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A lot of threads showcasing installs with expensive HU , Amps , subs , speakers and expensive wiring seem to be missing something valid .

In music reproduction the most important thing is the source ..which is the HU , sound card , ipod or whatever .

Many installs feature expensive HU and expensive audio gear , but what I have noticed is with 50 % volume the lights on the HU start dimming when there is a bass transient . Seen some installers / members exclaiming that their HU has the best DAC and it is supposedly the best sounding HU etc .

I have installed caps for my HU power and simply installing the caps for the HU gives a totally different dimension to the SQ of the system as a whole . Has anyone else tried and found any differences or is it that i am under an illusion ?

Your HU has a small power amplifier inside it. This power amp is fed by a small power supply (with capacitors). The lights on the HU dim becuase the power supply cannot supply enough power to both the display of the HU and the power amps (bass requires more energy) during these bass transients.

If your power supply wiring to the battery is good the battery itself will supply the power to the power amps and the internal capacitors (of the Hu's power supply) should be stressed. Think of the battery as a large capacitor.

I cannot see how adding more capacitance outside the HU when you already have a large capacitor (aka the battery) will help. However I will not debunk your observation. Every observation is valid as it is the real world. Theory (like the one stated above) is just theory.

What power wires connect the HU to the battery? Is it that these power wires are the limitation and the HU is unable to get enough power from the battery during these tranients to feed both the bass and the display?

That is the exact point . The power supply cannot supply enough power when the bass transients happen . Even without a power amp turning up the volume of a HU to say above 60-70 % causes the leds to dim . Even the small power amp inside the car draws up a lot of amperes as most of the car HU are designed to operate at 4 or sometimes even at 2 ohms due to 12 v . some speakers I have seen are rated at 2ohms .

now here is the catch . If the battery is connected directly to the HU through the batt cable then the batt can be a huge virtual capacitor . The Hu is connected to the wiring harness and the harness seems to have a bit of resistance and some times also causes inductance as well . I have not experimented with a direct heavy gauge wire run from the HU to the batt , but may be I will try sometime .

Yes , that is what I feel is the issue . The length of the wire from the battery and the terminations from the battery to the final wire ..the fuse box , relays and the power switches all add up resistance is my feeling . Another point is the voltages in a car are not so constant . A/c when it switches off and on introduces a drop in the voltage , Dipping headlights reduces voltage and also current .

Even with low volume on just the HU adding capacitors adds a totally new dimension . The bass becomes tighter , the highs become smoother and the midrange gets the presence .
May be I sound surreal , but I have noticed significant changes and I smile when someone has a thread with the title "High end install " .

As I found out, Caps isn't the only solution. My amps were running out of juice, leading to severe sound fluctuation (link to thread). Eventually, we moved to a set of amps that aren't as power-hungry and can also function in fluctuating supply.

Though caps were recommended to me, Navin & Ajay were dead against it.

And yes, no lights dimming even at loud volume!

The amps have an SMPS power supply inside them . So they can kind of operate on good voltage swings . For example they can operate from 10-15 v power . Plus the Amps do not need caps because the power supply cable is directly wired from the battery . A HU normally uses stock wiring harness and it does pass through a lot of resistance . A HU also does not have any SMPS type supply and more of relies on caps to "smooth out" the voltages and the currents . That is where the difference comes into play . As said in my previous post even without the amps the LED lights on the HU will dim on the HU with high volumes . I have seen this across Pioneer , sony HU . Dont really know abt the other HU since I have not really tested them until now . Probably other forum members will be able to do a check on other brand HU and let us know .

I did go through the link about your amps . Probably your HU was not getting the juice because the Amps were drawing all the available current . When the A/C or the radiator fan switches on there will definitely be a dip .May be as a test you can just fix caps to the power supply and the ignition wires of your HU and I am sure you are not going to experience any DIPS in volume or the amps switching off .Incase if you are going to try the value of the caps would be 10,000uf /35v for the main HU power and 3300uf for the ign power . Make sure you get the industrial grade caps as the temperatures inside a car are quite high .

The symptoms you are describing are all related to a stiffened power supply. Where is the capacitor connected. After the harness or before the harness?

Steg amplifiers are a bit more efficient than your older amps but the primary reason was that the Steg amps can operate as low as 10V giving your alternator the opportunity to 're-fill' the battery.

Point to note, GTO's first set of amps needed a minimum of 11.5V to put out rated power. If the voltage dropped below 11.5 the head lights would dim till the alternator recharged the battery. Also this is partly due to the Civic's electonics that cut off the alternator till the battery voltage was below 11V (I think) and the whole viscious cycle started again.

By moving to amps that put out rated power as low as 10V we resolved that issue.

It is only the lights on the HU that dim. Nothing else dims. This means the battery still has enough juice only it is not getting to the HU. You are correct in mentioning that all HUs are wired through the harness. Question is doe the harness limit the supply from the battery?

OK , I had posted the same q in a couple of other forums and below is the response from DIYAUDIO .

cap install for HU - diyAudio

Seems that people on other forums have been discussing and using the caps and they do confirm that the SQ is definitely better .

Alpine CDA-7990 + Mundorf cap - DIYMA.com - Scientific Car Audio - Truth in Sound Quality

Mundorf HU cap - DIYMA.com - Scientific Car Audio - Truth in Sound Quality

It is connected just before the HU ,right at the back of the HU .





Most of the alternators outupt lower currents and voltages at lower RPM . As and when the RPM increases then the power delivery is increased upto a certain voltage . After that any increase in RPM will not increase the voltage . But , the description of the problem by GTO , for example when he is at Signals or when he is in a stop and go situation the volume goes down . This is more likely caused by even a faulty radiator fan which might be taking up more amps to start due to age of the fan or some issue and which in turn might temporarily "short " the power supply when it is turning on since the power for the fan goes from the wiring harness . Same might be the case with the clutch of the air conditioner . Alternators are considered "smarter" compared to dynamos . They will make sure the voltage does not go below 13.8 amps . I just cannot figure where the 11 volt comes from . To be plain speaking a lead acid battery requires 13.6 -13.8 volt minimum to charge and alternators are designed to keep the voltage in the supply lines .When the peak current draw exceeds the capacity of the alternator only then does the voltage go down and that is when an alternator upgrade is needed . I do not understand why Honda would limit the voltage to 11 volt and underchage the battery .
By moving to amps that put out rated power as low as 10V we resolved that issue.

According to me , after connecting a cap to the HU if the lights do not dim then it does imply that the wiring harness does not provide enough power to the HU.
The links provided in my earlier post from various other forums do confirm that the best way to wire up the HU is either directly wiring the power supply of the HU directly off the battery . Someone has used a 12ga wire for that . This is a good solution if someone wants to use the onboard power amps of the HU . If the preouts are just going to be used then the HU can just be wired with a cap in parallel . some have recommended a low loss diode as well because the cap gets used exclusively by the HU and nothing else gets to the power supply cap .

ok , here is a sample cap ,but 68,000ufd for a HU . Sure it would rock .

Willkommen auf den Seiten der Chief-Rocker

1. I wont knock something till I try it. I have NOT tried a HU (head-cap) yet.
Maybe on my next install I will.

2. Given that the Head-cap did improve the HU's SQ by tightening up the power supply it is obvious that the if the HU would get adequate supply from the battery it would not need the head cap. The only way to check this is by connecting the HU directly to the battery and then comparing with and without head-cap.GM2000 if you get a chance to do this please do so and report your findings. I think you are on to something here

3. So far all the cap requests that we have recieved are from those who are using multiple amplifiers in the car. In this case the cap is between the battery and the amp (the amps are connected directly to the battery). So I cant see why when you got many ten of joules of energy in the battery, one would want to add half a joule or so more (via a cap). A Joule is a hell of a lot of energy. For those who remember high-school physics remember Q = CV? Q is joules.

A cap for an amplifier is not necessary as it is directly connected to the battery through a good thick power cable .This is true especially for class D amps . But , i still do feel that adding a cap will smooth out the power supply and probably influence the "sonic" signature .
When multiple amps are connected to individual power supply cables from the battery , then that is a different situation ,but most of the amps are connected to a single power cable and a cap must help especially if the power supply cable resists the total flow of current to the amplifiers connected . Then again , I have not done this , so must really check to see if it does the work .

Exactly what DA and I were saying in the beinging of this discussion. I think what happened was that we did not know you are refering to the head-unit cap.

In an HU too, the external cap will make negligible difference. And if one is listening through speakers connected to the HU internal amp, the difference is inaudible at that level. The effect of 10% voltage reduction is significantly visible on the display - that is the nature of the display. That does not mean the same 10% is going to affect the internal amp's output greatly - the amp is fed DC differently.

Sorry , but i beg to differ . It makes a very huge difference to the SQ when connected to the HU. The bass is much much better , the highs are smoother and the mids are cleaner . This is also the experience that various others from different forums have expressed and I have posted the links as well . When the internal amp of the HU is used it makes more difference since the internal amp requires more current for the HU than when using just the pre-outs . I dont know what you meant by "DC fed differently " . Could you please explain if you dont mind ? All I know is that the DC for the amps are fed directly through caps internally and there is no "special " circuit in there .