

 

You, Sir, need to re-read my posts. I offered the info as a suggestion. If you don't agree then pay no attention to it. If you don't like Audio Control products then don't buy any. I don't have a hiss issue but some have as you said. The hiss issue is not from Audio Control units from what I am able to research. Without the problem myself, I'm not at liberty to comment on it. By the way, I have a couple of amps in my shop that essentially disintegrated their circuit boards.....thermal shutdown didn't work in time for these!